ROTATING-BENDING FATIGUE PROPERTIES OF NEW NITROGEN ALLOYED, COBALT-CHROME-MOLYBDENUM BIOMEDICAL IMPLANT ALLOY FABRIBRICATED VIA POWDER METALLURGY TECHNIQUES

摘要

In addition to good corrosion resistance and adhesive wear resistance, high cycle fatigue properties are essential to the selection of alloys for use in structural biomedical implants such as hip prostheses. This paper presents the static mechanical and rotating-bending fatigue properties of three cobalt-chromium-molybdenum alloys having nitrogen contents of 0,19, 0,47, and 0,65 wt.%. The results indicate that nitrogen alloying increases the static yield strength, but in the as-HIPed condition, segregation of nitrogen as brittle second phase reduces ductility. Nonetheless, the static mechanical properties of the materials clearly exceed those of castings, and even approach those of forgings. Correspondingly, the highest nitrogen material endures 10^7 cycles of fully reversed loading at a maximum stress of 600 MPa. Powder metallurgy techniques alone also have a substantial impact on increasing the mechanical properties, due to the uniform, fine grain size and second phase particle dispersion in the microstructure resulting from the powder atomization.