Microstructural evolution and mechanical properties of (TiZrHfNbTaCrx)C multi-metal carbides by adjusting Cr content

(TiZrHfNbTaCr x )C multi-metal carbides with varying Cr contents were synthesized via carbothermal reduction coupled with spark plasma sintering (SPS) at different temperatures. The influence of Cr content on its solid solubility as well as microstructure and mechanical properties were systematically investigated. At 1900°C, the formation of secondary phase Cr 3 C 2 is distributed at triple junction of grain boundaries. Increasing Cr content leads to significant grain refinement, demonstrating the beneficial role of liquid Cr-rich carbides in inhibiting grain growth. At 2000°C, Cr exhibits a pronounced tendency to segregate at the grain boundaries. The solid solubility of Cr within grains (up to ∼3 at%) displays limited sensitivity to Cr content and temperature variation, which is possibly related with limited time of SPS process. Optimal mechanical properties are achieved at x =1.0 and 1900 °C, exhibiting the flexural strength of 493 MPa and Vickers hardness of 23.1 GPa, albeit with slightly reduced fracture toughness (3.82 MPa·m 1/2 ). A transition in fracture mode from intergranular to transgranular with Cr addition is also revealed, correlated with the enhanced grain boundary strength caused by second-phase distribution.