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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 60 (2019), No. 11

  • Anisotropy of Magnetostriction of Functional BCC Iron-Based Alloys

    Shigeru Suzuki, Toru Kawamata, Rayko Simura, Shimpei Asano, Shun Fujieda, Rie Y. Umetsu, Masaki Fujita, Muneyuki Imafuku, Tsuyoshi Kumagai, Tsuguo Fukuda

    pp. 2235-2244

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    DOI:10.2320/matertrans.MT-M2019146

    Abstract

    This paper provides an overview of recent studies on the anisotropy of magnetostriction of functional iron-based alloys with the body-centered cubic (bcc) structure; these are potential ferromagnetic materials for use in actuators and sensors at ambient temperature. The magnetostrictive properties of these functional iron-based alloys (such as Fe–Ga, Fe–Al, and Fe–Ge alloys) are known to strongly depend on the crystallographic orientation. In these functional iron-based alloys, non-Joulian magnetostriction, in which volume is not conserved, was observed; generally, the Joulian magnetostriction in a volume is not altered by magnetic fields. As the magnetostrictive properties of these iron-based alloys are correlated to their elastic properties through the magnetoelastic effect, their elastic properties have also been investigated using single crystals of iron-based alloys. In the present paper, we discuss the characteristic features of the anisotropy of magnetostriction and inverse magnetostriction, which occur when magnetic fields and external stresses, respectively, are applied. In order to clarify the microscopic processes underlying the magnetostriction and inverse magnetostriction, the alterations in the magnetic domains by magnetic fields and external stresses were observed. The results revealed that the magnetic domain structure in the functional iron-based alloys is altered in a complex manner when applied with external fields. For example, it was demonstrated that unique motions of different types of Bloch domain walls are observed with the application of magnetic fields or external stresses along specific directions of single crystals of Fe–Ga alloys. The characteristic features of the motion of the domain walls are likely to correspond to the occurrence of magnetostriction and inverse magnetostriction, in which magnetic fluxes are induced during alternative vibration.

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  • Selective Reduction of Laterite Nickel Ore

    Sungging Pintowantoro, Fakhreza Abdul

    pp. 2245-2254

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    DOI:10.2320/matertrans.MT-M2019101

    Abstract

    Nickel is an important metal in the industry. To obtain nickel metal, the extraction process from nickel ore should be conducted. Recently, nickel ore resources from sulphide ore becomes rare which makes nickel laterite ore as the future of nickel extraction. Unlike sulphide nickel ore processing, laterite nickel ore processing requires higher processing energy through smelting. Therefore, a novel method to process laterite nickel ore using lower energy is needed. The novel method is done via direct reduction and magnetic separation. In laterite nickel processing by direct reduction, the challenges are to conduct selective reduction of nickel and to let iron unreduced. The addition of additive in the direct reduction process is needed to achieve this selective reduction. Additives used for the selective reduction includes Na2SO4, MgCl2, CaSO4, NaCl and CaCl2·H2O. This article will further review the role of additive used in selective reduction of laterite nickel ore and the current trends on selective reduction research.

  • Vacancy Behavior during Aging at 50 and 100°C in Al–Mg–Si Alloys with Excess Si Studied by Positron Annihilation Spectroscopy

    Koji Inoue, Ken Takata, Koji Ichitani, Yasuharu Shirai

    pp. 2255-2259

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    DOI:10.2320/matertrans.L-M2019846

    Abstract

    We have investigated the aging behavior of quenched-in vacancies in excess Si type Al–Mg–Si-alloys by coincidence Doppler broadening of positron annihilation radiation and positron lifetime spectroscopy. The chemical composition around the quenched-in vacancies is initially rich in Si. For aging at both 50°C and 100°C, the Mg/Si composition ratio around the vacancies increases with aging time. The final Mg/Si composition ratio around the vacancies was found to be almost the same for aging at both 50 and 100°C. The difference of the aging time dependence of the chemical composition around the vacancies at 50 and 100°C was observed in the initial stage, i.e., the vacancy-Si-rich solute complexes was formed at 50°C, while the formation of the vacancy-Si-rich solute complexes was avoided at 100°C. Therefore, the avoidance of the formation of the vacancy-Si-rich solute complexes by pre-aging around 100°C before storage at room temperature may be a key to avoid negative effect of artificial aging in Al–Mg–Si alloys.

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  • Stability of γ′ Precipitates in Nickel Based Oxide Dispersion-Strengthened Superalloys under High-Temperature and Heavy Irradiation Conditions

    Azusa Konno, Naoko H. Oono, Shigeharu Ukai, Sosuke Kondo, Okinobu Hashitomi, Akihiko Kimura

    pp. 2260-2266

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    DOI:10.2320/matertrans.M2019050

    Abstract

    The stability of cuboidal γ′ precipitates under heavy irradiation was studied for newly developed Ni-based Oxide Dispersion-Strengthened (ODS) superalloys, to explore the suitability of these as core structural materials in Very High-temperature Reactors (VHTR) or Gas-cooled Fast Reactors (GFR). Ion irradiation was applied at a dose level of 100 dpa at 873 K, 1073 K and 1273 K. Under these conditions, γ′ precipitates retained their cuboidal shape at 873 K, were deformed somewhat at 1073 K (as predicted by the Nelson-Hudson-Mazey (NHM) model), and were massively deformed and agglomerated at 1273 K. This deformation-agglomeration process is attributed to cascade collision, whereby the increased Gibbs free energy of the disordered phase induces a change in element distribution inside the irradiated area. Ordered, cuboidal γ′ precipitates were reproduced from the disordered state after cooling and the cessation of ion irradiation.

