热-力循环作用下β-γ型TiAl合金片层组织的分解与球化行为研究

Ingot breakdown of β-γ TiAl via hot forging is the basis for optimization of the mechanical properties and the prerequisite for secondary processing. Due to the high anisotropy of the lamellae structure and the uniaxial forging direction, generally there are some remnant lamellae in the forged billets. Meanwhile, the remnant lamellae can be effectively reduced by multi-pass forging, which therefore suggests that the thermo-mechanical cycles can promote the lamellae decomposition and globalization. Till date, most studies concerning the hot deformation for TiAl alloys are concentrated in hot-workability or deformation kinetics, The lamellae decomposition and globalization mechanisms are not clear. Hence, this project is proposed to systematically study the lamellae evolution during thermo-mechanical cycles. The lamellae globalization mechanism and kinetics during thermo-mechanical cycles will be revealed, the promoting mechanism of thermo-mechanical cycles on decomposition of remnant lamellae will be indentified. This project not only is helpful for understanding the deformation mechanism and microstructure evolution of β-γ TiAl alloys, but also is of significance for the optimization of forging routes design.

通过锻造破碎铸态组织、实现片层球化是提高β-γ型TiAl合金的综合性能、进行二次加工的基础。由于片层组织显著的各向异性以及单轴镦粗的锻造方式，TiAl锻坯中往往存在未球化的残余片层。而通过引入中间退火、增加变形道次可有效减少残余片层、提高球化比例，表明热-力循环能够促进TiAl片层的分解与球化。然而，目前关于TiAl合金热变形的研究多集中于热加工窗口或变形动力学分析，热-力循环作用下的片层球化机理不明、残余片层的分解机制不清。为此，本项目拟开展“热-力循环作用下β-γ型TiAl合金片层组织的分解与球化行为”研究。通过系统分析热-力循环条件下的片层组织演变行为，揭示热-力循环作用下片层球化机理及动力学特征，阐明热-力循环对残余片层的分解的诱导机理。该项目不仅对深入理解β-γ型TiAl合金的热变形机制和组织演变具有理论意义，而且对实现该类合金锻造组织的均匀化具有重要的指导意义。

通过锻造破碎铸态组织、实现片层球化是提高β-γ型TiAl合金的综合性能、进行二次加工的基础。由于片层组织显著的各向异性以及单轴镦粗的锻造方式，TiAl锻坯中往往存在未球化的残余片层。而通过引入中间退火、增加变形道次可有效减少残余片层、提高球化比例，表明热-力循环能够促进TiAl片层的分解与球化。然而，目前关于TiAl合金热变形的研究多集中于热加工窗口或变形动力学分析，热-力循环作用下的片层球化机理不明、残余片层的分解机制不清。为此，首先利用VAR+ISM熔炼了Ti-43.5Al-8Nb-0.2B合金，并通过两次锻造和热处理获得了细小均匀的全片层组织；其次，对全片层组织进行了等温压缩实验，详细研究并统计了变形组织特征，对动态再结晶的显微机制、动力学特性进行了分析，利用先进的电子显微分析及有限元数值仿真研究了片层的变形特征，揭示了残余片层的形成机制。再次，对于变形组织在热处理过程中的演变行为进行了系统研究，阐明了亚动态/静态再结晶动力学。最后，完成了TiAl合金的多道次压缩，重点研究了应变路径对残余片层演变的影响。