Nanoscale L12 phase precipitation induced superb ambient and high temperature mechanical properties in Ni–Co–Cr–Al system high-entropy superalloys

Abstract

Designing high-entropy alloys with sufficient high temperature bearing capacity is highly expected for practical structural applications. In this work, we developed a new class of Ni–Co–Cr–Al system high-entropy superalloys (HESAs) with superb high temperature mechanical properties in a wide temperature range by controllably introducing stable and coherent nanoscale L12 precipitates into a face-centered-cubic (fcc) structure matrix with low stacking fault energy (SFE). The structural features, mechanical properties, underlying deformation and strengthening mechanisms at room temperature (RT) and elevated temperatures were systematically investigated. It has been shown that the addition of Ti, Nb, Ta, Mo and W into Ni–Co–Cr–Al base alloy reduces the SFE of the fcc matrix and results in the precipitation of nanoscale near-spherical multicomponent particles with coherent interface. The HESAs exhibit the RT yield strength (YS), ultimate tensile strength (UTS) and elongation up to 1167 MPa, 1632 MPa and 14.8 %, respectively, and the UTS up to ∼1100 MPa at 750 °C, which are superior to those of traditional fcc-type HEAs and typical wrought Ni-based superalloys. The superb mechanical properties of the HESAs are attributed to multiple work-hardening behavior, resulting from pronounced multisets of stacking faults (SFs), deformation-induced microbands, dislocation cells and high density of dislocation walls. Specifically, the high temperature strengthening of the HESAs may be attributed to parallel SFs, Lomer-Cottrell locks and the dislocation shearing of γ′ precipitates via the antiphase boundary mechanism.