Spark ignitable ball milled powders of Al and Ni at NiAl composition

Low-energy ball milling of aluminum and nickel particles with an overall composition corresponding to the NiAl intermetallic phase was performed up to milling durations of 13 h. The milled powders and cold-compacted pellets were ignited using a low-energy spark. Interrupted thermal analysis and X-ray diffraction was performed to investigate the effect of milling time on intermetallic phase formation. The results show that microstructural refinement with increasing milling times increases reactivity, where the intermetallic formation temperatures reduce to those of sputtered multilayer foils with a similar phase formation sequence. NiAl intermetallic phase starts forming at 12 h of milling. Loose powders milled for 11 and 12 h and the corresponding pellets ignite locally with uniform thermal wave fronts self-propagating at velocities up to 0.24 m/s.