Test temperature and strain rate effects on the properties of a tungsten heavy alloy
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INTRODUCTION
T U N G S T E N heavy alloys were originally developed for radiation containment, although subsequent uses have exploited the unique combination of strength, density, ductility, thermal expansion, machinability, and corrosion resistance. J-5 Of the various uses for heavy alloys, penetrator applications have the most demanding mechanical property requirements. Penetrators must have a high toughness and a high kinetic energy; thus, there is a desire for high tungsten contents and excellent mechanical properties. 6'7'8 The uses include armor piercing projectiles and perforation devices for rejuvenation of stagnant oil and gas wells. For penetration, the most useful compositions are based on the W-Ni-Fe ternary, with tungsten contents ranging up to 97 wt pct and nickel to iron ratios of 7:3. Generally, best penetration behavior is associated with a high density, strength, hardness, toughness, and ductility. As the tungsten content increases there is a higher density and strength, but lower ductility and toughness. Consequently, most heavy alloy penetrators are fabricated using 90 to 93 wt pct tungsten with postsintering warm swaging and strain aging treatments for optimal properties. A eutectic liquid forms in the W-Ni-Fe system at temperatures over approximately 1435 ~ thus, the tungsten heavy alloys are fabricated by liquid phase sintering mixed elemental powders at temperatures near 1480 ~ Near full density can be achieved with sintering times as short as 15 minutes above the eutectic temperature. Since the sintered properties are sensitive to residual porosity, processing must be closely controlled to maximize density. 9'~~ Consequently, considerable research has been performed on heavy alloys with a focus on isolation of processing effects on properties. ~2-~9 Invariably, this research involves slow strain rate testing at room temperature. However, the most demanding uses are dependent on the high strain rate properties. Additionally, success in warm swaging depends on the properties at high strain rates and elevated temperatures.
A. BOSE, Postdoctoral Researcher, D. SIMS, Graduate Research Assistant, and R . M . GERMAN, Professor, are with the Department of Materials Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180-3590. Manuscript submitted November 10, 1986. METALLURGICAL TRANSACTIONS A
The past reports on strain rate and test temperature effects on heavy alloys are limited in scope. 6'19-25 Penrice6 provides data at three strain rates for a 97 pct W alloy with a Ni-Fe-Cu matrix, showing increasing strength and decreasing ductility as the strain rate increases, presumably at room temperature. Woodward et al. 24 recently reported room temperature strain rate effects on the compressive flow stress of three heavy alloys. The alloys were nominally 90W-7.5Ni-2.5Cu, 95W-3.5Ni-l.5Fe, and 97.4W2.6(Ni, Fe, Cu), with relatively low ductilities. Softening was reported at the higher strain rates, which was attributed to cracking and self heating of the specimens. There was a slight flow str
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