孔洞形态对镍基单晶合金蠕变行为的影响

摘要

通过蠕变性能测试及组织形貌观察,研究不同形态孔洞缺陷对单晶镍基合金蠕变性能的影响,针对合金中存在有/无裂纹孔洞等铸造缺陷,对高温蠕变期间近有/无孔洞区域的应力分布进行有限元分析,根据拉应力载荷下近孔洞区域的微观应力分布特性,分析不同形态孔洞区域应力分布对单晶合金蠕变行为及组织演化的影响.结果表明:在高温蠕变期间,近有/无裂纹孔洞区域的应力分布对合金中)γ'相筏形化的形态有明显影响,在有/无裂纹孔洞两侧极点处,存在最大应力值,且可致使其裂纹沿垂直于应力轴方向发生萌生与扩展;与无裂纹孔洞相比,在有裂纹孔洞两侧的极点处应力值较大,随着蠕变的进行,在较大应力处易于发生裂纹的扩展是合金具有较低蠕变寿命的主要原因.%By means of creep properties measurement and microstructure observation, the influence of cavity morphology on the creep behaviors of a single crystal nickel-base alloy was investigated. Due to the cavity with or without cracks exists in the as-east superalloy, the stress distribution near the cavity with or without cracks during high temperature creep was analyzed by finite elements analysis method (FEM), and the influence of the stress distribution near the cavity regions on the creep behaviors and microstructure evolution of the superalloy was discussed according to the feature of the stress distribution near the cavity. The results show that, during high temperature creep, the stress distribution near the cavity with or without cracks has an obvious effect on the morphology of the rafted γ' phase in the superalloy, the maximum stress value which appears in two sides of the cavity with or without cracks may promote the initiation and propagation of the cracks along the direction vertical to the applied stress axis. Compared with the crack-free cavity, the bigger stress value appears in two sides of the cavity with cracks which propagates easily as creep goes on, this is the main reason resulting in the alloy with shorter creep lifetime.