Tribological behaviour of Ti/HA and Ti/SiO2 functionally graded materials fabricated at different strain rates

Abstract

Functionally graded materials (FGMs) have found extensive applications in the biomedical industry, due to their excellent mechanical and tribological properties. However, new FGM fabrication techniques are yet to be examined for possible enhancements in their properties. This study investigates the tribological properties of Titanium/Hydroxyapatite (Ti-HA) and Titanium/Silicon oxide (Ti-SiO₂) FGM samples fabricated by three die compaction techniques for the application of dental implants. The constituting powder particles were functionally dispersed and mixed using a newly-designed mixer and consolidated by hot dynamic and quasi-static compaction techniques at three different strain rates. Microstructure, hardness, wear resistance, wear penetration depth, and friction coefficient of the FGM samples were then studied in this work. Optical microscopy images exhibited smooth dispersion of powders conforming to a linear grading function. Vickers hardness values of the FGM samples was found to be directly proportional to the strain rate and inversely proportional to the content of the reinforcing phase (HA or SiO₂). Higher strain rate also resulted in higher wear resistance and lower wear penetration depth in all FGMs, with the highest wear resistance being observed in the samples prepared using the Split Hopkinson Bar. Similarly, the coefficient of friction was also shown to be the lowest in Ti-HA samples prepared using Split Hopkinson Bar. Further, microscopic observations revealed that adhesion, delamination and abrasion as the dominant wear mechanisms in all FGM samples. It was concluded that the Ti-HA sample produced by the SHB method enjoyed superior tribological properties, being comparable to that of natural human teeth.