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MATERIALS TRANSACTIONS Vol. 48 (2007), No. 7

ISIJ International
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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678
Publisher: The Japan Institute of Metals and Materials

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MATERIALS TRANSACTIONS Vol. 48 (2007), No. 7

Microstructural Change by Friction Stir Processing in Zr-Al-Cu-Ni Bulk Metallic Glass

Yorinobu Takigawa, Junpei Kobata, Sung Wook Chung, Hiroshi Tsuda, Kenji Higashi

pp. 1580-1583

Abstract

Microstructural change by friction stir processing (FSP) is examined in Zr-Al-Cu-Ni bulk metallic glass. The microstructure in the friction zone (FZ) exhibits an amorphous “band-like” structure, and a small number of nanoscale crystalline particles are observed along the “band-like” structure. The change in hardness with the microstructural change is examined and it is revealed that the hardness in FZ greatly increases although the volume fraction of crystalline phase is very limited. The increasing hardness is possibly explained from the combined effect of low temperature annealing during FSP and nano-size of crystalline particles.

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Microstructural Change by Friction Stir Processing in Zr-Al-Cu-Ni Bulk Metallic Glass

Twin-Roll Strip Casting of Iron-Base Amorphous Alloys

Yoon S. Oh, Hakcheol Lee, Jung G. Lee, Nack J. Kim

pp. 1584-1588

Abstract

In this study, three Fe-base amorphous alloys with quite different critical cooling rates were subjected to twin-roll strip casting to see the possibility of fabricating amorphous sheet by the same process. Continuous cooling transformation (CCT) diagrams of the alloys were calculated using the heterogeneous nucleation theory coupled with thermal data obtained during cooling to evaluate their critical cooling rates and glass forming abilities (GFAs). It shows that the GFAs calculated by CCT diagram are in agreement with the experimental results, while the well known empirical thermal parameters do not agree with the experimental results. Optimum twin-roll strip casting conditions have been determined based on the calculated critical cooling rates and the simulated thermal behavior of the sheet during twin-roll strip casting.

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Twin-Roll Strip Casting of Iron-Base Amorphous Alloys

Microstructure and Mechanical Properties of Porous Zr55Cu30Al10Ni5 Bulk Metallic Glass Fabricated by Spark Plasma Sintering Process

Guoqiang Xie, Wei Zhang, Dmitri V. Louzguine-Luzgin, Hisamichi Kimura, Akihisa Inoue

pp. 1589-1594

Abstract

We investigated the microstructure and mechanical properties of the porous Zr55Cu30Al10Ni5 bulk metallic glassy specimens fabricated by a spark plasma sintering process starting from the low sintering temperature, short holding time and rapid cooling. No crystallization within powder particles as well as at the interfaces between powder particles was identified by scanning and transmission electron microscopic observations. The sintered porous bulk metallic glassy specimens exhibited larger plastic strain and lower Young’s modulus than those of the as-cast alloy specimen. The increase in the plastic strain can be related to the pores in the sintered porous bulk glassy samples which generate multiple shear deformation events.

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Microstructure and Mechanical Properties of Porous Zr55Cu30Al10Ni5 Bulk Metallic Glass Fabricated by Spark Plasma Sintering Process

Preparation and Characterization of Dual-Phase Bulk Metallic Glasses through Powder Metallurgy Route

Pee-Yew Lee, Sung-Ting Chung, Chung-Kwei Lin, Wen-Ta Tsai, Hong-Ming Lin

pp. 1595-1599

Abstract

In the present study, amorphous Mg49Y15Cu36 and Ti50Cu28Ni15Sn7 alloy powders were synthesized separately by using a mechanical alloying technique. The dual-phase (Mg49Y15Cu36)100−x(Ti50Cu28Ni15Sn7)x (x=0, 10, 20, 30, 40, and 50 vol%) powders were prepared by mixing the corresponding amorphous powders. The amorphous dual-phase powders were then consolidated into bulk metallic glass (BMG) discs. The amorphization status of as-prepared powders and BMG discs was confirmed by X-ray diffraction and by using a differential scanning calorimeter. The microstructure of the BMG discs showed that the Ti50Cu28Ni15Sn7 phase is distributed homogeneously within the Mg49Y15Cu36 matrix. The (Mg49Y15Cu36)50(Ti50Cu28Ni15Sn7)50 BMG disc exhibited a relative density of 97.2% and its Vickers microhardness was 526±20 kg/mm2.

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Preparation and Characterization of Dual-Phase Bulk Metallic Glasses through Powder Metallurgy Route

Ceramic Particulate Reinforced Zr55Cu30Al10Ni5 Metallic Glassy Matrix Composite Fabricated by Spark Plasma Sintering

Guoqiang Xie, Dmitri V. Louzguine-Luzgin, Hisamichi Kimura, Akihisa Inoue

pp. 1600-1604

Abstract

Two-type sintered specimens of Zr55Cu30Al10Ni5 glassy alloy powder blended with and without 10 vol% ZrO2 ceramic powder, which had the similar relative density, were fabricated by a spark plasma sintering process in order to clarify the reinforced mechanical effect of ZrO2 particulates in the metallic glassy matrix composite. The structure, thermal stability and mechanical properties of the two-type sintered specimens were investigated. Two-type sintered specimens as well as original metallic glassy powder exhibited similar thermal stability. No crystallization of the metallic glassy matrix was demonstrated during the spark plasma sintering process. The plastic ductility of the sintered Zr55Cu30Al10Ni5 glassy matrix composite was enhanced by adding the ZrO2 particulates into the metallic glassy alloy. The improvement was originated from the structural inhomogeneity caused by the micro particles inclusion.

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Ceramic Particulate Reinforced Zr55Cu30Al10Ni5 Metallic Glassy Matrix Composite Fabricated by Spark Plasma Sintering

Fabrication of Bulk Metallic Glass Sheet in Cu-47 at% Zr Alloys by ARB and Heat Treatment

Yufeng Sun, Nobuhiro Tsuji, Shiro Kato, Satoru Ohsaki, Kazuhiro Hono

pp. 1605-1609

Abstract

Pure Cu (99.96%) and pure Zr (99.8%) sheets were stacked and severely deformed up to equivalent strain of 16 by the accumulative roll bonding (ARB) process conducted at RT. The ARB processed sheets showed nanolamellar structure of Cu and Zr. The DSC curves of the ARB processed multi-layers exhibited characteristic exothermic peaks, which were similar to the previous results reported in a mechanical alloying study. When the ARB processed specimen was annealed at 400°C, at which the first exothermic peak appeared, most of the volume transformed into amorphous phase. The ARB processed and then 400°C annealed specimen showed obvious glass transition. That is, there is a possibility to fabricate bulk metallic glass sheet through severe plastic deformation and thermally activated amorphization.

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Fabrication of Bulk Metallic Glass Sheet in Cu-47 at% Zr Alloys by ARB and Heat Treatment

Development of Low Density Ca-Mg-Al-Based Bulk Metallic Glasses

O. N. Senkov, J. M. Scott, D. B. Miracle

pp. 1610-1616

Abstract

Low density Ca-Mg-Al-based bulk metallic glasses containing additionally Cu and Zn, were produced by a copper mold casting method as wedge-shaped samples with thicknesses varying from 0.5 mm to 10 mm. The compositions of the alloys were selected using recently developed specific criteria for glass formation. A structural assessment using the efficient cluster packing model was applied and showed a good ability to represent these glasses. Thermal properties of the new metallic glasses, such as the glass transition, crystallization and melting temperatures, as well as heats of crystallization and melting are reported. The effect of the alloy composition on glass forming ability is discussed.

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Development of Low Density Ca-Mg-Al-Based Bulk Metallic Glasses

Effect of Purity and Superheating on the Glass-Forming Ability of Mg-Cu-Y Alloys by an Electromagnetic Vibration Method

Takuya Tamura, Shinsuke Maki, Daisuke Kamikihara, Naoki Omura, Kenji Miwa

pp. 1617-1620

Abstract

It is known that cooling rate from the liquid state is an important factor for producing the bulk metallic glasses. However, almost no other factors such as electric and/or magnetic fields were investigated. The present authors have reported that the glass-forming ability of Mg-Cu-Y and Fe-Co-B-Si-Nb alloys is enhanced with increasing electromagnetic vibration force. The electromagnetic vibrations affect the increase of the cooling rate and the decrease in the number of crystal nuclei directly, but don’t affect the crystal growing rate. However, effects of the electromagnetic vibrations are not fully investigated so far. Thus, this study aims to investigate effect of the purity and superheating on the glass-forming ability of Mg-Cu-Y alloys by the electromagnetic vibration method. It was found that the glass-forming ability of Mg-Cu-Y alloys is sensitive to the purity of an Ar atmosphere under which the mother alloy is prepared. However, the glass-forming ability was enhanced by the electromagnetic vibrations even if the mother alloy was prepared under low purity Ar. The enhancement of the glass-forming ability by the electromagnetic vibrations in the liquid state was decreased with the increase of superheating. These results support the presumption that disappearance or decrement of the clusters by the electromagnetic vibrations applied to the liquid state causes suppression of crystal nucleation.

