Effect of particle size on thermal residual stress in WC–Co composites

Abstract

Thermal residual stresses (TRS) were studied in a series of tungsten carbide (WC)–cobalt (Co) composites using neutron powder diffraction. Samples with 10, 20, and 40 wt.% Co and WC particle sizes of 0.5, 1, 3, and 5 μm were used. As expected, the mean WC TRS increased in magnitude as the Co content increased, i.e. as the WC content decreased. The corresponding stresses in the Co phase were computed from force balance equilibrium requirements. For fixed Co content, the mean (compressive) stresses in the WC increased in magnitude with decreasing WC particle size. The change was most dramatic for the 40 wt.% Co samples, where the mean TRS increased in magnitude from −440 to −1137 MPa as the WC particle size varied from 5 to 0.5 μm, respectively. The stress distribution in the WC phase was studied using the breadths of the WC diffraction peaks. The full-width at half-maximum (FWHM) values indicate a broad range of strain within WC particles that increases with increasing stress in the WC and is attributed primarily to point-to-point variation in the angular WC particles.