439 / 2019-03-05 20:07:06

Dynamic Responses of Polycrystalline NiTi Alloy under Shock Compression: Experiments and Molecular Dynamics Simulations

shock compression, quasi-isentropic compression, dynamic behaviors, plastic deformation, microstructure evolution, formation mechanism

全体主题 > High Pressure Physics and Materials Science

Gaining the dynamic properties and understanding the deformation and microstructure evolution characteristics of polycrystalline NiTi under high strain rates and high pressures is of significance and importance for its science insights and engineering applications. In this paper, the equation of state and constitutive relationships of Ni52Ti48 alloy at pressures of 20-50 GPa and strain rates from 104s-1 to 107s-1 were investigated by means of magnetically driven quasi-isentropic compression and by shock compression from the impact of magnetically launched flyer plates. An inflection point at a pressure of 2 -3 GPa was found on plots of Lagrangian sound speed versus particle velocity in both quasi-isentropic and shock compression experiments, and it shows the elastic-plastic transition of austenitic Ni52Ti48 alloy. The effect of the strain rate on the elastic limit of Ni52Ti48 alloy was clearly seen between strain rates of 104s-1 and 107s-1.
Meanwhile, the shock recovered experiments of Ni52Ti48 by copper momentum trapping were conducted by magnetically driven high velocity flyer plates, and then the method of Electron backscatter diffraction (EBSD) was used to characterize the microstructure evolution characteristics of recovered Ni52Ti48 samples. To unravel the relationships between the plastic deformation and microstructures of shocked Ni52Ti48 samples, molecular dynamics (MD) simulations were performed to simulate and compare the experimental cases. The simulated results show good agreement with the experimental ones. The simulated results show very good agreement with the experimental ones. After shock plastic deformation, high density dislocations, deformation twins (112 type) and new grains are produced in the recovered samples. And no phase transition from austenite to martensite structures is observed, which is consistent with our previous results of shock wave profile experiments. On this basis, the detailed MD simulations were conducted to explore the microstructure evolution regularities and formation mechanisms of Ni52Ti48 at different initial ambient temperatures (300 K, 500 K) and shock loading velocities (0.6 kms−1, 0.8 kms−1 and 1.0 kms−1), which give some new insights into the relationships of shock plastic deformation and microstructure evolution and a reasonable explanation of experimental phenomena.