Fracture toughness and R-curve behavior of BCP/YTZP nanocomposites produced using the spark plasma sintering process

The aim of this study is to evaluate the fracture toughness and R-curve behavior of synthesized biphasic calcium phosphate (BCP) and yttria-tetragonal zirconia polygonal (YTZP) nanocomposites produced by spark plasma sintering (SPS) method. BCP comprising of 30 wt% hydroxyapatite and 70 wt% betatricalcium phosphate, was mixed with various amounts of YTZP nanopowder and sintered using SPS at different processing conditions (e.g. various pressures, times, temperatures, cooling and heating rates). Fracture toughness (KIC) of the samples was calculated by the indentation-strength method and the phase composition of the samples was evaluated by x-ray diffractometry (XRD). Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) analyses were also utilized to study the powder morphology, microstructure and fractured surfaces of the samples. According to the results, the bulk density can reach to about 97% of the theoretical density using SPS process. The maximum fracture toughness of 3.04 MPa m0.5 was obtained for the sample containing 3 vol% of YTZP (BCP-3SZ) in optimum conditions of the SPS process. The obtained fracture toughness value was approximately triple of the pure BCP (1.07 MPa m0.5) and was comparable with that of the cortical human bone. Rising crack growth resistance (R-curve) behavior of the sample BCP-3SZ at different indentation loads was also observed due to the martensitic phase transformation. Furthermore, YTZP nanoparticles persuade HA to β-TCP phase transformation during the SPS process.