WORKABILITY BEHAVIOUR OF Cu-TiB2 POWDER-METALLURGY PREFORMS DURING COLD UPSETTING

An investigation was carried out to find the workability behaviour of a Cu-TiB2 composite under triaxial stress-state conditions. Initially, the TiB2 powder was prepared by using a self-propagating high-temperature synthesis (SHS) technique and the same was added to a Cu matrix in order to make Cu-TiB2 composites. Cylindrical preforms with three different TiB2 weight percentages (2 %, 4 % and 6 %) with aspect ratios of 0.50, 0.75 and 1 were prepared using a uniaxial load. Then the preforms were pressureless sintered in a tubular furnace with a continuous flow of pure argon gas at 950 degrees C for a period of 1 h. The cold upsetting test was carried out on the sintered specimens. The relationships between the various stresses, strains and the relative density were determined. The results for the various stress-ratio parameters, namely (sigma(theta)/sigma(eff))and (sigma(m)/sigma(eff)), the formability stress index (beta(sigma)) under triaxial stress-state conditions were systematically analysed. The formability stress index was found to increase with the increase in preform fractional density and it decreased with the aspect ratios. This was because the preform contains more pores and the porous bed height is high. A statistical fitting method was performed on the curve drawn between the axial strain and the stress-formability index. The compacts with a higher value of the aspect ratio and the initial preform density showed a very high fracture strain.