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TiC/Fe 0.6 MnNi 1.4 medium entropy alloy matrix composites with different volume fractions of TiC particles (i.e., 5, 10 and 15 vol%) were prepared by induction melting method. The experimental results showed that both the base alloy and the composite matrix possess face-centered cubic structure. The in-situ TiC reinforcement phase can significantly increase the mechanical properties of the composites at room temperature. In particular, the hardness, yield strength and ultimate tensile strength of the 10 vol%TiC/Fe 0.6 MnNi 1.4 composite are found respectively to be 528 HV, 345.1 MPa and 716.7 MPa, representing a marked increase by 51.7%, 41.1% and 30.7% in comparison with the Fe 0.6 MnNi 1.4 medium entropy alloy. The ductility of the composite in terms of the elongation to failure is reduced from 65.8% to 36.6% with the increase of the TiC content, which remains attractive for load-bearing structural applications. The strength improvement is underpinned by a combination of the load-bearing effect, Orowan process, dislocation interactions and solid solution effect. [ABSTRACT FROM AUTHOR]

In this work, the CrMnFeCoNi 0·8 Nb 0.2 high-entropy alloys (HEAs) were fabricated through vacuum induction melting and subsequently annealed at various temperatures (namely, 900 °C, 1000 °C, and 1100 °C). The microstructure and mechanical properties of the HEAs following heat treatment were investigated systematically. It reveals that the annealed alloys demonstrate the coexistence of the face-centered cubic (FCC) matrix phases and Laves phases, wherein partial dissolution of primary NbCo 2 phases into the matrix while the remaining part precipitation as secondary phases. The alloy annealed at 1000 °C exhibits a ductility of 13.2%, along with high yield strength of 497.8 MPa, ultimate tensile strength of 851.1 MPa and hardness of 393.9 HV. The high strength of the alloy primarily originates from the hetero-deformation induced (HDI) strengthening of the eutectic-like structure, while additional strengthening is provided by precipitation strengthening caused by nano-sized second precipitates and solution strengthening. • All the alloys display a eutectic-like morphology of FCC matrix and Laves phases. • The secondary NbCo 2 phases are found to be precipitated in the annealed HEAs. • The mechanical properties of the HEA annealed at 1000 °C are further improved. • The enhancement of strength is attributed to multiple strengthening mechanisms. [ABSTRACT FROM AUTHOR]

Here, judicious heat treatment is used to enhance the mechanical properties of 5 vol%TiC/Fe 0.6 MnNi 1.4 composites. After annealing at 1100 °C, M 23 C 6 (M = Fe, Mn, Ni) precipitates formed, imparting the composites remarkable mechanical properties, with the ultimate tensile strength and ductility determined to be 805.5 MPa and 51.1%, respectively. • TiC/Fe 0.6 MnNi 1.4 composites were annealed, in which fine M 23 C 6 precipitates formed. • M 23 C 6 precipitates played a decisive role in microstructural refinement and property enhancement. • Annealing at 1100 °C yielded an optimal combination of the strength and ductility in the composites. [ABSTRACT FROM AUTHOR]

In-situ TiC particulate reinforced CrMnFeCoNi 0.8 high entropy alloy (HEA) matrix composites were prepared by induction melting method. The effect of TiC content upon the microstructure and tensile properties of as-cast samples were analyzed and discussed. The HEA matrix has single-phase face-centered cubic (FCC) structure, determined by X-ray diffraction (XRD) pattern. Compared to the CrMnFeCoNi 0.8 matrix, 7.5 vol%TiC/CrMnFeCoNi 0.8 composite possessed remarkable yield strength (517.1 MPa vs 240.9 MPa), ultimate tensile strength (926.2 MPa vs 527.5 MPa) and excellent uniform elongation (38.0%). Strong dislocation interactions, load-bearing effect and Orowan mechanism afforded by in-situ TiC particles, together with solid-solution strengthening via C and Ti elements, are responsible for the strength enhancement. • TiC/CrMnFeCoNi 0.8 composites were synthesized by vacuum induction melting. • In-situ TiC/CrMnFeCoNi 0.8 composites has a FCC base reinforced with TiC particles. • 7.5% TiC/CrMnFeCoNi 0.8 achieved the combination of tensile strength and ductility. • Dislocations, load bearing and Solid-solution are key strengthening factors. [ABSTRACT FROM AUTHOR]

