Hot explosive compaction of aluminum-nickelide composites
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Hot Explosive Compaction of Aluminum-Nickelide Composites LASZLO J. KECSKES, STEVEN T. SZEWCZYK, AKAKI B. PEIKRISHVILI, and NIKOLOZ M. CHIKHRADZE Two series of nickel-coated aluminum (Al-Ni) powder compositions were consolidated to full or near-full density by a hot-explosive-compaction (HEC) technique. Mixtures of 78Al-22Ni at. pct (63Al37Ni wt pct) or 39Al-61Ni at. pct (23Al-77Ni wt pct) were placed in cylindrical containers, preheated to a range of temperatures from ambient to 1000 °C, and once at a uniform temperature, explosively compacted into a 150-mm-long and 15-mm-diameter rod-shaped billet using a cylindrical detonation arrangement. The resultant billets were sectioned and prepared for examination by optical microscopy and scanning electron microscopy (SEM). Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and microhardness measurements were used to characterize the billet morphology, structure, and chemical composition. Analysis revealed that depending on the preheating temperature, the initial Al-Ni composition transformed into several aluminum nickelide (Al-Ni) intermetallics. The onset and nature of the shock-induced transformation from the precursors into the products are discussed.
I. INTRODUCTION
ALUMINUM nickelides (Al-Ni’s) have been the subject of many studies over the past three decades. As indicated in Reference 1, of the five Al-Ni intermetallic phases in the Al-Ni system, AlNi and AlNi3 have received the most attention. Because of their high strength-to-weight ratio, good hightemperature stability, and corrosion resistance, Al-Ni’s may be found in a large variety of structural applications. A wide range of methods has been explored to process aluminides.[2–6] Of these methods, combustion synthesis (CS), wherein the products are directly synthesized from their precursors, offers a latitude in process conditions that is unmatched by more conventional routes. CS of Al Ni mixtures has been extensively studied by several research groups.[7–12] It has been shown that the CS reaction initiates once a threshold temperature, TRT, is exceeded. Typically, TRT is near the melting point of Al, Tm(Al) 660 °C. It has been found that the stability of the CS reaction strongly depends on conditions such as the initial pressure, temperature, size, and heating rate of the reactants. Products obtained by CS are often porous; the primary source of porosity is the intrinsic specific volume difference between the Al and Ni reactants and the resultant Al-Ni phase. The porosity may be reduced by the application of a high intensity pressure, or shock wave. Shock compaction techniques have been successfully used to generate unique Al-Ni intermetallic phase structures directly from the precursor Al Ni powder mixtures.[13–17] During shock consolidation, the pressure wave rapidly passes through the distended material, causing a particle-particle friction-induced rise in internal temperatures that is followed by rapid cooling. Usually, this sequence of events retain
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