两相钛合金再结晶退火组织与织构演变的蒙特卡罗模拟

蒙特卡罗(MC)方法被广泛应用于模拟金属材料在退火过程中的静态再结晶行为. 在已有两相材料晶粒长大MC模型基础上, 引入形核阶段, 综合考虑再结晶晶粒吞并形变晶粒和再结晶晶粒竞争长大两种情况, 建立了退火时两相合金再结晶MC模型.结合电子背散射衍射所测 初始晶粒形貌、相成分、晶体学取向及应变储能相对值, 该模型被应用于TC11钛合金退火过程中的微观组织及织构演变模拟.结果表明, 所建模型能够较好体现退火过程中两相晶粒的形核及晶粒长大行为. 与β相相比较, α相具有较低的再结晶速率和较高的晶粒长大速率, 前者主要归结于α相较低的初始应变储能, 后者则体现了该条件下初始组织形貌、分布及两相比例对晶粒长大具有重要影响; 由于非均匀形核的影响, 模拟得到的再结晶速率变化与 假设均匀形核的Johnson-Mehl-Avrami-Kolmogorov 再结晶方程存在明显差异.同时, 两相的基本织构特征在退火过程中无明显变化, 但织构强度增加. 关键词： 两相钛合金 再结晶 蒙特卡罗方法 织构

Monte Carlo simulations of microstructure and texture evolution during annealing of a two-phase titanium alloy

Nucleation and grain growth are important phenomena during static recrystallization of metallic materials and both processes have significant influences on the material properties. The Monte Carlo (MC) method has been widely used to simulate static recrystallization behavior during annealing of metallic materials. In this study, an MC model for static recrystallization of two-phase alloys is proposed by extending an existing MC model, through the introduction of the nucleation stage to account for the grain growth by both consuming deformed grains and competing with other recrystallized grains. The two-phase MC model is used to simulate the evolution of microstructure and texture during annealing of a TC11 (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) titanium alloy, accounting for initial grain morphology, phase compositions, crystallographic orientations, and relative values of strain stored energy determined by electron back-scattered diffraction. The results show that the model can reproduce satisfactorily the recrystallization and grain growth behavior in annealing. Compared with the β phase, the α phase depicts a lower recrystallization rate but a higher grain growth rate: the former difference can be mainly attributed to the lower strain stored energy in the α phase before annealing, whereas the latter suggests that the grain growth in the system is significantly influenced by the grain morphology, distribution of grains, and relative volume fractions of the two phases in the initial condition. Due to the influence of heterogeneous nucleation accounted for in the model, the simulated recrystallization rate deviates considerably from that described by the Johnson-Mehl-Avrami-Kolmogorov equation. The simulation also indicates that for both phases the textures strengthen with little changes in their basic features during annealing.
Keywords： dual-phase titanium alloy recrystallization Monte Carlo method texture