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As a representative multicomponent alloy (MA) system, CoCrNi MAs and their derivatives have shown good strength-ductility combinations but the friction behaviors have been less studied. In this work, the influence of high-carbon addition on the microstructure, (nano)hardness, and wear behavior of the Co 37 Cr 28 Ni 31 Al 2 Ti 2 MA are investigated in detail. Different from the face-centered-cubic (FCC) solid solution and ordered L1 2 precipitates in the base alloy, massive orthorhombic (Cr,Co,Ni) 7 C 3 and FCC (Cr 0.2 Ti 0.8)C particles together with some long-strip-shaped graphite-3R crystals appear in the L1 2 -strengthened FCC matrix for the high-carbon-bearing sample, resulting in an enhancement of hardness from 292 ± 11 HV to 581 ± 29 HV. Moreover, the wear rates (WRs) and the friction coefficients (COFs) under dry sliding conditions for the base alloy are measured to be ∼9.55 × 10−5 mm3/N∙m and ∼0.6, and ∼6.02 × 10−4 mm3/N∙m and ∼0.8, respectively, at loads of 2 N and 10 N. After adding carbon, the wear resistance is significantly improved (average WR: ∼2.81 × 10−6 mm3/N∙m and ∼1.89 × 10−5 mm3/N∙m; average COF: ∼0.5 and ∼0.7 at loads of 2 N and 10 N). This improvement surpasses similar compositions prepared by casting and is comparable to surface-treated MAs. During friction and wear experiments, the fracture and detachment of hard carbides introduce additional abrasive particles into the tribosystem, resulting in a transformation from adhesive wear-dominated to abrasive wear-dominated. The wear resistance enhancement and friction mechanism transformation are further evidenced by the surface morphologies of the alumina counterbody materials after friction. The present findings indicate that the in-situ formation of carbides should be a promising strategy to enhance the wear resistance of MAs. • Microstructures and mechanical properties of multicomponent alloys with/without high carbon addition were observed. • High carbon addition greatly enhances the hardness and wear resistance of base alloys. • In-situ formed various carbides are a promising method to explore high wear-resisting multicomponent alloys. [ABSTRACT FROM AUTHOR]

[Display omitted] Designing multiscale heterostructures by taking lessons from Nature provides a promising strategy for achieving excellent strength-ductility synergy in metals and alloys. The achievement of this goal usually requires intricate multi-step thermomechanical processing, but this is still a challenge with casting alloys rather than wrought ones. Here, we developed a Cr 30 Fe 30 Ni 30 Al 5 Ti 5 (at.%) casting multi-principal element alloy (MPEA) which exhibits, in the as-cast condition, a hierarchically heterogeneous structure involving precipitates at multiple length scales. Microscale body-centered-cubic (BCC) grains are dispersed throughout a continuous face-centered-cubic (FCC) structural framework. Coherent L1 2 nanoparticles form in the FCC matrix, while abundant nanoparticles with hierarchical dimensions (i.e., of η , B2, and η /L2 1 phases) precipitate inside the BCC grains. The synergistic interactions between dislocations and multiscale precipitates which induce massive dislocation networks and stacking faults result in stable strain-hardening behavior, endowing the alloy with an exceptional combination of strength and ductility without the need for homogenization and complex processing. We believe that this represents a breakthrough that surpasses known casting MPEAs and offers implications for developing new high-performance casting alloys. [ABSTRACT FROM AUTHOR]

Lightweight refractory high-entropy alloys (LW-RHEAs) are promising candidates for high-temperature applications, which have become a research hotspot in materials community. In this work, the phase formation, microstructures, and mechanical properties of a lightweight Ti 22 Sc 22 Zr 22 Nb 17 V 17 multi-phase high-entropy alloy (HEA) fabricated by hot extrusion and annealing are investigated. Experimental observations show that the homogenized sample exhibits a relatively uniform microstructure containing body-centered-cubic (BCC), hexagonal closed-packed (HCP) and a few face-centered cubic (FCC) phases, while the HCP structures display two chemical compositions. The subsequent hot extrusion promotes the formation of hierarchical heterostructure which is composed of elongated coarse dendrites and extremely fine dynamically recrystallized mixtures. The BCC and FCC phases exhibit different morphologies and chemical compositions. Upon annealing, equiaxed BCC and HCP grains, slender BCC dendrites, and two types of FCC particles dominate the microstructures. Compared to reported refractory HEAs, the present alloys exhibit an good balance between elongation and specific strength. Compared with the homogenized sample, the strength of the hot-extruded sample is significantly improved, while annealing after hot extrusion induces larger ductility. The improved mechanical properties are attributed to grain boundary strengthening, precipitation strengthening, and the hierarchical heterostructure. The present studies are expected to open ever-bright prospects for fabricating high-performance lightweight HEAs. [Display omitted] • Multi-phase lightweight high-entropy alloys were prepared by hot extrusion and annealing. • Dynamic crystallization induced by hot extrusion results in the grain refinement and hierarchical structure. • Solid phase separation plays an important role in manipulating the hierarchical structure. • Good strength-ductility balance with high specific strength is achieved by the synergistic effect of multi-phase structures. [ABSTRACT FROM AUTHOR]