Hot explosive consolidation of W-Ti alloys
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INTRODUCTION
IN scale model studies, it has been demonstrated that the performance of a long-rod kinetic energy (KE) penetrator is not dependent on the mechanical and engineering properties of the material but rather on its ability to fail by the formation of adiabatic shear bands at oblique planes with respect to the penetrator-target interface. Specifically, in the two most common penetrator materials, Magness and FarrandtX] have shown that the penetration of depleted uranium (DU) is by adiabatic shear localization, whereas the penetration of tungsten heavy alloy (WHA) is by plastic deformation. Because of the health hazards associated with the use of depleted uranium alloys, current efforts are underway to develop a new WHA with a matrix phase susceptible to adiabatic shear instabilities. The requirements for such alloys are high density, high strength, high hardness, modest to high ductility, and easy machinability. The metallurgy of the composition must be such that no weak intermetallic phases are formed. Although several metals such as titanium, Ti-6A1-4V, zirconium, hafnium, and certain steel alloys (4340) are prone to adiabatic shear failure, undesirable intermetallic phases, WZr2, WHf2, and those between W and Fe, usually form if a critical temperature is exceeded. Since no intermetallic phase is known for the W-Ti system,t2J this material combination is under primary consideration. The WHA KE penetrators currently in use are two-phase composites consisting of spheroidal tungsten particles embedded in a nickel-iron or copper-nickel matrix.t3] Because of the highly refractory nature of W, these alloys are fabricated by time consuming, energy intensive methods such as liquid-phase sintering (LPS).[4.5,6] Ideally, an approach similar to LPS is desired for the fabrication of W-Ti heavy alloys; however, other alternate fabrication methods are of interest as well. One such route envisions the use of explo-
LASZLO J. KECSKES, Research Physical Scientist, is with the United States Army Research Laboratory, Aberdeen Proving Ground, MD 210055066. IAN W. HALL, Associate Professor of Mechanical Engineering, and Chair, Materials Science Program, is with the University of Delaware, Newark, DE 19716-3106. Manuscript submitted July 15, 1994. METALLURGICAL AND MATERIALS TRANSACTIONS A
sive compaction to consolidate and sinter the powdered precursors into fully dense products. Explosive compaction has been applied to materials that otherwise may be difficult to fabricate conventionally or have dissimilar, nonequilibrium, or unique metastable substructures.t7.s] Due to the rapid densification rate, these samples often suffer from low nonuniform densities, poor interparticle bonding, and severe cracking.[7.s.9] Although there is a temperature rise due to the irreversible work during the consolidation of distended solids, in an attempt to avoid some of the former structural integrity problems, hot explosive compaction has been suggested,v~ 13] In hot explosive compaction, the precursor powder mixture is placed in a sea
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