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MATERIALS TRANSACTIONS Vol. 47 (2006), No. 10

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. 47 (2006), No. 10

Coarse Columnar Structure of Transformation-Grown Ferrite in Pure Iron —On Wrought Iron and Sintered Iron—

Hidenori Kuroki, Hiroyuki Y. Suzuki

pp. 2449-2456

DOI:

10.2320/matertrans.47.2449

Abstract

When a nucleus of ferrite crystal is formed in cast-and-rolled or sintered iron, either of which contains less than approximately 50 ppm interstitial elements, namely, carbon and nitrogen, the ferrite crystal may grow into a coarse crystal joining many austenite crystals. Furthermore, such coarse ferrite crystals may compose a columnar macrostructure by unidirectional phase transformation under the condition accompanying a gradient of temperature. The formation of the macrostructure gives a maximum linear expansion of the sample that is numerically equal to the volume expansion at the same time. Even a small amount of carbon in pure iron can cause the condensation of carbon atoms or the formation of a fairly large number of minute cementite precipitates at ferrite/austenite phase boundaries. Both the condensation of carbon and the precipitation of cementite may cause the nucleation of new ferrite crystals, leading to the development of a fine-grained macrostructure.

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Coarse Columnar Structure of Transformation-Grown Ferrite in Pure Iron —On Wrought Iron and Sintered Iron—

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Immobilization of Mn(II) Ions by a Mn-Oxidizing Fungus Paraconiothyrium sp.-Like Strain at Neutral pHs

Keiko Sasaki, Minoru Matsuda, Tsuyoshi Hirajima, Keishi Takano, Hidetaka Konno

pp. 2457-2461

DOI:

10.2320/matertrans.47.2457

Abstract

A Mn-oxidizing fungus was isolated from a constructed wetland of Hokkaido (Japan), which is receiving the Mn-impacted drainage, and genetically and morphologically identified as Paraconiothyrium sp.-like strain. The optimum pHs were 6.45–6.64, where is more acidic than those of previously reported Mn-oxidizing fungi. Too much nutrient inhibited fungal Mn-oxidation, and too little nutrient also delayed Mn oxidation even at optimum pH. In order to achieve the oxidation of high concentrations of Mn like mine drainage containing several hundreds g·m−3 of Mn, it is important to find the best mix ratio among the initial Mn concentrations, inoculumn size and nutrient concentration. The strain has still Mn-tolerance with more than 380 g·m−3 of Mn, but high Mn(II) oxidation was limited by pH control and supplied nutrient amounts. The biogenic Mn deposit was poorly crystallized birnessite. The strain is an unique Mn-oxidizing fungus having a high Mn tolerance and weakly acidic tolerance, since there has been no record about the property of the strain. There is a potentiality to apply the strain to the environmental bioremediation.

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Immobilization of Mn(II) Ions by a Mn-Oxidizing Fungus Paraconiothyrium sp.-Like Strain at Neutral pHs

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Calculation of Potential Energy for Fe Atom around Entrance of (10,0) Carbon Nanotube

Yohei Kudo, Takahisa Hira, Soh Ishii, Tsuguo Morisato, Kaoru Ohno

pp. 2462-2464

DOI:

10.2320/matertrans.47.2462

Abstract

The structure of carbon nanotubes constitutes graphene sheets that are rolled to form cylinders with extremely small diameters. It is interesting to investigate the interaction between single-walled carbon nanotubes and an Fe atom because such nanotubes are fabricated with the aid of metal catalysts (Fe, Co, etc). Using an ab initio program DMol3, we have calculated the total energy of a system of (10,0) nanotube incorporated with an Fe atom. We have determined the most stable position of Fe near the entrance of the nanotube and the potential map for that position.

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Calculation of Potential Energy for Fe Atom around Entrance of (10,0) Carbon Nanotube

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New Model for the Overall Transformation Kinetics of Bainite. Part 1: the Model

María Jesús Santofimia, Francisca G. Caballero, Carlos Capdevila, Carlos García-Mateo, Carlos García de Andrés

pp. 2465-2472

DOI:

10.2320/matertrans.47.2465

Abstract

A new model for the overall transformation kinetics of bainite has been developed. Based on the displacive mechanism for the bainite transformation, the model distinguishes between the nucleation kinetics of bainitic ferrite in prior austenite grain boundaries, and at tips and adjacent positions of previously formed subunits. Some geometrical aspects of the development of the transformation have been used in the modelling. The theoretical results show that the tendencies obtained with the model are in agreement with experience. The second part of this work deals with the experimental validation of this model.

