Particle bonding, annealing response, and mechanical properties of dynamically consolidated type 304 stainless steel pow
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I.
INTRODUCTION
D Y N A M I C consolidation has been suggested as a means of forming monolithic components from particulates without the high bulk temperatures associated with conventional consolidation processes. To accomplish consolidation with this technique, a large amplitude compressive stress wave is propagated through the powder material, resulting in densification by plastic flow of the particles. Under the appropriate conditions, bonding can occur by interparticle melting, tl-sJ The stress wave can be generated by a number of different methods, including projectile impact and the direct application of explosives, t~l The magnitude and duration of the stress wave are important in determining the degree of interparticle bonding, and their influence has been investigated for several materials. ~ In addition, it is apparent that the morphology, size distribution, and relative motion of the particles influence the localized particle interaction and subsequent degree of bonding.tl.2] Details of the mechanism responsible for the surface melting which results in particle bonding are difficult to resolve experimentally. Several models have been proposed that suggest that frictional heating from the relative motion of particles is sufficient to cause melting, t2m More recent work suggests that the intense, high strain rate plastic flow associated with particles extrusion to fill interparticle voids is responsible for high localized temperatures. ~8,9a~ Fully dense monoliths with reasonable tensile strength have been produced from A1, several AI alloys, and Type 304 stainless steel using both projectile impact and explosive techniques. ~6,7,1~ However, due to the high density of defects introduced during dynamic consolidation, ductility is usually low. Limited results reported on the relationship between microstructural evolution in dyR.N. W R I G H T , G.E. KORTH, and J.E. FLINN, Scientific Staff Members, are with the Materials Technology Group, Idaho National Engineering Laboratory, EG & G Idaho, Inc., Idaho Falls, ID 83415. Manuscript submitted December 7, 1987. METALLURGICAL TRANSACTIONS A
namically consolidated powders during annealing and the resulting mechanical properties indicate that there is a concurrent decrease in yield stress and increased ductility. 16'71 In addition, it appears likely that heat treatment will result in sintering and enhanced bonding. In the current experiments, the process of interparticle bonding has been examined in detail for two Type 304 stainless steel powders consolidated using the direct application of explosives. The powder particle size and the magnitude of the stress wave are observed to influence the microstructure and extent of interparticle bonding. The substructure in the interparticle regions and the relationship to particle bonding are of particular interest. The annealing response of the consolidated materials is also characterized, and the tensile properties of asconsolidated and annealed material are related to the substructural observations.
II.
EXPERIMENTAL P
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