Synergistic effect of NiB/Co variation on microstructural evolution, shape distortion, mechanical, and thermal properties of 90W-10(NiB-Co) alloys

Abstract

The present investigation delves into the vital role of NiB and Co ratio on the sintered densification, phase, microstructure, distortion, mechanical, and thermal characteristics of 90W-xNiB-(10-x)Co alloys. The sintered density of the alloys showed an upward trend with an increase in the NiB/Co ratio. The phase analysis confirmed W-containing intermetallic formation in the sintered alloys. FESEM micrographs depicted the prevalence of a third phase or W-rich phases along with W and matrix phases. The grain size of W and the grain growth rate were found to increase with an increase in the NiB/Co ratio. EPMA analysis was also carried out to get a deeper insight into the distribution of the elements in W-rich intermetallics. The highest compressive strength of -1672 MPa was obtained in the W alloys with a NiB/Co ratio of 5, whereas the highest tensile strength of -710 MPa was offered by W-alloys with NiB/Co of 2. The maximum bulk hardness of 462 +/- 36 HV3 was obtained in W-alloys with the NiB/Co ratio of 1. It was noticed that with an increase in the NiB/Co ratio, the shape distortion of the investigated alloys was prevented. The W-alloy with a NiB/Co ratio = 2 resulted in the lowest coefficient of thermal expansion.