Cast vs. wrought cobalt-chromium surgical implant alloys

The measured tensile and fatigue strengths of wrought and heat-treated cobalt chromium-molybdenum-carbon alloys such as HS21 were found to be more than twice those of as cast alloys of the same composition. The resistance of wrought HS21 to crevice corrosion at metal-Teflon contacts in isotonic salt solution at 37 degrees C was found to be considerably greater than that of cast HS21, wrought HS25, wrought MP35, or 316L stainless steel which are currently used for surgical implants. The increased crevice corrosion resistance and mechanical strength of wrought HS21 as compared to as cast HS21 was attributed to greater chemical and structural homogeneity as well as to finer grain size and distribution of secondary phases. Fabrication of shaped implants from wrought HS21 is possible by techniques currently used for the fabrication of industrial parts from other wrought cobalt-chromium base alloys.