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High-speed laser cladding was introduced to prepare a CoCrFeNiMo high-entropy alloy (HEA) coating. The microstructure, composition distribution, micromechanical properties, and corrosion resistance of the CoCrFeNiMo coating were characterized. As a result, the coating exhibited a dual FCC- and BCC-phase structure, and the grain size of the coating prepared through high-speed laser cladding was only 2~5 μm. The upper and lower parts of the coating were composed of equiaxed cellular crystals and slender columnar crystals, respectively. The interdendritic structure was a Mo-rich phase that was distributed in a network-like pattern. The nanoindentation tests revealed that the interdendritic BCC phase had high hardness and an elastic modulus as well as excellent resistance to deformation, while the intradendritic FCC phase possessed superior crack propagation resistance. In addition, the two phases could generate cooperative elastic deformation during the elastic deformation stage. The electrochemical performance of the coating was tested in 3.5 wt% NaCl solution, and the corrosion potential Ecorr and corrosion current density Icorr of the coating were −0.362 V and 3.69 × 10−6 A/cm2, respectively. The high-speed laser cladding CoCrFeNiMo HEA coating had excellent corrosion resistance thanks to the presence of the easily passivating element Mo and grain refinement. [ABSTRACT FROM AUTHOR]

Nickel based composite coatings with La 2 O 3 addition were fabricated on medium carbon steel by laser cladding processing. The microstructure, phase composition, microhardness and corrosion resistance of the laser cladding coatings were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness tester and electrochemical workstation. The results show that the herringbone cracks generated in the deposited Ni-based ceramic coatings and the fracture mechanism exhibits quasi-cleavage fracture, while many tearing ridges and micro plastic deformations are present. A crack-free Ni-based composite ceramic coating is prepared with 0.6 wt% La 2 O 3 addition, and refined dendritic microstructures are formed with higher microhardness (659HV 0.2 ). However, the introduction of La 2 O 3 addition has little effect on the phase composition of the Ni-based ceramic coating, composed of γ-(Fe, Ni) solid solution, CrB, Cr 23 C 6 , Cr 7 C 3 and WC. In addition, the E corr values of two kinds of laser cladding Ni-based coatings are all more positive than that of the as-received medium carbon steel, while the E corr value of Ni-based cladding ceramic coating with 0.6 wt% La 2 O 3 addition is more positive than that of Ni-based coating. Compared with Ni-based cladding coating, addition of 0.6 wt% La 2 O 3 leads to lower corrosion current density, which indicates the improved corrosion resistance. [ABSTRACT FROM AUTHOR]

Laser cladding Nickel–WC–CaF 2 coatings with high hardness were prepared on medium carbon steel assisted by ultrasonic vibration processing. The microstructure, element distribution, phase composition and microhardness as well as wear resistance of the cladding coatings were investigated. It is found that ultrasonic vibration during laser cladding could reduce the degree of WC particle aggregation. The laser cladding Ni–WC–CaF 2 coatings is composed of γ-(Fe, Ni) and WC particles while the cladding coating with ultrasonic vibration consists of γ-(Fe, Ni), Cr 23 C 6 , W 2 C and WC. In addition, the coarse dendrite has been replaced by some fine grain structure at the bonding interface. When the ultrasonic vibration power of 800 W is applied, the average microhardness of cladding coating increase to 1235HV 0.1 resulted from the combined effect of refined grain, dispersion strengthening from hard WC phase and solid solution strengthening. And the wear mass loss and friction coefficient of Ni–WC–CaF 2 coating are lower than the coating without ultrasonic vibration and the coating with the ultrasonic vibration power of 900 W. Especially, the worn mechanism on the surface is uniform ploughing. [ABSTRACT FROM AUTHOR]

Fe-Cr 3C 2 hard coatings with varying Cr 3C 2 content were produced on 35CrMo steel substrates by laser cladding. The experimental results showed that the coatings were uniform, continuous, and free of cracks. High adhesions between all produced coatings and their corresponding substrates were obtained due to the metallurgical interfaces between them. The microstructures of the coatings were mainly composed of austenitic dendrites and M 7C 3. The microhardness gradually increased from the bottom to the top of the coating, and increased with elevation of Cr 3C 2 content. The Fe-Cr 3C 2 coatings improved the sliding wear resistance of the 35CrMo steel substrates obviously, and the dominant wear mechanism was spalling fatigue, with plowed grooves on the worn surfaces. [ABSTRACT FROM AUTHOR]

• 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]

Abstract: Laser surface melting of high chrome steels was achieved by a 5kW continuous wave CO2 laser. The microstructure of the laser surface-melted steels was investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffractometry, and the hardness profiles were determined by a Vickers hardness tester. The corrosion behavior in 3.5% NaCl solution was studied by electrochemical corrosion equipment. The large carbides of high chrome steels are completely dissolved and ultrafine dendrites of austenite with submicroscopic M23C6 carbides precipitation are formed in the melted zone. The austenite in the melted zone has a high tempering stability. The corrosion resistance of the laser surface-melted steels is significantly improved due to the dissolution of carbides and the increase of the alloying elements in the solid solution as well as the large amount of austenite. [Copyright &y& Elsevier]

