Deformation induced FCC to HCP transformation in a Co-27Cr-5Mo-0.05C alloy

In this work, the role played by plastic straining on the FCC(gamma) -> HCP(epsilon) strain induced transformation (SIT) epsilon-martensite in a Co-Cr-Mo-0.05C alloy was investigated. It was found that alloy plastic deformation at room temperature promotes the development of epsilon-martensite giving rise to the formation of intragranular striations. Moreover, aging at 800 degrees C of pre-strained specimens initially promotes SIT epsilon-martensite. This is followed by a time plateau (1 h) delay after which isothermal epsilon-martensite develops. Apparently, prior plastic straining leads to increasing incubation times for the onset of the isothermal epsilon-martensite transformation. In addition, tensile specimens containing various amounts of isothermal epsilon-martensite were tested all the way to fracture and their respective stress-strain properties were experimentally determined. Comparisons between experimental and simulated flow curves using the rule of mixtures indicated some deviations in the simulations at volume fractions above 0.25 epsilon-martensite. In contrast, predictions of yield and tensile strength were in good agreement with the experimental outcome. In particular, linear trends were exhibited by both, the yield and tensile strength as a function of the volume fraction of epsilon-martensite. Finally, the alloy elongation remained nearly constant with the volume fraction of epsilon-martensite in the range of the 0.15< HCP <0.55. Higher or lower values lead to a rapid decrease in the exhibited elongation. Published by Elsevier BM.