Design and fabrication of TiC-based symmetrically compositional functional graded materials

TiC-based cermets with Ni–Mo alloys are now increasingly used in industry. For further improving the properties of TiC-based cermets with the aim to replace more kinds of WC-based cemented carbides, TiC(Mo, Ni)x/TiC(Mo, Ni)y/TiC(Mo, Ni)x symmetrically compositionally functional graded materials (SCFGM) are proposed and fabricated, which have the following advantages: (1) more wear resistant surface layers composed of less Ni–Mo alloying in combination with tougher mid-layer(s) composed of more Ni–Mo alloying; and (2) artificial residual compressive stress created on both surfaces of the specimen due to the difference in the thermal expansion coefficient between surface layers and mid-layer(s), which remarkably increases the bending strength and the fracture toughness of the SCFGM. The analytical model for SCFGM is established based on elasticity mechanics, mechanics of composite materials and computing mathematics. Triangle series are employed to describe distributions of residual thermal stress on both surfaces of the FGM caused by the difference in thermal expansion coefficients between surface layers and central layers. As an example, TiC-based SCFGM is successfully fabricated based on calculated thermal stress distribution by the self-developed SCFGM CAD system.