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在恒塑性应变幅εp1控制条件下研究了含富Cr沉淀颗粒的单滑移取向Fe-35%Cr合金(质量分数)单晶体的疲劳变形特征.实验结果和分析表明,当εp1≥2.5x 10-3时,由于运动的位错易于切过细小富Cr沉淀颗粒,导致在循环刚开始第1周的拉伸阶段出现了明显的应力软化现象,并接着在疲劳早期阶段表现出轻微循环软化现象.而且,晶体在循环过程中表现出一定程度的拉一压应力不对称性,这种增强的应力不对称性与细小富Cr沉淀颗粒的变形不稳定性有关.由大量细小滑移线聚集而成的粗滑移带以及高应变幅下形成的扭折带是该晶体主要的滑移变形特征.主裂纹大致沿主滑移面发展并最终沿此开裂,同时伴随有一些形态各异的二次裂纹在表面萌生.微观结构观察发现,在低应变幅(εp1=5.0x 10-4)下就有类驻留滑移带(PSB)楼梯结构形成,其体积分数随εp1的增大而增加.当εp1增大到5.0×10-3时,位错胞结构成为其主要微观结构特征.

Although some knowledges about the fatigue deformation mechanisms of fcc alloy single crystals containing precipitates have been obtained the past severa decades,few relevant research findings have been reported on precipitates containing bcc alloy single crystals.In the present work,a single-slip-oriented bcc Fe-35%Cr aLlloy(mass fraction)single crystal containing Cr-rich pre-cipitates was prepared as the target material,and its fatigue deformation features were investigated under constant plastic strain amplitude control.Experimental results and analyses demonstrate that, when the plastic strain amplitude εpl1≥2.5×10-3,the Cr-rich precipitates can be readily sheared by the moving dislocations during deformation,leading to an obvious stress softening phenomenon observed at the tensile 10ading stage of the first cycle,and subsequently to a slight cyclic softening phenomenon at a very early stage of cycling.In addition,the tension-compression stress asymmetry was found during cyclic deformation of the crystals,and this enhanced stress asymmetry should be related to the deformation instability of Cr-rich precipitates.The slip deformation features were mainly manifested by the formation of coarse slip bands comprising a quantity of fine slip lines and also by the formation 0f the kink band at high gpl(e.g.,5.0×10-3).The primary crack develops roughly along the primary slip plane(101)and the crystal finally cracks along this plane,accompanied with some secondary cracks having various morphologies being formed on the crystal surface.Microstructural observations indicate that persistent slip band(PSB)ladder-like structures can be found at a low εp1 of 5.0 x 10-4,and the volume fraction of them increases with increasing εp1.As εp1 is raised to 5.0×10-3,the microstructural features are primarily characterized by the formation of dislocation cells.