High temperature tensile properties of as-cast and forged CrMnFeCoNi high entropy alloy

Abstract

High entropy alloys (HEAs) are a new kind of basic materials with excellent properties, which can be used in extreme service environment. In this paper, high temperature tensile properties of as-cast and forged CrMnFeCoNi high entropy alloy with a single-phase face-centered cubic (FCC) crystal structure were investigated. The coarse equiaxed structure was transformed into a fine structure with the average grain size of ∼18.5 μm after hot forging, and twinning and low angle grain boundaries (LAGBs) were observed in as-forged alloy. Tensile properties of the alloy in the as-cast and forged states were characterized in the temperature range of 25–950 °C. An outstanding strength had been achieved at every range of temperature for as-forged alloy, especially at 650 °C, the ultimate tensile strength and yield strength of the as-forged alloy increased by 40% and 158% compared with the as-cast alloy. Prominent serrations occurred from 350 °C to 650 °C for as-cast HEAs and from 350 °C to 500 °C for as-forged HEAs. The serration features varied from type A to type C in a specific temperature range and strain. Fracture mode changed from ductile fracture to brittle fracture at intermediate temperatures in both states, and the transformation temperature was 800 °C and 650 °C for the as-cast and as-forged HEAs, respectively. The temperature dependence of deformation mechanisms in as-forged HEAs were also studied. The deformation mechanism changed from mixed dislocation slipping and twinning to wavy slip and dislocation cells with the increase of temperature. Dynamic recrystallization occurred at 950 °C, resulting in softening of the HEAs.