Shock consolidation: Microstructurally-based analysis and computational modeling

The most important microstructural processes involved in shock consolidatio n are identified and discussed; the energy dissipated by a shock wave as it traverses a powder is assessed. The basic microstructural phenomena are il lustrated for a metal (nickel-based superalloy), an intermetallic compound (rapidly solidified Ti3Al), and ceramics (silicon carbide). Interparticle m elting, vorticity, voids, and particle fracture are observed and the plasti c deformation patterns are identified. Various energy dissipation processes are estimated: plastic deformation, interparticle friction, microkinetic e nergy, and defect generation. An analytical expression is developed for the energy requirement to shock consolidate a powder as a function of strength , size, porosity, and temperature, based on a prescribed interparticle melt ing layer. This formulation enables the prediction of pressures required to shock consolidate materials; results of calculations for the superalloy an d silicon carbide as a function of particle size and porosity are represent ed. The fracture of ceramic particles under shock compression is discussed. Tensile stresses are generated during compaction that may lead to Fracture . It is shown that the activation of flaws occurs at tensile reflected puls es that are a decreasing fraction of the compressive pulse, as the powder s trength increases. These analytical results are compared to numerical solut ions obtained by modeling the compaction of a discrete set of particles wit h an Eulerian finite element program. These results confirm the increasing difficulty encountered in shock consolidating harder materials, and point o ut three possible solutions: (a) reduction of initial particle size; (b) re duction of shock energy; (c) post-shock thermal treatment. Two possible and potentially fruitful approaches are to shock densify (collapse voids with minimum bonding) powders and to apply post-shock thermal treatments, and to shock consolidate nanosized powders. The latter method requires high shock energy and careful minimization of the shock reflections. (C) 1999 Publish ed by Elsevier Science Ltd, On behalf of Acta Metallurgica Inc. All rights reserved.