Observation of a minimum reaction initiation threshold in ball-milled Ni plus Al under high-rate mechanical loading

Two types of microstructurally distinct ball-milled Ni+Al powder compacts are characterized for the investigation of reaction initiation threshold under high-rate mechanical loading using a modified rod-on-anvil Taylor impact-test setup. It is observed that the kinetic energy threshold for reaction decreases to a minimum then increases with milling time. It is also observed that the kinetic energy required for reaction initiation is lower for the 95% theoretical maximum density (TMD) ball-milled powder compacts than for the 65% theoretical maximum density (TMD) compacts. The results are discussed on the basis of competing effects of reactivity enhancement and deformability reduction caused by prior ball-milling of the powder mixtures. (C) 2011 American Institute of Physics. [doi:10.1063/1.3549822]