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Effect of Purity and Superheating on the Glass-Forming Ability of Mg-Cu-Y Alloys by an Electromagnetic Vibration Method

Development of Mg Based Amorphous Alloys with Higher Amounts of Rare Earth Elements

T. H. Hung, Y. C. Chang, Y. N. Wang, C. W. Tang, J. N. Kuo, H. M. Chen, Y. L. Tsai, J. C. Huang, J. S. C. Jang, C. T. Liu

pp. 1621-1625

Abstract

There have been many alloy systems for the Mg based bulk metallic glasses (BMGs), with the previous optimum composition being Mg65Cu25Y10. In this study, new optimum alloy designs are made based on the theoretical model involving the electron per atom ea-related criterion and the recent model of optimum composition extension from the binary eutectic-pair criterion. Both models suggest that the optimum Mg based BMGs might possess a composition with a lower amount of Mg element. It follows that a series of Mg based BMGs with 50–65 at% Mg and 10–25 at% rare earth element are prepared. The glass forming ability, thermal characteristics, and mechanical performance are examined and discussed.

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Development of Mg Based Amorphous Alloys with Higher Amounts of Rare Earth Elements

Glass-Forming Ability and Mechanical Properties of the Ternary Cu-Zr-Al and Quaternary Cu-Zr-Al-Ag Bulk Metallic Glasses

Qingsheng Zhang, Wei Zhang, Guoqiang Xie, Akihisa Inoue

pp. 1626-1630

Abstract

The effects of addition of Al and equivalent atomic ratio of Ag and Al on the glass-forming ability (GFA) of the Cu50Zr50 alloy are investigated. It is found that the alloy with the highest GFA is the Cu46Zr46Al8 alloy in ternary (Cu50Zr50)100−xAlx alloys, and the critical diameter is at least 8 mm. The simultaneous addition of Ag and Al is more effective to increase the glass-forming ability of the binary Cu50Zr50 alloy. The critical diameter of a glassy rod is 12 mm for the Cu42Zr42Al8Ag8 alloy. High stabilization of the supercooled liquid is the reason for high GFA of the Cu46Zr46Al8 and Cu42Zr42Al8Ag8 alloys. Both glassy alloys exhibited high fracture strength above 1960 MPa, but no distinct plastic strain is seen. There is no evident difference in the mechanical properties of the as-cast Cu42Zr42Al8Ag8 glassy rods with different diameters.

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Glass-Forming Ability and Mechanical Properties of the Ternary Cu-Zr-Al and Quaternary Cu-Zr-Al-Ag Bulk Metallic Glasses

Phase Equilibrium in the Cu–Ti–Zr System at 800°C

Wei-Ren Chiang, Ker-Chang Hsieh, Y. Austin Chang, Guojiang Fan, Donchun Qiao, Donchun Qiao, Feng Jiang, Peter K. Liaw

pp. 1631-1634

Abstract

The isothermal Cu–Ti–Zr phase diagram at 800°C was constructed by means of 36 equilibrated alloys. Electron microprobe analyses were used to determine the phase compositions and phase relationships. Most of the Cu–Zr binary intermetallic phases show a large Ti solubility and extend to the ternary region. CuTi2 and CuZr2 form a complete solid solution as a Cu(Ti,Zr)2 phase. One ternary phase, Cu2TiZr, formed at the central region. These phase relationships are quite different from the 703°C isotherm mainly determined by X-ray analysis.

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Phase Equilibrium in the Cu–Ti–Zr System at 800°C

Evaluation of the Glass-Forming Ability of Nb-Ni-Ti-Zr Quaternary Alloys Using the CALPHAD Approach

Tatsuya Tokunaga, Hiroshi Ohtani, Mitsuhiro Hasebe

pp. 1635-1638

Abstract

The glass-forming ability of Nb-Ni-Ti-Zr quaternary alloys has been evaluated by combining the Calculation of Phase Diagrams method with the Davies-Uhlmann kinetic approach. Time-temperature-transformation (TTT) curves were obtained for steady state nucleation for the calculations, which give the time required for the formation of detectable amounts of a crystalline phase from a supercooled liquid as a function of temperature. Then, the critical cooling rates for glass formation were calculated from the TTT curves. Among the input parameters for the calculation of the TTT curves, the driving force for crystallization of the crystalline phase was derived using the thermodynamic function of each phase formulated in previous studies. The calculations show that the critical cooling rates for Nb40−xyNi60TixZry alloys decrease with increasing Zr content up to 20 mol%Zr. In particular, the calculated values for the Nb10Ni60Ti10Zr20 and Nb5Ni60Ti15Zr20 alloys were around 100 K/s.

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Evaluation of the Glass-Forming Ability of Nb-Ni-Ti-Zr Quaternary Alloys Using the CALPHAD Approach

Phase Separation and Crystallization in Cu-Zr Metallic Glasses

N. Mattern, U. Kühn, A. Concustell, A. Schöps, M. D. Baro, J. Eckert

pp. 1639-1643

Abstract

The structural behavior of rapidly quenched Cu-Zr amorphous alloys was analyzed. High energy X-ray diffraction patterns and atomic pair correlation functions exhibit monotonic changes with composition. The experimental results can be well described by a solid solution-like replacement of Cu and Zr atoms in the whole composition range. No indications are observed that would support the existence of phase separation in the supercooled liquid state of the binary Cu-Zr alloys. For Cu60Zr30Ti10 and Cu60Zr20Ti20 bulk metallic glasses the formation of ultrafine nanostructures are proven upon heating. The transformation starts below the glass transition temperature. Phase separation in Cu-Zr-Ti bulk metallic glasses is related to primary crystallization.

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Phase Separation and Crystallization in Cu-Zr Metallic Glasses

Electron Irradiation Induced Crystallization Behavior in Zr66.7M33.3 (M=Cu, Ni, Pd) Metallic Glasses

Yukichi Umakoshi, Takeshi Nagase, Takashi Hosokawa

pp. 1644-1650

Abstract

The difference in electron irradiation induced crystallization behavior of melt-spun amorphous phase among Zr66.7M33.3 (M=Cu, Ni and Pd) alloys was investigated. An amorphous phase was unstable under electron irradiation and the irradiation induced crystallization of the amorphous phase occurred in the three alloys. The phase selection of electron irradiation induced crystallization in Zr66.7Pd33.3 was obviously different from that in Zr66.7Cu33.3 and Zr66.7Ni33.3, while there was no significant difference between the latter two. The origin of the unique phase selection in Zr66.7Pd33.3 alloy was discussed based on the database of electron irradiation induced crystallization in Zr-based alloys.

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Electron Irradiation Induced Crystallization Behavior in Zr66.7M33.3 (M=Cu, Ni, Pd) Metallic Glasses

Electron Irradiation Induced Crystal-to-Amorphous-to-Crystal Transition in Some Metallic Glasses

Takeshi Nagase, Akihiro Nino, Takashi Hosokawa, Yukichi Umakoshi

pp. 1651-1658

Abstract

Electron irradiation induced crystal-to-amorphous-to-crystal (C-A-C) transition in metallic glasses was investigated in various metallic glasses among binary Zr-based, ternary Fe-Nd-B and Fe-Zr-B alloys. In situ observation of the TEM microstructures and corresponding SAD patterns was performed by ultra high-voltage electron microscope (UHVEM). The origin of amorphization, crystallization and C-A-C transition was discussed based on the temperature-Gibbs free energy diagram.

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Electron Irradiation Induced Crystal-to-Amorphous-to-Crystal Transition in Some Metallic Glasses

Electron Irradiation Induced Phase Transformation in Fe-Nd-B Alloys

Akihiro Nino, Takeshi Nagase, Yukichi Umakoshi

pp. 1659-1664

Abstract

The effect of electron irradiation on the phase transformation in binary Fe-Nd and ternary Fe-Nd-B alloys was investigated. Electron irradiation induced nano-crystallization of amorphous-to-crystal (A-C) transition was observed in several Fe-Nd-B metallic glasses. In Nd2Fe14B compound, solid-state amorphization (SSA) of crystal-to-amorphous (C-A) transition occurred under electron irradiation. With further irradiation, the amorphous phase obtained by SSA transformed to the nano-crystalline phase through irradiation induced crystallization, resulting in crystal-to-amorphous-to-crystal (C-A-C) transition. A-C, C-A and C-A-C transition were also observed in some ternary Fe-Nd-B and binary Fe-Nd alloys. The electron irradiation technique is effective for the formation and control of nano-crystalline structure through A-C transition of amorphous phase and/or C-A-C transition of metallic compounds.

