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• Al 1.5 CoCrFeMnNi high entropy alloy was fabricated by laser cladding. • Ultrasonic impact treatment (UIT) was applied on high entropy alloy coating. • UIT optimized the surface roughness and refined grains. • The surface mechanical properties and corrosion resistance were improved after UIT. [Display omitted] To investigate the effect of plastic deformation with high strain rate on the microstructure and properties of Al 1.5 CoCrFeMnNi high entropy coating, ultrasonic impact treatment (UIT) was applied on the surfaces of the cladding coatings. According to the results, before and after UIT, the phase composition of Al 1.5 CoCrFeMnNi cladding coating did not change, remaining FCC and BCC dual-phase structure. Enormous dislocations were produced and accumulated introducing a cumulative strain by severe plastic deformation, forming a gradient structure. Moreover, the impacted layer with a low surface roughness exhibited the higher hardness, plastic deformation resistance and elastic modulus for the grain refinement and the preferred orientation on (1 1 1) crystal plane. But the surface toughness of the impacted specimen was decreased. There is an evident improvement of corrosion resistance for Al 1.5 CoCrFeMnNi cladding coating after UIT. The application of UIT on high entropy alloy provide a general and efficient method to strengthen the surface of block material. [ABSTRACT FROM AUTHOR]

In this research, ultrasonic impact treatment was introduced on the surfaces of laser cladding Al 0.5 CoCrFeMnNi high entropy alloy coatings. The results showed that obvious solidification boundaries with some lamellar cluster and polygonal precipitations generated inside the cladding coatings. After UIT for one time, a thin impacted layer with obvious plastic deformation was formed. When treated for two times, many floccules formed near the surface while with the increase of impact times evident impact tracks were found on the surface of ultrasonic impact layer due to excessive plastic deformation. In addition, original precipitations located along the solidification boundaries were broken into small ones, and the particles inside the matrix were also cracked. The minimum surface roughness and maximum surface hardness of ultrasonic impact layers can be obtained for one impact time. XRD analysis indicated that Al 0.5 CoCrFeMnNi cladding coating was composed of single FCC phase while application of UIT technology did not change the phase structure of coatings. It also was noted that the weight losses of ultrasonic impact layers were lower than those of cladding coatings whilst the current density was decreased by 69.6%, 87% in the 3.5%NaCl and 1 mol/L NaOH solutions, respectively, indicating better corrosion resistance of impact layers. • Al 0.5 CoCrFeMnNi high entropy alloy coating was prepared successfully by laser cladding technology. • Ultrasonic impact treatment was introduced on the surfaces of cladding coatings to improve surface properties. • Strengthening mechanism and model of high entropy alloy cladding coating by ultrasonic impact treatment was provided. [ABSTRACT FROM AUTHOR]

In the present study, ultrasonic impact treatment was applied to promote the as-cast Al x CoCrFeMnNi (x = 0, 0.5, 1.0 and 1.5) high entropy alloys, and the microstructures, phase composition and surface properties were investigated. The increase in Al mole fraction from 0 to 0.5, 1.0 and 1.5 led to the different phase compositions from single FCC, duplex FCC + BCC to single BCC phase as well as the increased microhardness and reduced corrosion resistance. Ultrasonic impact treatment did not change the phase compositions of Al x CoCrFeMnNi alloys, while the successive network structures were broken and the short rod-like structures formed rather than long strip-like structures in the impacted hardening layer. The microhardness of Al x CoCrFeMnNi alloys (x = 0, 0.5 and 1.0) were improved by 92% (approximately 308.5 HV, 312.5 HV and 450.8 HV, respectively) after ultrasonic impact treatment due to the refine microstructures and precipitation strengthening mechanisms. Owing to the application of ultrasonic impact treatment the surface roughness of Al x CoCrFeMnNi alloys (Ra = 0.54–0.57 μm) decreased. Additionally, the impacted hardening Al x CoCrFeMnNi alloys exhibited higher corrosion resistance than the as-cast alloys resulted from the lower surface roughness. • Structure, phase, hardness and corrosion resistance of Al x CoCrFeMnNi alloys. • Comparative analysis on structures and properties after UIT. • Calculation of phase formation for HEAs and comparison with the as-cast specimens. [ABSTRACT FROM AUTHOR]

