Influence of spark plasma sintering temperature and hydroxyapatite nanoparticles on properties of HA based functionally graded materials for bone prosthesis

Functionally graded materials (FGMs) have exhibited great potential to be used for biomedical implants, joint replacements, and bone prostheses. Variation of spark plasma sintering (SPS) temperature and nanoparticles have been utilized in the matrix to fabricate fully-densified FGMs based on hydroxyapatite (HA), and AISI 316L stainless steel. FGMs based on five layers of HA/AISI 316L composites were fabricated through spark plasma sintering (SPS) at 1000 and 1100 degrees C. To study the effect of the addition of HA nanoparticles, a mixture of micro- and nanosized HA particles was also used as a matrix for the AISI 316L reinforcements, along with 100 wt% micro-sized HA powders. The concentration of the AISI 316L particles in the layers ranged from 0 to 40 wt%. Results showed that the FGMs sintered at 1100 degrees C exhibited better mechanical properties than those prepared at 1000 degrees C. However, regardless of the sintering temperature, phase transformations and chemical reactions involving the HA and the AISI 316L precursors were observed. Furthermore, no microcracks were observed in the matrix around the AISI 316L particles and at interlayer boundaries. The addition of the HA nanoparticles in the matrix improved the physical and mechanical properties of the fabricated FGMs, making these comparable to the standard materials for a bone prosthesis.