SHS metallurgy of high-entropy transition metal alloys

Materials Science and Engineering: A

Chernichenko

et al. 2019

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.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Klimova

Materials Science and Engineering: A

Chernichenko

et al. 2019

“…The use of highly exothermic thermite-type SHS mixtures makes it possible to achieve temperatures high enough (above 2500°C) to obtain molten combustion products and, as a result, cast products (ingots). Previous studies have demonstrated that the SHS process under high gravity conditions is optimal for the chemical homogeneity of the produced ingot and easy removal of the slag (Al 2 O 3 ) [42,43]. The high gravity SHS-casting has been already successfully used to produce different 3d transition metals HEAs [43][44][45].…”

Section: Methodsmentioning

confidence: 99%

“…Previous studies have demonstrated that the SHS process under high gravity conditions is optimal for the chemical homogeneity of the produced ingot and easy removal of the slag (Al 2 O 3 ) [42,43]. The high gravity SHS-casting has been already successfully used to produce different 3d transition metals HEAs [43][44][45]. The synthesis of the program alloy was carried out in a centrifugal SHS setup [46] under artificial gravity of 50-60 G. The initial products were taken in the form of a mixture of powders including oxides of the target elements, Al (both as the metal reducer and alloying element), and pure C (graphite powder).…”

Section: Methodsmentioning

confidence: 99%

Mechanical properties of a new high entropy alloy with a duplex ultra-fine grained structure

Stepanov

Materials Science and Engineering: A

Chernichenko

et al. 2018

A new approach to increase the tensile performance of high entropy alloys (HEAs) by producing a duplex ultrafine-grained (UFG) structure was reported in this work. A novel HEA based on the CoCrFeNiMn system with substantial amounts of Al and C was used for the illustration of this approach. In the as-cast condition the alloy had almost entirely a single face-centered cubic (fcc) phase structure with an insignificant amount of M 23 C 6 carbides. After cold rolling and annealing at 800-1000°C an increased amount of fine second phases, namely M 23 C 6 carbides and B2 phase, effectively pinned boundaries of recrystallized fcc grains. As a result, a duplex UFG structure composed of the recrystallized fcc grains and M 23 C 6 and B2 particles was produced. The alloy with the UFG structure demonstrated attractive mechanical properties. For example, after annealing at 900°C the alloy had the yield strength of 785 MPa, the ultimate tensile strength of 985 MPa, and elongation to fracture of 32%. The phase composition of the alloy in different conditions was compared with the equilibrium phase diagram obtained using a Thermo-Calc software. Strengthening mechanisms were qualitatively analyzed, and some possibilities for further improvement of strength of the alloy were discussed.

“…In the present work FSW of the CoCrFeNiMn alloy doped with C was studied. The alloy was produced by self-propagating high-temperature synthesis (SHS) which acquired a reputation as a suitable method for HEAs production [23,28].…”

Section: Introductionmentioning

confidence: 99%

Friction stir welding of a сarbon-doped CoCrFeNiMn high-entropy alloy

Materials Characterization

Stepanov

Malopheyev

et al. 2018

Butt-joint seam of a high entropy alloy (HEA) of the CoCrFeNiMn system was successfully obtained by friction stir welding (FSW). The HEA was produced by self-propagating high-temperature synthesis. Along with the principal elements, a small amount (0.9 at.%) of C was added to the alloy. The as-cast alloy was cold rolled and annealed at 900°C to produce refined microstructure. The structure of the annealed alloy consisted of a recrystallized face-centered cubic matrix with a grain size of 9.2 μm and fine Cr-rich M 23 C 6 carbides. FSW of the HEA resulted in microstructure refinement to d = 4.6 μm in the stir zone. A noticeable rise in strength and some decrease in ductility of the processed alloy in comparison with the initial condition can be associated with the microstructure refinement and some increase in the volume fraction of M 23 C 6 carbides.