Effects of V and Co Element Addition on Microstructures and the Mechanical Properties of In Situ Biphasic Hybrid (TiCxNy–TiB2)/Ni Cermets

Abstract

In situ micro-(TiCxNy–TiB2)/Ni cermets with different Co and V content (2,5 and 8 wt.%) were successfully fabricated by combustion synthesis and hot press consolidation in Ni–(V/Co)–Ti–B4C–BN systems. The results indicate that as Co content increased from 0 to 8 wt.%, the average sizes of the ceramic particles decreased, when the content of V increased from 0 to 8 wt.%, the size of the ceramic particles first decreased and then increased, and when the V content is 5%, the ceramic particle size is the smallest. The Co element did not participate in the SHS reaction and was a diluent; therefore, when the Co element was added, the combustion temperature continued to decrease. When the V content was no more than 5 wt.%, as the V content increased, the maximum combustion temperature decreased. When the content of V was less than 5 wt.%, the concentration of V was not sufficient to greatly promote the generation of VN. Therefore, V absorbed a large amount of heat during the reaction, resulting in a continuous decrease in the reaction temperature of the reaction system during the reaction. When the content of the added V continued to increase to 8 wt.%, V participated in the reaction, which was exothermic. The results indicate that as Co content increased from 0 to 8 wt.%, the average sizes of the ceramic particles decreased, and the cermets with 5 wt.% Co possessed the best comprehensive properties: the highest hardness (1967 Hv), superior compression strength (3.25 GPa) and higher fracture strain (3.3%). Correspondingly, when the V content was 8 wt.%, the ultimate compressive strength and hardness of the cermets reached 1823 Hv and 3.11 GPa, respectively, 262 Hv and 0.17 GPa higher than those of the unalloyed cermets, respectively. Furthermore, the effects of Co and V on strengthening mechanisms were analyzed.