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

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.

Key words:pure nickel N6;cold rolling (CR);microstructure;mechanical properties;fracture behavior