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]

• Ultrasonic vibration was applied during laser cladding for Ni-60%WC-0.8%La 2 O 3 coating. • As the ultrasonic power 800 W was applied, the hardness and wear resistance were obviously improved. • The heat damage of WC particles is controlled by the dissolution-diffusion mechanism. Ultrasonic vibration was introduced during laser cladding Ni-60%WC-0.8%La 2 O 3 coatings in this study. The microstructure, elemental distribution, and properties of the cladding coatings, as well as the morphology of WC particles were also investigated. Results showed that with WC ceramic particles, the columnar dendrites that formed at the bottom of the cladding coating without ultrasonic vibration were dissolved, crystallized, and aggregated. As ultrasonic vibration was introduced, the dendrites in the cladding coating were disrupted, and the grains were refined. WC particles concentrated at the bottom of the cladding coatings at an ultrasonic power of 600, 700, and 900 W, resulting in obvious degradation in surface hardness and wear resistance. However, when an ultrasonic power of 800 W was applied, improved hardness and wear resistance, which are attributed to the strengthening of precipitated carbides, refined microstructure, and homogenous distribution of WC particles in the cladding coatings, were observed. For laser cladding coatings without ultrasonic vibration, typical characteristics of abrasive and fatigue wear could be found on the wear tracks after a ring-on-disk (ROD) wear test, and flaking pits appeared along the sliding direction. For the composite coatings prepared with different ultrasonic vibration power, typical abrasive wear occurred on the surfaces of the coatings under 600, 700, and 900 W during ROD wear tests, with additional shallow and mild ploughing for that under 800 W. [ABSTRACT FROM AUTHOR]

Two kinds of CoCrFeNi high entropy alloy coatings were prepared by normal laser cladding (N-) and high-speed laser cladding (HS-), respectively. The comparative analyses of crystallographic orientation distribution, microstructure, microhardness, wear resistance and corrosion resistance of both coatings were conducted. The results show that the phase structures of HS-CoCrFeNi and N–CoCrFeNi coatings are single FCC solid solutions. The dendrite size of HS-CoCrFeNi coating is only half of that of N–CoCrFeNi coating. The microhardness of HS-CoCrFeNi coating (380 HV 0.2) is about 2.3 times that of N–CoCrFeNi coating (165 HV 0.2), due to the combined effect of grain refinement, dispersion strengthening and dislocation strengthening. The wear resistance and corrosion resistance of HS-CoCrFeNi coating are better than N–CoCrFeNi coating. With the increase of friction speed, the same wear mechanism of the two coatings is obtained, changing from abrasive wear to adhesive wear and fatigue wear. High-speed laser cladding is a promising technology to promote the development and application of high entropy alloys in the industry. [Display omitted] • Two CoCrFeNi coatings were prepared by high speed and normal speed laser cladding. • Consistent orientation of HS-CoCrFeNi coating ensured the continuity of microstructure. • HS-CoCrFeNi coating possessed better microhardness, wear and corrosion resistance. • High speed laser cladding furthur reduce the dilution ratio of CoCrFeNi HEA coating. [ABSTRACT FROM AUTHOR]

The application of high entropy alloy (HEA) as coating materials has become a research hotspot. The combination of laser cladding technology and ultrasonic impact treatment (UIT) may provide an opportunity for better performance of HEA and it is possible to enhance the application prospect of HEA. To research the effects of UIT on microstructure and properties of laser cladded HEA coating, AlCoCrCuFeNi HEA coating was prepared by means of laser cladding and UIT was applied to strengthen the surface properties of AlCoCrCuFeNi HEA coating. The phase structures of laser cladded AlCoCrCuFeNi HEA coating were composed of FCC and BCC phases. There were no new phases formed in the AlCoCrCuFeNi HEA coating after UIT, while the BCC phase volume fraction was increased. Additionally, a hardening layer with a depth of ~15 μm was formed at the top surface and the average values of grain sizes were refined from 34.4 μm to 18.6 μm. As expected, the hardness of AlCoCrCuFeNi HEA coating with UIT was significantly improved to 715 HV 0.2 benefitted from the nano crystal structure and enhanced plastic deformation and then decreases gradually along the depth to approximately the same hardness value as that of without UIT (530 HV 0.2). More impressively, the impact hardening AlCoCrCuFeNi HEA coating exhibited higher corrosion resistance in 3.5% NaCl solution resulting from the lower surface roughness and fewer microstructure defects. • UIT was applied to promote the surface properties of AlCoCrCuFeNi HEA coating. • Microstructures of AlCoCrCuFeNi HEA coatings with and without UIT were analyzed. • The effects of UIT on properties of AlCoCrCuFeNi HEA coating were studied. [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]