Chemical strengthening of zirconia/swelling mica composites by ion-exchange in molten salts

Abstract

ABSTRACT In this study, strengthening of machinable zirconia/mica composites was attempted by exchanging interlayer ions of mica in composites for larger ions, like chemically strengthened glasses. So the sintering behavior and ion-exchange of the composites fabricated using swelling mica and the mechanical properties of the ion-exchanged composites were investigated. The dense composite was obtained by sintering at 1200°C for 1 min and was ion-exchanged in molten potassium salts at 800°C. Na+ ions in the interlayer of mica near surface of the composites were exchanged for K+ ions. However, K+ ions were not inserted in the interlayer of mica. Mica reacted with molten salts to form an amorphous phase near surface of the composites. Simultaneously with the reaction, Na+ ions in mica were discharged into molten salts and K+ ions in molten salts were penetrated into the amorphous phase. Then other crystalline phases were formed in the amorphous phase. By the ion-exchange, the cracks developed from Vickers indentation corners were obviously shortened, which is one of the evidence that the compressive stress was generated near surface. By the compressive stress, the fracture toughness (3.5 MPa・m0.5) and the bending strength (322 MPa) of the composites were increased to 5.6 MPa・m0.5 and 447 MPa, respectively.