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Electron Irradiation Induced Phase Transformation in Fe-Nd-B Alloys

Nanocrystalline Transformation and Inverse Transformation in Metallic Glasses Induced by Electropulsing

H. Mizubayashi, T. Takahashi, K. Nakamoto, H. Tanimoto

pp. 1665-1670

Abstract

Electropulsing by means of discharge of a condenser with the decay time (τ) of ms causes the athermal crystallization of metallic glasses when the initial current density (id0) is higher than the threshold value (id0,c). It is indicated that the major local amorphous structures in Zr50Cu50 are the amorphous structures with the short range order (SRO) similar to crystalline cubic (c) ZrCu which is the equilibrium crystalline phase above 988 K, although the mixture of crystalline Zr2Cu and Zr7Cu10 is the equilibrium phase below 988 K. Electropulsing tests on Zr50Cu50, Zr50Cu40Al10 and Zr50Cu35Al10Ni5 metallic glasses indicate that the amorphous structures with SRO similar to cZrCu are the major local amorphous structures in these metallic glasses, and their volume fractions decrease in the order of Zr50Cu50, Zr50Cu40Al10 and Zr50Cu35Al10Ni5. The amount of the amorphous structures with SRO similar to cZrCu may govern the thermal stability of these metallic glasses. Further in Zr50Cu50 metallic glasses, the inverse transformation from the electropulsing-induced fine crystallites to the amorphous phase for subsequent electropulsing with increasing id0, and the Ostwald-ripening-like phenomenon under electropulsing were observed.

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Nanocrystalline Transformation and Inverse Transformation in Metallic Glasses Induced by Electropulsing

Estimation of Relative Glass Forming Abilities of Multicomponent Alloy Systems

Deok Kim, Yoon S. Oh, Geun T. Bae, Byeong-Joo Lee, Nack J. Kim

pp. 1671-1674

Abstract

A thermodynamic calculation scheme based on a CALPHAD method has been studied to evaluate the relative glass forming abilities (GFAs) of multicomponent alloy systems. The concept of the normalized driving force has been developed for estimation of the relative GFAs of different alloy systems. Driving forces of formation of crystalline phases under metastable supercooled liquid state have been calculated for different alloy systems to predict the possible crystalline phases and the maximum driving forces normalized by the respective melting temperatures are correlated with the experimentally obtained GFAs of the alloys. It shows that the estimated relative GFAs of different alloy systems based on the normalized driving forces agree well with the experimental results.

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Estimation of Relative Glass Forming Abilities of Multicomponent Alloy Systems

A Simple Model for Examining Composition Effects in Eutectic Nucleation

J. R. Morris, F. Jiang, P. K. Liaw

pp. 1675-1679

Abstract

We present a simple thermodynamic calculation for a strongly partitioning eutectic system, to examine how the critical nucleus energy changes, depending upon assumptions of the chemical diffusion. The calculations show that for strongly partitioning systems, the maximum undercooling may occur at a composition significantly different than the eutectic composition, particularly if the rate of diffusion is slow in the undercooled state. These simple calculations emphasize the role that partitioning and composition may play in determining optimal compositions in metallic glass systems, which typically occur near (but not at) deep eutectic compositions.

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A Simple Model for Examining Composition Effects in Eutectic Nucleation

The Influence of Similar Element Coexistence in (La-Ce)-Al-(Co-Cu) Bulk Metallic Glasses

Ran Li, Fengjuan Liu, Shujie Pang, Chaoli Ma, Tao Zhang

pp. 1680-1683

Abstract

In this paper, a pseudo-ternary (La0.5Ce0.5)65Al10Co25 alloy with high glass-forming ability (GFA), identified by the formation of glassy rods up to 12 mm in diameter by copper mold casting, was reported. Furthermore, according to the viewpoint that similar element coexistence can be beneficial to improve the GFA, Cu was chosen as the similar element to substitute for solute Co in (La0.5Ce0.5)65Al10(Co1−xCux)25 alloys (0≤x≤1). The influence of this substitution on thermal stability, melting and solidification behaviors of these metallic glasses was evaluated. The optimized (La0.5Ce0.5)65Al10(Co0.6Cu0.4)25 alloy with high reduced glass transition temperature (0.66) and the large nominal supercooled degree (114 K) can form the fully glassy rods up to at least 25 mm in diameter by tilt-pour casting.

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The Influence of Similar Element Coexistence in (La-Ce)-Al-(Co-Cu) Bulk Metallic Glasses

Glass Forming Ability and Thermal Properties of the Mg-Based Amorphous Alloys with Dual Rare Earth Elements Addition

J. S. C. Jang, C. C. Tseng, L. J. Chang, C. F. Chang, W. J. Lee, J. C. Huang, C. T. Liu

pp. 1684-1688

Abstract

The Mg58Cu31Y11−xNdx (x=0∼11) amorphous alloy rods with 3∼10 mm in diameter were prepared by Cu-mold injection method. The XRD result reveals that these entire Mg58Cu31Y11−xNdx alloy rods exhibit a broaden diffraction pattern of amorphous phase. A clear Tg (glass transition temperature) and supercooled region (about 70 K) were revealed for all of those Mg58Cu31Y11−xNdx amorphous alloy rods. The single stage crystallization of the Mg58Cu31Y11 alloy was found to change into two stages crystallization when large amount of Nd element was added into this alloy. In parallel, the crystallization temperature (Tx) and supercooled region (ΔTx) present a decreasing trend with increasing Nd content. The highest γ value of 0.414 occurs at the alloy compositions of Mg58Cu31Y4Nd7 and Mg58Cu31Y6Nd5 in this alloy system. Therefore, suitable addition of Nd element can obviously increase the glass forming ability for the Mg58Cu31Y11−xNdx alloy system.

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Glass Forming Ability and Thermal Properties of the Mg-Based Amorphous Alloys with Dual Rare Earth Elements Addition

Comparison of Crystallization Process of Amorphous Zr2Ni Alloy and Metallic Zr2Cu Glass

D. Okai, T. Fukami, M. Asada, I. Noda, T. Yamasaki, Y. Yokoyama, A. Inoue

pp. 1689-1693

Abstract

Crystal nucleation and time evolution during isothermal annealing in amorphous Zr2Ni at several temperatures just below a crystallization temperature Tx and in supercooled liquid of metallic glass Zr2Cu are examined using a technique of differential thermal analysis. Time dependence of the fraction of crystallization at several temperatures is analyzed by the Johnson-Mehl-Avrami equation. The Avrami exponent is 3.0±0.2 for Zr2Ni and varies from about 3 to 7 for Zr2Cu with increasing temperature. It is suggested for Zr2Ni that the crystal growth at temperatures just below Tx is ruled by a short range diffusion process of constituent elements. The time evolution of crystallized fraction was not well scaled by the half of complete time for full crystallization.

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Comparison of Crystallization Process of Amorphous Zr2Ni Alloy and Metallic Zr2Cu Glass

Effects of P Content on Nanocrystalline Morphology Formed by FIB Irradiation in Ni-P Amorphous Alloy

Koji Sato, Chiemi Ishiyama, Masato Sone, Yakichi Higo

pp. 1694-1697

Abstract

We studied the effects of phosphorus (P) on the Ni nanocrystalline morphology of Ni-P amorphous alloy thin films subjected to focused ion beam (FIB) irradiation. The P contents in the amorphous alloys varied from 14 to 20 at%. The nanocrystals induced by FIB irradiation of Ni-20.2, 15.6, and 14.0 at%P amorphous alloys had a face-centered-crystal (f.c.c.) structure and showed unique crystallographic orientation relationships to the geometry of the focused ion beam, with {111}f.c.c. parallel to the irradiated plane and ⟨110⟩f.c.c. parallel to the direction of the projected ion beam, respectively. The Ni nanocrystals formed by FIB irradiation precipitated in the same manner as aggregates, and the average size of the Ni nanocrystals increased as the P content decreased. These results indicate that the P content does not affect the crystallographic orientation relationships but does influence precipitation distribution of the Ni nanocrystals.

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Effects of P Content on Nanocrystalline Morphology Formed by FIB Irradiation in Ni-P Amorphous Alloy

Voronoi Analysis of the Structure of Ni-Zr-Al Ternary Metallic Glass

T. Fukunaga, K. Itoh, T. Otomo, K. Mori, M. Sugiyama, H. Kato, M. Hasegawa, A. Hirata, Y. Hirotsu, A. C. Hannon

pp. 1698-1702

Abstract

Ni-Zr metallic glasses have been recognized to be unstable in comparison with Cu-Zr metallic glasses. An analysis of Voronoi polyhedra in the RMC simulations based on the diffraction data could characterize the atomic configurations around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prism-like, Archimedian antiprism-like, and similar polyhedra. In contrast, icosahedron-like polyhedra are preferred for Cu. The Ni-Zr glasses have been reported to stabilize by adding Al. Therefore, in this work, the analysis of Voronoi polyhedra around Ni, Zr and Al atoms for Ni25Zr60Al15 ternary metallic glass was carried out in order to clarify the difference between the atomic structures for the binary and ternary metallic glasses. Trigonal prism-like, Archimedian antiprism-like and similar polyhedra, which are dominated in the Ni-Zr metallic glasses, decreased in number by adding Al to the Ni-Zr system. On the contrary, the number of icosahedron-like polyhedra was found to increase. The results apparently indicate that the addition of Al into Ni-Zr binary system promote the formation of icosahedron-like polyhedra in the structure. Therefore, from these results, we can easily recognize that icosahedron-like polyhedra play an important role to stabilize the structure of metallic glasses.

