Effect of Carbon Addition on Microstructure and Mechanical Properties of a Wrought Co-CrMo Implant Alloy

The wrought Co-Cr-Mo alloys with C contents of 0.02, 0.09 and 0.18% (mass%) were fabricated by hot-forging process to study the influence of carbon contents on the microstructures and mechanical properties. The microstructures of Co-29Cr-6Mo-0.02C and Co-29Cr-6Mo-0.09C consist of equiaxed uniform grains which contain stacking faults, twins and (epsilon) martensite bands. No carbide found at inter- and intra-granular region. Co-29Cr-6Mo-0.18C consists of irregular grain sizes and carbide found at inter- and intra-granular region. The carbide in Co-29Cr-6Mo-0.18C was identified as M23C6 type carbide from the XRD pattern analysis. It is found that the amount of stacking fault and (epsilon) martensite are strongly dependent upon the C content. The density of stacking faults and (epsilon) martensites observed in Co-29Cr-6Mo-0.09C decrease as compared with those observed in Co-29Cr-6Mo-0.02C. Moreover, the volume fraction of the (gamma) phase slightly increased with C content. Within an extent of C addition that no carbide precipitation occurs, the carbon addition reduces the amounts of crystal defects such as stacking faults and twins, and (epsilon) martensites. In addition, tensile strength slightly increases with C content and ductility reaches a maximum at C content of 0.09%, though 0.2% proof strength shows no noticeable differences.