Reduced pressure requirements for production of nanoceramic composites

Transformation assisted consolidation (TAC) permits production of sintered, nanoscale ceramics at reduced temperatures. The method requires the use of metastable starting materials, and also very high pressures, up to 8 GPa, making manufacturing of large samples impractical. The use of supersaturated single phase starting powders produced by plasma spraying and rapid solidification enables the production of nano-composites in which multiple phases exist which are all homogeneously distributed and nanoscale. This process enables several composite materials to be successfully sintered at pressures lower than those usually required by TAC. Some multi-component starting materials, such as yttria stabilized zirconia plus 20% alumina, form the final composite structure by transforming into the stable phases, one of which exists as the original parent structure seen in the metastable starting material. This transformation to a parent/children final structure, as opposed to a children only structure, appears to be independent of pressure. The resulting structures and structural evolution from the plasmas-sprayed material to the final sintered structure is discussed. The TAC method appears to be a universal method applicable to multi-component systems as well as single-component systems. The additional complexities of multiple daughter phases in the multi-component systems results in additional grain-growth inhibition mechanisms, allowing the possibility of lowered pressures in the application of the TAC method. In the YSZA system this has resulted in the opportunity for utilizing HIP and ambient pressure in the creation of nanoceramics, and ultimately the production of larger samples.