A Functionally Graded Carbide in the Ta-C System.

Hard materials used in such abrasive wear applications as cutting tools and wear inserts in drilling tools require high hardness to resist wear, high fracture toughness to withstand mechanical and thermal shock, and high chemical and thermal stability. Such a combination of properties is difficult to achieve in single-phase materials. Functional grading is an approach that overcomes this limitation by designing and processing a graded microstructure that provides high hardness and chemical resistance at the surface with a tough interior or bulk. While functional grading is a widely used practice in the cemented carbides industry, it has not been demonstrated with 'pure' carbides. This article reports the feasibility of designing and processing a graded carbide in the Ta-C binary system. It is shown that a simple carburization treatment of the high-toughness carbide, ζ-Ta₄C_{3− x}, can lead to the formation of the hard carbide phase, γ-TaC _y, on the surface. The thickness, microstructure (grain size), and composition (C/Ta atomic ratio, y) of the γ-TaC _y layer can be optimized to obtain both high hardness and high strength for the graded material. [ABSTRACT FROM AUTHOR]