High-temperature deformation of amorphous AlPO4-based nano-composites

High-temperature compressive deformation of an amorphous aluminium phosphate nano-composite was investigated at 1200-1300 C. Microstructural and XRD investigations of sol-gel-derived material revealed an amorphous structure with a relatively high fraction of closed porosity of about 15 vol%. TEM revealed nanocrystallites, predominantly of carbon, dispersed in the amorphous matrix. Steady-state flow stresses were 10-50 MPa and 50-70 MPa for test temperatures of 1200 and 1300 C, respectively, as the strain rates were varied from 5 x 10 exp(-6) to 2 x 10 exp(-5)/s. Flow stresses increased with strain rates at a fixed temperature: stress exponents were 2.2-2.8 for various test temperatures, indicative of non-Newtonian flow. The non-Newtonian flow was attributed to the presence of the nanocrystalline phases. The creep resistance was found to be on a par with those of conventional oxide ceramics. 19 refs.