Exothermic reaction characteristics of continuously ball-milled Al/Ni powder compacts

Self-propagating reactions in compacted pellets of continuously low-energy ball-milled aluminium (Al) and nickel (Ni) powders at a composition corresponding to AlNi3 were investigated. The formation of a bi-modal structure with nanoscale lamellae of Al and Ni surrounding thicker Ni layers was observed. The milled powder sizes decreased for milling durations longer than 4 h, but the pellet green densities remained mostly constant for longer than 2 h of milling. The ignited pellets observed using high-speed optical and infrared imaging revealed that the thermal wave velocity, maximum reaction temperature, ignition initiation duration and ignition temperature decreased with increasing milling times due to solid-state diffusion. X-Ray Diffraction (XRD) analysis after ignition tests showed that the AlNi3 amount increased with milling time. Thermal analysis using interrupted Differential Scanning Calorimetry (DSC) in combination with XRD revealed that the ball-milled pellets have similarities to nanoscale magnetron sputtered multilayer foils in terms of phase formation sequence and exothermic peak shifts. (c) 2013 Elsevier Ltd. All rights reserved.