热轧变形对纯钴显微组织和力学性能的影响

Effect of hot rolling deformation on microstructure and mechanical properties of pure cobalt

为研究不同热轧变形量对纯钴的显微组织和力学性能的影响,对高纯钴(99.95%)进行500℃下的热轧处理,将试样水冷后进行XRD、EBSD表征。结果表明:初始态试样中HCP相、FCC相两相共存,且以HCP相为主;随轧制进行,最大晶粒尺寸从28.08μm细化到12.35μm,∑3退火孪晶和相变孪晶的含量降低,残余应变增加,两相含量发生改变,FCC相含量上升,HCP相含量降低;不同相中大小角度晶界呈现相同的变化趋势,小角度晶界(LAGB)含量上升,大角度晶界(HAGB)含量降低;压下量27%的试样性能最好,其屈服强度、抗拉强度、硬度和伸长率(657.18 MPa、964.05 MPa、298.2HV_(0.5)和42.87%)相较于初始态(408.34 MPa、862.53 MPa、214.4HV_(0.5)和38.07%)均有提升;塑性随强度的增加不降反升,主要是由FCC相含量上升、大尺寸片层状HCP相晶粒发生细化和均匀化所致。

In order to study the effect of different hot rolling deformations on the microstructure and mechanical properties of pure cobalt,high-purity cobalt(99.95%) was hot-rolled at 500 ℃,and the rolled samples were characterized by XRD and EBSD after water cooling.The results show that the annealed initial state sheet has two-phase structure of HCP phase and FCC phase,with HCP phase being the main component.With rolling process,the grain size is refined from 28.08 μm to 12.35 μm,the content of ∑3 annealing twin bounady and phase transition twin boundary decreases,the residual strain increases,and the dislocation accumulates continuously,two-phase content changes,FCC phase content increases,and HCP phase content decreases.The grain boundaries of different phases exhibit the same trend of change with the increase of low angle grain boundaries(LAGB) content and the decrease of high angle grain boundaries(HAGB) content.Under different reduction amount,the performance of pure cobalt sheet with 27% reduction amount is the best.At this time,the yield strength,tensile strength,hardness and elongation of pure cobalt(657.18 MPa,964.05 MPa,298.2HV_(0.5),42.87%) are improved compared with the initial state(408.34 MPa,862.53 MPa,214.4HV_(0.5),38.07%).The plasticity of cobalt does not decrease but increases with the increase of the strength,mainly due to the increase of FCC phase content and the refinement and homogenization of large-sized grains in layered HCP phase.