Structure formation and properties of WC-(W,Ti)C-Ti(C,N)-TaC-Co gradient cemented carbides with cubic phases free in the surface layer

Abstract

In this paper, gradient cemented carbides with the cubic-phase free in the surface layer were prepared, and the compositional gradient formation was explored. The relations between the properties of the gradient cemented carbide and the TaC addition were investigated. The results showed that the inward Ta migration during the gradient-structure formation of the cemented carbide WC-Co-(W,Ti)C-Ti(C,N)-TaC-W was mainly driven by the thermodynamic coupling between Ta and Ti. The thickness of the cubic-phase free layer decreased as the total Ta/C ratio is enlarged in the gradient cemented carbide. With TaC added in the gradient cemented carbide, the undissolved Ti(C,N) cores was rarely observed in the bulk owing to the solid solution of Ta. The average sizes of WC phases and (W,Ti)C phases could be reduced by the TaC addition, but hardly refined further when TaC exceeds its solubility in the binder. All of the transverse rupture strength, the hardness and the fracture toughness increased with the low TaC content but decreased with the high TaC content. The coercive force was elevated with TaC added in the gradient cemented carbide, and the magnetic saturation increased when increasing TaC contents. Additionally, the coercive force was raised while the magnetic saturation fell down after the cubic-phase free layer was removed.