Synthesis of heavy tungsten alloys via powder reduction technique
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K.S. Abdel Halim Central Metallurgical Research and Development Institute (CMRDI), Helwan, Cairo 11421, Egypt; and Department of Chemical Engineering, College of Engineering, University of Hai’l, Hail, Saudi Arabia
M.I. Nasr Central Metallurgical Research and Development Institute (CMRDI), Helwan, Cairo 11421, Egypt (Received 9 March 2016; accepted 22 August 2016)
Heavy tungsten alloys with the following compositions 98W2Fe, 93W7Fe, and 95W2Fe3Ni were successfully prepared through gaseous reduction of metal oxide mixtures in the temperature range of 850–1000 °C. Reduced samples were subjected to sintering processes in reducing atmosphere (Ar/4% H2) at different temperatures (1200–1300 °C) and dwell times (30, 90 min). The prepared alloys together with the sintered samples were characterized by x-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and optical microscope. The microhardness of the sintered samples was measured and correlated to sintering temperature and dwell time. The presence of iron oxide decreases the reducibility of WO3 whereas the presence of NiO increases the reducibility of both iron oxide and tungsten oxide. With the increase of sintering temperature and dwell time, porosity of samples decreases forming dense structure which is coupled with the increase of hardness particularly for 95W2Fe3Ni alloy.
I. INTRODUCTION
Tungsten heavy alloys (WHAs) are two phase composites consisting of nearly pure tungsten grains dispersed in a low melting temperature ductile matrix of other metals such as iron (Fe), nickel (Ni), cobalt (Co), or copper (Cu).1,2 The typical mean tungsten grain size varies from 20 lm to 60 lm depending on the initial particle size, volume fraction of tungsten, sintering temperature, and sintering time. Due to their high density and high strength associated with the bcc tungsten phase, and high ductility attributed to the fcc matrix, these alloys are used in various applications such as kinetic energy penetrators, radiation shielding, counter balance, vibrational damping devices, and other military and civil applications.3,4 During the last two decades, the research of WHAs has concentrated on strengthening methods, which do not compromise their density, that is especially important in military applications. The combination of a powder with a particular microstructure and a consolidation technique that can maintain that microstructure is an effective method for obtaining bulk samples with a unique microstructure. The mechanical properties of WHAs are determined by various factors; in particular, the strength of W/W and W/matrix interfaces.5,6 Microstructural factors, such
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected], [email protected] DOI: 10.1557/jmr.2016.318
as tungsten particle size, matrix volume fraction, and tungsten–tungsten contiguity, affect the mechanical properties of WHAs.7 WHAs are usually fabricated by conventional powder metallurgy (PM), which consumes too much sinter
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