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Voronoi Analysis of the Structure of Ni-Zr-Al Ternary Metallic Glass

Local Structure Study in Zr-Based Metallic Glasses

Junji Saida, Takashi Sanada, Shigeo Sato, Muneyuki Imafuku, Eiichiro Matsubara, Akihisa Inoue

pp. 1703-1707

Abstract

The local structure in the glassy state is investigated in the Zr80Pt20 and Zr70Cu30 binary and Zr70Al10Ni20 ternary alloys in correlation with the quasicrystalline (QC) phase formation. The Zr80Pt20 alloy has a high QC-forming ability. It is easily formed in the as-quenched state with a considerably low cooling rate or by annealing the glassy alloy. The radial distribution function (RDF) and extended X-ray absorption fine structure (EXAFS) analysis clearly indicate the existence of icosahedral local structure around Pt atom. The Zr70Cu30 binary and Zr70Al10Ni20 ternary metallic glasses have a QC-forming ability by the addition of a very small amount of noble metals such as Pd. We can also investigate the icosahedral local structure in these alloys. These results are realized that the icosahedral local structure can be applied as a dominant local atomic configuration in the supercooled liquid and/or glassy states in the QC-forming metallic glasses.

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Local Structure Study in Zr-Based Metallic Glasses

Precise Measurement of Density in the Isothermal Relaxation Processes of Pd42.5Cu30Ni7.5P20 and Zr50Cu40Al10 Glasses

Osami Haruyama, Yoshihiko Yokoyama, Akihisa Inoue

pp. 1708-1710

Abstract

The isothermal relaxation processes of bulk Zr50Cu40Al10 and Pd42.5Cu30Ni7.5P20 glasses were examined by density reduction associated with relaxation. Density experiments were carried out by buoyancy method at room temperature. The isothermal relaxation curves were best fitted by a stretched exponential function with a Kohlrausch exponent less than unity. Based on free volume model, the reduced free volume xfas=0.0355 and flow defect concentration Cfas=5.80×10−13 in as-quenched state was obtained for Pd42.5Cu30Ni7.5P20 glass. However, the temperature at which the free volume started to deviate from equilibrium concentration on cooling of the melt was not in accordance with calorimetric glass transition temperature.

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Precise Measurement of Density in the Isothermal Relaxation Processes of Pd42.5Cu30Ni7.5P20 and Zr50Cu40Al10 Glasses

Cluster Expansion Approach for Relative Stability among Different Atomic Structures in Alloys: an Approach from a Dilute Limit

M. Asato, H. Takahashi, T. Inagaki, N. Fujima, R. Tamura, T. Hoshino

pp. 1711-1716

Abstract

We demonstrate the ability of our cluster expansion approach (CEA) for cohesive energies of alloys, which allows one to study the chemical trends of the relative stability of different atomic structures of alloys, as an example, X dependence of the atomic structures of Al-rich AlX (X = Sc-Zn) alloys, including ordered structures (L12(Al3Sc), DO22 (Al3V)), a Mackay icosahedron (a local structure in the Al80Mn20 quasicrystal), and precipitate shapes in decomposition phases (Al1−cCuc, Al1−cZnc; c<0.05). All the terms in the CEA for Al-rich AlX alloy can be determined uniquely and successively from low-order to high-order by using the total energies of isolated Al and X atoms, pure Al and X metals, and X impurities in Al metal. The total energies of impurity systems are calculated accurately by using the all-electron full-potential Korringa-Kohn-Rostoker (FPKKR) Green’s function method, combined with the density-functional theory in the generalized-gradient approximation (GGA). We show: (1) the binding energies of X (X = Cu, Zn) impurities in Al are reproduced very well by the CEA including two- and three-body interaction energies of X impurities; (2) the chemical trends of structural stability among ordered structures (L12, DO22, DO23) of Al3X (X = Sc, Ti, V), being determined by use of the screened-FPKKR and GGA band-structure calculations, are reproduced by the CEA including only two-body (X-X) interaction energies in Al.

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Cluster Expansion Approach for Relative Stability among Different Atomic Structures in Alloys: an Approach from a Dilute Limit

Thermal Stability and Mechanical Properties of Spray-Formed and Melt-Spun Al89La6Ni5 Metallic Glass Matrix Composites

M.-L. Ted Guo, Chi Y. A. Tsao, K. F. Chang, J. C. Huang, J. S. C. Jang

pp. 1717-1721

Abstract

A spray-formed Al89La6Ni5 metallic glass matrix composite plate was obtained in thickness of 1 mm and diameter of 200 mm, comprising over 64% primary crystals (e.g. Al11La3) uniformly dispersed in the glass matrix. The microstructure can not be achieved by annealing corresponding amorphous precursor. The crystals existing in the glass matrix were found to increase the hardness of the composite. Through nanoindentation test, the hardness and modulus of the composite at ambient temperature were found superior than its amorphous ribbon counterpart. The hardness of the composite was estimated with the rule of mixture from the constituents to be 4.4 GPa, which agreed well with the nanoindentation results. From loss modulus measurement and TMA test at elevated temperatures, a weak Tg signal in the range of 213–240°C was revealed in the as-spray-formed composite. Furthermore, the dimension shrinkage of the composite was only 0.5% during the TMA test, which is much smaller than that of amorphous ribbon counterpart by up to 20%. The enhanced hardness by constituent second phases and the dimension stability of the composite are associated with their inherent microstructure, the primary crystals in particular.

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Thermal Stability and Mechanical Properties of Spray-Formed and Melt-Spun Al89La6Ni5 Metallic Glass Matrix Composites

Structural Relaxation and Crystallization of a Zr44Ti11Cu9.8Ni10.2Be25 Bulk Metallic Glass

Kwang Seok Lee, Hyun-Joon Jun, Dae Woo Kim, Jürgen Eckert, Young Won Chang

pp. 1722-1728

Abstract

The influence of annealing on the structural changes and the room temperature mechanical properties of a Zr44Ti11Cu9.8Ni10.2Be25 bulk metallic glass has been investigated. The structural evolution upon relaxation or crystallization after annealing at a temperature within the supercooled liquid region was studied by thermal analysis, x-ray diffraction, transmission electron microscopy, extended x-ray absorption fine structure and dilatometer measurements. The effects of structural relaxation and nanocrystallization on the mechanical properties were also examined by hardness and compression tests using specimens annealed for various times. The apparent disappearance of plastic strain was found to be due to embrittlement induced by considerable crystallization of the amorphous phase.

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Structural Relaxation and Crystallization of a Zr44Ti11Cu9.8Ni10.2Be25 Bulk Metallic Glass

Atomic Dynamics in Metallic Liquids and Glasses

T. Egami, V. Levashov, R. S. Aga, J. R. Morris

pp. 1729-1733

Abstract

How atoms move in metallic glasses and liquids is an important question in discussing atomic transport, glass formation, structural relaxation and other properties of metallic glasses. While the concept of free-volume has long been used in describing atomic transport, computer simulations and isotope measurements have shown that atomic transport occurs by a much more collective process than assumed in the free-volume theory. We introduce a new approach to describe the atomic dynamics in metallic glasses, in terms of local energy landscapes related to fluctuations in the topology of atomic connectivity. This approach may form the basis for a new paradigm for discussing the structure-properties relationship in metallic glasses.

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Atomic Dynamics in Metallic Liquids and Glasses

Ab-Initio Data for Interatomic Interactions in Zr-Rich ZrX (X=Sc-Cu) Alloys and Stability of Icosahedron-Like Zr13−nCun (n=3, 4) Clusters in Zr70Cu30 Metallic Glass

N. Fujima, M. Asato, R. Tamura, T. Hoshino

pp. 1734-1738

Abstract

We give ab-initio data for the study of the stability of the atomic structures of Zr-rich ZrX (X=Sc-Cu) alloys, such as the cohesive energies and equilibrium Wigner-Seitz radii of elemental metals X (X=Sc-Cu, Zr-Ag) and X-X (X=Sc-Cu) interaction energies in Zr. The calculations are based on the density functional thoery in the generalized gradient approximation and employ the full-potential Korringa-Kohn-Rostoker Green’s function method. Using the calculated results, we elucidate the fundamental features of interatomic interactions of Zr-rich ZrX alloys. Especially, we found that the pair interaction of Cu impurities in Zr becomes strongly attractive around the interatomic distance of 0.45∼0.46 nm. It is shown that this interaction may be important for the stability of icosahedron-like local atomic structures of Zr10Cu3 and Zr9Cu4 clusters in the Zr70Cu30 bulk metallic glass, being proposed experimentally. We also found that the atomic structure of an isolated Zr10X3 cluster transforms from the hcp structure (initial state) to an icosahedron-like structure (final state) for X=Cu, but not for X=Ni.

