Microstructural evolution and mechanical behavior of WC–4wt.%TiC–3wt.%TaC–12wt.%Co refractory cermet consolidated by spark plasma sintering of mechanically activated powder mixtures

Abstract

The paper studied the structural features and physicomechanical properties of the WC–4wt.%TiC–3wt.%TaC–12wt.%Co composite refractory hard alloy system obtained by spark plasma sintering (SPS) from a preliminarily mechanically activated powder. It has been shown that preliminary mechanical activation in a planetary mill contributed to the comminution of agglomerates and the formation of a monomodal particle size distribution with a predominance of the submicron fraction, which intensifies the densification processes during subsequent consolidation by the SPS method. Kinetic analysis of the SPS process showed a two-stage sintering pattern with intense densification at temperatures above 790 °C due to rearrangement of WC, TiC, TaC particles and melting of the cobalt binder. It has been found that the SPS method does not lead to the formation of undesirable secondary phases in the entire sintering temperature range. A sintering temperature of 1200 °C is optimal for achieving the best structural homogeneity, density and mechanical properties, providing optimal distribution of carbide phases and the cobalt binder. The microstructure of the sample obtained at 1200 °C represents a refractory skeleton of WC grains with TiC and TaC carbide particles uniformly distributed throughout the volume. Improved fluidity of the melted cobalt binder and its mobile redistribution contribute to increased compactness of the structure and reduced porosity of the material. Samples sintered at 1200 °C possess high physicomechanical characteristics: relative density 99.99 %, hardness HV30 1623.2, bending strength 1125.1 MPa, fracture toughness 10.5 MN⋅m1/2. The abrasive wear resistance of a newly synthesized hard material was evaluated through a turning operation. Results showed durability, indicating promise for cutting tool applications and the need for further research to fully characterize the performance of this novel material.