冷轧对纯镍N6组织和力学性能的影响

Effect of Cold Rolling on the Microstructure and Mechani-cal Properties of Pure Nickel N6

摘要:

研究了冷变形对纯镍N6组织和力学性能演变的影响。对纯镍N6试样进行了冷轧变形（20%、30%、50%、70%、90%）。采用扫描电子显微镜（SEM）、电子背散射衍射（EBSD）、X射线衍射（XRD）、显微硬度测量和拉伸试验对冷轧试样的组织和力学性能进行了表征。结果表明，纯镍N6的晶粒得到了细化，不规则取向晶粒转变为与轧制方向平行的条状晶粒。纯镍N6在轧制压下量为90%时，晶粒尺寸达到微纳米级别，其中晶粒直径主要在10 μm以下，占全部晶粒尺寸的94%。轧制试样中低角度晶界分布均匀，与相邻点的10°错向角比例较高。随着冷轧压下量的增加，抗拉伸强度和显微硬度升高，伸长率降低。当冷轧程度为90%时，抗拉强度为837 MPa，显微硬度为2479 MPa，分别是退火态的2.32倍和2.7倍。纯镍N6在不同轧制压下量的断口形貌均包括等轴韧窝、棱纹和台阶断口，为韧性断裂。

Abstract:

The effects of cold deformation on the evolution of the microstructure and mechanical properties of pure nickel N6 were investigated. Samples of pure nickel N6 were deformed by cold rolling (CR) to different thickness reductions (20%, 30%, 50%, 70%, 90%). Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), microhardness measurements, and tensile tests were used to characterize the microstructure and mechanical properties of the cold-rolled samples. The results show that the grains of pure nickel N6 are refined, and the grain with irregular orientation transforms into a strip-like grain with a preferred orientation parallel to the rolling direction. Micro- and nano-grains of pure nickel N6 are obtained under CR reduction of 90%, at which the grain diameter is mainly below 10 μm, accounting for 94% of the entire grain size. The distribution of low-angle grain boundaries (LAGBs) in the rolled samples is uniform, with a relatively high fraction of misorientation angles of 10° from neighboring points. Upon increasing the cold rolling reductions, the tensile strength and microhardness increase, but the elongation decreases. At a CR thickness reduction of 90%, the tensile strength is 837 MPa, and the microhardness is 2479 MPa, which are 2.32 and 2.7 times higher than those in the unrolled condition, respectively. The fracture morphology of pure nickel N6 at various CR reductions include equiaxed dimples, ridges, and a step morphology, which indicate ductile fracture.