Effects of Long-Term Aging on the Microstructures and Tensile Properties of Ni-Based Single Crystal Superalloy

摘要:

利用微观分析方法研究了第二代镍基单晶合金 DD6 标准热处理和980 ℃/1050 ℃/1200 ℃/长期时效对γ/γ′形态演化和拉伸性能的影响。结果显示：镍基单晶合金DD6在较高温度时效处理后会发生形态不稳定，1050 ℃/时效800 h后γ′强化相逐渐连接成筏；1200 oC时效100 h后，γ/γ′微结构的立方度明显下降并逐渐向球形边界转化，并伴有少量细小基体相嵌入强化组织。在γ/γ′界面附近分布着大量位错线，位错运动随着时效处理时间和温度的增长而加强。1050 ℃/时效1000 h后在固溶元素富集区析出块状沉淀相，其脆性特征在低温拉伸时会塞积位错运动形成应力集中。760 ℃高温下的抗拉强度、屈服强度和延伸率随着时效时间增长而减小，断面收缩率有所波动

Abstract:

The microstructure evolution and the tensile properties of the second generation single crystal superalloy DD6 were investigated after full heat treatment and aging process at 980~1200 oC. The results indicate that the morphological instability occurs at relatively high temperature, and the γ′ phase gradually connects and rafts after aged for 800 h at 1050 oC. After aged for 100 h at 1200 oC, the γ/γ′ microstructure cubicity gradually becomes weaker and transforms into spherical boundary, accompanied with a few finer matrix phase embedded into strengthening phases. Whereas the dislocation lines are homogeneously distributed in the γ/γ′ interface area, and dislocation motions are also strengthened with increasing of aging time and temperature. After aged at 1050 oC for 1000 h, the precipitation phase in the form of blocky appears in the enrichment areas of solution strengthening elements and its brittle characteristics will pile up dislocation motions at lower temperature. The ultimate tensile strength, yield strength and elongation percentage decrease with increasing of aging time, while a fluctuation of contraction area will occur at 760 oC