The combined effects of vanadium additions and in-situ TiC particle formation upon the microstructure and mechanical properties of FeCrNiCu high entropy alloys were investigated. The addition of V changed the FeCrNiCu matrix structure from FCC (i.e., face-centered cubic) to FCC+BCC (i.e., body-centered cubic). The as-cast 10 vol.%TiC/FeCrNiCuV 0.1 high entropy alloy matrix composite showed excellent mechanical properties, with the yield strength and ultimate tensile strength determined to be 653.5 MPa and 1006.5 MPa, respectively. The extra strength generated by V addition and in-situ TiC particles in FeCrNiCu was evaluated, and the theoretical predictions match the experimental results well. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Nb-doped CrMnFeCoNi x (x = 0.2, 0.4, 0.6, 0.8 and 1) high entropy alloys were prepared by vacuum induction melting. The effects of Ni and Nb content on the microstructure evolution and tensile properties of the alloys were investigated. With increasing Ni content, the CrMnFeCoNi x alloy changed its structure from a combination of face-centered cubic phase and σ phase to a single face-centered cubic phase. The yield strength, ultimate tensile strength and ductility of CrMnFeCoNi x alloys first increased and then decreased with the increase of Ni content. Compared with other CrMnFeCoNi x alloys, CrMnFeCoNi 0.8 HEA has shown superior mechanical properties, exhibiting a high yield strength (240.9 MPa), ultimate tensile strength (527.5 MPa) and an impressive elongation-to-failure (62.5%). The addition of Nb significantly increased the volume fraction of Laves phase in the CrMnFeCoNi 0.8 alloy, which further enhanced the tensile properties of CrMnFeCoNi 0.8 high entropy alloys. The yield strength and ultimate tensile strength of the CrMnFeCoNi 0.8 Nb 0.2 alloy were determined to be 406.9 MPa and 662.8 MPa, representing a 68.9% and 25.6% increase over CrMnFeCoNi 0.8 alloy. • CrMnFeCoNi x alloys were synthesized by vacuum electromagnetic induction melting. • Niobium was added to CrMnFeCoNi 0.8 alloy for enhanced mechanical properties. • The CrMnFeCoNi 0.8 Nb 0.2 alloy has a yield strength of 406.9 MPa, ultimate strength of 662.8 MPa and elongation of 15.8%. • Solid solution strengthening, grain refinement and the formation of Laves phase are responsible for enhancing strength. [ABSTRACT FROM AUTHOR]

• The NbTiC 2 /FeCrNiCu composite contains a single FCC phase and NbTiC 2 particles. • NbTiC 2 additions can enhance the tensile strength of the alloy up to 1148.8 MPa. • Dislocation strengthening accounts for 89.6% of the strength increase. The high entropy alloy matrix composite FeCrNiCu on the basis of the face-centerd cubic structure and reinforced with 5 vol% NbTiC 2 particles was synthesized by vacuum induction melting. NbTiC 2 particles are found to be densely distributed on the substrate in polygonal shapes. The tensile strength of the NbTiC 2 /FeCrNiCu high entropy alloy matrix increased phenomenally, from 517.5 MPa to 1148.8 MPa. Though the ductility of composite is lower than the matrix, but it still presents an acceptable value of 7.1%. It is found that dislocation strengthening, loading bearing effect and Orowan mechanism are positive for enhancing the tensile properties of the high entropy alloy. [ABSTRACT FROM AUTHOR]

A series of NbC/FeCrNiCu high entropy alloy matrix composites (2.5, 5, 7.5 and 10 vol% of NbC) were prepared by vacuum induction melting. The microstructures and mechanical properties of the composites were investigated using X-ray electron diffraction, scanning electron microscopy, transmission electron microscopy, tensile and hardness tests. The results show that the FeCrNiCu high entropy alloy matrix composites are composed of FCC solid solution embedded with NbC particles. A coherent relationship was identified between the alloy matrix and reinforcement phase. The formation of NbC particles increases the hardness from 337.6 HV to 591.3 HV. Moreover, compared with the base alloy, the tensile yield strength, ultimate tensile strength and ductility of the new composite first increases and then decreases with the increase of NbC content. The tensile yield strength, ultimate tensile strength and ductility reaches maximum for the composites containing 5 vol% of NbC, which is 458.2 MPa, 691.6 MPa and 24.7%, respectively. The strengthening mechanisms of the composites are discussed and the contributions of dislocation strengthening, load bearing effect and Orowan mechanism are quantified. • The in-situ NbC/FeCrNiCu composites has a FCC base reinforced with NbC particles. • A distinct coherency exists between the alloy matrix and NbC particles. • For 5 vol% of NbC, the tensile strength and ductility increase simultaneously. • Dislocations, load bearing and Orowan mechanism are key strengthening factors. [ABSTRACT FROM AUTHOR]

Developing body-centered-cubic (BCC) typed high/medium-entropy alloys (H/MEAs) with an exceptional combination of high strength and ductility remains a challenge for structural applications. Herein, by adjusting phase composition, an ambient ductile Ti x Ni 0.6 CoFe 1.4 (x = 0, 0.05 and 0.1) MEAs were prepared. The effects of Ti on the mechanical properties of Ti x Ni 0.6 CoFe 1.4 MEAs are revealed by combination of experiments and first principles calculations. The addition of Ti not only promotes the formation of (Co, Ti)-rich face-centered cubic (FCC) and (Ni, Ti)-rich R phases in BCC matrix, but also refines the microstructure of the Ti x Ni 0.6 CoFe 1.4 alloys. The mechanical results show that a proper Ti content can significantly improve the ductility of the alloys with sustaining a high strength. Specifically, the yield strength, tensile strength and fracture elongation of Ti 0.1 Ni 0.6 CoFe 1.4 alloy are 733.0 ± 2.5 MPa, 1003.9 ± 14.9 MPa and 20.1 ± 0.4 %, respectively, which are increased by 22.4 %, 33.3 % and 286.5 % compared to single-phase Ni 0.6 CoFe 1.4 alloy. The impressive mechanical properties are mainly attributed to the synergetic effect of the grain refinement, precipitation strengthening and the coherent boundaries between the precipitate-matrix. Furthermore, the first principles calculation results suggest that the charge enrichment of the Ti site and its induced sparseness of the surrounding charge are responsible for the strength-ductility equilibrium. [ABSTRACT FROM AUTHOR]