Monoclinic-to-tetragonal transformation and mechanical property recovery in low temperature water-degraded 3Y-TZP processed by a carburizing treatment

The reverse transformation (from monoclinic to tetragonal phase) by carburizing at different temperatures and mechanical property recovery in a low temperature water-degraded 3Y-TZP ceramic was investigated. The effect of the introduction of carbon on the monoclinic-to-tetragonal transformation for the aged 3Y-TZP ceramic was compared with that for a pure annealing process (1200°C for 1 hr). The stronger stability found by carburizing than by pure annealing is attributed to the combined effects of anion- and cation-stabilizers, carbon and yttrium ions, since carbon ions occupy mainly the octahedral interstitial sites, rather than yttrium ions, which stabilize TZP by creating oxygen vacancies to maintain charge neutrality after substitution of zirconium in TZP. It is believed that their effects on the stabilization of zirconia are additive due to the different stabilizing mechanisms and positions (carbon for surface, yttrium for bulk). For aged 3Y-TZP, the degraded mechanical properties bending strength and fracture toughness, can be effectively recovered by carburizing.