Superplastic tensile ductility enhanced by grain size refinement in a zirconia-dispersed alumina

Substantial superplasticity, where total tensile elongation to failure reaches 340 and 550% at 1723 and 1773 K, respectively, can be attained in a 10-vol%-ZrO₂-dispersed alumina when the alumina grains are reduced to a size of 0.45 μm by colloidal processing. The reduced grain size brings about a characteristic strain hardening which starts from lowered stresses and persists up to large strains without impairing tensile ductility. The hardening can be attributed to the dynamic grain growth which proceeds gradually owing to ZrO²-particle pinning. The enhanced tensile ductility may be due to a large clearance for dynamic grain growth up to the critical size from which failure process is accelerated to lead failure.