含晶界孔洞粗晶工业纯铁的循环变形及损伤特征

为了更好地了解体心立方(bcc)结构金属的循环变形机制,在恒总应变幅控制的条件下研究了含晶界孔洞粗晶工业纯铁的疲劳变形特征.结果表明,含晶界孔洞的粗晶工业纯铁在不同总应变幅"εt/2下均发生不同程度的循环硬化现象,无循环饱和阶段出现.疲劳寿命与塑性应变幅的关系基本符合Coffin-Manson法则.循环变形的表面变形特征与外加总应变幅具有一定的相关性:随着总应变幅的增加,滑移变形及其导致的挤出侵入现象更为严重,滑移开裂更趋显著;越来越多的原来位于晶界上的微观孔洞发生扭曲变形、聚合、长大而产生裂纹,甚至导致沿晶开裂.在相对较高的总应变幅下,在表面还观察到了滑移扭折现象以及沿晶裂纹扩展进入晶粒内部的现象.在低应变幅"εt/2=1.0×10-3下循环变形后发现了类驻留滑移带(PSB)楼梯位错结构,随着应变幅的增加,位错胞结构发展成为主要结构特征,其平均尺寸逐渐减小.

Cyclic Deformation and Damage Features of Coarse-Grained Commercially Pure Iron Containing Grain Boundary Voids

To better understand the cyclic deformation mechanism of body centered cubic(BCC) metals,a kind of coarse-grained commercially pure(CP) iron containing grain boundary(GB) voids was selected to examine its fatigue deformation characteristics under different total strain amplitudes,Δεt/2.The coarse-grained CP iron exhibits different degrees of cyclic hardening,and no stress saturation stage appears.The relationship of plastic strain amplitude versus fatigue life meets the Coffin-Manson law.The cyclic deformation surface characteristics are somewhat dependent upon the applied Δεt/2.As Δεt/2 increases,the slip formation and thus-induced extrusions and intrusions become more serious,and slip cracking is getting more significant;more and more micro-voids at GBs are distorted and/or evolved into long cracks along GBs,even leading to GB cracking.Slip kinking and intergranular cracks propagating into grains are just observed at large strain amplitudes.Persistent slip band(PSB) ladder-like dislocation structures were observed just at a low total strain amplitude of Δεt/2=1.0×10-3.With increasing Δεt/2 applied,dislocation cells are developed as the major microstructural features,and the average size of them decreases.