  • Solid Solutions with bcc, hcp, and fcc Structures Formed in a Composition Line in Multicomponent Ir–Rh–Ru–W–Mo System

    Akira Takeuchi, Takeshi Wada, Hidemi Kato

    pp. 2267-2276

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    DOI:10.2320/matertrans.MT-M2019212

    Abstract

    Five Ir–Rh–Ru–W–Mo alloys selected based on alloy design with valence electron concentration (VEC) were examined for their formation of single, dual, and triple phases of bcc, fcc, and hcp structures. These structures were predicted with Thermo-Calc 2019a and the TCHEA3 database on a cross-sectional phase diagram along a composition line: Ir0.415254(100−2x)Rh0.415254(100−2x)Ru0.169492(100−2x)WxMox (x: 0–50 at%). At T = 2100 K, four types of phases were predicted: (1) a single bcc, fcc, and hcp phase, respectively, at x = 35 (Alloy A, VEC = 6.849), 15 (Alloy C, VEC = 7.981), and 5 (Alloy E, VEC = 8.574); (2) a mixture of bcc+hcp and hcp+fcc at x = 24 (Alloy B, VEC = 7.472) and 8 (Alloy D, VEC = 8.378), respectively; (3) a triple mixture of bcc+hcp+fcc; and (4) a mixture of bcc+fcc in Alloys A–E at low temperature. Experiments at 2100 K revealed that Alloys C–E tended to exhibit better reproducibility and that Alloy E can be regarded as a new refractory high-entropy alloy (HEA) with fcc structure. Alloy C annealed at T = 1273 K for 200 h maintained a single-hcp structure. The non-appearance of thermodynamically stable phases at low temperature in the Ir–Rh–Ru–W–Mo system was analogically explained as slow diffusion. The VEC analysis for HEAs with hcp structures was extended by including the range of 7.5 ≤ VEC ≤ 8.4 for alloys consisting of 4d and 5d transition metals annealed near their solidus temperature. The Ir–Rh–Ru–W–Mo system was significant in providing all possible simple solid solutions of bcc, hcp, and fcc phases.

  • Effect of Heavy Swaging on Cracking Behavior of Tungsten Electrode for Fusing Joining

    Bahram Mirzaei, Takamichi Ono, Goroh Itoh, Akira Kurumada, Shingo Mukae

    pp. 2277-2281

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    DOI:10.2320/matertrans.P-M2019843

    Abstract

    Cracking behavior of tungsten electrode for fusing joining (a kind of resistance spot welding where the work material is insulating-resin-coated conducting metal such as copper and aluminum) was investigated. The electrode specimens with a fine fibrous microstructure were produced by the heavy swaging process without intermediate annealing after sintering, while reference electrode specimens with normal fibrous microstructure conventionally swaged with intermediate annealing were also prepared. Both types of electrode specimens were subjected to repeated joining tests with tough pitch copper sheets as a workpiece material up to 3000 cycles. The effect of compressive applied force at the joining on the cracking behavior was also examined. The total crack length and the maximum crack width tended to be smaller in the heavily swaged electrode than the traditionally swaged electrode. Therefore, the resistance against cracking during many cycles of joining was revealed to increase by refining the fibrous microstructure. Microcrack initiation and growth was presumed to be caused by the mechanism proposed in the previous paper: the surrounding portion is cooled faster at the earlier stage of cooling followed by small amount of plastic deformation in the central portion, and shrinkage of the central portion occurs in the later cooling stage resulting in tensile stresses in radial and circumferential directions. The effect of applied force was complicated since, in this study, different currents were applied depending on the compressive force to keep the temperature constant at the first cycle.

  • Improvement of High-Temperature Shape-Memory Effect by Multi-Component Alloying for TiPd Alloys

    Hiromichi Matsuda, Hirotaka Sato, Masayuki Shimojo, Yoko Yamabe-Mitarai

    pp. 2282-2291

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    DOI:10.2320/matertrans.MT-MAW2019012

    Abstract

    The influence of multi-component alloying on the phase transformation and shape-memory effect was investigated to develop new high-temperature shape memory alloys (HT-SMAs). Four alloys—35Ti–20Pd–15Ni–15Pt–15Zr, 40Ti–20Pd–15Ni–15Pt–10Zr (high-entropy alloys, HEAs), 45Ti–20Pd–5Ni–25Pt–5Zr, and 45Ti–20Pd–10Ni–20Pt–5Zr (medium-entropy alloys, MEAs, at%)—were prepared. At room temperature, the B2 structure was stable in the HEAs, and no martensitic transformation (MT) was observed. However, in the MEAs, an MT from the B2 structure to a B19 structure was clearly observed. The MT temperature of the MEAs was comparable to or higher than those of binary and ternary TiPd alloys. The strengths of both the martensite and austenite phases in 45Ti–20Pd–5Ni–25Pt–5Zr were higher than those in 45Ti–20Pd–10Ni–20Pt–5Zr and ternary TiPd alloys. We attempted to explain the high strength using the δ parameter, which indicates the lattice distortion for various atomic sizes, but a clear correlation was not observed, as there were no significant differences in the δ parameter among the tested alloys. The shape recovery was investigated via a thermal cyclic test under an applied stress in the range of 15–200 MPa. Although a small plastic strain was introduced during the thermal cyclic test, a shape recovery over 80% was obtained for both MEAs. Training, that is, the thermal cyclic test under the same applied stress, was conducted to investigate the change of the irrecoverable strain and the work output. For 45Ti–20Pd–5Ni–25Pt–5Zr, the irrecoverable strain was deleted after 50 cycles, and perfect recovery was obtained. The largest work output (3.5 J/cm3) was obtained under 200 MPa. In 45Ti–20Pd–10Ni–20Pt–5Zr, perfect recovery was obtained from the first cycle. However, the recoverable strain was small, and the largest work output was 1.5 J/cm3 under 200 MPa. The shape recovery of 45Ti–20Pd–5Ni–25Pt–5Zr is promising for new HT-SMAs compared with the ternary Ti–Pd–Zr alloys and other HEA-SMAs.

