In situ processing of silicon carbide layer structures

A novel route to low-cost processing of silicon carbide (SiC) layer structures is described. The processing involves pressureless liquid-phase cosintering of compacted powder layers of SiC, containing alumina (Al2O3) and yttria (Y2O3) sintering additives to yield a yttrium aluminum garnet (YAG) second phase. By adjusting the β:α SiC phase ratios in the individual starting powders, alternate layers with distinctly different microstructures are produced: (i) homogeneous microstructures, with fine equiaxed SiC grains, designed for high strength; and (ii) heterogeneous microstructures with coarse and elongate SiC grains, designed for high toughness. By virtue of the common SiC and YAG phases, the interlayer interfaces are chemically compatible and strongly bonded. Exploratory Hertzian indentation tests across a bilayer interface confirm the capacity of the tough heterogeneous layer to inhibit potentially dangerous cracks propagating through the homogeneous layer. The potential for application of this novel processing approach to other layer architectures and other ceramic systems is considered