Effect of Grain Size on Mechanical Properties of y-TiAl Alloy by Nanoindentation

To study the effect of grain size on the mechanical properties and deformation behavior of y-TiAl alloy in nanoindentation process, a polycrystalline y-TiAl model was established by Voronoi method, and the nanoindentation process for different grain sizes was simulated by molecular dynamics method. According to the simulation results, the Load-depth curves of different grain sizes were obtained, and the hardness of y-TiAI alloy with 7 kinds of grain sizes was calculated. The results show that the relationship between hardness and grain size exhibits an inverse Hall-Petch when the grain size is less than 9.9 nm. Meanwhile, the grain boundary activity and dislocation sliding promote the plastic deformation of matrix, and the grain boundary activity plays a major role. However, the relationship between hardness and grain size conforms to Hall-Petch when the grain size exceeds 9.9 nm. The grain boundary has little effect on the plastic deformation, and the plastic deformation of matrix is dominated by dislocation. In addition, the stress transfer and deformation recovery of y-TiAI were analyzed in the nanoindentation process, it was found that the dense grain boundary grid can effectively inhibit the indentation defects and the internal stress transfer to the matrix. When the grain size becomes smaller, the stress distribution will be more uniform under the indenter and the elastic recovery ratio will be smaller along the indentation direction.