EFFECT OF MO ON MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF TIC-NI-BASED CERMETS PRODUCED BY COMBUSTION SYNTHESIS IMPACT FORGING TECHNIQUE

The effect of Mo additions on the microstructure and mechanical proper ties of TiC-30 wt.% Ni cermets produced by the combustion synthesis-im pact forging technique was investigated. The Mo content was varied bet ween 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 abov e 99%. Microscopically, the addition of Mo resulted in a decrease in t he number of microstructural defects such as interphase debonding and binder microcracking. The microstructure consisted of a spheroidal car bide phase with a high degree of contiguity (decreasing with increasin g Mo content). The Mo additions did not have a profound effect on the carbide phase morphologies (faceted vs. spheroidal), mean apparent par ticle diameters (3.5 mu m-4.5 mu m), or particle size distribution Ene rgy-dispersive X-ray analysis revealed Mo preferentially in the carbid e phase, with trace amounts in the Ni alloy binder. A significant amou nt of Ti was found in solution with Ni. Vickers' microhardness did not vary significantly with Mo content and was approximately 13 GPa. Comp ressive 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 M Pa m(1/2), and 340 GPa respectively. The beneficial effect of Mo is du e to the improved wettability of the Ni alloy binder on the carbide ph ase. Improved wettability results in a decrease in detrimental microst ructural defects and an increase in the interphase bond strength and p hase uniformity.