Effects of Isothermal Aging on Microstructure Evolution of Biomedical Co-Cr-Mo Alloy

Abstract:

Cobalt based alloys have been widely used in orthopedic implants. These alloys are an allotropic metal, which commonly exhibits two crystal structures, namely, FCC and HCP lattice. In this work, developed microstructure and hardness of a Co-Cr-Mo alloy after isothermal aging treatment were investigated. The applied aging procedure included soaking at the temperature of 850°C for five different holding times of 1, 3, 6, 9 and 12 h with subsequent water quenching. Microstructure examination, X-ray diffraction analysis and micro-hardness test were carried out for both as-received and heat-treated cobalt based alloys. The results showed that the FCC to HCP phase transformation occurred during the isothermal aging. It was observed that phase fraction of the identified HCP phase increased with longer aging time. Microstructure of the samples aged for 12 h showed very fine lamellae morphologies similar to a pearlitic structure with different orientations within each FCC grain. Apparently, these occurred lamellae structures could be well correlated with the formation of the HCP martensite. Additionally, it was found that in the Co-Cr-Mo alloy sigma phase precipitated early at the grain boundaries and further grew along these boundaries by increasing aging time. The hardness value of the examined alloy slightly increased with larger HCP phase fraction. The increased aging time certainly led to higher amount of the HCP martensite and consequently increased hardness and possible wear resistance properties.

• Periodical: Key Engineering Materials (Volume 658)
• Pages: 31-35
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.658.31
• Online since: July 2015
• Authors: Pitak Khaimanee*, Paiboon Choungthong, Viton Uthaisangsuk
• Keywords: Co-Cr-Mo Alloy, HCP Martensite, Isothermal Aging, Phase Transformation

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