Journal of Alloys and Metallurgical Systems (Sep 2023)
Effect of nickel to cobalt ratio on mechanical properties of tungsten heavy alloys
Abstract
The present study investigates the effect of Ni and Co on the mechanical properties of the W-Ni-Co alloy system. The alloys, based on 90 % W with varying Ni: Co ratios of 6:4, 7:3 and 8:2 (90W-6Ni-4Co, 90W-7Ni-3Co and 90W-8Ni-2Co) were processed through liquid phase sintering followed by a cyclic heat treatment (6 cycles). Thermomechanical treatment was carried out to improve strength and toughness levels. Quantitative metallography was employed to extract microstructural parameters including the volume fraction of the matrix phase, tungsten particle size, precipitate volume fraction and the contiguity of the W particles. The microstructural details at a finer scale were studied using scanning and transmission electron microscopy. Mechanical properties, such as tensile strength, elongation, hardness and impact toughness were also evaluated. The study shows that increasing the Ni: Co ratio decreases the precipitation of W in the matrix, which affects the mechanical behaviour of the alloys. The alloys having 7:3 and 8:2 Ni to Co ratio were additionally processed with an increased number of cycles (8 cycles) in the cyclic heat treatment to enhance the precipitation of fine W particles in the matrix. Since the alloy 6:4 showed brittle behaviour, it was not included for 8 cycles heat treatment study. The alloy with Ni to Co ratio of 8:2 resulted in superior combination of mechanical properties.
