马氏体组织Ti-6Al-4V钛合金多向等温锻造组织演变及力学性能强化研究

将铸态Ti-6Al-4V钛合金经过β相区热处理水淬之后获得马氏体组织，经过两步多向等温锻造之后获得了平均晶粒尺寸为1.5 μm的均匀等轴细晶组织，其室温拉伸屈服强度为906 MPa，抗拉强度为954 MPa，伸长率为16.7%，相比铸态Ti-6Al-4V钛合金，其室温力学性能得到了极大提升。研究表明，获得马氏体组织对钛合金晶粒细化有着巨大促进作用。第一步等温锻造之后的钛合金坯料组织并不均匀，存在变形区和“变形死区”，在变形区域内，心部位置应变量最大，组织细化最为明显，从心部到两端应变量逐渐减小，片层组织变形量相应减小；经过90°换向后的第二步等温锻造之后，钛合金坯料组织内的片层组织基本全部细化，形成了均匀的等轴晶组织，从心部到两端，随着应变量的减小，晶粒取向变化相应减小。

Microstructure and Mechanics Property Variations during MDIF of Ti-6Al-4V Alloy with a Martensitic Microstructure

The as-cast Ti-6Al-4V alloy was subjected to a heat treatment condition to obtain a typical α′ martensitic microstructure. After two-step isothermal forging, a homogeneous equiaxed grained microstructure with an average grain size of 1.5 μm was achieved. The refined microstructure led to a significant mechanics property improvement. The fine grained Ti-6Al-4V alloys exhibited high yield strength(906 MPa), high ultimate tensile strength(954 MPa), and good ductility(16.7%). The finer grain size and better mechanics properties indicate that the phase transformation of α′/α+β strongly contributed to the microstructure refinement during isothermal forging of Ti-6Al-4V alloys. After the first step forging, the microstructure near the center of the forging is highly deformed, while very little deformations are present in the center regions near the die due to the effects of die chilling and friction. After the second step forging, α lamellae are fully globularized and the microstructure is homogeneous. The crystal rotations of the grains near the center are larger than that of the grains in the midway from the center to the outer edge.