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Ab-Initio Data for Interatomic Interactions in Zr-Rich ZrX (X=Sc-Cu) Alloys and Stability of Icosahedron-Like Zr13−nCun (n=3, 4) Clusters in Zr70Cu30 Metallic Glass

Topological Instability as a Criterion for Design and Selection of Easy Glass-Former Compositions in Cu-Zr Based Systems

C. S. Kiminami, R. D. Sá Lisboa, M. F. de Oliveira, C. Bolfarini, W. J. Botta

pp. 1739-1742

Abstract

In the present work we propose a new approach for predicting the best glass-former composition(s) in multi-component metallic glasses. By applying the λ criterion, a topological instability criterion proposed to predict the crystallisation behaviour of Al-based systems, we show that it is also successfully possible to reproduce compositional ranges where binary and ternary bulk metallic glasses (BMGs) have recently been obtained. Our results indicate that the good glass-former composition(s) lie(s) within fields of mutual and simultaneous topological instability of all the crystalline phases competing with glassy phase.

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Topological Instability as a Criterion for Design and Selection of Easy Glass-Former Compositions in Cu-Zr Based Systems

Microindentation of a Zr57Ti5Cu20Ni8Al10 Bulk Metallic Glass

Rong Chen, Fuqian Yang, Peter K. Liaw, Guojiang Fan, Hahn Choo

pp. 1743-1747

Abstract

Using microindentation technique, the indentation behavior of a Zr57Ti5Cu20Ni8Al10 bulk-metallic glass is studied over a range of the indentation load from 200 mN to 5000 mN. For the indentation load larger than 1000 mN, the indentation load-depth curves during unloading display three regions, a) a fast unloading phase at the onset of unloading, b) a linear phase at which the indentation load is proportional to the indentation depth, and c) a slow unloading phase after the linear phase. The size of the linear region increases with the increase in the indentation load, and the slope is independent of the indentation load. The indentation hardness decreases slightly with the increase in the indentation load. The plastic energy dissipated in an indentation cycle is proportional to the 3/2 power of the indentation load. The effect of the indentation loading rate on the indentation behavior is discussed.

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Microindentation of a Zr57Ti5Cu20Ni8Al10 Bulk Metallic Glass

The Influence of Viscous Flow Deformation on the Thermal Stability and Hardness of ZrCuAlNi Bulk Glassy Alloy

Shengli Zhu, Xinmin Wang, Fengxiang Qin, Akihisa Inoue

pp. 1748-1751

Abstract

We investigated the thermal stability and hardness of a Zr55Cu30Al10Ni5 bulk glassy alloy after isothermal viscous flow deformation in the supercooled liquid region. The influence of deformation temperature, holding time and initial strain rate on the thermal stability and hardness of a Zr55Cu30Al10Ni5 bulk glassy alloy subjected to the high temperature compression test was examined by differential scanning calorimetry (DSC) and with a Vickers micro-hardness tester. The results showed that the incubation time for isothermal annealing crystallization reduced during the viscous flow deformation. Thermal stability of supercooled liquid decreased after viscous flow deformation. As the deformation temperature increased, the SCL region decreases. At lower temperatures below 713 K the structural relaxation occurred, resulting in a slight increase in hardness. The crystallization at higher temperatures of over 723 K caused a rapid increase in hardness. The supercooled liquid region decreased and the hardness increased with increasing deformation time. Higher strain rate resulted in larger deformation in the same deformation time, and had slight influence on the thermal stability and hardness of the Zr55Cu30Al10Ni5 glassy alloy. When the Zr55Cu30Al10Ni5 bulk glassy alloy was compressed for 300 s with an initial strain rate of 3.3×10−3 s−1 at the temperatures of 723 K, nanocrystallization occurred, and the grain size was evaluated to be smaller than 5 nm.

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The Influence of Viscous Flow Deformation on the Thermal Stability and Hardness of ZrCuAlNi Bulk Glassy Alloy

Temperature-Dependent Mechanical Property of Zr-Based Metallic Glasses

Hongqi Li, Cang Fan, Hahn Choo, Peter K. Liaw

pp. 1752-1754

Abstract

The compression tests were conducted on four Zr-based bulk metallic glasses (BMGs) with different Nb contents. The results show that the addition of few percent Nb did not change the mechanical property. At 77 K, the strength increased notably without embrittlement. Furthermore, it is suggested that the normalized strength changes linearly with the normalized temperature. Current results provided important evidences that BMGs have a great application perspective at cryogenic temperatures. In addition, it is found that at ambient temperature, the BMGs do not exhibit strain rate sensitivity. However, the strength is dependent on the strain rate at high and cryogenic temperatures.

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Temperature-Dependent Mechanical Property of Zr-Based Metallic Glasses

Internal Friction of Nitrogen-Doped Zr-Based Glassy Composite Alloy

Masashi Hasegawa, Daisuke Nagata, Takeshi Wada, Akihisa Inoue

pp. 1755-1758

Abstract

Internal friction of Zr-based glassy composite alloys containing dispersed-ZrN particles, which were prepared by a powder compact melting and liquid-quenching process using Zr-Al-Ni-Cu glassy alloy and AlN powders as the starting materials, has been investigated using a reed method over the temperature range of ∼90–350 K. It should be noted that a broad multi-composed peak was observed around 260 K. The peak internal friction was about 3×10−3. It was also noteworthy that the so-called ΔM effect of the Young’s modulus in its temperature dependence was observed. In addition, the internal friction at the peak temperature depended little on the strain amplitude in the range of about ∼1×10−6–∼2×10−4. These results indicate that the observed internal friction peak is related to the relaxation process. Since the hydrogen content in the sample was very low (0.24 at%H), the observed internal friction peak is suggested to be induced by the interstitially doped nitrogen in the glassy phase.

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Internal Friction of Nitrogen-Doped Zr-Based Glassy Composite Alloy

Characterization of Shear Banding in La-Based Bulk Metallic Glasses through Indentation

Wei Peng, Bingchen Wei, Taihua Zhang, Yuan Liu, Lei Li

pp. 1759-1764

Abstract

La64Al14(Cu,Ni)22, La63.1Al15.2(Cu,Ni)21.7, La57.6Al17.5(Cu,Ni)24.9, and La55Al25Cu10Ni5Co5 bulk metallic glasses (BMGs) with low glass transition temperature (Tg) were prepared by copper-mould casting method. The homologous temperature (the ratio of room temperature to Tg) of the four BMGs ranges from 0.64 to 0.73. Plastic deformation behavior of the BMGs at various loading rates was studied by nanoindentation. The results showed that the loading rate dependency of serrated flow, which is related to the nucleation and propagation of shear bands, depends strongly on the homologous temperature. The alloys with relatively high homologous temperature exhibit an increase in flow serration with increasing loading rate, whereas, the alloys with low homologous temperature exhibit prominent serrations at low rates. No distinct shear band is observed around the indents for all alloys after nanoindentation at all the studied loading rates. Alternately, shear band pattern are characterized through macro-indentation, which shows that shear band spacing decreases with the increase of the homologous temperature.

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Characterization of Shear Banding in La-Based Bulk Metallic Glasses through Indentation

Influence of Indenter Geometry on the Deformation Behavior of Zr60Cu30Al10 Bulk Metallic Glass during Nanoindentation

Byung-Gil Yoo, Ju-Young Kim, Jae-il Jang

pp. 1765-1769

Abstract

As a first step in examining a new aspect of inhomogeneous plastic flow in bulk metallic glasses (BMGs) during nanoindentation, a series of nanoindentation experiments were performed on Zr60Cu30Al10 BMG with two pyramidal indenters (Berkovich and cube-corner indenters) having different centreline-to-face angle. It was revealed that the indenter angle can be a new controllable factor affecting the serrated flow behaviour of the BMG during nanoindentation, since a sharper cube-corner indenter induces different stress field under the contact from Berkovich indenter typically used. Results are discussed in terms of preliminary ideas for improving analysis of the shear-band-ruled deformation behaviours in the BMG during nanoindentation.

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Influence of Indenter Geometry on the Deformation Behavior of Zr60Cu30Al10 Bulk Metallic Glass during Nanoindentation

Fatigue Crack Initiation and Small-Crack Propagation in Zr-Based Bulk Metallic Glass

Yoshikazu Nakai, Shohei Hosomi

pp. 1770-1773

Abstract

Fatigue tests on Zr-based bulk metallic glass were conducted under fully reversed cyclic bending (R=−1), and the surfaces of the fatigued specimen were observed to elucidate the fatigue crack initiation mechanisms. The fracture surface was also observed to examine the crack propagation mechanism. In contrast to most brittle materials, the metallic glass showed fatigue behavior. Its fatigue strength was much lower than its tensile strength, and it had a fatigue limit. In the S-N curve, the number of cycles at the knee point was much lower than that for crystalline metals. The fatigue crack initiation process observed by atomic force microscopy (AFM) showed that cracks were initiated at the bottom of shear steps just after their formation.

