Superplastic-like flow in a fine-grained equiatomic CoCrFeMnNi high-entropy alloy

Abstract

A CoCrFeMnNi high-entropy alloy (HEA) showed elongation to failure ∼ 320% at T = 1023 K and a strain rateε = 10 −4 s −1. Strain hardening and texture weakening occurred at lowε, whereas flow softening and texture strengthening were observed at highε(> 3 × 10 −2 s −1) experiments. The strain rate sensitivity (m) decreased from 0.5 to ∼ 0.25 with increasingε. Deformation with m ∼ 0.5 and deformation-enhanced grain growth at lowε indicated superplasticity associated with grain boundary sliding. The grain boundary diffusion coefficient diminished by a factor of ∼ 4 in the HEA. Concurrent nucleation, growth and cavity interlinkage caused premature failure compared with conventional superplastic alloys. IMPACT STATEMENT FCC CoCrFeMnNi HEA shows superplastic-like flow with ∼ 320% elongation at 1023 K and 10 −4 s −1 strain rate originating from grain boundary sliding.

Dislocation creep behavior of CoCrFeMnNi high entropy alloy at intermediate temperatures

“…The grain size of the annealed CoCrFeMnNi was 21.7 μm excluding twin boundaries [13]. Chokshi [9] reported that CoCrFeMnNi exhibited superplasticity for samples with initial grain sizes of 1.4 μm [9,15] whereas coarser grained HEA ( ∼ 12 μm) exhibited power-law creep at 850°C. The grain size of the specimens in the present study is therefore large enough to induce the dislocation creep [9,[10][11][12].…”

Effect of a minor titanium addition on the superplastic properties of a CoCrFeNiMn high-entropy alloy processed by high-pressure torsion

“…The high temperature mechanical properties of HEAs were studied earlier [9][10][11][12] and some limited results are now available documenting the occurrence of superplasticity in a number of HEAs [13][14][15][16][17]. A recent brief review summarizes the major superplastic results obtained to date [18] and also includes a description of a recent report of superplastic-like flow in a CoCrFeNiMn HEA [19]. It is well established that superplasticity requires a grain size smaller than ~10 m [20] and this may be achieved most readily through the application of severe plastic deformation (SPD) [21,22].…”

Strain-path controlled microstructure, texture and hardness evolution in cryo-deformed AlCoCrFeNi 2.1 eutectic high entropy alloy

“…This is considered to be an effect of high configurational entropy of mixing of a large number of elements, which diminishes the free energy sufficiently to stabilize phases with simple crystal structures [1]. The emergence of HEAs has opened up the massive composition space of hyperdimensional phase diagrams with the possibility of finding alloys with novel composition and unprecedented properties [7][8][9][10][11][12][13][14][15].…”