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New Model for the Overall Transformation Kinetics of Bainite. Part 1: the Model

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New Model for the Overall Transformation Kinetics of Bainite. Part 2: Validation

María Jesús Santofimia, Francisca G. Caballero, Carlos Capdevila, Carlos García-Mateo, Carlos García de Andrés

pp. 2473-2479

DOI:

10.2320/matertrans.47.2473

Abstract

A new model for the overall kinetics of the bainite transformation has been validated experimentally. The new model, presented in the 1st part of this work, is based in the displacive mechanism for bainite transformation. Thus, the bainite transformation kinetics of three medium carbon-high silicon steels has been studied. Results show that the model, which does not consider the effect of carbide precipitation in the bainite kinetics, predicts with a high degree of agreement the time evolution of bainitic ferrite volume fraction, even when lower bainite is present at the microstructure. Data from two additional medium carbon-high silicon steels, frequently reported in the literature, have been also used for reinforcing the validation, obtaining, again, a high agreement between the kinetic results for bainite transformation predicted by the model and those obtained experimentally.

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New Model for the Overall Transformation Kinetics of Bainite. Part 2: Validation

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Evaluation of Interdiffusion in Liquid Phase during Reactive Diffusion between Cu and Al

Yasuhiko Tanaka, Masanori Kajihara

pp. 2480-2488

DOI:

10.2320/matertrans.47.2480

Abstract

Using Cu/Al diffusion couples initially composed of pure Cu and Al, the reactive diffusion in the binary Cu–Al system was experimentally examined in a previous study. The diffusion couple was isothermally annealed in the temperature range of T=973–1073 K. Due to annealing, compound layers of the β, γ and ε phases are formed between the Cu-rich solid (α) phase and the Al-rich liquid (L) phase, and the L⁄ε interface migrates towards the ε phase. At each annealing time, the migration distance of the L⁄ε interface is much greater than the total thickness of the compound layers. Furthermore, there exists the parabolic relationship between the migration distance and the annealing time. This means that the migration of the interface is controlled by the volume diffusion in the L phase. The mathematical model for the interface migration controlled by volume diffusion was used in order to analyze quantitatively the migration rate of the interface. Through the analysis, the interdiffusion coefficient D of the L phase was evaluated to be 1.24×10−9, 2.91×10−9 and 3.62×10−9 m2/s at T=973, 1023 and 1073 K, respectively. Expressing the temperature dependence of D as D=D0exp(−Q⁄RT), values of D0=1.42×10−4 m2/s and Q=93.5 kJ/mol were obtained by the least-squares method. According to the analysis, the interdiffusion coefficient is much greater for the L phase than for the solid phases. Consequently, the L⁄ε interface migrates towards the ε phase, and the migration rate of the interface is much greater than the overall growth rate of the compound layers.

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Evaluation of Interdiffusion in Liquid Phase during Reactive Diffusion between Cu and Al

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Crystallization Kinetics of Ti50Ni25Cu25 Melt-Spun Amorphous Ribbons

Shih-Hang Chang, Shyi-Kaan Wu, Hisamichi Kimura

pp. 2489-2492

DOI:

10.2320/matertrans.47.2489

Abstract

The Avrami exponent n of Ti50Ni25Cu25 amorphous ribbons during isothermal annealing derived from the Johnson-Mehl-Avrami equation is about 3.0 and shows good agreement with that obtained by Schloßmacher et al. This indicates that the main crystallization mechanism of Ti50Ni25Cu25 ribbons is interface-controlled three-dimensional isotropic growth with early nucleation-site saturation. According to the Arrhenius relation, the activation energy for crystallization is 314 kJ/mol. This value is similar to that obtained using the Kissinger method, which implies that the crystallization during continuous heating or isothermal annealing follows a similar crystallization mechanism.

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Crystallization Kinetics of Ti50Ni25Cu25 Melt-Spun Amorphous Ribbons

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Internal Stress during Creep in a Die-Cast AM50 Magnesium Alloy at 473 K

Yoshihiro Terada, Yukako Mori, Tatsuo Sato

pp. 2493-2496

DOI:

10.2320/matertrans.47.2493

Abstract

The internal stress during high temperature creep was investigated for the die-cast AM50 magnesium alloy at 473 K through the strain-transient dip test technique. The microstructure of the alloy is characterized by fine α-Mg grains together with the β-Mg17Al12 particles located on the grain boundaries. The internal stress is proportional to the applied stress, when the applied stress ranges below the yield stress. The ratio of the internal stress to the applied stress is 0.36 for the alloy, which is about half of those for conventional pure metals such as Cu, α-Fe and Ni. The small internal stress is a characteristic feature in the creep for the alloy.

