Abstract
? 2022 Elsevier B.V.L12-structured Ni3(Al, Ti) precipitates are promising strengthening particles in face-centered-cubic high entropy alloys (HEAs). However, if the Al/Ti ratio (R) is not carefully controlled, brittle intermetallic compounds can form, especially at the grain boundaries (GBs). In this study, a series of Ni35(CoCrFe)55AlxTi10?x HEAs with different R values, R = x/(10-x), were prepared, and the evolution of precipitates and their effects on the mechanical properties were investigated. The dispersed spherical precipitates within the grains act as an effective barrier to dislocation slip, producing high strength. However, increasing R (increasing Al) reduces the volume fraction of the precipitates within the grains, resulting in a decrease of yield strength. Both experimental measurements and first-principles calculations show that Al, Ti and Ni segregate to the GBs. This leads to the formation of L12 precipitates at the GB that, upon aging, coarsen to layer-like structures. When R ≥ 3 the local supersaturation of Al and Ti also leads to formation of a Heusler phase at the GBs, which reduces the ductility. However, when R > 3.5 the volume fraction of the Heusler phase decreases, and the plasticity increases again. These findings provide important guidance and inspire new strategies for the microstructural control in precipitate-strengthened HEAs.
NSTL
Elsevier