Strength and fracture toughness of alumina-glass dental composites prepared by melt-infiltration.

摘要

Mechanical properties of alumina-glass composites, prepared by a process that is similar to a commercial process for making dental crowns, are reported in this thesis. Alumina compacts were prepared by slip casting concentrated (55 vol.% alumina) slurries made with citric acid and pH adjustment. The alumina was fired at 1100{dollar}spcirc{dollar}C for 2 hours to fuse the alumina particles together, then infiltrated with molten glass at {dollar}sim{dollar}1100{dollar}spcirc{dollar}C for 8 hours. The effects of colloidal processing, alumina-glass thermal expansion mismatch, and particle size on composite strength and toughness were investigated. Fracture toughness, measured by a chevron-notch method, was {dollar}sim{dollar}3.8 MPa{dollar}cdot{dollar}m{dollar}sp{lcub}1/2{rcub}{dollar} and was relatively insensitive to the volume fraction of alumina in the range of 0.62 to 0.72. Composite flexural strength and Weibull modulus were {dollar}sim{dollar}460 MPa and 7, respectively. Typical Griffith flaws were pores and cracklike voids formed by poor particle packing and differential sintering near agglomerates of alumina in the composite. The expansion coefficient of the glass, varied from 5.9 to {dollar}7.8times10sp{lcub}-6circ{rcub}rm Csp{lcub}-1{rcub}{dollar}, didn't significantly affect strength and fracture toughness. Additions of 20 {dollar}mu{dollar}m or 40 {dollar}mu{dollar}m alumina particles to 3 {dollar}mu{dollar}m alumina particles decreased composite strength but had little effect on fracture toughness. The fracture mode of 3 {dollar}mu{dollar}m particles was intergranular, while 20 {dollar}mu{dollar}m and 40 {dollar}mu{dollar}m particles failed by transgranular fracture. The effects of crack size on fracture toughness and strength were investigated by an indentation-strength test with indentation loads varying from 5 N up to 300 N. The composites did not display R-curve behavior and flaw tolerance, although crack bridging from 3 {dollar}mu{dollar}m particles was observed in indentation cracks. The strength and fracture toughness of the alumina-glass composites were {dollar}sim{dollar}2 times higher than those of most dental ceramics. High strength and toughness can be attributed to a high Young's modulus ({dollar}sim{dollar}270 GPa), low porosity ({dollar}sim{dollar}2%), crack deflection, and crack bridging.