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Internal Stress during Creep in a Die-Cast AM50 Magnesium Alloy at 473 K

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High Temperature Deformation of a Fine-Grained and Particle-Dispersed V-2.3%Y-4%Ti-3%Mo Alloy

Tatsuaki Sakamoto, Hiroaki Kurishita, Sengo Kobayashi, Kiyomichi Nakai, Hideo Arakawa, Hideki Matsui

pp. 2497-2503

DOI:

10.2320/matertrans.47.2497

Abstract

The high temperature deformation behavior of a fine-grained and particle-dispersed V-2.3%Y-4%Ti-3%Mo (mass%) alloy was investigated. The alloy was fabricated by powder metallurgical methods utilizing mechanical alloying and hot isostatic pressing (HIP), followed by annealing at 1273 K for 3.6 ks. Tensile tests were performed at temperatures from 873 to 1273 K at initial strain rates from 2.5×10−5 to 1.0×10−1 s−1. X-ray diffraction analyses show that the HIPed and annealed specimens contain a significant amount of (Y, Ti)2O3 and small amounts of YN, Ti2O3 and TiO. Transmission electron microscopy observations show that the matrix contains approximately 3%Ti and 3%Mo in solution and that the average diameters of the matrix grains and dispersoids are about 620 and 42 nm, respectively. Tensile test results show that the yield stress depends strongly on test temperature and strain rate. From the dependence of the yield stress measured at 1073 and 1273 K on plastic strain rate, it is found that the dependence is divided into three regions with different deformation controlling mechanisms: a recovery controlling process of a long range internal stress field associated with dispersed particle (the high-strain-rate region), grain boundary sliding (the medium-strain-rate region) and presumably solute atmosphere dragging (the low-strain-rate region). Effects of 4%Ti addition on the microstructures and high temperature deformation behavior are discussed.

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High Temperature Deformation of a Fine-Grained and Particle-Dispersed V-2.3%Y-4%Ti-3%Mo Alloy

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Effect of Prior Deformation on Tensile and Vibration Fracture Resistance of Friction Stirred 5052 Alloy

Kuo-Tsung Huang, Truan-Sheng Lui, Li-Hui Chen

pp. 2504-2511

DOI:

10.2320/matertrans.47.2504

Abstract

In this study, Al-2.5Mg alloy was prepared with different cold rolling reductions, and then friction stir processing (FSP) was performed to investigate the effect of prior microstructure variations on friction stirred materials. The experimental results indicate that the FSP specimens not only had better tensile properties but also better vibration fracture resistance, which would be expected from the microstructural refinement which resulted from the phenomenon of dynamic recrystallization. The stress-elongation curves of all specimens showed the serrated yielding. The higher grain boundary introduced by FSP could hold the mobile dislocations long enough to let Mg atoms form atmospheres around them. Consequently, the effect serration magnitude was more significant on the specimens which were given FSP. This can be ascribed to the grain refinement and the resulting increase of the boundaries which is the main source of obstacles. In addition, the vibration fracture resistance of the FSP specimens shows that the duration of stage I decreases with increasing the prior deformation rate before FSP.
Meanwhile, the prior deformation samples possessed better vibration fracture resistance under the same initial deflection amplitude (6.5 mm). Based on the observed microstructures, this can be attributed to a large number of retained dislocation tangles introduced by prior cold rolling, even after FSP, which improved the crack propagation resistance and reduced the crack propagation rate. The experimental results confirmed that vibration fracture resistance can be quantitatively correlated with the crack tortuosity value which corresponds to the crack propagation behavior.

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Effect of Prior Deformation on Tensile and Vibration Fracture Resistance of Friction Stirred 5052 Alloy

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Detection of Micro-Damage Evolution of Air Plasma-Sprayed Y2O3-ZrO2 Thermal Barrier Coating through TGO Stress Measurement

M. Tanaka, M. Hasegawa, Y. Kagawa

pp. 2512-2517

DOI:

10.2320/matertrans.47.2512

Abstract

The micro damage evolution behavior in air plasma-sprayed 8 mass% Y2O3 stabilized ZrO2 thermal barrier coating (APS-TBC) after isothermal heat exposure at 1150°C up to 200 h was observed. Residual stress of thermally-grown-oxide (TGO) layer was measured through the TBC layer using Cr3+ luminescence spectroscopy and the measured stress levels were compared with micro damage evolution behavior stored in the TBC system. With heat exposure time of longer than 10 h, microfracture behaviors were noted in the TBC layer. In-plane residual stress of the TGO layer increased for up to 50 h of heat exposure time, and thereafter, diminished with further increase. These behaviors are strongly correlated with the thickness and the residual stress of the TGO layer. This decrease in the TGO stress well contrasts with the evolution of the micro fracture behavior, which is also related to the thickness and undulation of the formed TGO layer. The change of TGO stress, σtgo, depending on the average thickness of the TGO layer, \\barhtgo, i.e., dσtgo⁄d\\barhtgo is a useful indicator of the damage evolution in TGO: dσtgo⁄d\\barhtgo>0: slight damage stage, dσtgo⁄d\\barhtgo<0: micro fracture evolution stage. The result suggests that Cr3+ luminescence spectroscopy is a good indicator for micro damage evolution in the TBC layer and is a useful tool for nondestructive evaluation (NDE) of APS-TBC systems.

