Superplastic Tensile Ductility Enhanced by Grain Size Refinement in a Zirconia-Dispersed Alumina

摘要

High-temperature tensile ductility in fine-grained pure alumina is limited to -20% in engineering strain owing to rapid dynamic grain growth accompanied by large strain hardening and resultant severe cavitation [1-4]. Accordingly, many trials have been made to suppress the dynamic grain growth by use of an additive such as MgO or ZrO_2. The dynamic grain growth of MgO-doped alumina, however, is still active to limit the tensile ductility to -80% at 1623-1773 K [1,2,5,6]. Although some additional improvement is possible by the codoping of CuO or NiO, the maxium tensile elongation has remained 140% [7]. On the other hand, ZrO_2-particle dispersion is much more effective in suppressing grain growth and hence strain hardening, whereas the esultant tensile ductility stays up to 110% or less at 1723-1773 K [6,8,9]. It has been attributed to the increment of flow stress [6] caused inherently by ZrO_2-dispersion through the suppression of grain boundary dliding [6,8,10-12].