Ti-6Cr-5Mo-5V-4Al合金中α相的析出行为及对力学性能的影响

Precipitation behavior of α-phase and its influence on mechanical propertiesin Ti-6Cr-5Mo-4Al alloy

摘要:

本文对比研究了Ti-6Cr-5Mo-5V-4Al合金双时效和单时效对α相析出行为及力学性能的影响。组织观察显示,合金固溶淬火后得到等轴β晶粒。经过低温预时效后,在β晶内获得均匀弥散的α相团簇组织,但在β晶界出现无析出区(PFZ)。这种β晶内/晶界分区析出特征直接影响后续高温时效形貌。双时效后,在β晶内析出细小均匀的α相,但在β晶界,α相呈粗大片状。与之相比,单时效后,α相分布较为均匀,都为粗大层片。拉伸结果表明,与单时效试样相比,双时效试样抗拉强度高达~1630MPa,但延性较差(~2%)。这种高强度归结为组织中亚微米、纳米量级α粒子强烈的析出强化效应,而急剧的延性损失主要源于β晶界处粗大α片诱发的形变局域化进而导致早期沿晶脆性断裂。

Abstract:

Precipitation behavior of α-phase and its influence on mechanical properties has been systematically investigated in Ti-6Cr-5Mo-5V-4Al metastable β-Ti alloy by comparing the double aging and the single aging. The microstructural characterization shows that the quenched sample consists of equiaxed β-grains. After the following low-temperature pre-aging, dense clusters composed of numerous α nano-laths evenly distribute inside β-grain interiors, while there are precipitate free zones (PFZ) around β grain boundaries. This precipitation feature between β-grain interiors and their grain boundaries is inherited into the later high-temperature aged samples. It can be seen that fine equiaxed α precipitates homogeneously distribute in β-grain interiors but the α-phase exhibits a coarse plate shape adjacent to β-grain boundaries. On the contrary, the α-plates distributes much more evenly in the single-aged microstructure although the plates have larger dimensions. Tensile testing shows that the ultimate tensile strength can be tuned up to ~1630 MPa but accompanied by the degradation of ductility (~2%). The ultra-strength originates from the significant precipitation-strengthening effect as a result of the precipitation of α-particles at the submicron- and nano-scales, and the lost ductility can be attributed to the premature intergranular fracture caused by deformation localization along β-grain boundaries.