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TUNGSTEN heavy alloys (WHAs) possess a wide range of physical and mechanical properties that can gainfully be used for a variety of applications ranging from defence to medical engineering.[1–3] With density ranging from 17-19 g/cc, WHAs are excellent candidates for collimators and shielding components in radiation therapy. These alloys are ideally suited for balancing weight applications in propellers, avionics, radar systems, and targeting pods because of high density. These alloys are extensively used for damping applications especially as tool holders and high speed spindles for deep boring applications due to their high modulus. Another application of the WHAs is pre-fragment cubes or spheres which are regularly used in missile warheads. Thus, most of the research and development programs of WHAs are driven by the need to develop materials with optimized mechanical properties for aforementioned applications.

ASHUTOSH PANCHAL, U. RAVI KIRAN, T.K. NANDY, and A.K. SINGH are with the Defence Metallurgical Research Laboratory, Kanchanbagh P.O., Hyderabad, 500 058, India. Contact e-mail: singh_ashok3@rediffmail.com Manuscript submitted November 2, 2017.

METALLURGICAL AND MATERIALS TRANSACTIONS A

The WHAs are typically produced by conventional powder metallurgy route [Cold iso-static pressing (CIPing route)].[4,5] This involves consolidation of alloy powder in cold iso-static press followed by pre-sintering. The pre-sintered compact is then subjected to liquid phase sintering (LPS) at temperatures ranging from 1450 C-1500 C. Subsequently, the sintered product is heat treated. This process has been successfully employed to produce semi-finished products. However, it has some limitations with regard to complex geometry finished components. The WHA components with complex shapes can also be made by another potentially attractive process called gelcasting. This is a pressure-less consolidation technique proposed by Janney and Omatete for ceramic materials at the Oak Ridge National Laboratory.[6–9] It is primarily a ceramic-forming process, which involves slip gelcasting followed by monomer polymerization in order to realize complex shapes with high green strength. The technique is based on in situ polymerization that forms a continuous network of polymer holding the ceramic particles together in green condition. This has been successfully employed to produce alumina, zirconia, silicon carbide, and silicon nitride green components. The gelcasting technique has been extended in the present work to produce green samples of WHAs.[10] These green samples are then employed in

similar processing as described above in conventional CIPing route. The typical microstructure of WHAs contains two phases in which globular shape pure bcc tungsten (W: Im3m) grains embedded in a relatively soft and ductile fcc (Ni matrix, Fm3m).[11–13] The matrix phase is a solid solution of Fe and W in Ni and forms by eutectic reaction during liquid phase sintering. The liquid phase formed during eutectic reaction initially wets the tungsten p