一种镍基单晶高温合金870℃高周疲劳变形微观结构研究

Study of Dislocation Structure in a Single Crystal Nickel Base Duiring High Cycle Fatigue

摘要:

摘 要：本文研究了一种镍基单晶高温合金在870℃℃时的高周疲劳性能及其变形组织结构。结果表明：该合金的疲劳寿命随着应力水平的升高而减小，870℃℃时光滑试样的疲劳强度为443MPa；利用透射电镜（TEM）观察疲劳循环试样的位错组态，发现在疲劳变形的初始和中期阶段，位错组态主要为界面位错，位错在基体通道中{111}面运动，并交互反应形成3维位错网络结构。当应力水平提高到550MPa以上时，在变形的末期，观察到高密度位错集中于位错滑移带及位错切入??r" 相现象。在循环应力和高温叠加作用下，基体通道中诱发析出大量圆形细小二次?r’? 相。二次?r"?相的析出有益于阻止基体位错的滑动，抑制位错切入?r"?相，有利于提高合金的疲劳强度。

Abstract:

Abstract: An investigation of dislocation structure and its impact on the mechanical behavior of a ?? strengthened nickel base single crystal alloy under high cycle fatigue (HCF) at 870℃ is studied. The results indicate that HCF lifetime reduced with increase of applied stress amplitude. In the early stages, the fatigue deformation occurs by forced bowing of dislocations through the narrow ? matrix channels on {111} planes. During mid-term fatigue stages, most of the dislocations formed in the matrix are located in the r?/ r"?? interfaces, their intersection and reaction produce new dislocation segments and three-dimensional dislocation networks. The Burgers vectors of the dislocations in the network are 1/2<110>. The interaction of cyclic stress with high temperature induced the precipitation of homogeneous globular r"?? precipitates, that is beneficial to fatigue strength. At the end of fatigue test, the cyclic stress led to the formation of persistent slip bands moving through the r? matrix channels and ?r‘? particles. Dislocation shearing through the r"?? phase was found occasionally. The extrinsic stacking faults was also observed in the present study.