MICROSTRUCTURES OF HIGH PURITY NICKEL COMPRESSED BY DYNAMIC PLASTIC DEFORMATION

摘要

A high purity Ni (99.96 wt.%) has been subjected to dynamic plastic deformation (DPD) at room temperature to accumulative compressive strains from 0.3 to 2.9 at a rate of 10~2-10~3s~(-1). It is observed that the structural evolution dominated by dislocation glide follows the general pattern of structural evolution by formation of cell structures and extended dislocation boundaries forming cell blocks at low-to-medium strains transforming into a typical lamellar structure at high strains. The boundary spacing decreases with strain following a power-law relationship. Compared with the low strain rate deformation, DPD Ni shows: i) a higher dislocation density, ii) a smaller boundary spacing, iii) a higher fraction of low angle boundaries (misoriented ＜15°), and iv) a smaller critical strain leading to a saturation stage. The effect of the deformation rate on the structure is discussed. It is concluded that high strain rate deformation provides an opportunity to fabricate novel strong metals with nanometer-spaced low and high angle boundaries at relatively low strains.