Microstructure characteristics and mechanical properties of a novel heavy density Ni–W–Co matrix alloy prepared by VIM/VAR

Abstract

In present work, a novel heavy density matrix alloy (Ni–W–Co) was produced through vacuum induction melting (VIM) and vacuum arc remelting (VAR). The as-cast microstructure, element segregation, and mechanical properties were characterized by optical microscopy, scanning electron microscopy, electron probe microanalysis, and universal tensile testing machine. Results indicated that the present matrix alloy displays a considerable purity and chemical homogeneity. The microstructure exhibits typical dendritic features, which is composed of austenite single-phase structure entirely. The elements Ni and Co are evenly distributed in the matrix, while W shows a distinct segregation trend in the as-cast ingot. The tensile properties of the as-cast alloy at room temperature show that the maximum ultimate tensile strength and fracture elongation are up to 560Mpa and 55.79%, respectively. Tensile fracture morphologies reveal the presence of complex quasi cleavage and ductile fractures. The true stress-plastic strain curves display distinct linear deviation in the region of uniform plastic deformation and exhibit two groups of positive and negative slopes at the lower and higher strains, respectively. The instantaneous work hardening rate-true strain curves depict typical “three stages” hardening characteristics.