晶粒尺寸对γ-TiAl合金力学性能影响的纳米压痕研究

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

为研究纳米压痕过程中晶粒尺寸对γ-Ti Al合金力学性能及变形行为的影响,利用Voronoi方法建立多晶γ-Ti Al模型,采用分子动力学方法模拟压头压入不同晶粒尺寸模型的压痕过程,得到相应尺寸下的载荷-深度曲线,并计算了7种晶粒尺寸下γ-Ti Al的硬度。结果表明:当晶粒尺寸小于9.9 nm时,晶粒尺寸与硬度表现出反Hall-Petch关系,位错和晶界活动共同促使材料发生塑性变形,晶界活动起主导作用。当晶粒尺寸大于9.9 nm时,晶粒尺寸与硬度符合Hall-Petch关系,晶界对材料变形影响较小,位错主导基体发生塑性变形。另外,分析了γ-Ti Al在压痕过程中的应力传递和形变恢复过程,发现致密晶界网格结构能够有效抑制压痕缺陷及内应力向材料内部传递;晶粒尺寸越小,压头下方的内应力分布越均匀,沿压痕方向的弹性恢复比越小。

To study the effect of grain size on the mechanical properties and deformation behavior of γ-Ti Al alloy in nanoindentation process, a polycrystalline γ-Ti Al 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 γ-Ti Al 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 γ-Ti Al 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.