Mechanical Properties of Fine‐Grained Substoichiomebic Titanium Carbide

Abstract

An attempt was made to lower the ductile‐to‐brittle transition temperature (DBTT) of polycrystalline TiC and to prevent the premature intergranular fracture noted in stoichiometric Tic at high temperatures by producing four substoichiometric compositions chosen from the single‐phase TiC phase field. Each desired composition was prepared by blending and vacuum hot‐pressing the appropriate mixture of Ti powder and stoichiometric TiC powder. Each billet was characterized for density, hardness, lattice parameter, and microstructure. The actual bulk compositions were determined by averaging electron probe microanalysis data collected randomly from a polished section of each billet. Specimens cut from the billets were strength‐tested in four‐point bending from room temperature to 1400°C and in compression from room temperature to 1200°C. A qualitative determination of the material's ductility was obtained from a load vs deflection plot and by optical microscopy of polished surfaces after deformation. Both the hardness and strength dropped with decreasing C/Ti atom ratios. Billets produced at the lower C/Ti atom ratios showed a significant deviation from linearity of the load/ deflection curve at temperatures as low as 1200°C in bending, with little or no drop in strength, and as low as 600°C in compression.