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• The plastic strain and recrystallization behavior in CoCrNiCu x were studied. • A phase separation of Cu-lean and Cu-rich FCC phases was observed. • Recrystallization behavior was different between the Cu-lean and Cu-rich regions. • Grain boundary wetting occurred at the Cu-lean and Cu-rich coherent interface. • The plastic strain accommodation difference was caused by the hardness difference. The plastic strain accommodation and recrystallization behavior of the medium-entropy alloy (MEA) CoCrNiCu x (x = 0, 0.66, 1 in molar ratio) were investigated. The addition of Cu induced phase separation phenomenon due to the positive mixing enthalpy of Cu with other constituent elements. This resulted in an alteration of the microstructure from a single solid-solution face-centered cubic (FCC) structure to Cu-lean FCC1 and Cu-rich FCC2 phases. Here, a higher recrystallization concentration in the Cu-rich region was observed compared to that of Cu-lean region. This occurred due to the lower hardness of Cu-rich region than Cu-lean region, which caused a greater plastic strain was accommodated in the Cu-rich region than in the Cu-lean region. Consequently, Cu-rich region tended to be more extensively recrystallized compared to that of Cu-lean region. [ABSTRACT FROM AUTHOR]

The effects of annealing on the microstructure of pure Ni fabricated by laser powder bed fusion (LPBF) were investigated using two different beam profiles: Gaussian and flat-top. The dislocations in the as-fabricated samples were predominantly arranged as statistically stored dislocations, and the low driving force resulting from the insufficient accumulation of geometrically necessary dislocations (GNDs) in the as-fabricated specimens caused minimal static recrystallization in the as-annealed specimens, despite the high dislocation density in the as-fabricated samples, particularly the Gaussian-LPBF-derived specimens. However, static recovery occurred in both the Gaussian-LPBF and flat-top-LPBF-derived specimens, with the higher number of GNDs in the former specimens causing a more prominent misorientation of dislocation boundaries than in the latter. Furthermore, migration of high-angle grain boundaries (HAGBs; misorientation >15°) was not observed because of the insufficient strain gradient and the distribution of HAGBs in low-energy regions. [Display omitted] • The high-temperature microstructural stability of LPBF-derived products was explored. • The LPBF products were fabricated using Gaussian and flat-top beam profiles. • The dominant statistically stored dislocations deterred static recrystallization. • The dislocation boundary misorientation during static recovery showed a difference. • No significant high-angle grain-boundary migration was observed. [ABSTRACT FROM AUTHOR]

• The precipitate formation and its behavior in N-CoCrFeMnNi were characterized. • The formation of Cr- and N-rich Cr 2 N precipitate was observed. • Kikuchi crystal orientation relation was noticed between the Cr 2 N and the matrix. • Different annealing temperature affected the size and fraction of the Cr 2 N. • Zener pinning pressure and grain size was influenced by the presence of Cr 2 N. The precipitate formation and behavior in nitrogen-containing high-entropy alloy of equiatomic CoCrFeMnNi were characterized. The presence of 0.95 at.% nitrogen led to the formation of Cr 2 N precipitate in the as-recrystallized N-CoCrFeMnNi, in which annealing temperature affected the fraction and size of the formed Cr 2 N particles. It was observed that the Cr 2 N exhibited a Kikuchi crystal orientation relation (OR) with the face-centered cubic (FCC) matrix, and the OR was noticed to be in the plane of {1 1 1}γ//{0 0 0 1}Cr 2 N and direction of 1 1 0 γ / / 1 1 ¯ 0 0 Cr 2 N. [ABSTRACT FROM AUTHOR]

• The strengthening by nitrogen in ultrafine-grained CoCrFeMnNi was studied. • Addition of N caused the formation of Cr 2 N precipitate in N-CoCrFeMnNi. • The Cr 2 N formation suppressed the Cr–rich σ-phase formation. • Nitrogen addition improved the mechanical properties of ultrafine-grained CoCrFeMnNi. A design of precipitate-containing, ultrafine-grained equiatomic CoCrFeMnNi high-entropy alloy with the addition of nitrogen was introduced. The introduction of nitrogen led to the formation of Cr– and N–rich precipitate of Cr 2 N on the low temperature-annealed N-CoCrFeMnNi. It was noticed that the presence of nitrogen in N-CoCrFeMnNi suppressed the formation of σ-phase precipitate generally observed in low temperature-annealed CoCrFeMnNi system. Furthermore, it was observed that the addition of nitrogen could be utilized as a viable method in enhancing the mechanical properties of ultrafine-grained CoCrFeMnNi matrix, in which the addition of nitrogen successfully led to an improved yield strength and ultimate tensile strength of the ultrafine-grained CoCrFeMnNi system. [ABSTRACT FROM AUTHOR]

