Molecular Dynamics Simulation On Shape Memory Effect And Cyclic Superelasticity Of NiTi Alloys

Ni Ti alloys have two excellent functional properties: shape memory effect and superelasticity.They have been widely used in industry and daily life,which poses a higher challenge to the mechanical properties of Ni Ti alloys under complex loading environment.It is of theoretical significance to study the mechanical properties of Ni Ti alloys by molecular simulation method.In this paper,three structures of Ni Ti alloy models with singlecrystal,polycrystal and solid solution are constructed.The mechanical behavior of Ni Ti alloys under various loading environments is simulated by molecular dynamics method.The microstructure evolution of Ni Ti alloys in the process of "loading-unloading-heating" shape memory effect is studied in detail.In addition,the superelasticity of single crystal Ni Ti alloy under different temperature conditions and different loading forms is simulated.The results show that martensitic transformation and its inverse transformation,relative movement of grains,atomic equilibrium position and other factors can affect the shape memory effect to a certain extent.Ni Ti alloys show a strong sensitivity to temperature.The increase of temperature will reduce the stability of superelasticity of Ni Ti alloys,promote the excitation of martensitic transformation and inhibit the transformation.Complex loading forms can also induce the mechanical behavior of Ni Ti alloys under superelasticity.The fully unloaded loading will not change the path and structural evolution of Ni Ti alloys.The partially unloaded loading will change the path and enhance the strength of Ni Ti alloys.The reverse preloading loading will change the structural evolution and weaken the strength of Ni Ti alloys.The results of this paper provide a theoretical reference for the deformation mechanism of Ni Ti alloys under complex loading environment.