Room-temperature deformation micro-mechanisms of polycrystalline nickel processed by spark plasma sintering

The present work focuses on room temperature mechanical properties and deformation mechanisms of bulk polycrystalline nickel processed from a high purity micrometre-sized powder by means of spark plasma sintering. Optimisation of the conditions yielded bulk samples having a relative density ranging from 97 to about 99% and an average grain size in the range 5–45μm. EBSD experiments were carried out to characterise the microstructure of as-processed sample before and after room temperature compression tests. The microstructure investigations prior to compression tests revealed a high density of high-angle grain boundaries (HAGBs); a large fraction of them are Σ3 boundaries (20 to 52% depending on the sample), the majority of which are twin boundaries (TBs). Compression tests (at a strain rate of 10−3s−1) at fixed amount of strains (5, 8 and 50%) result in an increase of the amount of low-angle grain boundaries, probably as a consequence of an intense dislocation activity. As for HAGBs, the more prominent effects occur for Σ3 boundaries and TBs for which a sharp decrease in the course of deformation is found. This was attributed to interaction with dislocations that possibly induce misorientation changes across boundaries (e.g., TBs) as well as their partial disruption as evidenced by EBSD investigations.