• Precipitate behavior in Fe 75 (CoCrMnNi) 25, Fe 71.25 (CoCrMnNi) 23.75 Cu 3 Al 2 was studied. • Both alloys displayed the formation of lath martensite body-centered cubic matrix. • Dispersion of Ni-Mn-rich B2 nanoprecipitate was observed in Fe 75 (CoCrMnNi) 25. • Meanwhile, Cu-rich B2 nanoprecipitate was observed in Fe 71.25 (CoCrMnNi) 23.75 Cu 3 Al 2. • Interfacial energy difference led to different morphologies for these precipitate. The precipitate behavior in aging-treated medium-entropy alloys of Fe 75 (CoCrMnNi) 25 and Fe 71.25 (CoCrMnNi) 23.75 Cu 3 Al 2 was investigated. The applied aging treatment at 723 K for 7 h in both alloys led to the formation of B2 nanoprecipitate in a lath-martensite body-centered cubic matrix. By employing atom probe tomography, it was observed that the B2 precipitate was mainly enriched with Ni-Mn in Fe 75 (CoCrMnNi) 25 and Cu in Fe 71.25 (CoCrMnNi) 23.75 Cu 3 Al 2. Furthermore, the B2 precipitate in both of these systems also displayed a different morphology due to the difference in the interfacial energy, with the B2 precipitate in Fe 75 (CoCrMnNi) 25 and Fe 71.25 (CoCrMnNi) 23.75 Cu 3 Al 2 showing ellipsoidal and spherical morphology, respectively. [ABSTRACT FROM AUTHOR]

• Phase separation and its effect on atomic interaction in CoCrNiCu x were investigated. • The positive mixing enthalpy of Cu caused the Gibbs free energy to increase. • High Gibbs free energy caused phase separation to be more favorable in CoCrNiCu x. • Phase separation led to a lower atomic interaction by atomic size misfit modelling. • The similar tendency of atomic interaction was shown in the Vickers microhardness. Herein, the phase separation phenomenon and its effect on the atomic interactions of CoCrNiCu x (x = 0, 0.33, 0.66, 1 in molar ratio) medium-entropy alloys were investigated. Phase alteration from single solid-solution face-centered cubic (FCC) phase to Cu-lean FCC1 and Cu-rich FCC2 structures was observed when Cu was added. This occurred due to the positive mixing enthalpy of Cu with other constituents, causing higher Gibbs free energy of mixing with increasing Cu content. This phase separation also affected the atomic interactions in the CoCrNiCu x , as demonstrated by an atomic size misfit modelling. The tendency of the atomic interactions was also reflected in the mechanical properties, as displayed by Vickers microhardness result. [ABSTRACT FROM AUTHOR]

The effect of nitrogen addition toward nitride precipitate formation and the corresponding behavior in a medium-entropy alloy system of N-CoCrNi was investigated. It was observed that the addition of N induced the formation of a Cr- and N-rich precipitate of Cr 2 N. Cr 2 N and the face-centered cubic (FCC) matrix in the N-CoCrNi system exhibited a Kikuchi orientation relation in the {111} γ //{0001}Cr 2 N plane and 〈110〉 γ //〈 1 1 ¯ 00 〉Cr 2 N direction, where Cr 2 N was observed to be semi-coherent with the FCC matrix. The presence of Cr 2 N was also observed to contribute in the hindering of grain coarsening via Zener pinning pressure. The distribution of finer and higher fraction of Cr 2 N in the lower annealing temperatures of N-CoCrNi contributed more toward higher Zener pinning pressure compared to the coarser and lower fraction of Cr 2 N in the higher annealing temperatures, which subsequently affected grain growth during the annealing treatment. Unlabelled Image • The effect of nitrogen addition in CoCrNi medium-entropy alloy was investigated. • Cr 2 N precipitate was formed along with the face-centered cubic matrix. • A Kikuchi crystal orientation relation was observed between the Cr 2 N and the matrix. • Cr 2 N precipitate contributed in Zener pinning pressure. • These caused the formation of significantly finer grain size in N-CoCrNi than CoCrNi. [ABSTRACT FROM AUTHOR]