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Detection of Micro-Damage Evolution of Air Plasma-Sprayed Y2O3-ZrO2 Thermal Barrier Coating through TGO Stress Measurement

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Effect of Zincate Treatment on Adhesion of Electroless Nickel-Phosphorus Coating for Commercial Pure Aluminum

Koji Murakami, Makoto Hino, Minoru Hiramatsu, Kozo Osamura, Teruto Kanadani

pp. 2518-2523

DOI:

10.2320/matertrans.47.2518

Abstract

The present authors have conducted characterization of zincate films formed as a pretreatment for electroless nickel-phosphorus coatings on commercial pure aluminum substrate (JIS A1050P-H24, 99.5 mass%Al). By using a basic solution which consisted of sodium hydroxide and zinc oxide, a zincate film formed by single zincate treatment showed coarse zinc grains of 1–2 μm in size whose (0001) planes were mainly parallel to the surface of the substrate. A double zincate treatment by using the basic solution reduced the coarse grains, and the thickness of the uniform zincate film was 30–40 nm. A commercial zincate solution which contained iron decreased the number and the size of coarse zinc grains for the single zincate treatment compared with the case of the basic solution, and the double zincate treatment formed a further thin zincate film of 10–20 nm in thickness.
The single zincate treatment by using the basic zincate solution resulted in such poor adhesive strength of the electroless nickel-phosphorus plated film as to peel off the substrate due to its residual stress. Quantification of adhesive strength by 90° peeling test showed the double zincate treatment increased the adhesive strength of the plated film up to 30 N/m. In the case of the commercial zincate solution, the adhesive strength obtained by the single zincate treatment was 125 N/m. Furthermore, the adhesive strength of the plated nickel-phosphorus film was too high to conduct the peeling test in the case of the double zincate treatment by the commercial solution, where dimple patterns were observed due to ductile fracture of the substrate.
Observation by transmission electron microscopy of the interface between the nickel-phosphorus plated film and the substrate showed gaps in the case of the double zincate treatment by the basic zincate solution. On the other hand, the double zincate treatment by the commercial solution eliminated gaps and a strong interface was obtained.

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Effect of Zincate Treatment on Adhesion of Electroless Nickel-Phosphorus Coating for Commercial Pure Aluminum

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Chlorination Kinetics of ZnFe2O4 with Ar-Cl2-O2 Gas

Hiroyuki Matsuura, Tasuku Hamano, Fumitaka Tsukihashi

pp. 2524-2532

DOI:

10.2320/matertrans.47.2524

Abstract

Chlorination rate of ZnFe2O4 with Ar-Cl2-O2 gas was measured at 1023 to 1123 K by gravimetry. The effects of temperature, partial pressures of chlorine and oxygen on the rate were investigated. Zinc oxide contained in ZnFe2O4 specimen was selectively chlorinated and evaporated in gas, while iron oxide remained as oxide in a chlorinated residue. Chlorination rate increased with increasing partial pressure of chlorine. On the other hand, chlorination rate slightly decreased with increasing partial pressure of oxygen and chlorination of iron oxide was prevented. Since the order of chlorination rate with respect to partial pressure of chlorine was approximately 0.5, the rate-determining step of chlorination is considered to be the dissociative adsorption of chlorine gas on the surface of solid ZnFe2O4. Decrease of chlorination rate with the increase of partial pressure of oxygen could be explained by the occupation of adsorption sites of chlorine atoms by oxygen and the chlorination rate was expressed as functions of partial pressures of chlorine and oxygen as r=k·(P_Cl2^1/2/1+K_OP_O2^1/2) The activation energy of chlorination was 35.1±2.2 kJ/mol which is relatively small compared to that of ZnO chlorination reaction (58.2 kJ/mol). It is considered that this low activation energy is due to the weak adsorption of chlorine atom on the adsorption site.

