Phase Formation and Diamond Retention in C_diamond–(WC–Co)–ZrO₂ Composites Formed by Spark Plasma Sintering Method

New data on the effect of a ZrO₂ nanopowder additive (from 0 to 10 wt %) on phase formation and structural transformations in the hard-alloy matrix in the region of destruction under impact loading and on diamond retention in composite diamond-containing 25С_diamond–70.5WC–4.5Co materials formed by spark plasma sintering are presented. The sintered initial 94WC–6Co composite consists of the hexagonal WC phase with unit cell parameters a = 0.2906 nm and с = 0.2837 nm, the cubic Co₃W₃C phase (а = 1.1112 nm), and the hexagonal graphite phase. The sintered composites with ZrO₂ content from 0.5 to 10% is composed by the WC and Co₃W₃C structural phases, amorphous carbon, and the tetragonal ZrO₂ phase (а = 0.36019 nm, с = 0.5174 nm). It has been shown that, when the ZrO₂ content is increased, the sizes of phase components and average microstrains are more rapidly decreased in directions с and а of the 94WC–6Co composite. The addition of ZrO₂ to the 25С_diamond–70.5WC–4.5Co composite improves diamond retention. In the sintered composites, diamond retention is improved due to that they have a higher content of the tetragonal ZrO₂ phase, which provides the transformational mechanism of strengthening in the hard-alloy matrix material via its structural transformations into a denser one and the formation of a more fine-grained matrix structure with thin interlayers of cobalt bonds between WC grains.