Reactive structural materials consolidated by cold spray: Al–CuO thermite

The present study deals with the use of the Cold Gas Dynamic Spray (Cold Spray) process to consolidate reactive materials with low porosity (up to 99.8% of the theoretical maximum density) and controllable shapes for potential near-net shape applications. The study focuses on the Al/CuO thermite mixture. The microstructure and mechanical properties (four-point bending and microhardness) of the consolidated samples were investigated while varying the spray process parameters, such as stand-off distance, propellant gas pressure and feedstock powder (fuel) particle size. The reactive mixture was successfully consolidated without the onset of the thermite reaction. The consolidated sample reactivity was addressed through flame propagation velocity measurements as a function of sample density. Results show a relation between the sampleʹs porosity level and the flame propagation velocity. The reduction of porosity tends to decrease the flame speed from approximately 1400 mm/s at 20% density down to 150 mm/s at 100%. This indicates a transition from convection dominated energy transfer at low porosities to heat conduction dominated mechanism at vanishing porosities when gas percolation is not possible.