Combustion synthesis and quasi-isostatic densification of powder cermets

Self-propagating High-temperature synthesis (also known as SHS or combustion synthesis) presents a bright potential for the synthesis of compounds with high degree of purity. However, for many reactions, the product is highly porous, and it must either be pulverized for subsequent densification, or densified while it is still hot and ductile. Densification has successfully been applied to a number of ceramic and metal-ceramic systems by (a) a high-speed forging technique, and (b) by a quasi-static pressing technique using a granular pressure-transmitting medium (PTM). The reactive mixture and PTM are placed in a piston and cylinder setup and the system is pressurized by uniaxial compression at a pre-established time after reaction completion. The state-of-stress is close to isostatic and the process is therefore termed as quasi-isostatic pressing (QIP). Modeling of the densification was carried out using the Skorohod constitutive equation; comparison of the results with experimental distortion obtained in indentation experiments enables obtaining equation parameters. The distortion undergone by the combustion synthesis products during QIP densification was modeled using the appropriately verified constitutive equation and assuming a linear elastic response for the granular PTM. (C) 2002 Elsevier Science B.V. All rights reserved.