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Fatigue Crack Initiation and Small-Crack Propagation in Zr-Based Bulk Metallic Glass

Temperature, Strain and Strain Rate Dependence of Serrated Flow in Bulk Metallic Glasses

Florian H. Dalla Torre, Alban Dubach, Adrienne Nelson, Jörg F. Löffler

pp. 1774-1780

Abstract

New findings on the inhomogeneous plastic deformation of bulk metallic glasses (BMGs) have shown a disappearance of serrated flow below a critical temperature or above a critical strain rate. This correlates with a change in the strain rate sensitivity (SRS) from negative to positive values, suggesting a change in the deformation mechanism. In addition, a change in the SRS correlating with the increase in the stress drop magnitude is observed with increasing strain. Results on the serration and flow dependence for the binary BMG Cu50Zr50 show close phenomenological similarities with the Portevin - Le Châtelier or dynamic strain aging effect known for crystalline solids. An alternative model for the appearance and disappearance of serrated flow based on the structural relaxation of the atomic configuration of shear transformation zones is described.

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Temperature, Strain and Strain Rate Dependence of Serrated Flow in Bulk Metallic Glasses

Effect of Structural Relaxation on Mechanical Behavior of a Zr-Based Bulk-Metallic Glass

W. H. Jiang, F. X. Liu, H. Choo, P. K. Liaw

pp. 1781-1784

Abstract

Using the instrumented nanoindentation and differential-scanning calorimetry, the effect of the structural relaxation at the elevated temperature on the Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 bulk-metallic glass was investigated. The structural relaxation did not exert a significant influence on the plastic-flow behavior. However, the relaxation enhanced both the hardness and elastic modulus substantially. The decrease in the structural relaxation enthalpy before the glass transition indicates that the relaxation reduced the free volume significantly. The increase in the hardness and elastic modulus is attributed to the reduction in the free volume that resulted from the relaxation.

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Effect of Structural Relaxation on Mechanical Behavior of a Zr-Based Bulk-Metallic Glass

Evaluation of Micro-Sized BMG Tensile Specimen Fabricated by Electrolytic Polishing Technique

Mikito Kondo, Ryo Morihashi, Chiemi Ishiyama, Masato Sone, Yakichi Higo

pp. 1785-1788

Abstract

An electrolytic polishing technique was used to fabricate micro-sized tensile specimens from two Zr55Al10Ni5Cu30 bulk metallic glass samples. One sample had a fully amorphous phase, while the other had dendrites with an average size of 33 μm within the amorphous matrix. A scanning electron microscope showed that specimens fabricated by electrolytic polishing had smooth surfaces. The specimens were then subjected to tensile tests at room temperature. The fully amorphous specimen had a fracture strength of 1,640 MPa. This specimen also showed slight plastic deformation after yielding, as well as vein patterns and smooth surface on the fracture surface. Multiple thin shear bands generated from a shear band were observed on the side surface of fractured specimen. The specimen containing dendrites was quite low in strength compared to the fully amorphous specimen, and had yield and fracture strengths of 460 and 600 MPa, respectively. The specimen containing dendrites also showed plastic deformation and work hardening after yielding, as well as vein patterns and a brittle fracture region on the fracture surface.

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Evaluation of Micro-Sized BMG Tensile Specimen Fabricated by Electrolytic Polishing Technique

Bulk Glassy and Quasicrystalline (Zr65Al7.5Cu27.5)100−xTix Alloys and Their Mechanical Properties

J. B. Qiang, W. Zhang, G. Q. Xie, A. Inoue

pp. 1789-1792

Abstract

The glass-forming ability (GFA) and thermal stability of (Zr65Al7.5Cu27.5)100−xTix (x=0∼15; in at%) alloys have been investigated. It was revealed that a certain amount of Ti addition could improve the GFA of Zr65Al7.5Cu27.5 alloy effectively. The best bulk metallic glass (BMG) forming composition was found at (Zr65Al7.5Cu27.5)93Ti7. Bulk glassy samples with diameter of 7 mm were made by means of copper mold casting. Further Ti additions deteriorated GFA and led to the precipitation of icosahedral phase, and 3 mm quasicrystalline cylinder was obtained at (Zr65Al7.5Cu27.5)90Ti10. Room temperature compression testing showed that the quasicrystalline alloy had a fracture strength of 1875 MPa, being 300 MPa larger than that of the (Zr65Al7.5Cu27.5)93Ti7 monolithic BMG.

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Bulk Glassy and Quasicrystalline (Zr65Al7.5Cu27.5)100−xTix Alloys and Their Mechanical Properties

A Model for the Fragility of Metallic Glass Forming Liquids

Masaru Aniya, Takaki Shinkawa

pp. 1793-1796

Abstract

An expression for the temperature dependence of the viscosity and fragility is derived based on a simple model of the melt. According to the model, the fragility is determined by the relaxation of structural units that form the melt, and is described in terms of the bond strength, coordination number, and their fluctuations of the structural units. It is shown that the fragility of some metallic glass forming liquids such as Pd40Ni40P20, La55Al25Ni20 and Zr65Al10Ni10Cu15 are quite well reproduced by the model. The application of the theory to La55Al25Ni20 has revealed that the fluctuation in the bond strength between the structural units is about 6% and that the viscous flow occurs when the bonds in about 8 adjoining structural units are broken.

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A Model for the Fragility of Metallic Glass Forming Liquids

Mechanical Properties of the Hot-Pressed Amorphous Mg65Cu20Y10Ag5/NanoZrO2 Composite Alloy

L. J. Chang, G. R. Fang, J. S. C. Jang, I. S. Lee, J. C. Huang, Chi Y. A. Tsao, J. L. Jou

pp. 1797-1801

Abstract

Amorphous Mg65Cu20Y10Ag5/nano ZrO2 composite alloys are fabricated through mechanical alloying (MA) in the planetary mill, using amorphous matrix alloy prepared by melt spun and 3 vol% spherical nano-sized ZrO2 particles. The specimens were hot pressed in Ar atmosphere under the pressure of 700 MPa at the temperature of soft point which is determined by TMA (Thermo mechanical Analysis). The hot-pressed composite alloy can reach to a 96% density, the hardness of 315±10 in Hv scale, and the compressive strength of 690 MPa. In addition, the result of mechanical test revealed that the nano-sized ZrO2 dispersion can obviously increase hardness as well as toughness of the Mg based amorphous alloy. Moreover, after compression test at 426 K (sample has been deformed 60 vol%), the hardness of hot-pressed composite alloy dramatically increases to Hv 400±25. An image of shear band being stopped in front of the ZrO2 particle was found by the TEM observation. Base on these two evidences, suggests that the strength of amorphous Mg65Y10Cu20Ag5 with 3 vol% ZrO2 composite alloy could be potentially improved by healing its residue porosity with hot deformation method within the supercooled liquid temperature region.

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Mechanical Properties of the Hot-Pressed Amorphous Mg65Cu20Y10Ag5/NanoZrO2 Composite Alloy

Compression Behavior of Mg-Cu-Gd Bulk Metallic Glasses with Various Specimen Height to Diameter Ratios

H. M. Chen, Y. C. Chang, T. H. Hung, X. H. Du, J. C. Huang, J. S. C. Jang, P. K. Liaw

pp. 1802-1805

Abstract

The mechanical behavior of the Mg65Cu25Gd10 bulk metallic glasses (BMGs) in term of compression testing is reported in this study. Room-temperature compression tests are conducted on specimens with various height to diameter ratios (hd) from 2:1, 1:1, 1:2, to 1:4. The failure strength, deformation strain, and the fracture surface morphologies are seen to vary systematically in accordance with the specimen hd ratio. For specimens with hd of 2:1 or 1:1, the compression response is similar to those in most reports. In contrast, for specimens with lower hd ratios, especially at hd=1:4 (or 0.25), the shear band propagation appears to be constrained, resulting in the enhanced ductility. It suggests that different deformation mechanisms are operative for specimens with different hd ratios. The possible deformation mechanisms in specimens of different geometries are discussed.

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Compression Behavior of Mg-Cu-Gd Bulk Metallic Glasses with Various Specimen Height to Diameter Ratios

Impact of Microstructural Inhomogenities on the Ductility of Bulk Metallic Glasses

J. Eckert, J. Das, S. Pauly, C. Duhamel, K. B. Kim, S. Yi, W. H. Wang

pp. 1806-1811

Abstract

To circumvent the limited ductility of bulk metallic glasses (BMGs), heterogeneous materials with glassy matrix and different type and length-scale of heterogeneities (micrometer-sized second phase particles or fibers, nanocrystals in a glassy matrix, phase separated regions, variations in short-range order by clustering) have been developed in order to control the mechanical properties. As example, recent results obtained for Cu- and Ti-base structurally imhomogeneous bulk metallic glasses will be presented. This type of clustered glasses is able to achieve high strength together with pronounced work hardening and large ductility by controlling the instabilities otherwise responsible for early failure. We emphasize the possibilities to manipulate such spatially inhomogeneous glassy structures based on martensitic alloys in favor of either strength and ductility, or a combination of both and also discuss the acquired ability to synthesize such M-glasses in bulk form through inexpensive processing routes.

