Microstructure and tensile properties of hot-pressed Co-Cr-Mo alloy compacts for biomedical applications

Abstract

The gas atomized Co-29Cr-6Mo alloy powder was hot-pressed at various temperatures from 1223 K to 1357 K with applied pressures of 50 or 80 MPa for 7.2 ks. Mean grain size of the compacts hot-pressed at 1257 K is 2.7 μm and the relative density is 97%. The grain size of the compacts tends to increase with increasing sintering temperature. The σ phase is observed in the compacts hot-pressed at 1223 K to 1307 K. The ultimate tensile strength of the compacts hot-pressed at 1257 K and 80 MPa shows the highest value (1240 MPa) in the compacts due to the fine grain size (2.7 μm). Meanwhile, the compact hot-pressed at 1357 K and 50 MPa shows the highest plastic elongation (50%). This is attributed to the facts that the σ phase is dissolved in the fee matrix during hot-pressing at 1357 K and strain-induced martensite transformation (SIMT) proceeds during plastic deformation. These values are much higher than those of as-cast Co-29Cr-6Mo alloy and comparable to those of the forged Co-29Cr-6Mo alloy. © 2008 The Japan Institute of Metals.