  • Optimization of Pore Walls Microstructure in Open Cell Aluminum Foams Utilizing Self-Propagating Reaction

    Qiang Feng, Changzhong Liao, YuTian Ma, Guoren Yang

    pp. 2292-2297

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    DOI:10.2320/matertrans.MT-M2019124

    Abstract

    The Al(H2PO4)3 doped with thermite as the space holder is prepared for aluminum foams during powder metallurgy process. The pore walls of aluminum foams are covered with the in-situ synthesized residual phosphates produced from Al(H2PO4)3 after the self-propagating reaction in space holder. Influences of the thermite content dispersed in space holder on both phase transformation and the coating layers microstructure of pore walls are investigated. The results suggest that the added thermite could optimize the microstructure of pore walls coating layers even if the space holder sintered at the lower furnace temperature, due to the released larger energy from thermite reaction would increase the local reaction temperature for Al(H2PO4)3. The melted loose coating layers of the pore walls may shrink and lead to the higher porosity of aluminum foams can be obtained.

  • The Role of Dendritic Morphology and Segregation in fcc-fct Transformation and Damping Capacity of Mn–Cu Based Alloys

    Song Zhang, Xiping Guo, Shuai Zhong, Weixing You, Yonggang Xu

    pp. 2298-2304

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    DOI:10.2320/matertrans.MT-M2019131

    Abstract

    An alloy with a nominal composition of 70Mn–24.95Cu–3Al–2Zn–0.05Ce (at%) was prepared using vacuum induction melting (VIM) technology, or followed by directional solidification (DS) processing at withdrawal rates of 20 and 100 µm/s. Further, VIM, DS20 and DS100 alloys were aged at 703 K for 2 h. The microstructure, fcc-fct transformation and damping capacity of VIM and DS alloys have been investigated comparatively. The results show that the microstructure of VIM alloy mainly comprises equiaxial γ-MnCu dendrites while that of DS20 and DS100 ones is primarily composed of columnar γ-MnCu dendrites, and the directional effect of such columnar dendrite is obviously strengthened with increase in withdrawal rate. Two and three compositional segregations are present in VIM and DS alloys respectively, and fine α-Mn phase is formed in DS100 one. The starting fcc-fct transformation temperature of the alloy bears a relationship of TtVIM > TtDS20 > TtDS100. The stepped fcc-fct transformations occur and couple to promote the formation of phase transformation damping step due to compositional segregation, which is more obvious in DS alloys than in VIM one. The twin relaxation peak damping capacity of VIM and DS20 alloys is similar but evidently higher than that of DS100 one. The damping capacity of long columnar dendrite especially at 100 µm/s is also degraded due to strong grain boundary blocking effect. There exists a relationship of Q−1VIM > Q−1DS20 > Q−1DS100 for damping capacity of VIM, DS20 and DS100 alloys at room temperature over the whole strain amplitude range.

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  • Texture Evolution of Nickel Coatings Fabricated by Aerosol Deposition

    Makoto Hasegawa, Kyonosuke Kimura, Koichiro Aoki, Masahiro Komuro

    pp. 2305-2310

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    DOI:10.2320/matertrans.MT-M2019161

    Abstract

    In order to understand the evolution of texture during the aerosol deposition (AD) method, coatings were deposited under various conditions using pure nickel powder particles. These particles are thought to undergo plastic deformation during deposition. X-ray diffraction analyses of the surfaces of the coatings obtained revealed specific textures. A {101} fiber texture was observed in as-deposited specimens. Texture development was observed with increasing gas flow rate. The strain in the nickel coating was estimated to be about 1.0–1.4 in true strain. This strain is thought to be induced by the nickel particles impacting the substrate during deposition.

  • Performance Assessment of Ti–7.5Mo Alloy for Removable Partial Denture Application

    Yu-Po Peng, Jiin-Huey Chern Lin, Chien-Ping Ju

    pp. 2311-2318

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    DOI:10.2320/matertrans.MT-M2019160

    Abstract

    A head-to-head comparison was made between an in-house-developed Ti–7.5Mo alloy and commonly-used grade-2 commercially pure titanium (CP-Ti) for dental casting applications. Experimental results indicated that all impurity concentrations, densities, linear thermal expansion coefficients and solid/liquid transition temperatures of Ti–7.5Mo and CP-Ti were similar. The 7-day total release of metal ions from immersed Ti–7.5Mo was acceptably low (10 µg/cm−2) with no harmful elements detected. Cytotoxicity testing indicated that Ti–7.5Mo had a cell viability of 82.5%, higher than the generally accepted value (70%). X-ray diffraction patterns indicated that Ti–7.5Mo was comprised primarily of α′′ phase with a small amount of β phase, while CP-Ti showed a monolithic α/α′ phase. Light and scanning electron microscopy revealed that CP-Ti had a typical plate-shaped morphology, while Ti–7.5Mo alloy was featured by its much finer acicular-shaped α′′ crystals along with equi-axed retained β grain boundaries. The castability value of Ti–7.5Mo was almost double that of CP-Ti. Both grinding and cutting tests indicated that Ti–7.5Mo had much better machinability than CP-Ti. Tensile testing indicated that Ti–7.5Mo had higher tensile strength, higher elongation and lower modulus (respectively 806 MPa, 42% and 70 GPa) than CP-Ti (respectively 571 MPa, 22% and 113 GPa). Bending data showed that Ti–7.5Mo had higher bending strength, lower modulus and much larger elastic recovery angle (respectively 1154.7 MPa, 75.8 GPa and 31.5°) than CP-Ti (respectively 919.5 MPa, 125 GPa and 2.8°). From all present data it was concluded that Ti–7.5Mo alloy would be a much better material than CP-Ti for removable partial denture application.

