Development and characterization of Co-Cr-Mo (F-75 alloy)/hydroxyapatite composites fabricated by powder metallurgy for biomedical applications
Nur Maizatul Shima, Adzali
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Co-Cr-Mo (F-75) alloy is known to be used in biomedical field because of their excellent biocompatibility when implanted to human or animal body. Hydroxyapatite (HAP) powders have been used as filler because HAP is the one of the most effective biocompatible materials with similarities to mineral constituents of bones and teeth. This research reported the fabrication and characterization of F-75 alloy filled with HAP which have been prepared by powder metallurgy method. This study has focused on the effect of HAP addition into F-75 alloy and sintering temperature on the physical and mechanical properties of the F-75/HAP composites, its microstructure, and also its corrosion and bioactivity behaviour. In fabrication of the F-75/HAP composite, 2, 4, 6, 8 and 10 wt. % of HAP have been added to F-75 alloys. The reference samples of F-75 alloy (with no addition of HAP) also have been prepared for all sintering temperatures. The mixtures were milled on a rotation mill for 20 minutes at 154 rpm before cold compacted at 550 MPa using an uniaxial press machine. The samples then have been sintered at three different sintering temperatures (11000C, 11500C and 12000C) in a tube furnace for 2 hours. Physical properties were measured by means of bulk density and apparent porosity while mechanical property was measured in term of compressive strength. The corrosion behaviour of the F-75/HAP composite has been analysed using electrochemical test controlled by Gamry G300 potentiostat. Bioactivity test for the composite was conducted in-vitro by immersing the composite into simulated body fluid for 18 days. XRD, SEM, FTIR and pH analyses had been done in order to observe the presence of the apatite layer on the surface of F-75/HAP composites. From this study, the values of bulk density decreased as the HAP content increased. The highest value of bulk density was gained by the composite with 2 wt. % of HAP with value 6.6217 g/cm3 with sintering temperature 12000C, while the lowest bulk density value was given by the composite with 10 wt. % of HAP after sintered at 11500C (4.3915 g/cm3). The apparent porosity was increased in the range of 13.13% (for 2 wt. % HAP) to 37.58% (for 10 wt. % HAP). Compressive strength was decreased by the additional of HAP. The sample with 2 wt. % of HAP addition with sintering temperature 12000C gave the highest compressive strength (341.81 MPa). The microstructure of F-75/HAP composites after sintering at three different sintering temperatures showed that porosity and HAP agglomeration increased with HAP content and sintering temperature. The results of corrosion test showed that the samples with 8 wt. % HAP addition gave the lowest value for corrosion rate (16.59 x 10-6 mpy for F-75/8% HAP sintered at 11500C). From bioactivity test results, the carbonated apatite layer was formed on the surfaces of the composite. According to the results for physical and mechanical properties testing of the composites, the optimum HAP addition to F-75 alloy was 2 wt. %, while samples that have been sintered at higher temperature (12000C), showed good physical and mechanical properties and also corrosion behavior. From corrosion test, F-75/6% HAP and F-75/8% HAP composites that have been sintered at higher temperature showed good corrosion resistance. Bioinert F-75 alloys can be converted into F-75 bioactive type by adding up to 10 wt. % of HAP.