Densification behaviour, microstructural characteristics and mechanical properties of liquid phase sintered W–2Ni–1Fe alloy

Abstract

Tungsten heavy alloy, W–2Ni–1Fe (wt.%) with higher tungsten content and higher density was successfully prepared by powder metallurgical processing sequences comprising of mechanical alloying, compaction and liquid phase sintering. The process parameters such as mechanical alloying conditions, compaction pressure, sintering atmosphere, and sintering schedule were optimised to achieve the desired sintered density. DTA studies were carried out to identify the onset temperature for formation of liquid phase, which eventually decided the temperature regime of liquid phase sintering. The synthesized alloy was characterized for the evolution of microstructure, phases, mechanical properties and texture using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), tensile testing, X-Ray diffraction (XRD), electron back scattered diffraction (EBSD) etc. The sintered alloy was found to comprise with γ-Ni matrix phase along with bcc W grains of size ranging 20–45 μm. EBSD analysis revealed the preferred orientation in γ-Ni grains those undergone liquid to solid transition after cooling, whereas W grains were oriented randomly. Re-precipitation of fine size (∼1 μm) W grains from the liquid phase was identified at the liquid/solid interfaces. Sintering atmosphere altered the density and microstructure of the alloy significantly. The tensile strength and ductility of the as-sintered W–2Ni–1Fe alloy was found to be 863 MPa and 12.5%, respectively. SEM characterization of the tensile-fracture surface showed mixed mode of fracture, i.e. ductile and brittle fracture in γ-Ni and W grains, respectively.