C含量对铸造TiAl合金组织和力学性能的影响

Effect of Carbon Content on Microstructure and Mechanical Properties of Cast TiAl Alloys

在Ti-47.5Al-3.7(Cr,V,Zr)合金中添加0.05%~0.2%C(原子分数,下同),采用冷坩埚悬浮熔炼方法制备出了层片组织TiAl合金铸棒,通过组织观察、室温拉伸和蠕变性能测试研究了C含量对TiAl合金组织和力学性能的影响。结果表明,添加0.05%~0.2%C后,合金仍可获得择优取向层片组织。随C含量增加α2层片体积分数略有增加,层片间距呈细化趋势。当C含量超过0.1%时,在α2和γ层片内和层片界面上有细小的Ti2AlC型碳化物析出,碳化物析出相的尺寸和数量随C含量增加有所增加。添加0.05%~0.2%C后提高了合金室温的抗拉强度和屈服强度,且随C含量增加提升幅度逐渐增大,当C含量为0.2%时,分别将抗拉强度和屈服强度提升了101和123 MPa。添加C元素后显著改善了合金的蠕变性能,当C含量为0.1%时蠕变性能最佳,与不含C的合金相比,其塑性蠕变应变降低了一半、相同应变时的蠕变速率降低了1个数量级以上。添加0.1%C提升合金蠕变抗力的机制主要是通过抑制合金在蠕变初期的位错萌生和增殖过程;在γ层片中形成割阶和位错碎片阻碍位错继续运动,使得合金在蠕变第一阶段的应变硬化程度迅速增加;此外,析出的Ti2AlC型碳化物进一步强化层片界面和基体,与层片间距细化共同提高了穿层片滑移位错的运动阻力。

Cast rods of TiAl alloy with lamellar microstructure were prepared by cold crucible levitation melting using the Ti-47.5 Al-3.7(Cr,V,Zr)alloys with 0.05%~0.2%C(at%,the same below)addition.The effects of carbon content on microstructure and mechanical properties of TiAl alloys were investigated by microstructure observation,tensile test at room temperature and creep properties measurement.The results show that the preferred orientation lamellar microstructure can still be obtained after adding 0.05%~0.2%C.The volume fraction of theα2 lamellae increases slightly and the lamellar spacing tends to refine with the increase of C content,and the relationship between the lamellar spacing and yield strength is in accordance with the Hall-Petch relationship.When the carbon content exceeds 0.1%,fine Ti2 AlC-type carbides precipitate inside theα2 andγlamellae and at the lamellar interfaces as well,and the size and quantity of the carbides increase with the increase of carbon content.The ultimate tensile strength and yield strength of the alloy at room temperature are improved by adding 0.05%~0.2%C,and the improvement gradually increases with the increase of C content.The tensile strength and yield strength are increased by 101 MPa and 123 MPa,respectively,when the carbon content is 0.2%.The creep resistance has been improved significantly by adding carbon.When the carbon content is 0.1%,the creep performance is the best.Compared with that of the alloy without carbon addition,the plastic creep strain is reduced by half,and the creep rate at the same strain is reduced by more than one order of magnitude.The addition of C element can restrain the generation and multiplication of dislocations at the initial stage of creep.In the primary creep stage,the formation of jogs and debris in the gamma lamellae hinder the movement of dislocation which contribute to the remarkable increase in strain hardening effect of the C-containing alloy.At the same time,the Ti2 AlC-type carbides further strengthen the lamellar interfaces and the matrix,and the refinement of the lamellar spacing together improves the gliding resistance of dislocation across the lamellar interface.