A Comparison of Different Ni+Al Structural Energetic Materials
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A Comparison of Different Ni+Al Structural Energetic Materials B. Aydelotte and N.N. Thadhani School of Materials Science and Engineering Georgia Institute of Technology 771 Ferst Dr NW., Atlanta, GA 30332
Abstract A comparison of different Ni+Al reactive materials is conducted to elucidate the effects of microstructure morphology on performance. CTH, a multi-material Eulerian hydrocode, was utilized to study mesoscale deformation during simulated rod-on-anvil experiments. It is found that the cold sprayed Ni+Al, which has a more topologically connected nickel phase, is likely to be more reactive because of enhanced deformation in the Ni phase relative to explosively compacted Ni+Al, where the Ni phase undergoes less deformation. Rod-on-anvil impact tests verify that cold sprayed Ni+Al is indeed more reactive than explosively compacted Ni+Al when subject to impact.
Introduction Structural Energetic Materials (SEMs) are a topic of great interest to the energetics, pyrotechnics, and propellant communities. They need to have adequate strength for normal handling and launch and yet be relatively insensitive. When subject to impact or shock loading it is possible to initiate rapid, highly-exothermic reactions in these materials. SEMs based on metal-polymer composites [1], metal/metal-oxide thermites [2], and intermetallic-forming mixtures [3, 4, 5] have been studied for many applications, but the influence of microstructure on impact initiation of reaction is not fully understood. Efforts to study the effects of microstructure have typically focused on the effects of metric properties such as volume fraction of constituents or interface density [6]. Until recently, the influence of topology on impact initiation has received very little attention. Plastic deformation dissipates considerable energy as heat in metals [7, 8]. Differences in plastic deformation play a role in the reaction initiation of reactive pressed powder mixtures undergoing shock loading [3, 9]. Mesoscale features that lead to greater deformation in one or both phases were found to alter the reactive behavior of these systems significantly [3, 9]. In explosively compacted Ta+Al, Ni+Al, and W+Al mixtures, it has been found that large strains in both phases, but especially the stronger phase, are correlated with a lower impact velocity for reaction initiation [10]. This was found to be a result of the topology of the explosively compacted Ta+Al [10]. In the explosively compacted Ni+Al and W+Al, the hard phase, Ni and W respectively, were found to be simply connected particles. The Ta in the Ta+Al was found to be more topologically connected, forcing it to accommodate more deformation and therefore it is more prone to adiabatic heating due to plastic deformation than either the Ni in Ni+Al or the W in W+Al. This leads to the observed differences in sensitivity to impact. To gain a more complete understanding of this behavior, and remove constitutive behavior as a variable, two systems
VV SV (mm−1 ) λ = 4(1 − VV )/SV (µm) ρ (g/cm3 )
EC Ni+Al CS Ni+Al 0.
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