Effect of isothermal aging on the microstructural evolution of Co–Cr–Mo–C alloy

The microstructural evolution of a Co–28Cr–5Mo–0.3C alloy was investigated during isothermal aging at 850 and 950 °C for 4, 8, 16 and 24 h. The most important structural changes observed as a result of aging, were fcc (metastable) → hcp isothermal martensitic transformation, lamellar-type constituent formation at the grain boundaries and also carbides precipitation in the interior of grains on the stacking faults. According to the obtained results, it was found that isothermal aging at 850 °C resulted in the formation of lamellar-type constituent at the grain boundaries as well as progressive precipitation of carbides on the stacking faults (due to martensitic transformation) in the interior of grains. On the contrary, aging at 950 °C led to the progressive formation of carbides up to 16 h and then lamellar-type constituent formed abruptly at the grain boundaries.