Molecular Dynamics Simulation Of Phase Transformation And Tensile Deformation Of Ti-Al Alloy

Titanium alloy is one of the most important structural materials in the21st century. It is widely used in many industry fields such as aerospace, vehicles, ships and biological medicine, due to its small specific weight, high specific strength and good erosion resistance. It has became a focus for many researchers. The mechanical properties of materials are closely related with its micro structures. Alloying, thermal treatment and thermal mechanical treatment are the three main methods to control the microstructure of titanium alloy to adjust the matching relationship among the mechanical properties. With the rapid development of computer technology, computer simulation has became a important method in materials research. Molecular dynamics simulation is a very effective simulation method due to its ability to capture the evolution details of the microstructures which conventional experimental methods cannot.Thermal treatment and thermal mechanical treatment is two important methods to toughen the titanium alloy. In order to study the micro mechanism of the phase transformation and tensile deformation, molecular dynamics simulation with embedded-atom-method potential has been used to simulate the two processes of two Ti-Al alloys with low Al content on the atomic scale. In this paper, the evolution of the internal energy, radial distribution function and the content of different crystal structures of the phase transformation is analyzed, and the process of tensile deformation of Ti-Al alloy is also studied through stress-strain curves and the evolution of microstructure. The results are discussed in the following two aspects:(1) The βâ†'α phase transformation is a kind of shear transformation, which involves the shuffling of{110}p and is accompanied by a lattice distortion; the crystallographic relationship between new phase and parent phase accords with{0001}α||{110}β; the nucleation of Ti-10Al occurs faster than Ti-5A1and Ti-10Al has a higher amount of precipitation of a phase, showing the effect of Al as an a-stabilization element; stacking faults and twin crystals were easily formed to reduce the stress caused by the phase transition.(2) The tensile deformation in simulation is similar with experimental process, which has stages of elastic deformation and plastic deformation. In the stage of elastic deformation, the trend of the stress-strain curve accords with the Hooke’s Law, At the beginning of the plastic deformation, the stress-strain curve shows very high yield strength, followed a dramatic drop. In the stage of plastic deformation, the curve fluctuates with the strain, which is closely related with the mechanism of deformation. The dominant deformation mechanism of Ti-Al alloy is the (0001) slip system and{1012}<1011> and{1011}<1012> twinning. The lower strain rate and higher deformation temperature decrease the yield strength and then benefit the plastic deformation. The increasing of Al content in Ti-Al alloy reduces the ductility, which results in the earlier necking and cracking.