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  • Microstructural Evolution and Mechanical Properties of 6061 Aluminum Alloy Processed with Equal Channel Angular Pressing (ECAP) and Multi-Axial Compression (MAC)

    Zhi-chao Xu, Xue-feng Guo, Wen-peng Yang, Hong-bao Cui, Ying Wang

    pp. 2319-2327

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    DOI:10.2320/matertrans.MT-M2019170

    Abstract

    In this study, two of the severe plastic deformation (SPD) techniques, equal channel angular pressing (ECAP) and multi-axial compression (MAC) have been successfully applied to the Al-6061 alloy and the development of microstructure, texture and mechanical properties have been studied. It was found that the MEM (MAC+ECAP+MAC) and MEE (MAC+ECAP+ECAP) can effectively refine grains and hinder the movement of dislocations. The mechanisms of continuous dynamic recrystallization operating during severe deformation are discussed in the detail. The tensile strength and the macro-hardness of alloy after MEM and MEE deformation was increased. Refined grain and dislocation aggregation were mainly dedicated to the improvement of alloy mechanical properties.

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  • Ex Situ Electron Microscopy Study of the Lithiation of Single-Crystal Si Negative Electrodes during Charge Reaction in a Lithium–Ion Battery

    Yutaka Shimauchi, Sachi Ikemoto, Shigekazu Ohmori, Takaomi Itoi

    pp. 2328-2335

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    DOI:10.2320/matertrans.MT-M2019193

    Abstract

    Silicon (Si) has attracted considerable interest as a negative electrode material for next-generation lithium (Li)–ion batteries because of its high capacity density. In this study, ex situ electron microscopy was applied to observe Si negative electrodes under different charge states within an actual battery structure to reveal the Li intrusion direction and the effects of Li concentration on the electrode structure. All of the processes from disassembly of the charged battery and preparation of specimens for use in electron microscopy observation to specimen transport to the electron microscopes were performed under non-atmospheric exposure conditions. The orientation of the single-crystal Si powder in the charged state was observed by electron backscatter diffraction, indicating that lithiation occurred preferentially along the (110) plane of Si. The initial stage of amorphization was observed by high-angle annular dark field-scanning transmission electron microscopy, demonstrating that the Li atoms occupied the tetrahedral sites of Si crystals, and that the crystal structure was destroyed via the severing of Si–Si bonds between the {111} planes. During the charge reaction, Li occupied the tetrahedral sites via intrusion along the 〈110〉 direction of Si, and amorphization proceeded as the Li concentration increased. Thus, the amorphous region grew preferentially in the 〈110〉 direction of Si.

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  • Microstructure Evolution and Creep Behavior of Near-α Ti Alloy Produced by Thermomechanical Processing

    Haruki Masuyama, Kei Shimagami, Yoshiaki Toda, Tetsuya Matsunaga, Tsutomu Ito, Masayuki Shimojo, Yoko Yamabe-Mitarai

    pp. 2336-2345

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    DOI:10.2320/matertrans.MT-MAW2019010

    Abstract

    A microstructure evolution based on the processing and heat-treatment conditions was investigated for Ti–13Al–2Nb–2Zr (at%) alloy, which has a promising oxidation resistance. Three processing temperatures, 900°C and 1000°C in the α+β phase field, and 1080°C in the β phase field, and two rolling reduction ratios, 93% and 67%, were selected as the processing conditions. In the samples processed and heat-treated in the α+β phase field, an almost fully equiaxed structure, i.e., the equiaxed or ellipsoid α phase surrounded by the β phase, was formed through furnace cooling, and a bi-modal structure was formed using air cooling. The morphology of the α phase in the near fully equiaxed and lamellar structure depends on the rolling reduction ratio; in other words, the equiaxed and ellipsoid α phases are formed at rolling reduction ratios of 93% and 67%, respectively. The volume fraction of the equiaxed α phase in the bi-modal structure is processed at 900°C, which is higher than that of the bi-modal structure processed at 1000°C despite the same heat-treatment temperature applied. This is because the induced strain when processed at 1000°C is smaller than that when processed at 900°C. By contrast, in the samples processed in the β phase field and heat-treated in either the α+β or β phase field, a lamellar structure is formed. The creep behavior of the bi-modal structure obtained upon processing at 900°C and 1000°C for up to a 93% rolling reduction ratio was investigated. The creep life of the sample processed at 1000°C was two-times longer than the sample processed at 900°C. This is because a smaller volume fraction of the equiaxed α phase in the sample processed at 1000°C than that of the sample processed at 900°C.

  • Crack Growth Characteristics of Aluminum Alloys Dominated by the Mechanisms of Fatigue and Stress Corrosion Cracking

    Takeshi Ogawa, Shota Hasunuma, Shunsuke Kato, Shunpei Suzuki, Yuta Nakamura, Satomi Mano, Kazuo Miyagawa

    pp. 2346-2352

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    DOI:10.2320/matertrans.Z-M2019845

    Abstract

    Three aluminum alloys in the T6 state (6061, 6082, and 7075) were subjected to static and cyclic loading conditions in humid and dry air environments and the corresponding crack growth characteristics were investigated. The dominant crack growth mechanisms, i.e., stress corrosion cracking (SCC) and fatigue crack growth (FCG), were identified. Three types of testing machines were used to apply the cyclic loading at high stress ratio and frequencies ranging from 0.02 Hz to 20 kHz. Crack growth mechanisms are discussed based on the traditional model proposed by McEvily and Wei. Various test results revealed that SCC is the dominant crack growth mechanism at 0.02 Hz, whereas FCG is dominant at 20 Hz and 20 kHz. These results suggested that the crack growth behavior is controlled by either SCC or FCG with no mutual interaction. Very slow crack growth (rate: <10−13 m/cycle) occurred during ultrasonic fatigue tests performed at 20 kHz. For each alloy and stress ratio considered, this slow growth occurred only in humid air and at low values of the stress intensity factor. Scanning electron microscopy observations suggested that, owing to the numerous cyclic loads, the very slow crack growth behavior in the humid environment occurs via peeling-off of the oxide film near the crack tip.

