Damage tolerance andR-curve behavior of Al₂O₃–ZrO₂–Nb multiphase composites with synergistic toughening mechanism

In the present work, the damage tolerance andR-curve behavior of alumina–zirconia–niobium multiphase composites were studied by the indentation strength method. A matrix of yttria-stabilized zirconia (3Y–TZP) strengthened with particles of Al₂O₃(ATZ) and an alumina matrix strengthened with particles of 3Y-TZP (ZTA) were prepared by hot press of commercial powders, containing Nb metal particles as reinforcing phase. The crack growth behavior was analyzed, and it was found that stress-induced transformation toughening of ZrO₂and bridging of the Nb inclusions were the two main factors that can shield an advancing crack and exert crack closure stresses on the crack wake. Moreover, on the basis of quantitative toughening analysis, it is argued that a synergistic effect originated from the interaction between the toughening mechanisms of Nb grains and zirconia, takes place in the alumina–zirconia–Nb multiphase composites. This showed that the combined toughening effect was bigger than the sum of the individual toughening effects when either reinforcement acted alone.