High entropy alloy (HEA) as coating material has more economical application value. In this study, CoCrFeNiTi HEA coating without cracks and pores was successfully prepared on 304 stainless steel substrate by laser cladding. The phase structure of the CoCrFeNiTi HEA coating was composed of main phase with an FCC lattice, Fe and Cr rich phase with an SC lattice and CoTi 2 type Laves phase. The microstructure of the prepared coating consisted of bonding zone and cladding zone. It was an obviously metallurgical bonding between the coating and substrate and typical columnar dendrites were generated with growth direction perpendicular to the interface in the bonding zone. The cladding zone showed a typical long strip proeutectic structure and a lamellar eutectic structure. The average microhardness of CoCrFeNiTi HEA coating reached to 568 HV 0.2 , which was approximately 2.5 times higher than that of the substrate (236 HV 0.2). Erosion tests were conducted on both CoCrFeNiTi HEA coatings and the substrates with an erosion angle of 30 and 90°. The results showed that CoCrFeNiTi HEA coating exhibited much lower erosion rates with an erosion angle of 30° (0.68 mg/cm2) and 90° (0.42 mg/cm2). Ploughing and micro-cutting were the two primary erosion mechanisms of material loss for CoCrFeNiTi HEA coating at oblique erosion angles, while the erosion mechanism was replaced by the formation of craters at vertical erosion angles. • CoCrFeNiTi HEA coating was prepared by laser cladding. • Phase compositions, microstructures, hardness and solid particles erosion resistance were analyzed. • The mechanism of erosion for CoCrFeNiTi HEA coating was discussed. [ABSTRACT FROM AUTHOR]

Two kinds of CoCrFeMnNi high entropy alloy (HEA) coatings were prepared by high-speed laser cladding (HS-) and normal laser cladding (N-), respectively. The phase, microstructure, micromechanical properties, and corrosion resistance of both coatings were analyzed. According to the results, both coatings are stable single-phase FCC structures with the dendrites microstructure. However, the dendrites of the HS-CoCrFeMnNi coating are finer. Owing to the low heat input and the quick cooling and heating characteristics of high-speed laser cladding, the width of the heat affected zone and the dilution ratio of the HS-CoCrFeMnNi coating are reduced. In addition, the microhardness of the HS-CoCrFeMnNi coating (∼ 184 HV 0.2) is higher than that of the N-CoCrFeMnNi coating (∼ 160 HV 0.2). The elastic modulus (E r) of the HS-CoCrFeMnNi coating is significantly increased in order to enhance its resistance to plastic deformation. The plastic storage energy Q p of the HS-CoCrFeMnNi coating is higher, revealing the improved crack resistance. The self-corrosion potential E corr of the HS-CoCrFeMnNi coating positively shifted by 0.142 V compared with the N-CoCrFeMnNi coating, and the self-corrosion current density I corr decreased from 6.3 × 10−6 A/cm2 to 2.9 × 10−7 A/cm2 in 3.5% NaCl solution. Therefore, the HS-CoCrFeMnNi coating possesses better corrosion resistance and comprehensive mechanical properties. [Display omitted] • Two CoCrFeMnNi coatings were prepared by high-speed and normal laser cladding. • High-speed laser cladding can refine grains, and decline dilution and heat effect. • Ultra non-equilibrium solidification refined grains and altered pore evolution. • Higher plastic deformation storage energy means a decrease in crack sensitivity. • HS-CoCrFeMnNi coating possesses improved microhardness and corrosion resistance. [ABSTRACT FROM AUTHOR]

The ion sulfurizing technique was carried out on CoCrFeNiSi 0.4 and CoCrFeMoNi high entropy alloys (HEAs), the microstructures and tribological properties of the HEAs before and after sulfurization were tested and analyzed. Results indicated that the CoCrFeNiSi 0.4 and CoCrFeMoNi HEAs were both dominated by FCC solid solution. After sulfurization, the FeS and FeS/MoS 2 multisulfides lubricant films with thickness around 4 μm were successfully fabricated on CoCrFeNiSi 0.4 and CoCrFeMoNi HEAs, respectively. The grains of FeS/MoS 2 multisulfides films were more compact than those of single FeS films. After sulfurization, the friction coefficients of CoCrFeNiSi 0.4 and CoCrFeMoNi HEAs were decreased from 0.6 and 0.47 to 0.152 and 0.12, respectively. Because of the effectively synergistic work of FeS and MoS 2 lubricant phases, the FeS/MoS 2 multisulfides films performed lower stable friction coefficient (0.12) and weight loss (4.25 mg) than single FeS films, which were 0.152 and 5.9 mg, respectively. Unlabelled Image • The HEAs were firstly applied combining the ion sulfurizing technique. • The FeS/MoS 2 multisulfides lubricant films were fabricated on CoCrFeMoNi HEA. • The frictional properties of the HEAs were improved greatly by ion sulfurization. • The differences on frictional properties of FeS and FeS/MoS 2 films were discussed. [ABSTRACT FROM AUTHOR]