微量C对层片组织TiAl合金高应力蠕变变形的影响

Deformation Behavior during Creep of Lamellar TiAl Alloys at Relatively High Stress with Minor C Alloying Addition

通过研究C微合金化对层片组织Ti Al合金800℃/300 MPa蠕变变形行为、组织分解以及应变硬化的影响,以解释C微合金化对层片组织高应力蠕变变形均匀性的影响。结果表明:在Ti-47.5Al-2.5V-1.0Cr-0.2Zr合金中添加0.1%C(原子分数),显著改善了该合金的抗蠕变性能,其中,合金800℃/300 MPa蠕变变形进入第三阶段的时间增加了2.5倍,相同时间蠕变应变量降低了72%,同时使其最小蠕变速率降低了近一个数量级。添加C显著改善了该合金较高应力条件下抗蠕变性能及蠕变变形均匀性。其原因是C微合金化在合金层片团界和层片界面引入碳化物析出相,层片组织抵抗剪切变形的作用,从而延缓了蠕变变形过程中再结晶和层片组织分解的发生;同时,初始组织中的碳化物改善了合金的应变硬化能力,蠕变过程中在中断的γ层片台阶处析出的碳化物起到动态硬化效果,也是添加C改善Ti Al合金层片组织较高应力蠕变变形均匀性的原因。

The effect of minor carbon addition on creep at 800 ℃ and 300 MPa was investigated in lamellar microstructure Ti Al alloys through studying the creep deformation behavior,lamellar structure degradation and work hardening effect,which was used to interpreting the influence of minor carbon addition on creep deformation homogeneity at high stress. The results showed that 0. 1%（ atom fraction） carbon addition had positive impacts on improving creep resistance of Ti-47. 5Al-2. 5V-1. 0Cr-0. 2Zr alloy. In detail,the onset of tertiary creep stage was extended as much as two and half times,the creep strain was decreased by 72% compared to the same duration,and the minimum creep rate was reduced by an order of magnitude as well. The most remarkable improvement in creep resistance as well as creep deformation homogeneity at high stress was realized when small amounts of carbon was added to generate carbide precipitates along colony boundaries and lamellar interfaces,which enhanced the resistance to shear deformation and delayed the recrystallization and lamellar degradation during creep as a result. As well,the carbides precipitation in starting materials improved the work hardening capability,and carbide dynamic precipitation on disruptive γ lamellar ledges during creep also played a beneficial role in dynamic hardening,which were also the mechanism for the enhanced creep deformation homogeneity after adding carbon.