Effect of Mo on microstructure and mechanical properties of TiC-Ni-based cermets produced by combustion synthesis impact forging technique

Abstract

The effect of Mo additions on the microstructure and mechanical properties of TiC-30 wt.% Ni cermets produced by the combustion synthesis-impact forging technique was investigated. The Mo content was varied between 0 and 10 wt.%, in 2 wt.% increments. Cylindrical tiles 6.35 cm in diameter and 1.27 cm thick were produced with apparent densities above 99%. Microscopically, the addition of Mo resulted in a decrease in the number of microstructural defects such as interphase debonding and binder microcracking. The microstructure consisted of a spheroidal carbide phase with a high degree of contiguity (decreasing with increasing Mo content). The Mo additions did not have a profound effect on the carbide phase morphologies (faceted vs. spheroidal), mean apparent particle diameters (3.5 mu m-4.5 mu m), or particle size distribution Energy-dispersive X-ray analysis revealed Mo preferentially in the carbide phase, with trace amounts in the Ni alloy binder. A significant amount of Ti was found in solution with Ni. Vickers' microhardness did not vary significantly with Mo content and was approximately 13 GPa. Compressive strength, transverse rupture strength, fracture toughness, and Young's moduli increased with increasing Mo content; the mean values for the 8 wt.% Mo material were approximately 3400 MPa, 1300 MPa, 22 MPa m(1/2), and 340 GPa respectively. The beneficial effect of Mo is due to the improved wettability of the Ni alloy binder on the carbide phase. Improved wettability results in a decrease in detrimental microstructural defects and an increase in the interphase bond strength and phase uniformity.