A comparison of microstructure and mechanical properties of 12Ce-TZP reinforced with alumina and in situ formed strontium- or lanthanum hexaaluminate precipitates

Composites of 12 mol% Ce-TZP and 30 vol% of alumina 12Ce-30A, strontium hexaaluminate 12Ce-30SA6 and lanthanum hexaaluminate 12 Ce-30LA6 were produced by a mixing and milling method, shaped by slip casting and subsequently sintered in air at 1500–1600 °C. The microstructure, phase composition and mechanical properties of the materials were determined. 12Ce-30A showed the highest hardness, toughness and strength closely followed by the 12Ce-30LA6 composite, the 12Ce-30SA6 showed high toughness at moderate strength and low hardness. Phase analysis hinted at strong differences in the efficiency of transformation toughening. For 12Ce-30A contributions of dilatation and shear were almost fully exploited, 12Ce-30SA6 showed an intermediate efficiency while in 12Ce-30LA6 subcritical transformation was observed. The interaction of cracks with the reinforcement showed specific characteristics for each hexaaluminate. Beside high resistance to subcritical crack growth observed in all materials, 12Ce-30A and 12Ce-30LA6 showed uncommonly high values of crack tip toughness.