含Ta低Cr高W铸造镍基高温合金中α相的形成与转变

Formation and transformation of α phase in Ta-containing low Cr and high W content cast Ni-base superalloys

研究了不同含Ta量低Cr高W铸造镍基高温合金的铸态和1 100℃保温500 h、1 280℃保温20 min^3h热处理后的显微组织以及1 100℃,118 MPa条件下的持久性能。结果表明:低Cr高W铸造镍基高温合金中添加元素Ta会使共晶γ′相的数量显著增加。当(Ti+Nb)含量恒定在2.1%(摩尔分数),(Ta+Al)含量达14.4%(摩尔分数)时,合金凝固后期将形成(αW,Mo)+γ′共晶;少量α相不会明显降低合金的持久性能,但α相在高于1 260℃下固溶处理或在1 100℃长时热暴露时是不稳定的,它会溶解或转变成块状M6C,从而损伤合金的高温持久性能;Ta是一种有利于提高高温合金高温强度的元素,但Ta含量应与合金中的Al含量相适应,须按等摩尔分数原则相互替换;具有Ni-10Co-1.5Cr-16W-2Mo-1Nb-5Al-4Ta成分的合金性能最佳。

The microstructures of as-cast and specimens heat-treated at 1 100 ℃ for 500 h or 1 280 ℃ for 2 min^-3 h and stress ruptured properties at 1 100 ℃ 118 MPa for four heats of low Cr and high W content cast Ni-base superalloys were investigated. The results indicate that the addition of element Ta increases the amount of eutectic γ＇. （a＋γ＇） eutectic forms in the later stage of solidification as the amount of Nb and Ti maintains at 2.1%, Ta and Al reaches or exceeds 14.4% （mole fraction）. Small amount of a phase does not decrease the stress rupture life obviously. However, a phase is unstable during the period of solid solution heat treatment at 1 260 ℃ or thermal exposure at 1 100 ℃ because of its solid solution or transformation to blocky M6C carbides which result in a deterioration of the stress rupture properties of alloys at elevated temperature. Although tantalum is a beneficial element for increasing the high temperature strength of superalloys, its content should be matched with the suitable Al content. Therefore, the substitution of Ta for Al should follow the principle of equal atomic fraction. The alloy with the composition of Ni-10Co1. 5Cr-16W-2Mo-1Nb-5Al-4Ta possesses the optimum properties.