深冷异步轧制及退火处理对CrCoNi中熵合金微观结构演变和力学性能影响

Influence of asymmetric cryorolling and annealing treatment on microstructure evolution and mechanical properties of CrCoNi medium entropy alloy

采用1.0、1.2、1.4和1.6的轧制异速比对高温退火Cr Co Ni中熵合金进行室温和深冷异步轧制,并对轧后的材料在873、973和1073 K退火处理0.5 h。采用透射电子显微镜对轧制态样品进行微观表征,发现轧制态合金晶粒尺寸随着异速比增加而减小,且存在明显的孪晶。室温异步轧制实验显示,轧制后轧制态和退火态合金的抗拉强度均随着轧制异速比的增加而增加。深冷轧制制备的材料具有比室温轧制更高的强度,但深冷轧制过程异速比对材料强度影响不明显。在深冷异步轧制过程中,由于内应力和轧制缺陷的累积使得异速比强化有一定的饱和度。采用场发射扫描电子显微镜对拉伸试样的断口形貌进行表征,发现室温异步轧制后合金具有明显的韧窝,而深冷异步轧制韧窝相对较浅,为剪切断裂。

The high temperature annealed Cr Co Ni medium entropy alloy( MEA) was processed by asymmetric rolling( AR) at room temperature and asymmetric cryorolling( ACR) with rolling speed ratios of 1. 0,1. 2,1. 4 and 1. 6,then the rolled sheets were annealed at873,973 and 1073 K for 0. 5 h. The microstructure of the rolled samples was characterized by transmission electron microscope( TEM).It is found that the grain size of the rolled samples decreases with the increase of speed ratio and there are obvious twins. AR experiments at room temperature show that the tensile strength of both the rolled and annealed alloys increases with the increase of rolling speed ratio.The strength of material prepared by ACR is higher than that of rolling at room temperature,but the influence of the speed ratio during ACR on the strength of material is not obvious. In the process of ACR,due to the accumulation of internal stress and rolling defects,the reinforcement of speed ratio has a certain degree of saturation. The fracture morphology of tensile specimens was characterized by field emission scanning electron microscope( FE-SEM). It is found that the alloy has obvious deep dimples after AR,while dimples by ACR is shallow,which is shear fracture.