Evaluation of the micro-hardness and fracture toughness of amorphous and partially crystallized 3CaO·P2O5–SiO2–MgO bioglasses

In this work, the effect of the indentation load on the results of hardness and fracture toughness, determined by Vickers micro-hardness measurements, of some glasses and glass–ceramics has been investigated. Furthermore, in order to verify the effect of crystallinity on the results, glasses of composition 52.75 wt.% 3CaO·P2O5, 30 wt.% SiO2 and 17.25 wt.% MgO were fused at 1600 °C for 4 h and annealed at 700 °C for 2 h, and further heat-treated at 700, 775, 800 and 900 °C for 4 h. The obtained materials were analyzed by high resolution X-ray diffraction, HRXRD, to determine the crystallization degree in function of the heat-treatment temperature. The hardness of the different specimens was determined by Vickers’ micro-hardness measurements under various loads. It has been observed that with increasing crystallization of the materials their hardness increased. Furthermore, it has been possible to verify the so-called indentation size effect (ISE), i.e. hardness decreases as the indentation depth, under higher loads, increases. This effect has been more pronounced in the glass–ceramic samples. Fracture toughness has been determined by the crack length induced by the Vickers indentations and relating them to the applied loads. Glass materials presented a fracture pattern with characteristics of cleavage, forming cracks of the half-penny shaped type, while the glass–ceramic materials exhibited crack bridging effects and Palmqvist type cracks.

► Glass and glass–ceramics of 3CaO·P2O5–SiO2–MgO system.
► Heat treatment for partial crystallization.
► Vickers Indentation Method – effect of indentation load.
► Increase in loads resulted in a decrease of the hardness.
► The difference of hardness between the amorphous and crystalline materials tends to decrease with increasing indentation load.