Defect structure evolution and abnormal grain growth during spark plasma sintering of nano WC-Si powders

摘要

The microstructural evolution during spark plasma sintering of ultrafine WC-1 wt% Si (n-WC-Si) is presented. At 1323 K (T ＜ T_(m)~(Si)), extensive stacking faults on the 〈1010〉 prismatic planes are observed. The defect microstructure can be described as a combined shear of 1/6(1213) on the prism planes and simultaneous out-diffusion of carbon through the faults to the interparticle boundaries. At temperatures near T_(m)~(Si) (1673 K), a large fraction of abnormally grown platelets is observed. These platelets contain a single planar defect on their basal planes, described by a 1/3〈1010〉 translation of the carbon atoms across a Σ1 grain boundary (GB). Three factors contribute to the abnormally high density of platelets: (ⅰ) the low-temperature prismatic dislocations interact to form facet-roughening steps/kinks that act as nucleation sites, (ⅱ) a liquid phase triggers an increased growth rate in the vicinity of the Si inclusions, and (c) the basal twin produces a re-entrant edge for 2D nucleation.