Low-Cycle Fatigue Behavior of a Nickel Base Single Crystal Superalloy at High Temperature

摘要:

研究了2种高温条件下镍基单晶合金的低周疲劳行为。试验温度和总应变幅是影响合金低周疲劳寿命的 2 个主要因素，在相同温度下，低周疲劳寿命随应变幅的减小而增大；在同一应变幅下，870 ℃的疲劳寿命均小于760 ℃的疲劳寿命。二次细小g￠ 相有效阻碍了位错的滑移，提高了合金在760 ℃低周疲劳变形抗力，位错滑移带成为疲劳裂纹萌生及扩展的主要途径；870 ℃循环应力曲线前期出现短暂硬化和后期软化的现象，g￠ 相逐渐粗化和高密度的位错缠结是循环软化的主要原因。局部应力集中与合金内微孔的交互作用是疲劳裂纹萌生的源头

Abstract:

Total strain controlled low cycle fatigue tests have been performed at 760 and 870 oC on a nickel base single crystal supperalloy and its fatigue behavior and microstructural character have been studied. The dislocation characteristics and the fracture surface observation were evaluated through scanning electron microscopy and transmission electron microscopy, respectively. Results show that the fatigue life for specimens increases with the decreased strain amplitude. The homogeneous secondary γ′ particles distribution in the matrix is beneficial for enhancement of fatigue resistance. The formation of persistent slip bands (PSBs) enhances the fatigue crack initiation at micropores and the propagation along the PSBs. At 870 oC and higher strain amplitude, the locally higher stress concentration resulted from dislocation tangling, and progressive coarsening promotes a relatively soon initiation of fatigue microcracks