Rapid solidification often produces new and unique alloy microstructures. Retention of these microstructures may be accomplished by dynamic consolidation, the bulk temperature rise generated by this technique is quite low. However, at near-surface regions of powder particles the temperature rise can be substantial and may cause extensive recovery, recrystallization or remelting of these areas.
Examination of explosively-consolidated 304 stainless steel powders produced by dissolved gas atomization was performed by TEM. Particle interiors contained copious dislocations, twins and stacking faults, typical of shock-hardened materials. Some interparticle regions (Figure 1) contained few structural defects, apart from a network of low angle boundaries, indicating that extensive recovery occurred. The extent of these areas is typically ∼5 μm and the average subgrain is ∼0.5 μm in diameter. Precipitation also occurred in these areas, as discussed below, but was not observed in the particle interiors.