Molecular dynamics simulation and experimental study on nanoindentation response of polycrystalline γ-TiAl alloy

γ-TiAl alloy is a representative material for new lightweight and high-temperature resistant structures. The study of γ-TiAl alloys using the nanoindentation technique is instructive for improving room-temperature brittle defects. In this paper, we used the molecular dynamics method to simulate the nanoindentation process of polycrystalline γ-TiAl alloy at room temperature to obtain the hardness and Young's modulus of the workpiece. The microstructural evolutionary behaviors at different stages of the indentation process were also analyzed to reveal the plastic deformation mechanism of polycrystalline γ-TiAl alloy subjected to load impact. The results show that the hardness of the workpiece decreases with the increase of the press depth due to the larger space for atoms to move at the grain boundaries; the predominance of Shockley incomplete dislocation reactions within the grains during loading, and the restriction of the surrounding grain boundaries; the stress reduction inside the workpiece during unloading leads to defect annihilation, and the released energy is transferred through grain boundaries to promoting misshapen laminar nucleation of other grains. The nanoindentation experimental study of polycrystalline γ-TiAl alloy was conducted to analyze the mechanical property response of the workpiece under different indentation loads, which obtained a slight increase in folding modulus with increasing contact depth and a significant decrease in hardness with increasing contact depth. The variation of the hardness–depth curve has the same trend as the simulation, reflecting the significant indentation size effect of the γ-TiAl alloy.