Mechanical properties of Al2O3Si composites fabricated by pressureless infiltration technique

Two-phase interpenetrating systems with residual microstresses have been shown to exhibit high fracture toughness and strength. In this work, the microstress-induced strengthening concept was applied to Al2O3Si composites. The composites were fabricated by pressureless infiltration of porous Al2O3 preforms with a molten Si. The materials obtained exhibited superior fracture toughness, strength and hardness when compared with technical aluminas having the same volume fraction of Al2O3 but containing aluminosilicate glass phases instead of silicon. For example, an Al2O3Si composite with 30 vol% Si had K1c ≈ 4.8 MPa √m and a bending strength of ~ 320 MPa compared to ~ 3.5 MPa √m and ~ 230 MPa, respectively for the technical alumina AD-85 (‘Coors’). It is believed that the strengthening effect is caused by compressive residual microstresses in an inherently weak Si phase generated as a result of the solidification-related expansion of silicon.