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Chlorination Kinetics of ZnFe2O4 with Ar-Cl2-O2 Gas

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Surface Free Energy of Alloy Nitride Coatings Deposited Using Closed Field Unbalanced Magnetron Sputter Ion Plating

Chen-Cheng Sun, Shih-Chin Lee, Wen-Chi Hwang, Jenn-Shyong Hwang, I-Tseng Tang, Yaw-Shyan Fu

pp. 2533-2539

DOI:

10.2320/matertrans.47.2533

Abstract

The sticking of product material to injection molding tools is a serious problem, which reduces productivity and reliability. Depositing alloy nitride coatings (TiN, ZrN, CrN, and TiAlCrN) using closed field unbalanced magnetron sputter ion plating and electrodeposition of chromium, and characterizing their surface free energies in the temperature range 20–120°C have led to the development of a non-sticking (with a low surface free energy) coating system for semiconductor IC packaging molding dies. The contact angles of water, diiodomethane and ethylene glycol on the coated surfaces were measured at temperatures in the range 20–120°C using a Dataphysics OCA-20 contact angle analyzer. The surface free energy of the coatings and their components (dispersion and polar) were calculated using the Owens-Wendt geometric mean approach. The surface roughness of these coatings were investigated by atomic force microscopy (AFM). The adhesion force of these coatings were measured using direct tensile pull-off test apparatus. The experimental results revealed that TiAlCrN, CrN and ZrN coatings outperformed Hard-Cr and TiN coatings in terms of anti-adhesion, and thus have the potential as working layers for injection molding industrial equipment, especially in semiconductor IC packaging molding applications.

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Surface Free Energy of Alloy Nitride Coatings Deposited Using Closed Field Unbalanced Magnetron Sputter Ion Plating

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Oxidation or Nitridation Behavior of Pure Chromium and Chromium Alloys Containing 10 mass%Ni or Fe in Atmospheric Heating

Kaori Taneichi, Takayuki Narushima, Yasutaka Iguchi, Chiaki Ouchi

pp. 2540-2546

DOI:

10.2320/matertrans.47.2540

Abstract

The oxidation or nitridation behavior of pure chromium and chromium alloys containing 10 mass%Ni or 10 mass%Fe in atmospheric heating was investigated in the temperature range of 1073 to 1373 K. The formation behavior of the outer oxide phase of Cr2O3 and its growth kinetics in both chromium alloys was very similar to that of pure chromium. The nitride layer with the Cr2N phase was formed beneath the oxide phase at temperatures above 1273 K in pure chromium. Marked internal nitridation with the formation of the Cr2N phase was observed in the Cr-10 mass%Fe alloy, while the formation of Cr2N was negligible in the Cr-10 mass%Ni alloy. Neither Ni nor Fe were detected inside the Cr2O3 phase, and was enriched in the subsurface layer between the oxide layer and the base alloy in a respective alloy. The Ni-enriched layer in Cr-10 mass%Ni alloy had a relatively narrow width, but a very high concentration of Ni compared with the Fe-enriched layer formed in the Cr-10 mass%Fe alloy.

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Oxidation or Nitridation Behavior of Pure Chromium and Chromium Alloys Containing 10 mass%Ni or Fe in Atmospheric Heating

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Effects of Solid Fraction on the Heat Transfer Coefficient at the Casting/Mold Interface for Permanent Mold Casting of AZ91D Magnesium Alloy

Jer-Haur Kuo, Ruey-Jer Weng, Weng-Sing Hwang

pp. 2547-2554

DOI:

10.2320/matertrans.47.2547

Abstract

The interfacial heat transfer coefficient (HTC) between the steel mold and AZ91D magnesium (Mg) alloy that cast under various initial solid fractions were investigated in this study.
The interfacial HTC was determined by using an Inverse Method with measured temperature data and known thermo-physical properties. A Computer Aided Cooling Curve Analysis technique was used to determine the solid fraction versus temperature relationship. To comply with the requirements of the Inverse Method, a one-dimensional heat transfer system from the casting to the mold was designed for the permanent mold casting of AZ91D Mg alloy in molten and semisolid states.
Experiments were conducted with different initial solid fractions of 0, 30, and 50%. The results indicate that the HTC profile of molten AZ91D during solidification can be divided into five stages, while casting with semisolid AZ91D only into three. During each stage, the casting/mold interfacial conditions vary, which in turn causes the HTC values to vary. These data are critical for any solidification model of permanent mold casting and semisolid casting to obtain a reliable prediction of the thermal profile inside the solidifying casting and its freezing time.

