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Ultrasonic impact technology was applied to improve the property of laser cladded CoCrFeNiMo x (x = 0, 0.25, 0.5, 0.75) high entropy alloy coatings on the surface of low-carbon steel. The phase structures and the microstructural characteristics were studied in detail through X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The microhardness distributions, wear resistance, and corrosion resistance of the samples are illustrated using a microhardness tester, a micro-friction and wear tester, and an electrochemical test system. Single FCC phase solid solution was identified to be the main phase structure, with the interdendritic σ phase precipitating with the increasing Mo content. Although ultrasonic impact treatment did not change the phase composition of the high-entropy alloy (HEA) cladding coatings, evident plastic deformation and broken σ phase appeared near the surface of the impacted layers. Through the combined effects of dislocation, fine-grain, and dispersion strengthening, the microhardness of the CoCrFeNiMo x coatings was improved after ultrasonic impact treatment. In addition, ultrasonic impact treatment decreased the surface roughness and increased the wear resistance, and the main wear mechanism of the impacted layers changed from fatigue spalling to abrasive wear. The wear mass of the ultrasonically impacted layers was approximately 92 % of the laser cladded CoCrFeNiMo x coatings. Furthermore, ultrasonic impact treatment improved the corrosion resistance of the HEA coatings. • Microstructure examinations in CoCrFeNiMo x cladding coatings before and after UIT were conducted. • UIT brings out the refined grains, dislocation multiplication and broken σ phase. • UIT enhanced hardness, wear and corrosion resistance of cladding CoCrFeNiMo x coatings. [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]

• Enhanced surface layers were prepared by laser cladding and ion sulfurization. • Structure, phase composition of the composite layer are analyzed. • Hardness and wear resistance of the composite layer are studied. Enhanced surface layers with improved wear-resistance and self-lubrication performances were prepared by means of laser cladding and ion sulfurization processing. The microstructure, element distribution, phase composition, valence states, microhardness and wear resistance of the composited layers were investigated. The results show that Ni-based cladding coating is composed of γ-(Fe, Ni), Cr 2 C 3 , M 23 C 6 , M 3 C type carbides as well as a large number of dislocations and stacking fault in the austenite grains. FeS forms form on the surface of cladding Ni-based coating by ion sulfurizing treatment. Microhardness of Ni-based cladding coating reaches to 600HV 0.1 resulting from the combined effects of ultrafine dendrites and solid solution strengthening and dislocations strengthening, whereas microhardness of the composite layer decrease slightly near the surface (about 470HV 0.1). Due to the existance of FeS film both the wear mass loss and friction coefficient of the composite layers decrease dramaticlly. Moreover, there is a slight scratch on the worn surface of laser cladding-ion sulfurizing composite layer, while worn mechanism of medium carbon steel is serious abrasion along with long and deep grooves and fatigue wear occurs on the surface of Ni-based cladding coating. [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]

In this study, CoCrFeNiSi high entropy alloy (HEA) coating without pores or slag defects was prepared on 304 stainless steel surface by laser cladding. Thermodynamic parameters of CoCrFeNiSi HEA were calculated. Microstructure and phase composition were analyzed by means of scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Comparative studies on hardness, high temperature erosion and oxidation performances were conducted between the CoCrFeNiSi HEA and Stellite-6 Co-based alloy coatings. The results show that laser cladding CoCrFeNiSi HEA coating was composed of single FCC structure. Typical metallurgical bonding between cladding coating and the substrate was formed. Microhardness of CoCrFeNiSi HEA coating reached to approximately 580HV 0.2 , which was higher than that of Co-based alloy coating (485HV 0.2). There was little surface hardness reduction at 500, 600 and 700 °C for CoCrFeNiSi and Co-based alloy coatings. Erosion tests were conducted using quartz sand particles at 20, 500, 600 and 700 °C with an impact angle of 30, 60 and 90°, respectively. The HEA coating showed comparatively lower erosion rates than Co-based alloy coating under all test conditions. The erosion morphologies of both coatings showed that ploughing and micro-cutting were the two primary erosion mechanisms at oblique impact angles, while the erosion mechanism was replaced by the formation of craters and platelets at normal impact angles. A dense and continuous oxidation film could form on HEA coating at 700 °C which may protect the coating from erosion at high temperature to some extent. • CoCrFeNiSi high entropy alloy (HEA) and Stellite-6 Co-based alloy coatings were prepared by laser cladding. • Microstructure, eroded surface morphology and oxidation morphology were observed. • Phase structure, dilution ratio, hardness and high temperature erosion resistance were tested. • High temperature erosion mechanism for CoCrFeNiSi HEA coating was analyzed. [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]

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]

In the present work, Al x CoCrFeNiSi high-entropy alloy coatings with Al content of 0.3 and 1.0 were prepared by laser cladding technology. The microstructure and crystallographic structure evolution, hardness, and strengthening mechanisms were systematically investigated. The coherent interface between the BCC phase and Al–Ni nano-precipitate was confirmed by TEM analysis. Al 0.3 coating exhibited a greater dislocation density and lots of sub-grain structures with grain boundary misorientation of less than 2.5°. The average grain size decreased from 29.94 μm to 20.05 μm with the increase of Al from 0.3 to 1.0. Dislocation strengthening and solid solution strengthening were the major strengthening mechanisms for Al 0.3 coating resulting in a hardness of 692 HV 0.2 , while solid solution strengthening and fine-grain strengthening were the strengthening mechanisms for Al 1.0 coating with a hardness up to 711 HV 0.2. • Al x CoCrFeNiSi (x = 0.3, 1.0) HEAcs were prepared by laser cladding. • The influences of Al content on microstructure, crystallographic structure evolution, and hardness enhanced were investigated. • The strengthening mechanisms of prepared HEAcs were clarified. [ABSTRACT FROM AUTHOR]

Self-lubricating sulfide films have gained increasing interest because of their outstanding properties and promising functions in a wide range of applications. In this study, thin cuprous sulfide (Cu 2 S) films with a 13 μm thickness were produced on Ni55 substrates by low temperature ion sulfurizing to reduce wear and tear to the Ni55 coatings. The Cu 2 S film is composed of polygonal micro-rods that were constructed from successive Cu 2 S nano-sheets with SEM. The antifriction effects of the film were conducted by ball-on-disk dry sliding tests using various loads and speeds under dry friction conditions. The results indicated that the Cu 2 S film showed enhanced antifriction performance by significantly reducing the friction coefficients and the depths of wear. With the help of copper particles formed by cuprous sulfide and oxygen, the Cu 2 S film is able to separate the friction pairs from each other. Also, coating them with the film can significantly reduce the wear and tear to composite coatings caused by the plowing action of debris from the Ni55 coatings. [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]