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Impact of Microstructural Inhomogenities on the Ductility of Bulk Metallic Glasses

Mechanical Properties and Microstructures of Composites of Ti-Based Metallic Glass and β–Ti

Tokujiro Yamamoto, Hirofumi Ito, Masashi Hasegawa, Akihisa Inoue

pp. 1812-1815

Abstract

Microstructures and mechanical properties of Cu mold-cast Ti50Cu25Ni15Sn5Ta5 and Ti45Zr5Cu44Ni5Ta1 alloys were investigated by means of X-ray diffraction, electron microscopy and compressive testing. Ti50Cu25Ni15Sn5Ta5 alloys form microscopic composites consisting of Ti-based metallic glass as primary phase and β–Ti phases, while Ti45Zr5Cu44Ni5Ta1 alloys consisting of Ti-based metallic glass matrix and high density of nanocrystals dispersed in the matrix homogeneously. Ti50Cu25Ni15Sn5Ta5 bulk composite alloys showed 1.6% of plastic deformation and 2200 MPa of 0.2% of proof stress. The alloys also exhibited work hardening because of the presence of microscopic crystalline phases. Ti45Zr5Cu44Ni5Ta1 bulk alloys also deformed plastically after stress reached 2000 MPa without work hardening.

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Mechanical Properties and Microstructures of Composites of Ti-Based Metallic Glass and β–Ti

Free Volume Evolution in Metallic Glasses Subjected to Mechanical Deformation

Qi-Kai Li, Mo Li

pp. 1816-1821

Abstract

We define the Turnbull-Cohen free volume as the critical excess of the Voronoi volume of an atom less its core volume. Using molecular dynamics simulation we calculated the free volume change in two model binary metallic glasses undergoing tension and shear deformation. We show that the free volume change is an integral part of the deformation process; and the shear localization manifested as a shear band is directly related to the inhomogeneous distribution of the free volumes. Shear band formation may consist of two stages: the initial free volume production in the amorphous solids and the liquefaction of the regions with accumulated deformation strains. We show, for the first time, the formation of voids and the “vein” patterns on fracture surfaces at atomic scales; they are the combined result of the free volume change and loading and sample conditions.

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Free Volume Evolution in Metallic Glasses Subjected to Mechanical Deformation

Characterization of Zr-Cu Base Metallic Glasses by means of Hydrogen Internal Friction Peak

H. Mizubayashi, I. Nakamura, K. Yamagishi, H. Tanimoto

pp. 1822-1827

Abstract

The hydrogen internal friction peak in Zr50-metallic glasses (Zr50Cu50, Zr50Cu40Al10 and Zr50Cu35Al10Ni5) was studied. The hydrogen internal friction peak was shifted exponentially to lower temperatures with increasing hydrogen concentration similarly to other Zr-Cu base metallic glasses reported in the literature. The peak height increased in proportion to the square-root of hydrogen concentration. These results were discussed in the view point of the hydrogen induced structural relaxation in these metallic glasses.

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Characterization of Zr-Cu Base Metallic Glasses by means of Hydrogen Internal Friction Peak

Compression-Compression Fatigue and Fracture Behaviors of Zr50Al10Cu37Pd3 Bulk-Metallic Glass

Dongchun Qiao, Gongyao Wang, Wenhui Jiang, Y. Yokoyama, Peter K. Liaw, Hann Choo

pp. 1828-1833

Abstract

The compression-compression fatigue and fracture behaviors were studied on the Zr50Al10Cu37Pd3 bulk-metallic glasses (BMGs) under a load control, employing an electrohydraulic machine, at a frequency of 10 Hz (using a sinusoidal waveform) with an R ratio of 10, where Rmin.⁄σmax.min. and σmax. are the applied minimum and maximum stresses, respectively). The obtained results were compared with those of the tension-tension fatigue tests. The life under the compression-compression fatigue was improved significantly. However the fatigue-endurance limits in two different stress states are comparable. The fracture morphology and the specimen surfaces were observed. The possible different fracture mechanisms under two kinds of stresses were discussed.

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Compression-Compression Fatigue and Fracture Behaviors of Zr50Al10Cu37Pd3 Bulk-Metallic Glass

Annealing Effects on Viscosity of Zr55Cu30Al10Ni5 Supercooled Liquids

T. Yamasaki, S. Maeda, T. Fukami, Y. Yokoyama, H. M. Kimura, A. Inoue

pp. 1834-1837

Abstract

Viscous flow behavior in supercooled liquid region of as-cast and annealed Zr55Cu30Al10Ni5 bulk metallic glasses has been examined by using a penetration viscometer under various heating rates of 20, 200 and 400°C/min. Applied load for the cylindrical-shaped penetration indenter with a diameter of 1 mm was varied from 0.049 N to 0.294 N. Viscosity was quite independent of these applied loads under the various heating conditions. When the sample was slowly heated at the rate of 20°C/min, viscosity exhibited relatively high values that may be mainly due to the skin effects of oxides on the sample surface. At the heating rate of 200°C/min and above, viscosity (η) largely decreased and tended to saturate. By annealing the bulk metallic glasses at 400°C, the density of the glasses increased, while the crystallization temperature (Tx), the viscosity and the activation energy for viscous flow in their soopercooled liquid decreased gradually with increasing the annealing time. The specific behaviour of viscosity has been explained by the formation of particles during annealing for relaxation.

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Annealing Effects on Viscosity of Zr55Cu30Al10Ni5 Supercooled Liquids

Thermoplastic Deformation and Mechanical Properties of Zr-Based Bulk Metallic Glasses

Takamasa Yoshikawa, Masataka Tokuda, Tadashi Inaba

pp. 1838-1841

Abstract

The effect of heating and thermoplastic deformation on the fracture stress of Zr55Cu30Al10Ni5 and Zr60Cu25Al10Ni5 bulk metallic glass at room temperature (RT) was studied. These metallic glasses were easily crystallized by the influence of heating beyond their upper limit temperature of 685 K and 713 K, respectively. The fracture stress was maintained the strength of material as cast below these temperatures while it decreased easily by crystallization. It was possible to deform these materials below these temperatures. Their strength after thermoplastic deformation depended on the amount of strain, strain rate, and temperature during the deformation. The lower temperature and higher strain rate resulted in high strength after thermoplastic deformation at RT.

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Thermoplastic Deformation and Mechanical Properties of Zr-Based Bulk Metallic Glasses

Low Temperature Elastic Properties of CuZrTi Bulk Metallic Glass

R. Tarumi, M. Hirao, T. Ichitsubo, E. Matsubara, J. Saida, H. Kato

pp. 1842-1845

Abstract

Temperature dependent elastic constants Cij(T) of Cu60Zr30Ti10 bulk metallic glass (BMG) have been studied using MHz frequency range electromagnetic acoustic resonance (EMAR) from 4.5 to 300 K. At ambient temperature, the BMG shows low shear/bulk modulus ratio (or equivalently high Poisson ratio) compared with that of corresponding crystalline state dues to the dense random packed glassy structure. Analysis of Cij(T) based on the Einstein type lattice vibration model revealed the notable softening in transverse mode acoustic phonons. This unusual vibrational property suggests the existence of liquid like weakly bonded region in the BMG.

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Low Temperature Elastic Properties of CuZrTi Bulk Metallic Glass

Relations between the Thermal and Mechanical Properties of Cast Zr-TM-Al (TM: Cu, Ni, or Co) Bulk Glassy Alloys

Yoshihiko Yokoyama, Toru Yamasaki, Peter K. Liaw, Akihisa Inoue

pp. 1846-1849

Abstract

Ternary Zr-TM-Al (TM: Cu, Ni or Co) bulk glassy alloys were fabricated to clarify the relations between the thermal and mechanical features. These alloy systems show the distinct ternary eutectic point, and a bulk glassy phase also forms around the ternary eutectic composition. We determine the 12 standard Zr-TM-Al bulk glassy alloys in this study. In the twelve standard Zr-TM-Al bulk glassy alloys, the glass-transition temperature has large positive correlation coefficient with Young’s modulus and Vickers hardness. The melting temperature has large negative correlation coefficient with Charpy impact value, fracture strain and volume change due to structural relaxation. Furthermore, in order to recognize the origin of ductility, Poisson’s ratio (metallic bond nature) and volume change (free volume) were also examined.

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Relations between the Thermal and Mechanical Properties of Cast Zr-TM-Al (TM: Cu, Ni, or Co) Bulk Glassy Alloys

Corrosion Properties of Ca Based Bulk Metallic Glasses

James Dahlman, Oleg N. Senkov, James M. Scott, Daniel B. Miracle

pp. 1850-1854

Abstract

The corrosion properties of ternary (Ca65Mg15Zn20 and Ca50Mg20Cu30), quaternary (Ca55Mg18Zn11Cu16), and quinternary (Ca55Mg15Al10Zn15Cu5) amorphous alloys were evaluated using static aqueous submersion at room temperature. Ca-Mg-Zn and Ca-Mg-Cu alloy systems experienced destructive corrosion reactions. Ca-Mg-Zn-Cu and Ca-Mg-Zn-Cu-Al based amorphous alloys demonstrated positive corrosion properties, forming corrosion films up to 23 μm thick in the quaternary alloy and 11 μm thick in the quinternary composition. Corrosion products were evaluated using X-ray diffraction (XRD), X-ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS).

