Effect of heat treatment on microstructure and mechanical properties of hot-hydrostatically extruded 93W-4.9Ni-2.1Fe alloy

Microstructure, mechanical properties and strengthening mechanisms of tungsten heavy alloys consolidated by liquid-phase sintered, hot-hydrostatic extrusion and heat treatment were investigated. The results showed that ultimate tensile strength sigma(b) of 93W-4.9Ni-2.1Fe alloy with area reduction 75% extruded at 1200 degrees C could reach as high as about 1540 MPa and elongation could also reach 9.2%. Meanwhile, ultimate tensile strength and elongation by heat treatment remain 1487 MPa and 13.4%, respectively. Transmission electron microscopy observation revealed that as-extruded alloys were characterized by fine subgrains in elongated tungsten grains and dynamically re-crystallized grains in Ni-Fe-W matrix phase. Tungsten subgrains subsequently grew up a bit and nanocrystalline W with most of them being less than 100 nm in length showing a needle precipitated in Ni-Fe-W matrix phase after heat treatment at 1000 degrees C for 1 h. Results indicate that one of the strengthening mechanisms is interface strengthening between tungsten and matrix phase due to severe plastic deformation, which can be explained via aspect ratio correlated with deformed tungsten particles. The other strengthening mechanism can be attributed to precipitated nanocrystalline W during heat treatment in Ni-Fe-W matrix phase of the as-extruded alloy with area reduction 75%. (C) 2014 Elsevier B.V. All rights reserved.