Ti-48Al-2Cr-2Nb-( TiB2, Ni)合金凝固组织演变规律及力学性能研究

Solidification microstructure evolution and mechanical properties of casting Ti-48Al-2Cr-2Nb-( TiB2, Ni) alloy

摘要:

TiAl合金已成为航空航天工程升级换代的关键材料，然而其铸态晶粒尺寸粗大，室温塑性和强度低，限制其进一步工程应用。本文采用真空感应凝壳熔炼工艺系制备铸锭，系统研究TiB2和Ni元素共同添加对Ti-48Al-2Cr-2Nb合金凝固组织和力学性能的影响。结果表明，TiB2及Ni合金化后，合金的凝固路径和初生相并未改变，晶粒尺寸从700μm细化至100μm，生成片状TiB2和富镍τ3相。T4822-( Ni, TiB2)合金的室温拉伸强度与基体合金相近，断裂伸长率提高30%。700-900℃时，T4822-(Ni, TiB2)合金的抗拉强度始终高于基体合金，在900℃时抗拉强度达到365MPa，较基体合金提高9%。800℃和900℃时T4822-(Ni, TiB2)合金的断裂伸长率分别达到25.3%和36.1%，远高于基体合金。晶粒尺寸的细化和晶界处的块状γ相是T4822-(Ni, TiB2)合金塑性提升的主要原因，其良好的高温强度则可以归因于片层团内部和界面处的硬质硼化物和富镍τ3相。

Abstract:

TiAl-based alloys have become the key material for the update of aerospace engineering. However, the coarse as-cast grain size, low room temperature plasticity and strength limit their further engineering application. In this paper, the Ti-48Al-2Cr-2Nb ingot alloyed with TiB2 and Ni was prepared by the induction melting and the effects of TiB2 and Ni on the solidification microstructure and mechanical properties were studied systematically. The results showed that the addition of TiB2 and Ni exhibited little influence on the solidification path and primary phase. The grain size was refined from 700 μm to 100 μm, and the flake TiB2 and Ni-riched τ3 phase was determined. The room temperature tensile strength of T4822-(Ni, TiB2) alloy was similar to that of the matrix alloy, and the fracture elongation was increased by 30%. At 700 ℃-900 ℃, T4822-(Ni, TiB2) alloy showed the preferable tensile strength, and the tensile strength at 900 ℃ reached 365 MPa, 9% higher than that of the matrix alloy. At 800 ℃ and 900 ℃, the breaking elongation reached 25.3% and 36.1%, respectively, much higher than that of the matrix alloy. The refinement of grain size and the block γ phase at grain boundary are the main reasons for the plasticity improvement of T4822-(Ni, TiB2) alloy, and the outstanding high temperature strength can be attributed to the borides and Ni-riched τ3 phase at the inner and interface of the lamellar colony.