Mo含量对一种镍基单晶高温合金显微组织和持久性能的影响

EFFECT OF Mo CONTENT ON THE MICROSTRUCTURE AND STRESS RUPTURE OF A Ni BASE SINGLE CRYSTAL SUPERALLOY

采用螺旋选晶法制备镍基单晶高温合金,研究了Mo含量(质量分数)分别为2％,3％,4％时合金的显微组织和高温持久性能．结果表明: 3种成分合金的铸态组织均由γ和γ′相组成．1100℃, 500 h热暴露后, 4％Mo合金中的μ相大量析出并长大, 3％Mo合金中只有少量μ相析出, 2％Mo合金中不析出μ相．析出的μ相主要由Mo,Re,W,Cr, Co和Nb等元素组成．其中, Mo形成μ相倾向最强;Re,W和Cr次之; Nb和Co最小．大量棒状μ相的析出严重损害了合金的高温持久性能,少量μ相不降低合金的高温持久性能．考虑到Mo的固溶强化作用使合金高温持久性能升高,对于Ni-5Cr-10Co-4W-3Re-15．6Al-8Ta-1Ti-0．5Nb基础成分合金,最佳的Mo含量为3％．

Ni base single crystal superalloys of three kinds of Mo content were prepared by screw selecting method. The microstructures and stress rupture properties of the superalloys with 2%, 3% and 4% Mo were compared. The results showed that as-cast structures of the three alloys were composed of γ and γ′ phases. After heat treatment, μ phase obviously precipitated and grew in the alloys with 4% Mo, while only a few μ phase in the alloys with 3% Mo, and in 2% Mo containing alloy no μ phase precipitated after heat exposure to 1100℃ /500 h. The μ phase was mainly composed of Mo, Re, W, Cr, Co, Nb etc., in which for the tendency of forming μ phase Mo is the strongest, Re, W, Cr are the second place and Co, Nb are the weakest. A lot of precipitation of rod-like μ phases damaged high temperature stress rupture properties of alloys. Due to a few μ phase no effect on the stress rupture property and the solid solution strengthening of Mo, the optimum Mo content should be 3% for the based alloy Ni-5Cr-10Co-4W-3Re-5.6Al-8Ta-1Ti-0.5Nb.