Recrystallized microstructures and mechanical properties of a C-containing CoCrFeNiMn-type high-entropy alloy

Abstract

The effect of cold rolling to 80% thickness reduction and annealing at 973-1373 K for 1 h on the microstructure and mechanical properties of a C-containing CoCrFeNiMn high-entropy alloy was studied. Cold rolling significantly strengthened the alloy to the yield strength of 1310 MPa. Annealing at 973 K or 1073 K resulted in incomplete recrystallization of an fcc matrix and M 23 C 6-type carbide precipitations aligned with highly elongated grains/subgrains. Complete recrystallization occurred during annealing at 1173 − 1373 K. The ordered arrangement of the carbides was not observed after annealing at 1273 K or 1373 K. The volume fraction of carbides decreased with increasing the annealing temperature that can be reasonably described by a Thermo-Calc prediction. The coarsening behavior of the microstructure constituents was studied during isothermal annealing at 1173 K for 1-50 h. It was found that the grain growth and the particle coarsening can be expressed by power law functions of annealing time with grain/particle size exponents of about 2 and 3, respectively. An increase in the annealing temperature from 973 K to 1373 K led to a gradual softening of the alloy; the yield strength decreased from 870 MPa to 320 MPa, whereas total elongation increased from 24% to 47%, respectively. Contributions of various strengthening mechanisms into the overall strength of the alloy were discussed.

Effect of second phase particles on mechanical properties and grain growth in a CoCrFeMnNi high entropy alloy

“…The current development strategy of the high-strength HEAs is strongly associated with the finding of a single-phase composition which would be prone to the formation of strengthening second phases due to alloying with additional elements [14]. The results of the present work suggest that HEAs with a single-phase structure stable at high temperatures can be strengthened not only by the alloying but also by a proper thermomechanical/thermal treatment resulting in the formation of precipitates that either directly impede dislocation motion [19,20] or strongly restrict grain growth [24] (Figs. 9-10).…”

“…The yield strength of the alloy at room temperature is rather low, however. Precipitation strengthening due to alloying by additional elements, such as Al, Ti, C, etc., was found to be particularly effective [12][13][14][15][16][17][18][19][20].…”

“…Meanwhile, it is unclear if the same approach can work in the "pure" CoCrFeMnNi alloy. Moreover, the understanding of both grain growth and particle coarsening in HEAs is lacking at the moment [13,20,25,[27][28][29][30], despite the fact that both of these processes are crucial for the production of alloys with desirable microstructures and properties.…”

Interstitials in f.c.c. High Entropy Alloys

“…%) are subject to cold-rolling followed by recrystallization, large volume fractions of carbides are often present as well as changes in grain size. The carbide's effect on the mechanical properties in addition to the reduction in solute strengthening from the reduction in carbon in solution [30][31][32][33][34] make it infeasible to determine the solid-solution strengthening effect of the carbon. CoCrFeMnNi with very high carbon contents (2.2-8.9 at.…”

Экспериментально-теоретическое исследование эволюции атомной структуры высокоэнтропийных сплавов на основе Fe, Cr, Ni, Mn и Co при термическом и радиационном старении

“…Также было обнаружено образование хром-насыщенных предвыделений с ОЦК и тетрагональной кристаллической решеткой [33]. В работе [34] было показано, что в сплаве CoCrFeMnNi образуются σ -фаза, упорядоченная B 2 фаза и карбиды состава M 23 C 6 при температурах до 1000 K, 1200 K и 1400 K соответственно. B 2 фаза с ОЦК-решеткой, содержащая никель и алюминий, была обнаружена после пластической деформации [35].…”