Synthesis, Structural, and Mechanical Behavior of β-Ca3(PO4)2–ZrO2 Composites Induced by Elevated Thermal Treatments

Biocompatible β-Ca3(PO4)2 and mechanically stable t-ZrO2 composites are currently being combined to overcome the demerits of the individual components. A series of five composites were synthesized using an aqueous precipitation technique. Their structural and mechanical stability was examined through X-ray diffraction, Rietveld refinement, FTIR, Raman spectroscopy, high-resolution scanning electron microscopy, and nanoindentation. The characterization results confirmed the formation of β-Ca3(PO4)2–t-ZrO2 composites at 1100 °C. Heat treatment above 900 °C resulted in the degradation of the composites because of cationic interdiffusion between Ca2+ ions and O−2 vacancy in Zr4+ ions. Sequential thermal treatments correspond to four different fractional phases: calcium-deficient apatite, β-Ca3(PO4)2, t-ZrO2, and m-ZrO2. The morphological features confirm in situ synthesis, which reveals abnormal grain growth with voids caused by the upsurge in ZrO2 content. The mechanical stability data indicate significant variation in Young’s modulus and hardness throughout the composite.