NANO-SCALE HARDNESS & ABRASION RESISTANCE OF DIRECTED ENERGY DEPOSITED CO-CR-MO BIOMEDICAL ALLOY

The objective of this work is to investigate the hardness and abrasion resistance of a cobalt-chromium-molybdenum (Co-Cr-Mo) alloy fabricated via directed energy deposition (DED) additive manufacturing. Being a bio-compatible alloy, Co-Cr-Mo is commonly used in biomedical implants. Hence, its small-scale tribological behavior needs to be characterized, especially when fabricated via a newer process such as DED; thus the focus at nano scale. For this, a design of experiments was utilized to investigate the relevant process parameter design space for the laser engineered net shaping (LENS) process, with an objective to manufacture structurally-integral samples. Further, the effects of these process parameters were correlated with the resulting material properties at the nanoscale (viz., hardness modulus, and abrasion resistance). Results showed certain samples with competitively-high corresponding properties when compared to traditional made Co-Cr-Mo alloys, but with a large spread in properties, as is typical for such manufacturing processes. Also, microstructural characteristics were in line with traits observed when fabricating via traditional methods. Especially worth noting is the formation of metal carbides at the boundaries of cell-shaped grains; this causes a depletion of carbon at the center of the grain and thin carbides at the boundaries, thus significantly affecting the composite properties of the material. Altogether, this work shows the promise of using LENS to fabricate tailored structurally-integral Co-Cr-Mo alloys.