Processing and characterization of multiphase ceramic composites part II: Triplex composites with a wide sintering temperature Range

Three-phase (triplex) ceramic composites with improved thermal stabilities resulting from minimized grain growth due to extended grain separations are introduced. Al₂O₃, yttrium aluminum garnet (YAG, Y ₃Al₅O₁₂), and ZrO₂ were chemically compatible to make a stable triplex composite. Another stable composite could be made due to chemical compatibility among Al₂O₃, NiAl ₂O₄, and 3 mol% yttria-tetragonal zirconia polycrystals (3Y-TZP). The composites of 33 vol% Al₂O₃-33 vol% YAG-33 vol% ZrO₂, 33 vol% Al₂O₃-33 vol% NiAl ₂O₄-33 vol% 3Y-TZP, and 50 vol% Al₂O ₃-25 vol% NiAl₂O₄-25 vol% 3Y-TZP were fabricated using either sintering or hot pressing procedures. The sintered 33 vol% Al₂O₃-33 vol% YAG-33 vol% ZrO₂ and 33 vol% Al₂O₃-33 vol% NiAl₂O₄-33 vol% 3Y-TZP composites demonstrated a "self accommodating sintering effect" having a wide sintering range without any extensive change in properties. Annealing of the 33 vol% Al₂O₃-33 vol% NiAl ₂O₄-33 vol% 3Y-TZP composite at 1600°C for 50 h resulted in higher strength retention after heat treatment compared with that expected from the sum of the strengths of constituent phases. This was attributed to a mutual, grain growth retardation effect. Chemical compatibilities, mechanical properties, microstructures, and thermal stabilities of the composites were studied.