Strength and fracture toughness of MgO-modified glass infiltrated alumina for CAD/CAM

Objective: This study was conducted to investigate the effect of MgO additive to Al2O3 on the flexural strength, fracture toughness of glass infiltrated alumina for CAD/CAM application. Methods: Alumina blanks with additive of 0.5 wt% MgO were prepared via isostatic pressing and sintering at 1400°C for 2 h, and then alumina–glass composites were fabricated by infiltrating the molten glass into the partially sintered alumina compact. Flexural strength and fracture toughness were determined using three point bending methods and a single edge notched beam method. The mechanism of crack propagation was observed under a field emission scanning electron microscope. Results: The three-point flexural strength and fracture toughness of partially sintered alumina and alumina–glass composite were 210 MPa, 1.86 MPam1/2, and 432.2 MPa, 5.12 MPam1/2, respectively, and they were free of shrinkage during the processing of glass infiltration. The field emission SEM micrograph indicated that indentation caused a non-planar crack propagation including crack deflection and crack bowing. Significance: MgO was used as an additive to alumina to improve the strength and fracture toughness of partially sintered alumina and alumina–glass composite. The high strength and toughness are related to toughening by the distribution of alumina with uniform particle sizes, crack bowing, crack deflection and the beneficial wetting properties of the particle surface.