Low temperature densification behaviour of metastable phases in ZrO2-Al2O3powders produced by spray pyrolysis

It has been established that powder compacts of amorphous ZrO2-Al2O3, prepa red by spray pyrolysis, density up to nearly full density at temperatures b elow 923 K and above 573 K, when a moderately high pressure of 750 MPa is a pplied. The samples remain amorphous after hot pressing. Densification beha viour has been studied in the composition ZrO2-40 mol% Al2O3 with particle sizes in the ranges 15-35, 3-15 and below 3 mum. Temperatures of 573, 723 a nd 873 K were used along with applied pressures of 250, 500 and 750 MPa. Th e fine particle size led to a maximum final relative density of 96.5%. Pres sure is the dominant variable in densification once the temperature is abov e a minimum of 573 K. Time dependent densification is relatively insignific ant. Particle rearrangement at low pressures and deformation and fracture a t high pressures are likely to be responsible for the high relative densiti es between 84 and 92 obtained during pressurising the various particle size s up to 750 MPa. Hat pressing of composition with 62 mol% Al2O3 at 873 K, 7 50 MPa led to a final density of 99.6%, indicating that higher Al2O3 conten t imparts greater sinterability to the amorphous phase. (C) 2001 Elsevier S cience B.V. All rights reserved.