Effect of pressure on sintering of TiC-Fe-Cr-Mo cermets under vacuum conditions

Abstract

TiC-Fe-Cr3C2-Mo and TiC-Fe-Cr3C2-Mo2C powder mixtures have been consolidated by liquid phase sintering under different vacuum conditions. Densification is improved by reducing the pressure of the furnace chamber from 10−2 to 10−5 mbar. This is due to a more efficient carbothermal reduction of powder oxides, which enhances the diffusion phenomena needed for good wetting of ceramic grains by the liquid phase. Cermets based on fine Mo2C powders exhibit higher densities than those based on coarse Mo additions. This is associated to higher C losses after sintering suggesting that diffusion kinetics and removal of oxide layers from starting powders are key for successful liquid phase sintering of TiC-Fe-Cr-Mo cermets. Ar injection in the sintering chamber at 1300 °C, used for avoiding the evaporation of the binder phase, leads to residual porosity due to Ar entrapment in pores open to the sintering atmosphere. Compositional gradients found at the surface of cermets sintered at 10−2 mbar are not present at 10−5 mbar. This is likely associated to the slight surface oxidation once the close porosity state is reached. The hardness of TiC-Fe-Cr-Mo cermets can be modified by applying standard heat treatments, leading to values in the range of those used for certain hot rolling applications.