论文部分内容阅读
对Ti-43Al-4Nb-1.5Mo合金进行包套锻造和后续热处理实验,考察了该过程TiAl合金的热变形行为、流变软化机制以及热处理参数对微观组织和力学性能的影响。结果表明,TiAl合金包套锻造过程的高温流变软化以β相协调变形、片层相变分解、g相内位错滑移以及孪晶诱导的动态再结晶为主,最终组织为残余α_2/γ层片和等轴α_2、γ、B2相的混合组织。随热处理温度的升高,热变形组织由残余α_2/γ层片和多相混合组织转变为α_2/γ层片+γ相组织,在较高的温度下(1300℃)转变为全层片组织。其中,B2相随着溶质扩散程度的增加逐渐消失,残余层片组织发生分解转变为等轴α_2/γ层片团,同时发生γ→α转变,形成全层片组织。对热等静压、锻态和热处理试样的高温(800℃)拉伸性能进行比较,经热处理后获得的全片层组织具有最佳的综合性能,抗拉强度为663 MPa,延伸率达到26%。分析该样品的断裂行为可知,由于存在层片扭曲拉长、微孔钝化以及裂纹曲折延伸的断裂机制,全层片组织具有良好强度-塑性的综合力学性能。另外,热加工过程中(高温)bcc结构B2相能够协调变形,但服役条件下硬脆的B2相作为裂纹源容易引起裂纹萌生,对力学性能极其不利。因此,TiAl合金在热变形和服役过程中需要对组成相进行严格控制,从而获得良好的力学性能。
The Ti-43Al-4Nb-1.5Mo alloy was subjected to enveloping forging and subsequent heat treatment. The effects of thermal deformation behavior, rheological softening mechanism and heat treatment parameters on the microstructure and mechanical properties of the TiAl alloy were investigated. The results show that the high temperature rheological softening of the TiAl alloy during the forging process is dominated by the β phase, the phase transformation, the dislocation slip in the g phase and the twinning induced dynamic recrystallization. The final microstructure is residual α_2 / γ layer and the equiaxed α_2, γ, B2 phase of the mixed organization. With the increase of heat treatment temperature, the hot deformed microstructure was transformed into α_2 / γlayers + γphase by residualα_2 / γlayers and multiphasic mixed structures, and transforms to fulllayer at higher temperature (1300 ℃) . Among them, B2 phase disappeared gradually with the increase of solute diffusion, and the residual lamellar structure was decomposed and transformed into equiaxed α_2 / γ lamellae. At the same time, γ → α transformation took place, forming a full-layer lamellar structure. Tensile properties of hot isostatic pressing, forging and heat treatment specimens were compared at high temperature (800 ℃), the whole layer structure obtained after heat treatment has the best overall performance, the tensile strength of 663 MPa, the elongation reaches 26%. The analysis of the fracture behavior of the sample shows that the full-layered structure has good mechanical properties of ductility-plasticity due to the existence of the stretching mechanism of ductile deformation, micropore passivation and the fracture mechanism of crack propagation. In addition, during the hot working (high temperature) bcc structure B2 phase can coordinate deformation, but under service conditions, the brittle B2 phase as a crack source easily lead to crack initiation, which is extremely detrimental to the mechanical properties. Therefore, the TiAl alloy during the deformation and service in the need of the phase composition of the strict control, so as to obtain good mechanical properties.