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Effects of Solid Fraction on the Heat Transfer Coefficient at the Casting/Mold Interface for Permanent Mold Casting of AZ91D Magnesium Alloy

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Influence of Rolling Routes on Press Formability of a Rolled AZ31 Mg Alloy Sheet

Yasumasa Chino, Kensuke Sassa, Akira Kamiya, Mamoru Mabuchi

pp. 2555-2560

DOI:

10.2320/matertrans.47.2555

Abstract

Microstructure, tensile properties and press formability of AZ31 Mg alloy sheets processed by unidirectional rolling, reverse rolling and cross rolling were investigated. The intensity in (0002) plane texture for the reverse-rolled and the cross-rolled specimens was lower than that for the unidirectional-rolled specimen. In addition, the Erichsen values of the formers were larger than those of the latter. The superior press formability for the formers could not be explained from the viewpoint of the elongation to failure, n-value, average r-value and planar anisotropy of the r-value, but it was related to a reduction in directional dependence of the thickness-direction strain and width-direction strain normalized by the tensile-direction strain (εt⁄εL and εw⁄εL). Therefore, it is suggested that the minor texture formation due to reverse rolling and cross rolling gives rise to the reduction in anisotropy of strain, resulting in the superior press formability for the reverse-rolled and cross-rolled specimens.

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Influence of Rolling Routes on Press Formability of a Rolled AZ31 Mg Alloy Sheet

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Fabrication of TiC-20 mass%Ni Cermet Using MA-PCS Process

Keizo Kobayashi, Kimihiro Ozaki

pp. 2561-2565

DOI:

10.2320/matertrans.47.2561

Abstract

Mechanical alloying and pulsed-current sintering were used to synthesize TiC-20 mass%Ni cermet with ultra-fine TiC particles dispersed. The mixture, in which Ti and Ni elements were uniformly distributed, was prepared by mechanical alloying of Ti, Ni and graphite powders for 18 ks. TiC particles were produced in the mixture milled for longer than 18 ks through a combustion synthesis reaction during heating. Mechanically alloyed Ti-C-Ni composite powder milled for 18 ks was consolidated using pulsed-current sintering at 1223 K under 70 MPa pressure. The sintered compact consisted of TiC and Ni. The average grain size of TiC particles in the sintered body was 0.80 μm. The relative density of the sintered compact reached 92% of the theoretical one; its Vickers hardness was 2260 Hv.

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Fabrication of TiC-20 mass%Ni Cermet Using MA-PCS Process

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Corrosion Behaviour of [(Fe0.6Co0.4)0.75B0.2Si0.05]96Nb4 Bulk Glassy Alloy in Sulphuric Acid Solutions

Zhilin Long, Baolong Shen, Yong Shao, Chuntao Chang, Yuqiao Zeng, Akihisa Inoue

pp. 2566-2570

DOI:

10.2320/matertrans.47.2566

Abstract

The influence of structural changes such as structural relaxation and crystallization on the corrosion behavior of the [(Fe0.6Co0.4)0.75B0.2Si0.05]96Nb4 bulk glassy alloy has been investigated in aerated 0.1 and 0.5 kmol/m3 sulphuric acid solutions. All tests were carried out with the same materials in different states: as-cast and relaxed glassy and crystalline states. It was found that the multicomponent [(Fe0.6Co0.4)0.75B0.2Si0.05]96Nb4 glassy alloy had an ability to passivation in aerated sulphuric acid solutions irrespective of microstructure. The subsequent complete crystallization of the bulk glassy alloy leads to a significant decrease in corrosion resistance, while appropriate structural relaxation results in an increase in corrosion resistance. The corrosion results were discussed and correlated with the evolution of crystallization processes by means of XRD and DSC. The effect of temperature of the corrosive medium on the corrosion behavior of the as-cast [(Fe0.6Co0.4)0.75B0.2Si0.05]96Nb4 glassy alloy has also been analyzed.

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Corrosion Behaviour of [(Fe0.6Co0.4)0.75B0.2Si0.05]96Nb4 Bulk Glassy Alloy in Sulphuric Acid Solutions

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Microstructure and Mechanical Properties of (Zr0.5Cu0.4Al0.1)100−xTax Bulk Metallic Glass Composites

Koji Okazaki, Wei Zhang, Akihisa Inoue

pp. 2571-2575

DOI:

10.2320/matertrans.47.2571

Abstract

We investigated the microstructure and mechanical properties of (Zr0.5Cu0.4Al0.1)100−xTax (x=0–12) bulk metallic glass composites containing dispersed Ta-rich dendrites prepared by copper mold casting. With increasing Ta content, the volume fraction of the dendrite particle increases, while other crystalline phases are precipitated in the Ta content range of over 9 at%. The compressive fracture strength and plastic strain of the composites significantly increase from 1890 MPa and 0.7%, respectively, for the x=0 alloy to 2180 MPa and 15.9%, respectively, for x=9 alloy, and then significantly decrease with further increasing Ta content. The improvement of plasticity is attributed to an increase in the density of shear bands before final fracture resulting from the increase of the fracture strength.

