Effect of nitrogen on mechanical properties of CoCrFeMnNi high entropy alloy at room and cryogenic temperatures

Abstract

Specimens of a CoCrFeMnNi high entropy alloy with different content of nitrogen (0.5e2.0 at.%) were prepared by induction melting. Microstructure and tensile mechanical behavior of the alloys in the ascast condition were analyzed. The alloys with a low amount of N (0.5e1.0 at.%) had a single fcc phase coarse-grained microstructure. An increase in the content of N to 2.0 at.% resulted in the precipitation of a small amount (~1%) of Cr-rich M 2 N nitride particles. The yield strength of the alloys increased in proportion to the percentage of nitrogen by 117 MPa/at% N at 293 K or by 316 MPa/at% N at 77 K. The observed increase in strength was attributed to solid solution hardening. Ductility of the alloy with 0.5 or 1.0 at.% of N increased with a decrease in the testing temperature while ductility of the alloy with 2 at.% dropped from 67% at 293 K to 8% at 77 K. The plastic deformation of the alloys at both 77 K or 293 K was mostly associated with planar dislocation slip. No signs of mechanical twinning were found even at 77 K. Thermo-Calc software was used to produce a quasi-binary CoCrFeMnNieN phase diagram for comparing the experimental and calculated results. The effect of N on strengthening and deformation mechanisms at different temperatures was discussed.

Nitrogen-induced hardening in an austenitic CrFeMnNi high-entropy alloy (HEA)

“…This result is in agreement with the fact that, at this scale of observation, no primary precipitation was observed in any sample. This also indicates that cooling down to room temperature, which takes only a few minutes after solidification, is not long enough to provoke the precipitation of low temperature phases predicted at equilibrium, like Cr 2 N or , for instance in agreement with the observations of Klimova et al [26].…”

“…It should however be noted that nitride precipitation kinetics is believed to be relatively slow compared to carbide precipitation [30] explaining why Cr 2 N is nearly never observed in the as-cast state of a nitrogen-doped Cantor alloy. Klimova et al [26] showed that for a Cantor alloy doped with 0.22 wt. % N (0.88 at.…”

“…Similarly, nitrogen additions as an alloying element in bulk HEA has already been reported in several studies. While in most of them, nitrogen is introduced in the alloy during melting thanks to a high gas pressure [20], [21], [22], [23], it can also be introduced into the molten alloy in the form of nitride like FeCrN 2 [24], [25], [26], [27] or during mechanical alloying with nitride powders [28], [29]. Han et al [23], have shown the efficiency of nitrogen to increase the mechanical resistance of a cold-rolled Cantor alloy doped with 0.52 at.% of N (0.13 wt.…”

“…% N (0.49 wt. % N) at cryogenic temperature [26]. Nitrogen's strengthening through solid solution is even more important than at room temperature making nitrogen-doped HEAs promising solutions for cryogenic applications.…”

Hardening of Additive Manufactured 316L Stainless Steel by Using Bimodal Powder Containing Nanoscale Fraction

“…Mukhtar et al [ 24 ] show that nitriding as the thermo-chemical treatment can improve wear resistance and surface hardness and reduce the fatigue life of AM Ti64 compared to AM Ti64 subject to the same thermal treatment without nitriding. Klimova et al [ 25 ] studied the effect of nitrogen (0.5–2.0 at.%) on the structure and mechanical properties of CoCrFeMnNi high entropy alloy as-cast condition. They showed that increase in the N content to 2.0 at.% resulted in the precipitation of a small amount (<1%) of the Cr-rich M 2 N nitride particles at the face-centered cubic (FCC) grain boundaries.…”