The composition and temperature dependence of the mechanical properties of tungsten alloys
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The Composition and Temperature Dependence of the Mechanical Properties of Tungsten Alloys
hydrostatic stress state on properties. The work presents a more comprehensive data set than heretofore available on such alloys. The W-Ni-Fe alloys were all sintered at 1485 ~ in a hydrogen atmosphere for 2 hours, followed by an anneal at 1100 ~ in a vacuum, in accordance with conditions used in the production of the commercial 95W-3.5Ni1.5Fe alloy, t4j The alloys containing 90 wt pct or less of W showed considerable slumping due to the extreme liquid flow at the sintering temperature. The nominal compositions of all of the alloys are listed in Table I, along with phase volume fraction and tungsten grain size data measured with quantitative metallographic techniques. The compositions range in 2.5 wt pct tungsten increments from 87.5 pct to 97.5 pct W with N i / F e ratios of 7:3 and 1:1. These N i / F e ratios were chosen as they are the most common of the commercially available alloys. It is noted that the 87.5W-8.75Ni-3.75Fe alloy contained a small volume fraction (0.05) of voids, all other alloys being fully dense, and the 87.5W-6.25Ni6.25Fe alloy had a much finer tungsten grain size than the other alloys. The binder-phase compositions of two of the alloys with different N i / F e ratios were determined by electron probe microanalysis and found to be, in weight percent: 95W-3.5Ni- 1.5Fe (alloy): 21.4Fe, 55.3Ni, 23.4W (binder)
R.G. O ' D O N N E L L and R.L. WOODWARD Liquid-phase sintering of tungsten-nickel-iron (W-NiFe) alloys results in a semicontiguous network of tungsten spheroids, in a matrix comprising a saturated solid solution of W, Ni, and Fe whose composition is dependent upon the ratio of Ni to Fe in the alloy, tl-6] There have been a large number of reports on the effects of composition, interphase interface structure, sintering conditions, and thermomechanical processing on mechanical properties.t2,3,5-12] These show a wide variability in ductility, which is generally related to the fracture mode, transgranular cleavage of tungsten grains for good ductility and interfacial debonding for poor ductility, and can often be traced to poor bonding, interface segregation, or precipitation, t13,14,15~Poor bonding between tungsten grains can often be associated with the powder mixing or sintering atmosphere in the manufacture of the alloy. The 95W-3.5Ni-1.5Fe alloy used in this study is a welldocumented t4,15,16] commercial alloy giving consistent mechanical properties. By mixing and sintering the experimental alloys under the same conditions in the same plant, it is hoped that alloy variations associated with an experimental manufacturing process are not observed. The present work presents mechanical property data for a wide range of W-Ni-Fe alloy compositions, as well as test data for tension and torsion tests on the 95W-3.5Ni1.5Fe alloy in the temperature range of - 100 ~ to 300 ~ to allow evaluation of the influence of temperature and R.G. O'DONNELL, Research Scientist, and R.L. WOODWARD, Principal Research Scie
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