Papers by Keyword: Twin

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Authors: Y. B. Wang, M.L. Sui
Abstract: This paper reviews our recent studies on the effect of twin boundary (TB) on the deformation behavior in Cu with nanoscale growth twins. In situ straining transmission electron microscopy investigations on TB migration, TBs and twin ends acting as dislocation emission sources, and the interactions between dislocations and TBs are highlighted. Results provide some useful understanding of why Cu with nanoscale twins leads to a combination of ultrahigh strength and high ductility.
Authors: Fabio Sorbello, Peter E.J. Flewitt, A.G. Crocker, Gillian E. Smith
Abstract: It is well established that within the lower-shelf temperature range of Fe2-3Si polycrystalline steels, the brittle fracture occurs predominately by transgranular cleavage, unless subject to embrittling heat-treatments. The cleavage fracture develops on the well established {001} planes of the bcc structure. In this paper we revisit the growth, of these cleavage cracks by considering crack propagation in single crystals of Fe2Si steel. Three point bend specimens manufactured from oriented crystals have been tested by impact loading at a temperature of -196°C. High spatial resolution focused ion beam imaging combined with ion milling is used to examine in detail the crack propagation path and has provided a new insight into the mechanisms involved. In particular it has been established that within the process zone of the propagating cracks local strain is accommodated by the formation of {112} twins. The results are discussed with respect to the overall crack propagation mechanism.
Authors: Glenn E. Beltz, Margherita Chang, Anna Machová
Authors: Shujun Zhang, Zhen Xiang Cheng, Huan Chu Chen
Authors: Ping Yang, Li Meng, Q.G. Xie, F.E. Cui
Abstract: Basal slip and tension twinning are dominant deformation mechanisms of polycrystalline magnesium at low temperature. However, fracture originates mainly from compression twins or shear bands developed from compression twins. This work compared firstly the morphological difference of two types of twins. Then, the dependence of different deformation mechanisms on initial orientations is computed by Schmid factor analysis and compared with measured matrix orientations of twins. Finally, orientation relationships of compression twins with matrices are determined using EBSD technique and compared with theoretical value.
Authors: Kounosuke Nakamura, Hiromoto Kitahara, Shinji Ando
Abstract: {10 2} twin is common in pure hcp metals. In this study, initiation and development of {10 2} twin in hcp metal was simulated by molecular dynamics (MD) method. Two types of model crystals were stretched along the y-axis by applying displacement of 0.005a (a is lattice constant of the basal plane) every 1000 MD steps and relaxed atoms by molecular dynamics method. The Y-boundary of the model was applied fixed boundary condition and the X and the Z-boundary were free boundary condition. The Lennard-Jones type interatomic potential was employed in this simulation. In the single crystal, {10 1} pyramidal slip initiated at the crack tip and the pyramidal slip was stopped at Y-boundary atoms. After that, a {10 2} twin was initiated at a front of the slip. With increasing external strain, the twin grew with increasing external strain. In the bi-crystal, {10 0} prismatic slip occurred at the crack tip in Crystal 1 and a-dislocation of the slip stopped at a grain boundary between the Crystal 1 and 2. With increasing applied strain, {10 2} twin was initiated in the Crystal 2 at the grain boundary. From the simulation results, the ‘shuffling’ process of twin deformation was estimated.
Authors: Tian Mo Liu, Pan Xiao, Fu Sheng Pan, Qing Liu
Abstract: The cold-compressed AZ31 magnesium alloys with different (2.5%, 5%, 7.5%, 10%, 12.5% and 15%) were annealed at different temperatures (573, 623 and 673K) for different time. With aid of the optical microscopy, and microhardness tester, the microstructural evolution during annealing at different temperature of the compressed AZ31 has been investigated. The microstructural characterized results were further related to the hardness test results and the calculated activation energy. The results showed that for the compressed AZ31, the recrystallization can occur on the samples with the strain just above 10% and the deformation twinning plays an important role on the nucleation and grain growth of the recrystallization. It was found that the twinning boundary was the location of the recrystallization nuclei and a lot of recrystallized grains with equiaxed shape were found along the twinning boundaries. The relationships among the nuclei orientations and the crystallographic orientations on both sides of the twining boundary have been statistically investigated. The effects of the compressed strain and the annealing temperature on annealing behavior were also discussed based on the experimental results.
Authors: Xiao He
Abstract: An actual case of PTH fracture after soldering process was studied. By means of cross section analysis using metallography microscope and SEM, together with thermal analysis results, root cause of PTH fracture was concluded that a high density of twin copper weakened the mechanical strength so seriously that PTHs could not undergo thermal stress from soldering process, and higher CTE was attributed to an accelerative factor. Moreover, it is recommended to enhance current density properly and make sure the effectiveness of electroplating additives to prevent twin copper by theoretical analysis.
Authors: Akinobu Shibata, Shigekazu Morito, Tadashi Furuhara, Tadashi Maki
Abstract: This study investigated the substructure evolution in lenticular martensite. The substructure of lenticular martensite changes from fine transformation twins in the midrib and twinned region to a high density of dislocations in the untwinned region during growth. On the basis of careful observation of the morphology and substructure of midrib and examination of the stress-induced growth behavior of thin plate martensite, we concluded that the midrib in lenticular martensite is thin plate martensite itself. Tangled and curved dislocations appeared near the martensite-austenite boundary of the untwinned region in Fe-33Ni and in the entire untwinned region in Fe-31Ni, because the martensite inherited the accommodation dislocations in the surrounding austenite. The difference of Ms temperature causes the difference in the substructure between Fe-33Ni and Fe-31Ni. The higher Ms temperature of Fe-31Ni induces the plastic deformation of the surrounding austenite at an earlier stage of transformation, resulting in the appearance of tangled and curved dislocations in the entire untwinned region.
Authors: Kinga Kościewicz, Wlodek Strupiński, Andrzej Roman Olszyna
Abstract: Crystallographic quality of the epitaxial layers depends on the process temperature, partial pressures of active components and the surface polarity and also on the crystallographic quality of the subsurface layer resulting from the preparation of the substrate. The polishing etching in hydrogen-propane atmosphere of 4H-SiC substrate of different orientations and polarity was studied. The optimization of the polishing etching has been achieved with respect to the flow of C3H8, the duration and the temperature of the process. The investigation of the surface of SiC substrate before and after in situ polishing-etching in H2+C3H8 atmosphere was carried out by Nomarski interference contrast microscopy (DIC) and atomic force microscope (AFM).
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