Interfacial diffusion reaction and mechanical characterization of 316L stainless steel-hydroxyapatite functionally graded materials for joint prostheses

Functionally graded materials (FGMs) of 316L stainless steel (316L) matrix with the reinforcement of hydroxyapatite (HA) were fabricated successfully by a pressureless sintering technique for bioimplants. Hydroxyapatite content was varied among the layers of FGMs up to 20 wt% with 5 wt% gradient. Two types of FGMs were prepared with the same composition in the discrete layers. However, micro- and nano-sized hydroxyapatite was used to reinforce the 316L matrix in two different FGMs under similar conditions of compaction and sintering. FGMs with nano-sized HA (nHA) exhibited better densification than the FGMs prepared with micro-sized HA (mHA). The interdiffusion of chromium along the 316L and HA interface was observed, which improved the interfacial bonding and the FGMs properties. The hardness increased due to strong interfacial boundary for second layer, then due to dominant factor of porosity hardness decreased for succeeding layers of FGMs. Potentiodynamic polarization analysis of both FGMs are also presented and discussed in response to the particle size of HA and interfacial phase produced.