Achieving Excellent Elevated-Temperature Mechanical Properties in Dual-Phase High-Entropy Alloys via Nanoscale Co-Precipitation and Heterostructure Engineering

Abstract

Dual-phase high-entropy alloys (HEAs) combine the ductility of a face-centred cubic (FCC) constituent with the strength of an ordered body-centred cubic (B2) constituent, yet their load-bearing capacity collapses above roughly 0.5 of the homologous melting temperature because grain-boundary-derived strength decays and coarse lamellae lose constraint. This work develops and quantitatively evaluates an alloy-design route that couples three length scales in one microstructure: a heterostructured FCC/B2 matrix produced by cold rolling and intercritical annealing, coherent L12 (Ni,Co)3(Al,Ti) nanoprecipitates dispersed in the FCC domains, and coherent α-Cr nanoparticles co-precipitated inside the B2 lamellae. For the model composition Ni34.4Co16.4Cr16.4Fe16.4Al14.4Ti2.0 (at.%), the resulting architecture carries a total precipitate fraction of 14.9 vol.% with mean radii of 5.2 nm and 3.6 nm and inter-particle spacings of 11.6 nm and 9.2 nm in the FCC and B2 constituents, respectively. Micromechanical deconvolution predicts yield strengths of 1250 MPa at room temperature and 1030, 880 and 620 MPa at 600, 700 and 800 °C, with uniform elongations of 15.5–17.8% retained to 700 °C. Order and Orowan strengthening supply 35% of the yield stress at room temperature and 49% at 800 °C, whereas hetero-deformation-induced (HDI) hardening falls from 14% to 7% as geometrically necessary dislocations are recovered. Creep rupture life at 700 °C/250 MPa reaches 520 h, an increase of more than one order of magnitude over the conventional lamellar counterpart, the threshold stress for dislocation detachment being the controlling variable.