Abstract
The effect of crystallization on the mechanical properties (hardness, modulus of elasticity and fracture toughness) of lithium disilicate Li2O.2SiO2 glass-ceramic was investigated by indentation (instrumented indentation, and Vickers and Knoop microhardness). The heat treatments for crystallization were carried out in two stages: nucleation at 475 °C for 2, 5 and 10 h, and crystals growth at 563 °C for 0.5, 1, 2, 3 and 24 h. Crystal fractions were correlated to hardness, elastic modulus and fracture toughness. Hardness was measured by Knoop and Vickers indenters. The modulus of elasticity of the amorphous and crystalline regions was measured by instrumented indentation tests with a Berkovich indenter, performed in each phase separately. The morphology of cracks generated by indentation with pyramid indenters was investigated for samples with different crystalline fractions using optical microscopy. The highest values of hardness and toughness were obtained in samples with 100% crystalline fraction, with the highest nucleation time. The obtained values were: fracture toughness of 1.8 MPa.m1/2, Knoop microhardness of 7.2 GPa and elastic modulus of 155 GPa.
Keywords:
fracture toughness; microhardness; elastic modulus; Vickers indentation; glass-ceramic; lithium disilicate
