MOLECULAR DYNAMICS SIMULATION OF MICROCRACK HEALING IN TITANIUM ALLOY UNDER LASER SHOCK

Titanium alloy has been widely used in the engineering field due to its excellent properties, however, the microdefects are unavoidable near the surface during the processing and service environment. The laser shock peening technology can effectively repair the surface damage, improving the safety and reliability of titanium alloy. Understanding the microdefect healing mechanism and mechanical response of titanium alloy under the laser shock is of great significance for the material safety in service. Therefore, based on the Ti-6wt%Al alloy, the crack evolution mechanisms with different orientations under the laser shock are studied through the molecular dynamics simulation. The plastic deformation mechanism of titanium alloy shows the obvious orientation correlation. It is dominated by the partial pyramidal dislocation and short stacking fault (SF) for 0001 orientation model, and the crystalline reorientation accompanied by “sandwich” structure for 10-10 orientation model. The structure is superimposed by the atomic shuffling and reverse glide in interval basal plane, which can be compatible with the geometric deformation of impact direction and vertical direction. While for 10-11 orientation model, the phase transformation is induced by multiple SFs. The healing time of microcracks with different orientations is discrepant, which is closely related to the compression stress and dislocation activation. It is easiest to heal for 10-11 orientation crack due to the nucleation and accumulation of multiple dislocations on the crack surface. In addition, based on the comparison of tensile mechanical property of polycrystalline models before and after impact, the tensile strength and strain of polycrystalline models after crack healing is significantly improved. The theoretical relationship between MD simulation and laser shock is further discussed. The simulation results can provide a theoretical guidance for the laser shock peening and repair technology.