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  • Effects of Si Content and Pre-Strain on Aging Behavior in Al–Mn–Mg Alloys Containing a Small Amount of Cu

    Yasuhiro Aruga, Yuki Tanaka

    pp. 2353-2360

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    DOI:10.2320/matertrans.L-M2019847

    Abstract

    The paper reports the research results on precipitation hardening potentials of Al–Mn–Mg alloys containing a small amount of Cu, during aging at 150°C. The age-hardening response and phase transformation are significantly affected by the Si content of the order of 0.1%. The hardening response increases during aging with increasing Si content. The hardening potential decreases significantly by tensile deformation prior to heat treatment. The pre-strain causes an inhomogeneous nucleation of precipitation on dislocations and cell walls and restricts trans-granular precipitation during aging. In 10% pre-strained alloys, short-term aging leads to dislocation recovery, resulting in an increase in the n-value. Further decrease in dislocation density and increase in the n-value occur due to a small degree of precipitation hardening in a 0.15%-Si-added alloy, whereas dislocation recovery is suppressed by competitive precipitation in a 0.36%-Si-added alloy during prolonged aging. This Paper was Originally Published in Japanese in J. Japan Inst. Light Metals 68 (2018) 473–479.

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  • Effect of Multi-Pass Equal Channel Angular Pressing on the Microstructure and Mechanical Properties of a Directional Solidification Mg98.5Zn0.5Y1 Alloy

    Zhi-chao Xu, Chang Zhu, Xue-feng Guo, Wen-peng Yang, Hong-bao Cui, Ying Wang

    pp. 2361-2367

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    DOI:10.2320/matertrans.M2019088

    Abstract

    The microstructure evolutions and mechanical properties of a directional-solidification (DS) Mg98.5Zn0.5Y1 alloy during multi-pass equal channel angular pressing (ECAP) were systematically investigated in this work. The results showed that there was a large amount of lamellar structure in the DS alloy. These lamellar structure have almost the same orientation inside the grains. After ECAP, dynamic recrystallization (DRX) occurred and the diameter of DRXed α-Mg grains decreased to 2 µm. During ECAP, large volume fraction of LPSO phase experienced a four-step morphological evolution during ECAP, i.e. original lath → bent lath → cracked lath → smaller particles. Meanwhile, the schematic illustration of recrystallization in the DS-Mg98.5Zn0.5Y1 alloy during ECAP was established. Compression test results indicated that the alloy was markedly strengthened after multi-pass ECAP, and the main reason for the significantly enhanced mechanical properties can be ascribed to the DRXed α-Mg grains, kinking and refined 14H particles.

  • Evolution of Quasi-Brittle Hydrogen-Assisted Damages in a Dual-Phase Steel

    Tsubasa Kumamoto, Motomichi Koyama, Koichi Sato, Kaneaki Tsuzaki

    pp. 2368-2377

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    DOI:10.2320/matertrans.MT-M2019196

    Abstract

    We studied the statistical quantitative analysis of the hydrogen-assisted damage evolution behavior from nano- to micro-scale by combining positron annihilation spectroscopy (PAS) and scanning electron microscopy-based damage characterization in a dual-phase steel with a tensile strength of 960 MPa. The total elongation was markedly decreased by hydrogen pre-charging (0.32 mass ppm H) from 17% to 4%. We divided the damage evolution behavior into three stages: damage incubation; arrest; growth, and evaluated the effects of hydrogen pre-charging on each stage. The damage nucleation was caused by martensite fracture and enhanced by hydrogen pre-charging. However, PAS showed no enhancement of vacancy formation by hydrogen. The statistical damage quantitative analysis indicated in the damage arrest stage that the critical damage size corresponding to the blunt limit of the damage tip was decreased from ∼1 µm2 in the uncharged specimen to ∼0.5 µm2 in the hydrogen pre-charged specimen. The damage growth in the third stage was accelerated by hydrogen pre-charging owing to quasi-brittle damage propagation through the ferrite cleavage plane or ferrite/martensite interface. Microstructure observation showed that the cleavage propagation in ferrite was accompanied by the local plastic deformation. To explain this fracture acceleration, we proposed cooperative contribution of the enhancement of the local plastic deformation through adsorption-induced dislocation emission mechanism and the cleavage fracture through hydrogen enhanced decohesion mechanism. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 221–230.

  • Effects of Sigma Phase on the Embrittlement Behavior of Super Duplex Stainless Steel F55 under SSRT with a Cathodic Charge

    Yusuke Shimada, Masahiko Hatakeyama, Jyunichi Hirabayashi, Yuichi Yamamoto, Koichi Sato, Satoshi Sunada

    pp. 2378-2386

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    DOI:10.2320/matertrans.MT-MAW2019006

    Abstract

    In order to clarify the influence of sigma phase and hydrogen embrittlement on the mechanical properties of newly developed super duplex stainless steel F55, SSRT was conducted while performing cathodic charge. The installation potential of the constant potential SSRT was determined by polarization curve measurement. Based on the results obtained from polarization curve measurements, SSRT’s were conducted in the air, in corrosive solution, at +0.5 V constant potential, and at −0.5 V (vs. Ag/AgCl) constant potential. In order to observe the relationship between the test environment and the fracture mode, the fracture surface was observed with a scanning electron microscope and the influence of the σ phase on hydrogen embrittlement was examined. Hydrogen embrittlement was observed regardless of the amount of σ phase. As specimen having a σ phase area ratio of 30% showed larger embrittlement caused by the σ phase in air, it was suggested that σ phase embrittlement controls an embrittlement behavior. Enhancement of hydrogen embrittlement by σ phase precipitations was not observed in a cathodic charge condition used in this experiment.

