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Authors: Hong Bin Wang, Xiao Yu Wang, J.H. Zhang, T.Y. Hsu
Abstract: The grain growth and mechanical properties of nanograined bulk Fe-25at%Ni alloy prepared by an inert gas condensation and in-situ warm consolidation technique were investigated. About 43% high temperature face-centered-cubic (FCC) phase and 57% low temperature body-centered-cubic (BCC) phase were observed in the sample at room temperature, which was significantly different from that of the corresponding conventional coarse-grained alloy. The in-situ X-ray diffraction results show that the start and the finish temperature of BCC to FCC phase transformation are 450°C and 600°C, respectively. The isothermal grain growth exponent n from t k D D n n ¢ = − 1 0 1 for nanograined single FCC phase Fe-25at%Ni alloy is 0.38 at 750 °C . The mechanical properties changing with the grain size were studied by means of microindentation test.
3459
Authors: Shan Qing Xu, Zheng Hong Guo, T.Y. Hsu
Abstract: The possibility of Al2Cu( q) precipitation in nanosized Al-4wt%Cu alloy is predicted based on the theory of homogeneous nucleation. The result indicates that the initial concentration of Cu in parent phase has little influence on the nucleation event when the grain size is larger than a critical size. On the other hand, when the grain size is smaller than the critical size, the formation of a stable Al2Cu nucleus will be prohibited completely due to the insufficient initial concentration of Cu.
3463
Authors: Bin Lu, Dan Qing Yi, Biao Yan, Jun Lin Yin, Yan Liu, Hui Qun Liu, Biao Li Wu, Xiao Li Chen
Abstract: Mechanical alloying(MA) technique and single-roller melt spinning technique were used to prepare Fe86Zr5.5Nb5.5B3 nanocrystalline and amorphous powders, bulk alloys were prepared by cryogenically high-pressure quick sintering. The results showed that: (1) after MA process for 15 hours, the grain size of α-Fe phase was ≤10nm; (2) melt spinning powders were fragmented by ball milling, but remained amorphous state. The crystallization temperature of this amorphous powder was about 500°C. Apparent activation energy of the amorphous crystallization was E=294.1KJ/mol; (3) under the quick sintering conditions of P=5.5GPa/t=3min/Pw≥1050W, single phaseα-Fe nanocrystalline(8~15nm) bulk alloys with relative density≥98.7% can be obtained.
3467
Authors: Masafumi Noda, Kunio Funami, Yutaka Suwahara
Abstract: For the formation of ultrafine grain in Al alloys, various means have been investigated based on a process of continuous recrystallization using a high-strain technique that employs rigorous plastic working. However, utilization for practical application is difficult for small specimens that require constraining. In this study, the effects were studied of the use of constraining die walls in the multi-axial alternative forging process (MAF) on the formation of ultrafine grains and microstructural homogeneity. This technique has possible for scaling up to a practical scale. Our results showed that tensile strength and yield stress in these fabricated materials were tripled over those of the initial materials when strain was applied. The average grain size after strain application was 0.5 µm. We conclude that a loading technique that uses different applied directions is the key determinant in creating ultrafine grains.
3471
Authors: Tomokazu Sano, Hiroaki Mori, Osamu Sakata, Etsuji Ohmura, Isamu Miyamoto, Akio Hirose, Kojiro F. Kobayashi
Abstract: Quenching of the nanocrystalline high-pressure e phase of iron, which has not been observed under a conventional shock compression, was attained using a femtosecond laser. A small quantity of the g phase of iron also existed. We found that the e phase was induced by the shock itself but not the g phase. The g phase was suggested to be induced as an intermediate structure between the a-e transition. The femtosecond laser driven shock may have the potential to quench high-pressure phases which has not been attained using conventional methods.
3475
Authors: S.W. Youn, Chung Gil Kang
Abstract: The purpose of this study is to suggest a maskless pattern fabrication technique using the combination of machining by Nanoindenter® XP and HF wet etching. Sample line patterns were machined on a borosilicate surface by constant load scratch (CLS) of the nanoindenter with a Berkovich diamond tip, and they were etched in HF solution to investigate chemical characteristics of the machined borosilicate surface. After the etching process, the convex structure was made. On the basis of this fact, some line patterns with convex structures were fabricated.
3479
Authors: J.H. Seo, Jong Kweon Kim, T.H. Yim, Yong Bum Park
Abstract: The texture evolution due to grain growth that takes place during annealing was investigated in nanocrystalline Fe-Ni alloys fabricated by using a continuous electroforming method. In the current materials, grain growth occurred during annealing at much lower temperatures than in conventional coarse-grained counterparts. With regard to the macrotextures, the as-deposited textures were of fibre-type characterized by strong <100>//ND and weak <111>//ND components, and the occurrence of grain growth resulted in the strong development of the <111>//ND fibre texture with the minor <100>//ND components. It was clarified using orientation imaging microscopy that abnormal growth of the <111>//ND grains in the early stages of grain growth plays an important role on the texture evolution. The origin of the abnormal grain growth has been discussed in terms of the orientation dependence of energy density.
3483
Authors: Se Hyun Ko, Jin Man Jang, Won Sik Lee
Abstract: Al-Mg and Al-Mg-Cu alloys are known well to reveal superplasticity in tension at high temperatures. In this study, deformation behaviors of those alloys nanograined were investigated under compression test at room temperature. During plastic deformation softening phenomena occurred obviously in nanograined Al-1.5wt%Mg and Al-0.7wt%Mg-1.0wt%Cu alloys while slight strain hardening appeared in nanograined pure Al. These results suggest that the softening strongly depends on composition of alloys. The softening takes place over strain rate range from 10-4 up to 10-1.
3489
Authors: Si Joon Noh, Taek Kyun Jung, Mok Soon Kim
Abstract: The bulk Al84Ni10Ce6 alloy was fabricated by a powder forging process. The process involved pre-compaction of amorphous powder by cold pressing and subsequent isothermal forging at temperatures from 523 to 823K with the strain rate of 10-2 s-1. The porosity decreased rapidly with increasing forging temperature up to 648K, and a fully dense bulk specimen with the porosity less than 1% was achieved when the forging was carried out at and above 648K. TEM observation on the fully dense bulk alloys revealed a mixed structure consisting of nano-scaled crystalline particles and amorphous matrix. It was also revealed that the size and volume fraction of the crystalline phases increased with increasing forging temperature. Noticeably high compressive fracture strength of 1355MPa and Vickers hardness number of 530 were obtained at room temperature for the fully dense bulk specimen forged at 648K, which contains the refined crystalline particles (average size: 28nm, volume fraction: 44%) in an amorphous matrix.
3493
Authors: Seung Zeon Han, Cha Yong Lim, Chang Joo Kim, Sang Shik Kim
Abstract: The mechanical behavior of nano grain-sized pure copper produced by various SPD (severe plastic deformation) processes such as ECAP (equal channel angular pressing) and ARB (accumulated roll bonding) was investigated in relation to the microstructural evolution. These processes promoted the formation of equiaxed nanoscale grains in pure copper. The present observation suggested that the tensile behavior of the specimens prepared by the current SPD processes was influenced by several mechanisms involving strain hardening and dynamic recovery. The heat flow was measured by using a DSC (differential scanning calorimeter) to elucidate the relationship between the dislocation density and the tensile behavior in the specimens.
3497

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