Effect of cobalt addition on the morphology and mechanical properties of W–Ni–Cu–Co alloy

Abstract

This paper investigates the performance of a tungsten (W)–nickel (Ni)–copper (Cu) heavy alloy with 0·5, 1·0, 1·5 and 2·0 wt% cobalt (Co) additions. The alloys are prepared through spark plasma sintering at a sintering temperature of 1400°C following a heating step of 100°C/min. The alloy with 0·5 wt% cobalt is observed to have good mechanical properties in comparison with other alloys. The density and hardness of the alloys follow a decreasing trend with an increase in cobalt addition. Subsequently, microstructural characteristics, such as contiguity, average grain size and matrix volume fraction, are measured and investigated, as they are found to affect the mechanical properties of the alloys. The average grain growth of the alloys varies around 13 µm. As the cobalt percentage is increased, tungsten–tungsten contiguity is observed to increase. The W–Ni–Cu–0·5Co alloy exhibits higher yield and tensile strength in comparison with other heavy tungsten alloys. The fracture surface analysis shows a predominantly tungsten grain cleavage fracture for 0·5 wt% cobalt alloy. The other alloys show more features of matrix interface failure and tungsten decohesion.