Precipitation behaviour and mechanical properties of a new wrought high entropy superalloy

Abstract

A newly developed precipitation-hardened high entropy superalloy was produced using double vacuum melting, and its microstructural evolutions were examined after homogenization, hot rolling, annealing, and aging. The precipitation behaviour of the samples was studied using two different heat treatment cycles (with and without solution treatment). Microstructural observations using scanning electron microscope and transmission electron microscopy showed that the direct-aged samples consisted of nano-sized γ′ precipitates in γ matrix, while for the solution-aged samples, reprecipitation of the Laves phase occurred in the interior of the grain and at the grain boundaries. The sluggish diffusion present in the proposed alloy is what mainly accounts for the smaller than 20 nm of γ′ precipitates formed after about 18 h of aging. The strengthening effects of precipitation on the mechanical properties of the annealed and aged conditions were studied using a universal testing machine under a tensile load. The room temperature tensile strength and total elongation of the direct-aged samples were as high as 1310 MPa and 32%, respectively, which represent a promising combination of strength and ductility for industrial applications. In addition, the direct-aged specimens exhibit significant enhancements of 150% and 46% for yield and tensile strengths, respectively, as compared to the annealed condition. These results confirm that the precipitation-strengthening mechanism is an effective way of increasing the strength of face-centered cubic high entropy alloys.