Abstract
Abstract : The demand for durable hip/knee and dental metallic implants is rapidly increasing due to their high susceptibility to bio-tribocorrosion, specifically fretting corrosion, when they encounter friction of another surface in harsh body fluid. In this study, the effect of 4 wt.% Ti addition to the 67Co27Cr6Mo alloy’s bio-tribocorrosion behaviour was investigated. Four metallic alloys were sintered at 1075 oC for 15 mins with the compositions of 67Co27Cr6Mo, 67Co27Cr2Mo4Ti, 67Co23Cr6Mo4Ti and 63Co27Cr2Mo4Ti whereby the load and residence time were varied during bio-tribocorrosion tests (85 N and 175 N) and (16 hours and 4 hours) respectively. The alloys were tested Material characterisation using SEM, EDS, and XRD of the as-sintered alloy was performed in order to determine the microstructural characteristics and phases present before and after bio-tribocorrosion test. Micro-hardness and elastic modulus measurement tests were also conducted on the metallographically polished surface of the sintered specimens. Whilst the bio-tribocorrosion behaviour was tested using a fretting corrosion test machine under two test conditions; the first was subjection to fretting corrosion for 16 hours at 175 N load and the second was subjection to fretting corrosion for 4 hours at 85 N load. It was demonstrated that the addition of 4 wt. % Ti improved the homogeneity of the microstructure of the material. Higher hardness values were also obtained by the alloys with the addition of 4 wt. % Ti, with the 63Co27Cr6Mo4Ti alloy exhibiting the highest hardness value of 593.12 HV. The addition of 4 wt. % Ti increased the elastic modulus of the alloys due to its large atomic radius, however with the reduced amount of large Co atoms present in the 63Co27Cr2Mo4Ti alloy, the young’s modulus decreased from 92.23 GPa to 75.02 GPa. The 63Co27Cr2Mo4Ti alloy exhibited the best bio-tribocorrosion behaviour as it featured a low young’s modulus that provided a higher tolerance to a high load and adherence, a low COF, a low A-ratio (which denote that the slip regime was experienced), a low energy dissipated during fretting corrosion as well as the lowest wear volume of 0.52 x 105 μm. This is attributed to the reduced amount of coarse Co particles present within the material that may have contributed to third body wear as well as provide more space for the atoms to move around when subjected to a high load or adherence thus creating a lower elastic modulus and resulting in a material that is able to withstand the conditions encountered during fretting corrosion.
M.Tech. (Metallurgical Engineering)