Effect of heat treatment on microstructure and mechanical properties of Ni- and C-free Co-Cr-Mo alloys for medical applications

The effect of pre-heat treatments, followed by a hot forging process, on the microstructure and strength of Co-Cr-Mo alloys was investigated. Four pre-heat treatments were conducted at 1170, 1200, 1230 and 1260 degrees C for three different time condition: 2, 6 and 15 h and then water cooled to room temperature. Tensile tests and XRD analyses were carried out on both as-east alloy and heat-treated alloys. The volume fraction of retained gamma phase increases with increasing the heat treatment temperature, suggesting that the gamma -> epsilon martensitic transformation is suppressed by a higher temperature heat treatment. Tensile strength slightly decreases with increasing the heat treatment temperature and the heat treatment time, whereas the ductility slightly increases. The a phase completely dissolves into matrix when the alloy is heat-treated at 1260 degrees C for longer than 6 h.