Development of surface compressive stresses in zirconia-alumina compositesby an ion-exchange process

A two-step ion-exchange technique was developed for introducing compressive stresses on the surface of ZrO2-Al2O3 composites. In the first step, a thi n layer (similar to 250 pm) of Na-beta " -Al2O3 was formed on the surface o f the composite by a vapor-phase process at similar to 1400 degreesC. In th e second step, Na+ ions were replaced by K+ ions by a heat treatment at sim ilar to 385 degreesC for 2 h in a molten KNO3 bath, Replacement of sodium b y potassium led to the creation of surface compressive stresses. The flexur al strength and Weibull modulus of ZrO2-Al2O3 composite were similar to 915 MPa and 10, respectively, for the as-sintered samples, By contrast, the fl exural strength and Weibull modulus were similar to 1140 MPa and 26, respec tively, for the ion-exchanged samples. A residual surface compressive stres s of similar to 480 MPa was measured by a strain-gauge technique in K+-ion- exchanged samples. The presence of surface compressive stresses also was co nfirmed using an indentation technique, The technique developed here can be used to introduce compressive stresses on components of virtually any shap e.