  • Simultaneous Boronizing and Carburizing of Titanium via Spark Plasma Sintering

    Takato Karimoto, Akio Nishimoto

    pp. 2387-2391

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    DOI:10.2320/matertrans.L-M2019838

    Abstract

    This study focused on a diffusion coating method for the formation of a hard layer with excellent adhesion through the formation of an interlayer and a gradient layer on titanium materials. A limitation of conventional diffusion coating methods is the deterioration of the mechanical properties of the matrix resulting from the long-term, high-temperature processing. Therefore, spark plasma sintering (SPS) was used to form a ceramic layer, as it allows the suppression of the growth of crystal grains via rapid heating and enables low temperature and short processing time. The purpose of this study is to simultaneously form borides and carbides on a titanium surface using the SPS method and evaluate their properties. Commercially pure titanium (CP-Ti) was used as the substrate, and B4C powder was utilized as both the boronizing and carburizing source. An analysis of the sample surface subjected to SPS processing indicated the formation of TiC, TiB2, and TiB. As a ceramic layer was formed on the titanium surface, a surface hardness of ∼1700 HV was obtained, and the wear resistance was improved compared with that of untreated CP-Ti.

  • Deformation Type in Forming of Curved Conical Tubes: Fundamental Research for Forming Closed-Section Parts from Sheet Metal II

    Masahiko Sato, Masaaki Mizumura, Yukihisa Kuriyama, Katsuyuki Suzuki, Atushi Tomizawa

    pp. 2392-2398

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    DOI:10.2320/matertrans.P-M2019842

    Abstract

    The purpose of this research is the development of technology to make complex-shape closed-section parts directly from sheet blanks (direct sheet forming). Closed-section parts with large expansion of the circumferential length are expected to be formed by direct sheet forming. In this work, first, the deformation type of curved circular tubes is confirmed from the results of FEM analysis. Next, with reference to curved circular tubes, the deformation type of curved conical tubes is discussed. The validity of FEM analysis is confirmed by comparison with experimental results of curved circular tubes. It is clarified that curved circular tubes and curved conical tubes are formed with the same processes and deformation types (bending of sheet, axial bending of U-section, shrink flanging and plane-strain compression). However, in the 2nd process (axial bending of U-section) of forming curved conical tubes, longitudinal strain at the narrower side is greater than that at the wider side. This Paper was Originally Published in Japanese in J. JSTP 59 (2018) 229–234.

  • Prediction of Chevron Cracks in Multipass Drawing

    Akira Shiga, Tomohiro Yamashita, Yutaka Neishi

    pp. 2399-2405

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    DOI:10.2320/matertrans.P-M2019840

    Abstract

    The aim of this study was to examine the effect of accumulated equivalent plastic strain on the ductile fracture criterion. Spheroidized medium-carbon steel JIS-S55C was adopted as the test material. An investigation into the ductile crack initiation behavior of round-bar tensile specimens with/without circumferential notches was carried out. Tensile prestrain was applied by cold drawing. The stress triaxiality and accumulated equivalent plastic strain were calculated by the finite element method (FEM). The ductile fracture limit of tensile prestrained steel was expressed as a function of the stress triaxiality and accumulated equivalent plastic strain. The validity of the ductile fracture limit was confirmed by the prediction of chevron crack generation in multipass drawing. This Paper was Originally Published in Japanese in J. JSTP 60 (2019) 39–44.

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  • Controlling Factor for Maximum Tensile Stress and Elongation of Aluminum Alloy during Partial Solidification

    Ryosuke Takai, Rei Hirohara, Naoki Endo, Yoshihiro Nagata, Toshimitsu Okane, Makoto Yoshida

    pp. 2406-2415

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    DOI:10.2320/matertrans.L-M2019839

    Abstract

    To predict hot tearing of direct chill casting ingot, both the tensile constitutive behavior and elongation of alloy are inevitable during partial solidification. For predicting both the maximum true stress σss and the elongation εelong regardless of alloy systems, their dominant factor was examined in terms of the solidification microstructure. For an Al–Mg and an Al–Cu alloys, (i) temperature T dependences of the maximum true stress and elongation (σss = f(T) and εelong = f(T)) and (ii) dihedral angle θ of liquid phase formed at grain boundary were measured experimentally. Then, fraction of solid cohesion C was determined by the Campbell’s model using the angle.Firstly, the solid fraction dependence of the tensile properties (σss = f(fs) and εelong = f(fs)) were compared between the two alloys. The two dependences differ with each other. Secondly, the fraction of solid cohesion dependences of the tensile properties (σss = f(C) and εelong = f(C)) were compared and the result shows that the two dependences were consistent with each other. The fraction of solid cohesion enables to explain the difference in solid fraction dependence of the tensile properties for the two alloys. The result demonstrates that the dihedral angle should be essential to predict the two tensile properties of alloy during partial solidification. This Paper was Originally Published in Japanese in J. JILM 69 (2019) 255–262.

  • Development of Penetrating Tool Friction Stir Incremental Forming

    Wei Jiang, Takuya Miura, Masaaki Otsu, Masato Okada, Ryo Matsumoto, Hidenori Yoshimura, Takayuki Muranaka

    pp. 2416-2425

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    DOI:10.2320/matertrans.P-M2019841

    Abstract

    To form sheet metals into concave-convex mixed shapes without using special machines or dies, a novel forming tool, referred to as a penetrating tool, and a new forming method, referred to as penetrating tool friction stir incremental forming were developed herein. The proposed penetrating tool is composed of two dome shape tools, called the top and bottom tools. The top and bottom tools are vertically symmetric and joined by a middle screw. Pure aluminum (JIS: A1050-O) sheets with a thickness of 2 mm were used for workpieces. Forming of concave, convex, and concave-convex mixed shapes were implemented by using penetrating tool friction stir incremental forming under clockwise and counterclockwise tool path direction. Experimental conditions which obtained by a preliminary experiment were tool gap between the top and bottom tool of 1.8 mm, tool rotation rates of 1000–3000 rpm and tool feed rates of 200–3000 mm/min. Formability by the developed method was evaluated by the formable height or depth. Not only the shapes but also the distribution of thickness of the PTFSIFed sheets were measured. Material flow was discussed by thickness in Z direction due to keeping the volume constant before and after forming. From the experimental result, the concave, convex, and concave-convex mixed shapes can be formed using the proposed method. However, the formable depth or height remained relatively shallow. For more dramatic depth or height forming, groove-like defects occurred in advancing side of the formed sheet and the sheet fractured due to penetration of the sheet by the groove-like defect. From the distributions of thickness in Z direction of formed sheet, the material flow from the advancing to retreating side was shown to cause the groove-like defects.

