Microstructure and constitutive modeling of an ultrafine-grained refractory high-entropy alloy fabricated by powder metallurgy

Abstract

In the present study, a novel AlCr0.3FeMoNbTiV2 alloy was prepared by means of mechanical alloying and subsequent spark plasma sintering, resulting in an ultrafine-grained (UFG) microstructure consisting of a bcc matrix phase with an average grain size of 0.32 μm accompanied by Ti carbide, Laves phases, and minor contents of Al2O3. Excellent thermal stability was exhibited by the alloy, since no considerable phase transformations were observed after a heat treatment at 1350 °C for 16 h, beyond microstructural coarsening, as can be appreciated from the increase of the average bcc grain size up to 1.50 μm. Compression tests were performed at elevated temperatures (950–1100 °C) at strain rates ranging 0.0005–0.01 s−1. According to the constitutive analysis of the peak stress using the hyperbolic sine law, an experimental creep exponent of 2.17 was obtained, which indicates that deformation is mainly controlled by grain boundary sliding, as typically observed in UFG materials, with a large apparent activation energy of 527.7 kJ mol−1, superior to that of other RHEAs reported in literature.