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In this study, CoCrFeNiAl x (x = 0.1, 0.5, 1) high-entropy alloys (HEAs) are prepared using vacuum arc melting. In order to improve the surface properties of CoCrFeNiAl x HEAs, their microstructure is manipulated by laser surface remelting (LSM). The microstructure, the mechanical properties, and the corrosion resistance of the HEAs before and after LSM are studied systematically. The microstructural analysis reveals that the LSM-samples contained either a single FCC phase (CoCrFeNiAl 0.1 and CoCrFeNiAl 0.5) or a mixture of BCC + B2 phases (CoCrFeNiAl 1) with refined grains. Moreover, BCC precipitates and a spherical nano-dispersed phase (B2) are detected in the surface layer of CoCrFeNiAl 0.5 and CoCrFeNiAl 1 , respectively. The mechanical properties of CoCrFeNiAl x alloys are found to be significantly enhanced after LSM, which is mainly ascribed to the generation of the BCC phase, dislocation reinforcement and grain-strengthening as well as precipitation hardening. The electrochemical measurements confirm that all samples (after LSM) have a positive potential and a lower current density in 3.5 wt% NaCl solution compared to the untreated sample. The results indicate that LSM can help homogenize the structure and improve the properties of CoCrFeNiAl x HEAs. [Display omitted] • LSM treatment was conducted on the surface of as-cast CoCrFeNiAlx (x = 0.1,0.5,1) HEAs and the grains of each component were refined obviously. • A 365.2–1200 μm thick remelted layer was formed. • After LSM, abundant dislocation structures appeared on the surface, and spherical nano dispersed B2 phase was found in Al 1. • Surface microhardness, wear and corrosion resistance were improved evidently. [ABSTRACT FROM AUTHOR]

Laser remelting (LR) treatment was used to regulate the microstructure of AlCoCrFeNiTa x high-entropy alloys prepared by vacuum arc melting, and the microstructure and properties of the alloys before and after LR treatment were analyzed. The original AlCoCrFeNiTa x alloys have typical dendritic morphology and the addition of Ta element promoted the formation of a Laves phase, gradually changing the alloys from two phase (BCC + B2) to three phase (BCC + B2 + Laves phase). After LR treatment, the grains were significantly refined, elemental segregation was alleviated, and a dense remelting layer with a thickness of 1200–1600 µm was formed on the surface of the alloy. In addition, the hardness and wear resistance of the alloys were improved with increasing Ta content and LR treatment, mainly caused by the combined effects of solution strengthening, second phase strengthening and fine grain strengthening. At the same time, the corrosion resistance of the alloys before and after LR treatment in 3.5 wt% NaCl solution is significantly improved by a stable Ta 2 O 5 and TaO 2 passivation films and the formation of a dense uniform remelting layer. • Refractory element was added and LR treatment was conducted on the surface of AlCoCrFeNiTax high entropy alloy. • After LR treatment, elemental segregation on the alloy surface is alleviated and the alloy grains are refined. • A remelted layer of about 1200–1600 µm thickness was formed on the alloy surface after LR treatment. • The hardness and wear resistance of the alloys were improved with increasing Ta content and LR treatment. • The corrosion resistance of the alloys in 3.5 wt% NaCl solution is improved by passivation film and remelted layer. [ABSTRACT FROM AUTHOR]

Recently, high-entropy alloys have drawn lots of attention due to their outstanding properties. In this paper, a promising new surface modification technique was acted on CoCrFeNiMo 0.2 high-entropy alloy to improve its mechanical and corrosion properties. CoCrFeNiMo 0.2 high-entropy alloys were synthesized via vacuum arc melting then, their surfaces were processed by high-current pulsed electron beam (HCPEB). Microstructure, microhardness, wear and corrosion resistance were studied systematically by means of X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Before and after HCPEB irradiation, CoCrFeNiMo 0.2 high-entropy alloy had a face-centered cubic (FCC) structure, and the surface of the irradiated samples revealed preferential orientation on the (111) and (200) planes. In addition, a compact and homogenization surface layer formed after irradiation. Also, high-amplitude stress caused high-density dislocations and stacking faults on the surface. After HCPEB irradiation, the properties of the samples were significantly improved, the maximum microhardness (392.9 HV) and lowest wear rate (0.92 × 10−4 mm3·N−1·m−1) was obtained after 35-pulsed irradiation. Furthermore, corrosion resistance was obviously enhanced after 25-pulsed irradiation. [Display omitted] • HCPEB irradiation was conducted on the surface of as-cast CrFeCoNiMo 0.2 high entropy alloy. • A 3-8 μm thick compact remelted layer was formed after irradiation and the equiaxed grains along with σ phase were refined with the increase of the pulses. • Abundant structure defects such as subcrystals, high-density dislocations, dislocation cells, and stacking faults were also formed due to thermal stress induced by irradiation, resulting in intense plastic deformation of the material surface. • Surface microhardness, tribological behavior and corrosion resistance were improved due to grain refinement and compositional homogenization. [ABSTRACT FROM AUTHOR]