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Microstructure and Mechanical Properties of (Zr0.5Cu0.4Al0.1)100−xTax Bulk Metallic Glass Composites

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Thermal Expansions and Mechanical Properties of Al/C and Al/(SiC+C) Composites Based on Wood Templates

Tian-Chi Wang, Tong-Xiang Fan, Di Zhang, Guo-Ding Zhang

pp. 2576-2581

DOI:

10.2320/matertrans.47.2576

Abstract

Wood is a natural material with a rational and aesthetic structure. Recently, we have succeeded in using wood as a template to produce Al/C and Al/(SiC+C) composites. Porous carbon was first pyrolyzed from the wood template. The final composites were then obtained by injecting aluminum alloy and silicone resin into the porous carbon. The microstructures, thermal expansions, and mechanical properties of these products were then analyzed. The results indicated that the structures of the composites are controlled by the natural structure of wood. Moreover, the composites exhibit a lower coefficient of thermal expansion than aluminum and are stronger than the porous carbon.

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Thermal Expansions and Mechanical Properties of Al/C and Al/(SiC+C) Composites Based on Wood Templates

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Waste Input-Output Analysis on “Landfill Mining Activity”

Kazuyo Yokoyama, Takashi Onda, Shunsuke Kashiwakura, Tetsuya Nagasaka

pp. 2582-2587

DOI:

10.2320/matertrans.47.2582

Abstract

New environmental assessment model based on the Waste Input-Output analysis has been developed and applied for the “Landfill mining activity” for the recovery of valuable materials and energy resources and the saving of landfill site.
In this study, the landfilled wastes are assumed to be treated by the gasification/melting processes. Two kinds of reactors, the fluidized bed type and the shaft furnace type, have been considered in this work as the typical gasification/melting processes adopted in Japan. Both processes generate electric power by the recovered heat and fly ash as waste to be landfilled. It has been found in this study that the both processes can reduce the total volume of waste and save the available landfill space. The shaft furnace type seems to have higher potential for decreasing volume of wastes because of less emission than the fluidized bed type. The results of scenario analysis have also indicated that the landfill mining activity is effective for sustainable management of landfill sites.

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Waste Input-Output Analysis on “Landfill Mining Activity”

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Effects of High Niobium Addition on the Microstructure and High-Temperature Properties of Ti-40Al-xNb Alloy

Chau-Jie Zhan, Tso-Hao Yu, Chun-Hao Koo

pp. 2588-2594

DOI:

10.2320/matertrans.47.2588

Abstract

The effect of Nb content on the microstructure and high-temperature properties of the TiAl alloy with low Al content has been investigated. The as-cast Ti-40Al-10Nb alloy consists of a Widmanstätten lath and a γ phase in a B2 matrix. The increased addition of Nb to the alloy inhibits the solidification path β→β+α. Therefore, the as-cast Ti-40Al-xNb (x=15,16) alloys are composed of primary β/B2 phases as the major constituent. Following heat treatment, the microstructure of the heat-treated Ti-40Al-10Nb alloy resembles that of the as-cast Ti-40Al-10Nb alloy. The homogenized Ti-40Al-15Nb alloy has a two-phase microstructure of B2+γ, while the homogenized Ti-40Al-16Nb alloy has a four-phase microstructure of B2+γ+α+σ. The creep response of the studied TiAl-Nb alloy is correlated closely with the tertiary creep, and is affected strongly by its microstructure. The creep resistance of the alloy depends on the resistance to the propagation of the cracks in the B2 matrix. In the Ti-40Al-15Nb alloy, the resistance to the extending of cracks is the most apparent among these three alloys. Therefore, the Ti-40Al-15Nb alloy has the highest creep life of the three tested alloys. The oxidation resistance of the investigated TiAl-Nb alloy is independent of the addition of Nb. The differences among the oxidation resistances of these three alloys arise from their various microstructures. The oxide scales of the Ti-40Al-10Nb alloy are composed mainly of TiO2, while the oxide scales formed on the Ti-40Al-15Nb alloy are dense Al2O3-rich oxides. The Ti-40Al-15Nb alloy has the lowest mass gain among these three alloys due to the existence of the Al2O3-rich oxides. The formation of Al2O3-rich oxides appears to be related to the high Nb content of the alloy. The fact that the Ti-40Al-16Nb alloy has the largest weight gain of these three alloys is attributed to the formation of oxide scales of σ phase.