  • Applicability of As-Cast on β Type Titanium Alloys Proposed in the Compositional Region with Different Tensile Deformation Types

    Xi-Long Ma, Kazuhiro Matsugi, Zhe-Feng Xu, Yong-Bum Choi, Ryohei Matsuzaki, Jie Hu, Xin-Gang Liu, Hao Huang

    pp. 2426-2434

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    DOI:10.2320/matertrans.F-M2019848

    Abstract

    Three β type titanium alloys were proposed for as-cast applications in practical fields on the basis of the d-electrons parameters with both bond order (Bot) and d-orbital energy level (Mdt). Ti–5.5Cr–5.4Mn–5.1Zr–2.8Fe with the lowest Mdt, Ti–4.5Cr–2.5Mn–1.1Al with the lowest Bot and Ti–10.8Mo–2.3Sn–1.0Al with the highest Mdt were designed by using ubiquitous elements in the predicted regions showing the slip, twin and martensite dominant deformation behaviors in the Bot-Mdt diagram, respectively. Their ingots were produced by the cold crucible levitation melting technique. Ti–5.5Cr–5.4Mn–5.1Zr–2.8Fe showed mono β phase and similar stress-strain curves with highest tensile strength more than 1000 MPa at both as-cast and solution treated conditions, which corresponded to the slip dominant deformation. Ti–4.5Cr–2.5Mn–1.1Al showed β and a small amount of α′′ phases, and the stress-strain curves with stress-induced α′′ martensite at both conditions, which corresponded to the twin dominant deformation. Ti–10.8Mo–2.3Sn–1.0Al consisted of β and large amounts of α′′ martensite phases and showed the fracture strain more than 35% at both conditions, which corresponded to the martensite dominant deformation. Segregation degree in solidification process showed 4.8 times larger in the Ti–5.5Cr–5.4Mn–5.1Zr–2.8Fe position far from pure Ti position in the Bot-Mdt diagram, compared with that of Ti–10.8Mo–2.3Sn–1.0Al close to the pure Ti position. It was found that as-cast application possibility of both alloys of Ti–5.5Cr–5.4Mn–5.1Zr–2.8Fe and Ti–10.8Mo–2.3Sn–1.0Al could be promising in the view of tension behaviors.

  • Mechanical Properties of Cold-Rolled and Annealed Al–12%Mg Alloy Sheet with High Mg Solid Solubility Fabricated from Vertical-Type High-Speed Twin-Roll Cast Strip

    Yohei Harada, Nan Jiang, Shinji Kumai

    pp. 2435-2441

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    DOI:10.2320/matertrans.F-M2019850

    Abstract

    Al–Mg alloy is a representative non-heat-treatable aluminum alloy. The main strengthening mechanism of the alloy is solid solution hardening by magnesium. If we can increase Mg solubility much more in the solid solutions by using the excellent cooling capacity of the vertical-type high-speed twin-roll casting, further improvement of strength is expected. In this study, high Mg containing Al–8%Mg, 12%Mg and 23%Mg alloy strips were fabricated by using this method, and increase in Mg solid solubility and mechanical properties were investigated. Cold rolling was performed for Al–8%Mg and Al–12%Mg alloy strips. Although some porosities were observed in the mid-thickness region of the as-cast strips, they were reduced by optimizing the casting conditions. The slightly remaining porosities in the as-cast strip could be eliminated by the subsequent cold rolling. The lattice constant of the α-Al phase was calculated from the diffraction peak position of XRD profile, and by which the Mg solid solubility was estimated. The maximum solid solubility was about 12%. The β-Al3Mg2 phase particles which were observed in the original as-cast Al–12%Mg alloy strip were completely dissolved in to the matrix by the subsequent heat treatment. Compared with the typical commercial Al–Mg alloy, such as 5052 or 5083 alloy, the Al–12%Mg alloy sheets fabricated from the twin-roll cast strip had an excellent strength and ductility balance.

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  • Numerical Modeling of Glass Pouring Process at the Tin Bath Entry with Different Geometry

    Luyao Li, Zhongxi You, Huey-Jiuan Lin, Jianjun Han, Jian Ruan, Xiujian Zhao

    pp. 2442-2450

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    DOI:10.2320/matertrans.MT-M2019151

    Abstract

    In the float process, the spreading process of glass flow on the tin surface is important for the glass forming quality. The three-dimensional model at tin bath entry is established with the software of ANSYS Fluent 14.0. The glass spreading process is simulated based on the tin bath with production rate of 500 t/d. The width of wetback refractory and the angle between wetback refractory and restrictor tile are varied to investigate the influence on the glass forming quality. The wetback flow rate in each model is analyzed to evaluate the glass forming quality. As well, the movement of glass massless particles at wetback region is tracked to further investigate the wetback flow behavior. Generally, the wetback flow rate and massless particles ratio arrived at restrictor refractory are increased with the increases of wetback refractory width and the angle between wetback refractory and restrictor tile. With the large spread area in the model with θ = 150° and W = 1928 mm, the wetback flow rate is similar to that in the model with θ = 150° and W = 1614 mm. It is attributed to that the spreading effect is comparable with the restriction effect of restrictor refractory. The wetback flow rate is relatively higher in the model with θ = 135° and W = 1928 mm, and the model with θ = 150° and W = 1614 mm, which would indicate the better glass forming quality. The simulation results would be supposed to guide the design of tin bath entry, which would improve the glass forming quality.

