The shock-densification behavior of three distinct Ni+Al powder mixtures

Abstract

The shock-densification response of equivolumetric mixtures of Ni+ Al powders of varying particle size and morphology has been determined through instrumented parallel-plate impact experiments. The results reveal a variation in the densification response, with crush strengths ͑stress at full density͒ ranging from 0.5 to nearly 6 GPa. A modified Fischmeister-Artz contact model was proposed to predict the crush strength of configurationally varying Ni+ Al powder mixtures. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2896653͔The formation of near-net density solids from metal powders is usually thought to occur more easily at high strain rates. The stresses involved in dynamic compaction processes greatly exceed the yield strengths of the starting components and interfacial barriers, rapidly eliminating the interparticle voids. Recent work has shown, however, that the stress required to achieve full density is not invariant and depends upon parameters such as particle size. 1 The consolidation behavior of powders is characterized by the "crush-up" process, which describes the pressurevolume states linking the initial, distended state to the solid Hugoniot. Several approaches have been developed to predict the crush-up response, including the P-␣ ͑Ref. 2͒ and P-͑Refs. 3 and 4͒ models. Unfortunately, these models largely ignore the specifics of powder configuration and are therefore limited in application. Powder mixtures possess perhaps the widest potential for variability of any material, with limitless combinations of phases and constituent properties, particle sizes and shapes, and orientation, and nearest neighbor distributions. Proper prediction of the behavior of these materials requires models that consider these variables.In the current work, the influence of configuration on crush-up response was investigated for three distinct equivolumetric Ni+ Al powder mixtures ͑Fig. 1͒. The mixtures consisted of ͑a͒ micron-scale spherical Ni+ Al, 60% theoretical maximum density ͑TMD͒, ͑b͒ micron-scale flake Ni + spherical Al, 45% TMD, and ͑c͒ nanoscale spherical Ni + Al, 40% TMD. The micron-scale powders were obtained from a commercial vendor specified as −325 mesh. The nanoscale Al was supplied by Technanogy and was approximately 50 nm. The nanoscale Ni was produced through a reduction-in-solution chemical precipitation process, 5 yielding particles 50-300 nm in diameter. The powders were mixed with a v-blender for 24 h, and then statically pressed into discs approximately 50.8 mm in diameter and 1.5 to 3.75 mm in thickness. This large aspect ratio was necessary to avoid early-time radial effects and maintain a onedimensional shock-propagation event during the diagnostic lifetime. The pressed powder was confined within a specimen assembly, as shown schematically in Fig. 2. Polyvinylidene fluoride ͑PVDF͒ stress gauges, sandwiched between 25 m thick layers of Teflon insulation and coated with 100 nm of Al, were located at the driver/specimen and specimen/backer interfaces to provide a measure of the shock pro...

Impact-initiated behavior and reaction mechanism of W/Zr composites with SHPB setup

“…The most studied of these reactive materials are Al-based composite such as Al/Ni and Al/W owing to their high strength, high energy density, easy processing characteristics and rapid energy release properties. [5][6][7][8][9][10][11][12] To improve their intercept efficiency, some high density reactive fragments have been proposed as alternatives to traditional steel fragments of anti-air warheads. For instance, tungsten/zirconium (W/Zr) composites have enough mechanical strength to maintain stability under overload during warhead detonation, and can penetrate targets and rapidly react.…”

The influence of particle morphology on the dynamic densification of metal powders

“…The extent and distance over which these waves can be attenuated are important properties for shock mitigation, and rely upon understanding the behavior of powders under strong and weak loading. While earlier studies have shown the high stress behavior of porous materials to be insensitive to powder configuration [1], prior work on metal powder mixtures demonstrated that both powder morphology and particle size play a strong role in densification at low stresses [2,3].…”

“…For the low stress regime, the Wu-Jing model implements the Carrol-Holt form of the P − α model [5]. In the present study, the P − α model was modified according to the method outlined in [3], in which a configuration parameter, n, was introduced to take into account the surfacearea of the various powders. This parameter was used to scale the Fischmeister-Artz crush-strength, and establish new limits for the Wu-Jing crush-up regime.…”

Influence of additives on microstructures, mechanical properties and shock-induced reaction characteristics of Al/Ni composites

“…For dynamic behavior of Al/Ni composites, SHPB and high velocity flyer plate impact methods are used to determine the stressestrain relationship or EOS of the material. Eakins and Thadhani [20,29,30] conducted Hugoniot measurement experiments on Ni and Al powders of varying particle size and morphology mixed at a 1:1 volumetric ratio. In the experiments, "polyvinylidene fluoride (PVDF)" gauges coupled with "Velocity Interferometer System for Any Reflector (VISAR)" data were used to determine the shock states.…”