Introduction and Objectives: Cobalt–chromium–molybdenum (Co–Cr–Mo) alloy, owing to its favorable mechanical properties and biocompatibility, is widely used in medical and aerospace industries. Solution annealing plays a crucial role in improving the microstructure and mechanical properties of this alloy. The aim of this study is to investigate the effect of temperature, holding time, and cooling rate during solution annealing on the microstructure and secondary phases of Co–Cr–Mo alloy.
Materials and Methods: Solution annealing was performed at 1125, 1175, and 1225 °C for 1 and 3 hours. After annealing, the samples were cooled in furnace, air, and water environments. The microstructure was examined using optical microscopy, field-emission scanning electron microscopy, and X-ray diffraction analysis. The volume fraction of secondary phases was determined by image analysis. In addition, tensile and microhardness tests were conducted to evaluate the mechanical properties.
Results: Increasing the annealing temperature and time enhanced the dissolution of secondary phases and led to a more homogeneous microstructure. Rapid cooling in water significantly reduced the volume fraction of secondary phases from 19.46±1.07% to 1.03±0.02%. In contrast, slow cooling in the furnace resulted in grain growth and re-precipitation of some phases. Mechanical tests revealed that the hardness of the samples reached its minimum value under water and air cooling conditions.
Conclusion: Solution annealing at 1225°C for 3 hours, followed by rapid cooling in water or air, had the most pronounced effect on dissolving secondary phases and improving microstructural homogeneity. This condition enhanced the mechanical properties of the Co–Cr–Mo alloy and can be considered as the optimal heat treatment parameters for improving the performance of this alloy.