查看更多>>摘要：Microscopic stress and strain partitioning control the mechanical and damage behavior of multiphase steels. Using a combined numerical and experimental approach, local strain distributions and deformation localization are characterized in a carbide free bainitic steel produced by continuous cooling. The microstructure of the steel consists of bainite (aggregate of bainitic ferrite and thin film retained austenite), martensite and blocky retained austenite. Numerical simulations were done using a von Mises J2 plasticity flow rule and also a phenomenological crystal plasticity material model. The representative volume element (RVE) was created using a realistic 2D geometry captured through Electron Backscatter Diffraction (EBSD). These simulations describe the strain distribution and deformation localization in this steel. To validate the simulation results, local strain maps were obtained experimentally via in-situ tensile testing using micro digital image correlation (mu DIC) in scanning electron microscopy (SEM). The information gained from numerical and experimental data gave valuable insight regarding the microstructural features responsible for strain partitioning and damage initiation in this carbide free bainitic steel. The results of the modelling show that martensite, martensite/bainitic ferrite interfaces, interface orientation with respect to tensile direction, bainitic ferrite size and phase composition influence the strain partitioning in this carbide free bainitic steel.
查看更多>>摘要：Mg-Al-Zn series Alloys are a very significant class of magnesium alloys and play a vital role in future industrial and economic development due to its outstanding physical properties, such as excellent machinability, fine corrosion resistance, low cost-effectiveness, and so on. However, the structural phase transition mechanism and the evolution of electronic, mechanical and thermal properties under high pressure remain poorly known. Here, we have searched a series of crystal structures of MgAl9Zn alloy compound at pressure range from 0 GPa to 200 GPa by CALYPSO method. Our energetic and dynamic calculations suggest that the ground state structure of MgAl9Zn under ambient pressure is crystallized in the hexagonal phase with space group of P6(3) symmetry. As the pressure increased up to 54 GPa, a phase transition occurred, i.e., the P6(3) phase transforms to R3(c) phase. The electronic band structure results indicated that both P6(3) and R3(c) phases are metallic. The mechanical and thermal results show that, compared with P6(3) phase, the R3c phase possesses better strength and stronger abilities to absorb or release heats. The resent findings pave a way for future design of advanced alloyed materials.
查看更多>>摘要：Molecular dynamics (MD) simulation was applied to investigate the deposition process of gallium nitride (GaN) films on aluminum nitride (AlN) substrates, in which the effects of different crystallographic orientations and growth temperatures of AlN substrates were investigated. Furthermore, evolution of the surface morphologies, the dislocations, the crystalline structures and the atomic stress were discussed in detail. It could be indicated that the deposited heteroepitaxial GaN films were consisted of zinc blende and wurtzite crystal structures with obvious dislocations when deposited on the polar plane of the AlN substrate. The dislocation density varied in a similar trend as the crystal structure changes. On the other hand, there is no misfit dislocations in the GaN films when deposition on the semi-polar and non-polar planes of the AlN substrate. According to the simulation results, the epitaxial GaN films deposited on the non-polar a-plane of the AlN substrates could be of higher crystalline quality under the same growth conditions.
NSTL
Elsevier