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Corrosion Properties of Ca Based Bulk Metallic Glasses

Corrosion Behavior of a Ti-Based Bulk Metallic Glass and Its Crystalline Alloys

Fengxiang Qin, Masahiro Yoshimura, Xinming Wang, Shengli Zhu, Asahi Kawashima, Katsuhiko Asami, Akihisa Inoue

pp. 1855-1858

Abstract

The structure, thermal stability and corrosion behavior of the Ti40Zr10Cu36Pd14 bulk metallic glass and its crystalline alloys have been investigated in this paper. The results of potentiodynamic polarization measurements revealed that the Ti-based bulk metallic glass and its crystalline counterparts examined were spontaneously passivated by anodic polarization with the passive current density about 10−2 A/m2. The higher corrosion resistance for the Ti-based bulk metallic glass and partly crystalline alloys was attributed to stable and protective passive films enriched with titanium and zirconium. The Ti40Zr10Cu36Pd14 bulk metallic glass and its partial crystalline alloys produced recently without toxic elements are expected to be applied as biomaterials.

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Corrosion Behavior of a Ti-Based Bulk Metallic Glass and Its Crystalline Alloys

Microstructure and Elasticity of Glassy Alloy Surface by Reactive and Inert Ion Implantation

Shinji Muraishi, Hirono Naito, Tatuhiko Aizawa

pp. 1859-1863

Abstract

Present work focuses on the structural change of Zr-Cu glassy film via penetration of different reactivity of N+ and Ar+ and its elasticity measurement. Amorphous Zr-30 at%Cu film has been synthesized by ion beam sputtering on Si substrate. Nitrogen implantation induced precipitation microstructure with (Zr-Cu) nitride and Cu phase in glassy matrix. Inert gas element of Ar+ makes voids structure inside of the film at the mean penetration depth of Ar+ as maintained glassy phase. Resultant microstructures due to penetrated ions strongly depend on their degree of chemical reactivity with constituents. Surface elasticity of modified structure have been evaluated from nano-indentation test and given the normalization treatment for measured Young’s modulus.

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Article Title

Microstructure and Elasticity of Glassy Alloy Surface by Reactive and Inert Ion Implantation

Air Oxidation of an Fe48Cr15C15Mo14B6Er2 Bulk Metallic Glass at 600–725°C

H. H. Hsieh, W. Kai, R. T. Huang, D. C. Qiao, P. K. Liaw

pp. 1864-1869

Abstract

The oxidation behavior of an Fe48Cr15C15Mo14B6Er2 bulk metallic glass (Fe-BMG) was studied over the temperature range of 600–725°C in dry air. The oxidation kinetics of the glassy alloy followed a two-stage parabolic rate law at T≤650°C, while the single-stage linear rate was observed at higher temperatures (T≥675°C). The oxidation rates of the Fe-BMG at T≤625°C were much lower than those of the commercial 304 stainless steel (304 SS), revealing the excellent oxidation resistance of the amorphous alloy. A continuous, thin layer of chromium oxide (Cr2O3) containing some iron was formed at T≤650°C, while typical hump iron oxides intermixed with minor amounts of Cr2O3 and MoO2 were observed at T≥675°C. In addition, a substrate phase transformation from the amorphous structure to Fe-Cr and FeCrMo crystalline phases was detected after the oxidation. Very likely, the formation of the non-protective Fe3O4 and MoO2 breaks the scale integrity and allows the rapid cation/anion transportation, resulting in the fast linear-kinetics behavior of the Fe-BMG at T≥675°C.

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Air Oxidation of an Fe48Cr15C15Mo14B6Er2 Bulk Metallic Glass at 600–725°C

Oxidation Behavior of Ca-Based Bulk Amorphous Materials

Bryan R. Barnard, Peter K. Liaw, Raymond A. Buchanan, Oleg N. Senkov, Daniel B. Miracle

pp. 1870-1878

Abstract

In this study, the room-temperature oxidation behaviors of three Ca-based bulk amorphous alloys, Ca65Mg15Zn20, Ca50Mg20Cu30, and Ca55Mg18Zn11Cu16, were examined under normal flowing laboratory air and compared with the oxidation behaviors of these alloys in the crystalline form under identical conditions. The degree of oxidation for alloys in the amorphous and crystalline conditions was investigated by periodically measuring the mass change over the oxidation time. From the results of the oxidation mass change, and oxide thickness measurements obtained from scanning-electron-microscopy (SEM) studies, it was determined that the Ca55Mg18Zn11Cu16 BMG possessed the most favorable oxidation resistance, followed closely by the Ca50Mg20Cu30 BMG, with the Ca65Mg15Zn20 BMG having the least favorable oxidation resistance. The trend in glass-forming abilities of the three compositions follows the same trend as the oxidation resistance in the three alloys. In all cases, the oxidation resistance of the amorphous alloys was superior to the oxidation resistance of the same alloys in the crystalline state.

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Oxidation Behavior of Ca-Based Bulk Amorphous Materials

Formation and Biocompatibility of Ni-Free Zr60Nb5Cu20Fe5Al10 Bulk Metallic Glass

L. Liu, K. C. Chan, C. L. Qiu, Q. Chen

pp. 1879-1882

Abstract

A Ni-free bulk metallic glass (BMG) of Zr60Nb5Cu20Fe5Al10 with a diameter of 3 mm was successfully prepared by copper mold casting. The structure and thermal stability of the BMG were studied by x-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). It is found that the BMG is apparently of a single amorphous structure and exhibits a wide supercooled liquid region of 101°C. A static-state compression revealed that the BMG possesses a superior fracture strength of 1709 MP and extended plastic strain of 9.5%. The corrosion resistance of the BMG was examined by electrochemical polarization in phosphate buffered solution, which demonstrates that the BMG also exhibits an excellent corrosion resistance. Finally, the potential cytotoxicity of the Ni-free BMG was evaluated through cell culture followed by 3-(4,5-Dimethylthiazol-2-yl-)-2,5-diphenyltetrazolium bromide (MTT) assay and scanning electron microscope (SEM) observation. It is shown that the BMG exhibits a high cell viability and proliferation activity, and NIH/3T3 cells can closely adhere and well extend on the surfaces of the BMG alloy. The results indicate that the Ni-free Zr60Nb5Cu20Fe5Al10 BMG developed in the present work is promising for biomedical applications.

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Formation and Biocompatibility of Ni-Free Zr60Nb5Cu20Fe5Al10 Bulk Metallic Glass

Ab-Initio Study of Hyperfine Structure of M7 (M=Li, Na, K, Cu and Ag) Clusters, Using All-Electron Mixed-Basis Method

Mohammad Saeed Bahramy, Yoshiyuki Kawazoe

pp. 1883-1885

Abstract

Within density functional theory, the geometrical properties and the hyperfine structure of 7-atom clusters, 7Li7, 23Na7, 39K7, 63Cu7 and 107Ag7 are investigated using the so-called all-electron mixed basis method. The calculations reveal that all the clusters have a pentagonal bipyramidal geometry with a D5h symmetry in which an unpaired electron occupies an a2′′ state. It turns out that, the unpaired electron in all the clusters is mostly distributed on the axial sites with a minor contributions at the pentagonal ring sites. The calculated spin distributions and the isotropic hyperfine parameters are in excellent agreement with the corresponding experimental data.

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Ab-Initio Study of Hyperfine Structure of M7 (M=Li, Na, K, Cu and Ag) Clusters, Using All-Electron Mixed-Basis Method

Quantitative Analysis of Texture Evolution of Direct Chill Cast and Continuous Cast AA 1100 Aluminum Alloys during Cold Rolling

Hui Yuan, Jing Li, Dayong Cai, Qingxiang Yang, Wenchang Liu

pp. 1886-1890

Abstract

The hot bands of direct chill cast (DC) and continuous cast (CC) AA 1100 aluminum alloys were annealed at 454°C for 3 hours, and then cold rolled to different reductions. The texture of the cold rolled samples was measured by X-ray diffraction in order to compare the texture evolution of the DC and CC aluminum alloys during rolling. The texture volume fractions were calculated by an improved integration method. Mathematical formulae of the texture volume fractions and rolling true strain were established to simulate rolling texture evolution. The results show that the DC AA 1100 aluminum alloy exhibits a lower formation rate of the β fiber than the CC AA 1100 aluminum alloy.

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Quantitative Analysis of Texture Evolution of Direct Chill Cast and Continuous Cast AA 1100 Aluminum Alloys during Cold Rolling

Effect of Mo on Phase Separation in Fe-40 at% Cr Alloys Based on Numerical Solutions of the Cahn Hilliard Equation

Yoshihiro Suwa, Yoshiyuki Saito

pp. 1891-1895

Abstract

Effect of Mo on phase separation behavior of Cr in Fe-40 at%Cr-Mo ternary alloys was investigated with use of a model based on the Cahn-Hilliard eqaution. Simulation result indicates that the addition of a small amount of Mo to an Fe-40 at%Cr binary alloy was found to accelerate phase separation. With addition of small amount of Mo up to 5 at%, the rate of phase separtion concentration of Cr along the trajectory of its peak top increases with time. Mechanism of this acceleration behavior of Cr was analyzed by using a theory on asymptotic behavior of substitutional element in ternary alloy proposed by the present authors.

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