SUPERPLASTICITY IN AL2O3-20VOL-PERCENT SPINEL (MGO-CENTER-DOT-1-CENTER-DOT-5AL(2)O(3)) CERAMICS

Superplasticity in Al2O3-20 vol% spinel (MgO.1.5Al(2)O(3)) is investig ated by means of tensile testing in the temperature range 1300-1550 de grees C. The dispersion of spinel phase in Al2O3 slightly reduces the flow stress, and highly enhances the high-temperature ductility at the same stress level in comparison with 0.1 wt% MgO-doped single-phase A l2O3. A maximum elongation of 396% is obtained at 1550 degrees C and a strain rate of 24x10(-4)s(-1). The flow stress reduction is associate d with a slight reduction in activation energy for superplastic flow. The extensive ductility in Al2O3-20 vol% spinel cannot be explained on ly from the stress reduction. The Al2O3/spinel boundaries are expected to have much larger resistance to crack extension than Al2O3 grain bo undaries. (C) 1997 Elsevier Science Limited and Techna S.r.l.