Combustion synthesis/densification of an Al2O3-TiB2 composite

The self-propagating gasless combustion reaction 3TiO(2) + 3B(2)O(3) + 10Al --> 5Al(2)O(2) --> 3TiB(2) was used to produce an Al2O3-TiB2 composite, which was densified by uniaxial loading immediately following completion of reaction. The densification was enabled by the high temperatures produced by the combustion reaction( approximate to 2000 degreesC) which rendered the reaction product (approximate to 70% porosity) plastic. The microstructure was characterized by columnar TiB2 grains with a diameter of 1-2 mum and length of 5-10 mum embedded in equiaxed Al2O3 (grain size approximate to 50 mum); the TiB2 phase tended to agglomerate in clusters. A few of the TiB2 grains exhibited dislocations, while the Al2O3 was annealed. This indicates that recovery processes took place after the plastic deformation involved in densification. Several constitutive models (corresponding both to rigid-plastic and power-law creep material behavior) were used to describe the mechanical response of the porous and ductile ceramic product and compared to the experimental results, with satisfactory agreement for power-law creep models. These constitutive models have a temperature-dependent term that incorporates the effect of specimen cooling, that occurs concurrently with densification; thus, it was possible to obtain a flow stress dependence of temperature which is in reasonable agreement with values interpolated from literature experimental results. (C) 2001 Elsevier Science B.V. All rights reserved.