Co对铸态TiAl-Nb合金组织和高温氧化性能的影响

Effects of Co on Microstructure and High Temperature Oxidation Properties of Cast TiAl-Nb Alloy

摘要:

采用非自耗电弧熔炼方法经多次重熔制备了Ti45Al-6Nb-xCo合金(x=0, 0.5, 1, 2和4 at.%),研究了不同Co含量合金的组织结构和高温抗氧化性能。结果表明,增加合金中的Co含量能够细化α₂+γ片层组织,促进合金中形成γ和B₂相,并抑制α₂相形成；合金中Co含量超过2 at.%会导致富Co相析出和组织粗化。1000℃空气中的恒温氧化结果表明,适量的Co合金化能够显著改善TiAl-Nb合金的高温抗氧化性能；Ti45Al-6Nb-1Co合金的氧化的抛物线速率常数约为1.36×10^_-2mg^₂/cm^₄h,较Ti45Al-Nb合金低约1个数量级；但Co含量超过2 at.%后,随Co含量增加,合金的氧化速率呈增加趋势。

Abstract:

Ti45Al-6Nb-xCo (x=0, 0.5, 1, 2 and4 at.%) alloys were prepared using non- consumable arc melting method by three times of remelts. The microstructure and high temperature oxidation behavior of the alloys with different Co concentrations were investigated. The results show that increase of Co concentration in the alloy can significantly refine the α₂+γ lamellaer, promote the formation of γ and B₂ phases while inhibit the formation of α₂ phase. Co-rich precipitates and microstructure coarsening were observed when concentration of Co is higher than 2 at.% in the alloy. The static oxidation results at 1000 ℃ in air show that the oxidation resistance of TiAl-Nb alloy has been remarkably improved by appropriate Co alloying. The oxidation parabolic rate constant of the Ti45Al-6Nb-1Co alloy is about 1.36×10^_-2mg^₂/cm^₄h, lower than that of the Ti45Al-Nb alloy by about one order of magnitude. However, once the concentration of Co exceeds 2 at.%, increase of Co concentration in the alloy lead to an increase of the oxidation rate of the alloy.