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Effects of High Niobium Addition on the Microstructure and High-Temperature Properties of Ti-40Al-xNb Alloy

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Ultrahigh Vacuum Non-Contact Atomic Force Microscope Observation of Reconstructed Si(110) Surface

Akihira Miyachi, Hayato Sone, Sumio Hosaka

pp. 2595-2598

DOI:

10.2320/matertrans.47.2595

Abstract

We tried to observe a reconstructed Si(110) surface using an ultrahigh-vacuum (UHV) non-contact atomic force microscope (NC-AFM). The Si(110) surface has several characteristic structures, such as the 16×2, (17, 15, 1) 2×1, 1×1, zigzag structures. We succeeded in the AFM observation of the surface formed upon annealing the samples in direct current heating so as to clean the surface. We obtained the same structures in the AFM observation as the proposed 16×2 model of a Si(110) reconstruction in a STM observation. The UHV NC-AFM results demonstrate that the Si(110) surface has a characteristic 16×2 structure for the first time observation.

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Ultrahigh Vacuum Non-Contact Atomic Force Microscope Observation of Reconstructed Si(110) Surface

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New Ce-Cu-Al-Zn Bulk Metallic Glasses with High Oxidation Resistance

Zan Bian, Akihisa Inoue

pp. 2599-2602

DOI:

10.2320/matertrans.47.2599

Abstract

We reported the effect of Zn addition on the glass formation ability (GFA), thermal stability, melting behavior and oxidation behavior of Ce-based bulk metallic glasses (BMGs). The Ce-Cu-Al alloys with Zn addition also have high glass formation ability (GFA) and large supercooled liquid regions (ΔTx, ΔTx=Tx−Tg, Tx is the onset crystallization temperature and Tg is the glass transition temperature). The Tg, Tx and ΔTx are, respectively, 368, 437 and 69 K for the (Ce0.72Cu0.28)87.5Al10Zn2.5 alloy, and 394, 467 and 73 K for the (Ce0.72Cu0.28)82.5Al10Zn7.5 alloy. The ΔTx of the (Ce0.72Cu0.28)100−xAl10Znx alloys was above 70 K and the BMGs with diameters up to ∼6 mm could be produced successfully. The critical diameters and ΔTx of the alloys increase with increasing Zn content, and have maximum values of 6 mm and 73 K, respectively, at 7.5 at% Zn, and then decreases in the higher Zn content range. The melting behavior shows that the addition of Zn element causes the significant increase of both Tm and Tl. The investigation of oxidation behavior shows that the addition of Zn element is effective for the enhancement of the oxidation resistance.

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New Ce-Cu-Al-Zn Bulk Metallic Glasses with High Oxidation Resistance

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Preparation of Pyrochlore Ca2Ti2O6 by Metal-Organic Chemical Vapor Deposition

Mitsutaka Sato, Rong Tu, Takashi Goto

pp. 2603-2605

DOI:

10.2320/matertrans.47.2603

Abstract

Ca-Ti-O films were prepared by metal-organic chemical vapor deposition (MOCVD) using Ca(dpm)2 and Ti(O-i-Pr)2(dpm)2 precursors, and the effects of substrate temperature (Tsub) and Ca/Ti ratio (RCa/Ti) on the crystal structure and morphology were studied. Ca-Ti-O films consisting of pyrochlore Ca2Ti2O6 and perovskite CaTiO3 phase were obtained at Tsub=1073 K and 0.35<RCa/Ti<1. The content of pyrochlore Ca2Ti2O6 increased with decreasing RCa/Ti. Pyrochlore Ca2Ti2O6 almost in a single phase was obtained at RCa/Ti=0.46. The morphology of pyrochlore Ca2Ti2O6 was agglomerated fine grains about 50 nm in diameter having a columnar texture.

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Preparation of Pyrochlore Ca2Ti2O6 by Metal-Organic Chemical Vapor Deposition

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Ductile Metallic Glasses in Supercooled Martensitic Alloys

J. Das, K. B. Kim, W. Xu, B. C. Wei, Z. F. Zhang, W. H. Wang, S. Yi, J. Eckert

pp. 2606-2609

DOI:

10.2320/matertrans.47.2606

Abstract

We report ductile bulk metallic glasses based on martensitic alloys. The slowly cooled specimens contain a mixture of parent ‘austenite’ and martensite phase. The slightly faster cooled bulk metallic glasses with 2–5 nm sized ‘austenite’-like crystalline cluster reveal high strength and large ductility (16%). Shear bands propagate in a slither mode in this spatially inhomogeneous glassy structure and undergo considerable ‘thickening’ from 5–25 nm. A ‘stress induced displacive transformation’ is proposed to be responsible for both plasticity and work-hardening-like behavior of these ‘M-Glasses’.

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Ductile Metallic Glasses in Supercooled Martensitic Alloys

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