  • Preparation of a High-Performance Nanocrystalline Lithium/Graphene Composite Battery via High-Pressure Torsion Method

    Chenhao Qian, Ziyang He, Chen Liang, Weixi Ji

    pp. 2451-2455

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    DOI:10.2320/matertrans.MT-M2019142

    Abstract

    This paper creatively introduces the high-pressure torsion treatment (HPT) technique for the preparation of lithium ion battery electrodes. Through the preparation of a nanocrystalline lithium/graphene composite structure, a high-performance dendrite-free electrode was obtained. Furthermore, for light metal processing via the HPT method, the strain-grain relationship is still applicable under high-pressure torsion and results in excellent electrochemical performance. As a physical metallurgical method for the preparation of nano-metal composite materials, the HPT method has advantages that are not possessed by hydrothermal methods. These include a rapid, low-cost synthesis with minimal by-products from the chemical reaction.

  • Detachment of Mesenchymal Stem Cells and Their Cell Sheets Using pH-Responsive CaCO3 Particles

    Hironobu Sugiyama, Masataka Hakamada, Mamoru Mabuchi

    pp. 2456-2463

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    DOI:10.2320/matertrans.MT-M2019104

    Abstract

    Cell sheet technology contributes to advances in tissue engineering. Although various approaches to control cell adhesion and detachment to a culture dish have been devised for the purpose of recovering an intact cell sheet so far, they all have disadvantages in application. Therefore, the search for superior cell sheet detachment technology is still ongoing. The present study describes detachment of human mesenchymal stem cells (hMSC) and their cell sheets via decomposition of pH-responsive CaCO3 particles that are precipitated on a culture dish. A concern in this detachment technology is harmful effects of the acidic environment, which is needed to decompose the CaCO3 particles, on cell viability. The time course of detachment behavior showed that the hMSC sheet was detached in a shorter time than individual cells. Shortening of the operation time for detachment suppressed cell death in the acidic environment. Thus, the hMSC sheet was successfully detached without cell death.

  • Press Forming of Aluminum Foam during Foaming of Precursor

    Yoshihiko Hangai, Masataka Ohashi, Ryohei Nagahiro, Kenji Amagai, Takao Utsunomiya, Nobuhiro Yoshikawa

    pp. 2464-2469

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    DOI:10.2320/matertrans.MT-M2019192

    Abstract

    Al foam was press-formed utilizing a steel mesh die during the foaming of the precursor to shape the Al foam. The effects of the temperature of the precursor and the pressing velocity during press forming on the forming behavior of the obtained Al foam were investigated. It was found that Al foam was sufficiently softened above the liquidus temperature to conduct press forming. In contrast, press forming cannot be conducted below the liquidus temperature. The press forming of Al foam should be conducted after the Al foam has been sufficiently foamed above the liquidus temperature to obtain high-porosity Al foam. No extrusion of Al foam through the mesh openings occurred even when press forming was conducted above the liquidus temperature. The Al foam and steel mesh were easily separated. The mesh pattern was clearly observed on the surface of Al foams. There is little effect of conducting press forming on the pore structures of the obtained Al foams regardless of pressing velocity. Al foam with a triangular cross section having the same shape as the steel mesh die and a porosity of approximately 80% was obtained. The press-formed Al foam sufficiently filled the steel mesh die. Consequently, it was demonstrated that the press forming of Al foam after sufficient foaming is effective for fabricating Al foams with complex shapes.

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  • CuO-Doped Catalyst Synthesized from Red Mud and Rice Husk Ash Using Urea-Nitrate Combustion Technique for p-Xylene Deep Oxidation

    Huynh K. P. Ha, Nguyen Tri, Nguyen P. Anh, Nguyen T. T. Van, Do T. M. Hieu, Nguyen T. Anh

    pp. 2470-2474

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    DOI:10.2320/matertrans.MT-M2019120

    Abstract

    To propose an effective CuO-doped catalyst fabricated from red mud and rice hush ash for deep oxidation and emphasize the relation between properties and activity of catalysts, in this work, 5 mass% CuO-doped materials fabricated from red mud and rice husk ash were synthesized using urea/nitrate combustion technique. Effect of urea/nitrate molar ratios on properties and activity of prepared material in p-xylene deep oxidation was also investigated. The obtained catalysts were characterized by several techniques such as X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area and Hydrogen Temperature Program Reduction (H2-TPR). The results showed that the change in urea/nitrate ratio could reduce CuO crystallite size of catalyst and enhance its reducibility leading to an increase of catalyst’s oxidative activity. The 5 mass% CuO-doped material with nanoparticles of about 20 nm synthesized with urea/nitrate molar ratio of 2 showed the best activity in p-xylene deep oxidation at the temperature range of 275–400°C. The deep oxidation of p-xylene to CO2 was almost complete at 400°C and WHSV of 12,000 mL·h−1·g−1. This study found an alternative, low-cost and friendly way for the exploitation of catalyst based on waste materials – red mud and rice husk ash. The modification of CuO-doped material by using urea as a fuel in the preparation is one of the most promising approaches, toward the development of effective VOCs oxidation. The cheap catalyst obtained in this work can be applied in the treatment of VOCs in polluted air.

  • Influence of As-Cast Microstructure on the Impact Wear Resistance of 27 mass%Cr Cast Iron

    Ngo Huynh Kinh Luan, Koreaki Koizumi, Kuniaki Mizuno, Yutaka Yamada, Tetsuya Okuyama

    pp. 2475-2480

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    DOI:10.2320/matertrans.F-M2019844

    Abstract

    The impact wear resistance of 27 mass%Cr cast iron which as-cast microstructure influenced by cooling rate during solidification was investigated by using abrasive blasting machine. Hardness and volume fraction of martensite of samples with and without contacting with an iron chiller were measured before and after abrasive blasting test. Refinement of microstructure which was due to increase of cooling rate gave adverse effect on the impact wear resistance. Through impact of abrasive media on the surface, austenite in matrix was easy to transform into martensite, and it was obvious that there were much more micro-cracks in carbide and boundary of carbide and matrix. As volume of martensite increased, the abrasion occurred remarkably. This is explained by impingement heat generated which causes self-temper softening of martensite occur during abrasive blasting test.

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  • © 2019 The Japan Institute of Metals and Materials

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