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Ultra-high-speed laser cladding (UHSLC) not only offers an efficient solution to the limitations of conventional laser cladding but also aligns with the contemporary objectives of material conservation and efficiency enhancement in metal protective coatings. This study investigates the fabrication of CrFeCoNiMo 0.2 high-entropy alloy (HEA) coatings using UHSLC and traditional laser cladding (TLC) methods. Key aspects such as macroscopic forming quality, element distribution, dilution rate, grain morphology, hardness, and electrochemical corrosion properties of both UHSLC and TLC coatings are thoroughly examined. Notably, UHSLC-produced coatings, with their significantly reduced thickness ranging from 100 to 300 μm, demonstrate an impressively low substrate dilution rate compared to the 2–3 mm thickness of TLC coatings. The rapid solidification inherent in UHSLC leads to smaller grain sizes in the coating, resulting in enhanced hardness. Moreover, the UHSLC coating exhibits superior corrosion resistance, characterized by a lower maintaining-passivity current density in 1 mol/L H 2 SO 4 and a higher self-corrosion potential relative to TLC coatings. This work presents a novel approach, employing high-efficiency and low-cost laser-cladding technology, to minimize dilution in the matrix and improve the coating properties of HEAs. • There are no macroscopic and microscopic defects in HEAs prepared by UHSLC. • Uniform distribution of elements in ultra-thin coating of CrFeCoNiMo 0.2 HEA. • The CrFeCoNiMo 0.2 HEA nanocrystalline coating was synthesized by UHSLC. • Nanocrystalline CrFeCoNiMo 0.2 HEA coating exhibit excellent corrosion resistance. [ABSTRACT FROM AUTHOR]

The microstructural evolution, pitting performance, and passive-film properties of Al x CoCrFeNi high-entropy alloys (HEAs) fabricated via laser melting deposition (LMD) were investigated using material characterization techniques and electrochemical measurements. The substrates of the LMD HEAs transform from a face-centred cubic (FCC) to a body-centred cubic (BCC) structure with increasing Al addition. The BCC-structured B2 and A2 phases precipitate in the HEA substrate when the Al content reaches 10 mol.%. Ternary-phase HEA with Al addition of 10 mol.% exhibits the best corrosion resistance, which is attributed to favourable modifications in the Cr 2 O 3 content and passive-film thickness. • BCC-structured B2 and A2 phases are precipitated in the LMD HEAs with Al content higher than 5 mol. %. • Multi-phased HEAs with Al addition of 10–15 mol. % exhibit better corrosion resistance. • Corrosion resistance of the LMD HEA's is improved by modifying the passive film chemistry and thickness.. • Pitting will initiate at (Al, Ni)-rich B2 phase in multi-phased HEAs when passive film is broken down. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) have many attractive properties, while the thermodynamic mechanism and general behavior of the spinodal decomposition in HEAs remain unknown. In this work, we conduct an experimentally consistent calculation of the spinodal decomposition of HEAs. Against the "high mixing entropy" theory, we show that increasing the number of elements can increase the possibility of spinodal decomposition, and the effects of the temperature, entropy and enthalpy are clarified. The high entropy effect on the widely observed pseudo-binary decomposition is proposed. These results provide a necessary paradigm to understand and further harness the spinodal decomposition in HEAs. [Display omitted] [ABSTRACT FROM AUTHOR]

A novel AlCoCrFeNi 2.1 high-entropy alloy self-lubricating coating was prepared by multilayer graphene (MLG) enhancement. The AlCoCrFeNi 2.1 -MLG (3 wt%) high-entropy alloy self-lubricating coating was prepared on AISI1045 steel using laser cladding by introducing lubricant named MLG. The microstructure, phase structure, wear resistance and corrosion performance of the AlCoCrFeNi 2.1 -MLG coating were studied. It is shown that the microstructure of the AlCoCrFeNi 2.1 -MLG coating has typical dendritic (DR) and interdendritic (ID) structures, with the dendrites consisting of high density M 23 C 6 phase precipitation and FCC phase distributed in the interdendritic region. With the addition of MLG, the average hardness of the AlCoCrFeNi 2.1 coating increases from 306.71 HV to 486.68 HV (an increase of 58.68 %). The average coefficient of friction decreases from 0.59 to 0.48 (a reduction of 22.92 %). The wear rate decreases from 1.678 × 10- 6 mm3·N− 1 m−1 to 0.825 × 10- 6 mm3·N− 1 m− 1 (a reduction of 50.83 %). This is due to the formation of a lubricant film in the AlCoCrFeNi 2.1 -MLG coating. The wear mechanism changes from plastic deformation and abrasive debris wear to slight delamination and spalling of the lubricant film. However, the corrosion performance of the AlCoCrFeNi 2.1 -MLG coating is slightly reduced by the occurrence of micro-electro-coupling corrosion on the corroded surface. The M 23 C 6 phase is used as the anode and the FCC phase is used as the cathode. The subsequent generation of a passivation film prevents the appearance of severe electro-coupling corrosion. The wear resistance of the AlCoCrFeNi 2.1 -MLG coating is substantially improved while taking into account the corrosion performance. This study provides important values for laser cladding of self-lubricating composite coatings of high-entropy alloys. [Display omitted] • Microstructure of coating has a typical dendritic and interdendritic structure. • With the addition of MLG, the FCC phase and M 23 C 6 are formed. • Mechanism of grain refinement and carbide M 23 C 6 generation enhances microhardness. • The lubricant film improves the wear resistance of the coating significantly. • Micro-coupling corrosion occurs on the corroded surface. [ABSTRACT FROM AUTHOR]