Microstructural examination and mechanical characterization of Ti/HA and Ti/SiO2 functionally graded materials fabricated at different loading rates

Functionally graded material (FGM) is a heterogeneous composite material that consists of two or more constituent phases with continuous changes in the microstructure from one material to another with adjustable through thickness properties. FGMs are utilized in medical applications, such as dental implants, due to their excellent mechanical and tribological properties. In this study, the powder metallurgy method (PMM) is used to produce Titanum/Hydroxyapatite (Ti/HA) and Titanum/Silicon dioxide (Ti/SiO2) FGM samples. A new designed blender is employed to mix the particles constituting the FGM samples. The mixed particles are then compacted at different strain rates from quasi static loading, using a universal testing apparatus, to dynamic loadings, using a drop hammer and a split Hopkinson bar. The effect of strain rate on mechanical properties and microstructure of specimens is studied by conducting various tests such as indentation and compression tests and by microstructural examinations using scanning electron microscopy (SEM). The results showed that the relative density of fabricated specimens was increased with the increase of the strain rate. The highest relative density for the Ti/HA composite was achieved for the specimens produced by the split Hopkinson bar. For both of Ti/HA and Ti/SiO2 FGMs the maximum indentation force and indentation energy, obtained from the load-penetration depth curve, and the ultimate strength, obtained from the compressive stress-strain curve, were increased with the increase in strain rate. The results also indicated that the increase in volume fraction of reinforcing ceramic particles (HA or SiO2) led to the decrease of the maximum indentation force and indentation energy.