Influence of heat treatments upon the mechanical properties and in vitro bioactivity of ZrO2-toughened MgO-CaO-SiO2-P2O5-CaF2 glass–ceramics

Zirconia-toughened MgO-CaO-SiO2-P2O5-CaF2 glass–ceramics are prepared using sintering techniques, and a series of heat treatment procedures are designed to obtain a glass–ceramic with improved properties. The crystallization behavior, phase composition, and morphology of the glass–ceramics are characterized. The bending strength, elastic modulus, fracture toughness, and microhardness of the glass–ceramics are investigated, and the effect mechanism of heat treatments upon the mechanical properties is discussed. The bioactivity of glass–ceramics is then evaluated using the in vitro simulated body fluid (SBF) soaking test, and the mechanism whereby apatite forms on the glass–ceramic surfaces in the SBF solution is discussed. The results indicate that the main crystal phase of the G-24 sample undergoing two heat treatment procedures is Ca5(PO4)3F (fluorapatite), and those of the G-2444 sample undergoing four heat treatment procedures are Ca5(PO4)3F and β-CaSiO3 (β-wollastonite). The heat treatment procedures are found to greatly influence the mechanical properties of the glass–ceramic, and an apatite layer is induced on the glass–ceramic surface after soaking in the SBF solution.