Ti-44Al-4Nb-4V-0.3Mo-Y合金的高温变形行为及组织性能研究

发布时间：2018-02-25 00:03

  本文关键词： beta gamma TiAl合金 显微组织 性能 高温变形行为 锻造　出处：《太原理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：TiAl合金密度低、强度高、抗氧化性能以及抗蠕变性能优异,是航空航天及汽车工业领域非常有前景的一种轻质高温结构材料。Beta gamma TiAl合金被证明具有良好的热加工性能。本文采用非自耗真空电弧熔炼技术制备了Ti-44Al-(0,4Nb,4V,2Mo,4Mo)(at%)合金,研究了Nb,V,Mo对TiAl合金组织的影响;基于对V、Mo和Nb元素的分析,采用感应凝壳熔炼技术制备了成分为Ti-44Al-4Nb-4V-0.3Mo-Y(at%)的beta gamma TiAl合金,并对其组织、性能、高温变形行为以及锻造工艺进行了系统的研究。Nb、V、Mo这三种元素的β相稳定能力为MoVNb,4at%的Nb没有使合金形成稳定的B2相,而添加4at%的V或2at%的Mo可在合金中有效保留B2相,B2相将粗大的片层团分割成很多细小的片层团。当Mo的含量增加到4at%,合金形成了魏氏体组织。铸态Ti-44Al-4Nb-4V-0.3Mo-Y合金为近片层组织,热等静压和均匀化退火后成为近γ组织。在850℃高于该合金的韧脆转变温度,合金的断后伸长率快速增加到13%。该合金抗氧化性能较好,800℃循环氧化80h后氧化增重量只有1.92 mg/cm2。在β+γ两相区热处理时,α相同时遵循与γ相的Blackburn位向关系以及与β相的Burgers位向关系从β/B2晶粒中析出,得到粗大的近片层组织。在α+β+γ三相区进行热处理分别可以得到细小的近γ组织,双态组织和近片层组织。在α+β两相区进行热处理可以完全消除β相获得全片层组织。采用等温压缩热模拟实验研究了Ti-44Al-4Nb-4V-0.3Mo-Y合金的高温变形行为和组织演变规律。该合金变形抗力较小,热加工性能良好,但在TiAl合金的服役温度下仍能保持较高的强度。通过热力模拟数据计算出了该合金的热变形激活能,并建立了高温变形本构方程。该合金主要有两种典型的变形组织,在应变速率为0.01s-1时,合金动态再结晶比较充分。采用不同工艺对Ti-44Al-4Nb-4V-0.3Mo-Y合金进行了锻造。锻造工艺为1250℃/0.02 s-1时获得了尺寸约20μm的细小等轴近片层组织,并且锻态合金的室温拉伸性能得到显著提高,断后伸长率和抗拉强度分别达到了1.9%和842MPa。锻造工艺为1200℃/0.02s-1或采用降温锻造时可以得到晶粒尺寸非常细小的γ和B2混合组织,但锻态合金的室温拉伸性能依然较差。B2相可以阻碍裂纹的扩展,但近片层组织的断裂韧性高于细小的γ和B2混合组织的断裂韧性。
[Abstract]:TiAl alloy has low density, high strength, excellent oxidation resistance and creep resistance. Beta gamma TiAl alloy is a promising material in aerospace and automotive industry. It has been proved that it has good hot working properties. Ti-44Al-0NbC4NbC4NbC4V2MoO4MoTZ) alloy has been prepared by non-consumable vacuum arc melting technique in this paper. Based on the analysis of the elements of TiAl, Ti-44Al-4Nb-4V-0.3Mo-Yatai (Ti-44Al-4Nb-4V-0.3Mo-Yathe) beta gamma TiAl alloy was prepared by means of inductive shell melting technique, and the microstructure and properties of the alloy were also studied, and the microstructure and properties of Ti-44Al-4Nb-4V-0.3Mo-Yatai alloy were investigated. The deformation behavior at high temperature and forging process were studied systematically. The 尾 -phase stability of the three elements, I. e., MoVNbC4at% NB, did not make the alloy form a stable B2 phase. However, the addition of 4at% V or 2at% Mo can effectively retain B2 phase B 2 phase in the alloy and divide the coarse lamellar clusters into many small lamellar clusters. When Mo content increases to 4 att, the alloy forms Weiss structure, and the as-cast Ti-44Al-4Nb-4V-0.3Mo-Y alloy is near lamellar structure. After annealing under hot isostatic pressure and homogenization, the microstructure of the alloy is near 纬, which is higher than the ductile-brittle transition temperature of the alloy at 850 鈩，

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