铝含量对定向凝固Ni_3Al基合金显微组织和持久性能的影响

Effect of Al Content on the Microstructure and Stress Rupture Properties of DS Ni_3Al Based Alloy

研究了铝含量对定向凝固Ni3Al基合金铸态和热处理态显微组织的影响,用定向凝固技术制取合金.测试了合金的高温持久性能,利用SEM,EDS,XRD等考察了持久断裂试样的微观形貌.结果表明,铝含量在6.5%～9.5%(质量分数,下同)范围内,合金的铸态组织由γ',γ和MC碳化物组成,9.5%Al的合金形成大量的γ'初晶和少量β-NiAl相;1 300℃,4 h固溶热处理使次生γ'全部固溶,共晶γ'固溶很少,直到合金初熔γ'初晶和β-NiAl相仍不能固溶,严重损伤合金的高温强度;在1 100℃,70MPa条件下持久时间高于10 h时,合金即出现明显的筏排组织,持久裂纹主要沿柱晶横向段和枝晶间萌生扩展.7.5%～8.5%的铝含量是添加了W,Mo,Ta,Ti等合金元素的定向凝固Ni3Al基合金的适宜范围.

The DS Ni3Al based alloy was prepared by using directional solidification process and the effect of the Al content on the microstructure of as-cast and heat treatment specimens was investigated. Employing SEM, EDS, and XRD, the stress rupture of the alloy at high temperature was measured and the microstructure of stress rupture specimens was observed. The results show that the as casted microstructure of alloy is composed of gamma', gamma and MC carbide as the Al content is in the range of 6.5similar to9.5 mass percent. A large amount of primary prime gamma and a small amount of beta-NiAl phases were found in the alloy of 9.5 mass percent Al content. The solid solution heat treatment of 4 hrs at 1300degreesC can make secondary prime gamma dissolve completely, but eutectic prime gamma only dissolve a little. Solid solution of primary prime gamma and beta-NiAl were not still occur when the alloy started initial melting, this would greatly decrease the high temperature strength of alloy. As-raft structure can appear when the stress ruptured time is over 10 hrs under the condition of 1100degreesC/70 MPa. The cracks mainly initiated and extended along cross segment or interdendritic. The proper range of aluminum content of DS Ni3Al based alloy after adding W, Mo, Ti, Ta etc elements is 7.5 to 8.5 mass percent.