Search Results (9)

In response to the performance requirements of ship conductive rings in the coupled environment of high salt spray, high humidity, and mechanical wear in the ocean, a Cu-TiC composite coating was prepared on the surface of 7075 aluminum alloy by using the high-speed laser cladding (HLC) technology. The influence laws of the scanning speed (86.4–149.7 mm/s) on the microstructure, tribological properties, and corrosion resistance of the coating were explored. The results show that the scanning speed significantly changes the phase composition and grain morphology of the coating by regulating the thermodynamic behavior of the molten pool. At a low scanning speed (86.4 mm/s), the CuAl₂ phase is dominant, and the grains are mainly columnar crystals. As the scanning speed increases to 149.7 mm/s, the accelerated cooling rate promotes an increase in the proportion of Cu₂Al₃ phase, refines the grains to a coexisting structure of equiaxed crystals and cellular crystals, and improves the uniformity of TiC particle distribution. Tribological property analysis shows that the high scanning speed (149.7 mm/s) coating has a 17.9% lower wear rate than the substrate due to grain refinement and TiC interface strengthening. The wear mechanism is mainly abrasive wear and adhesive wear, accompanied by slight oxidative wear. Electrochemical tests show that the corrosion current density of the high-speed cladding coating is as low as 7.36 × 10⁻⁷ A·cm⁻², and the polarization resistance reaches 23,813 Ω·cm². The improvement in corrosion resistance is attributed to the formation of a dense passivation film and the blocking of the Cl diffusion path. The coating with a scanning speed of 149.7 mm/s exhibits optimal wear-resistant and corrosion-resistant synergistic performance and is suitable for the surface strengthening of conductive rings in extreme marine environments. This research provides theoretical support for the process performance regulation and engineering application of copper-based composite coatings. Full article

Zr-4 alloy tubes, as the primary cladding material in nuclear reactor cores, face the critical challenge of oxidative attack in 1200 °C steam environments. To address this issue, high-temperature oxidation-resistant coatings fabricated via extreme high-speed laser cladding (EHLA) present a promising mitigation strategy. In this study, Y₂O₃-modified (0.0–5.0 wt.%) Cr/FeCrAl composite coatings were designed and fabricated on Zr-4 substrates using the EHLA process, followed by systematic investigation of Y doping effects on coating microstructures and steam oxidation resistance (1200 °C, H₂O atmosphere). Experimental results demonstrate that Y₂O₃ doping remarkably enhanced the oxidation resistance, with optimal performance achieved at 2.0 wt.% Y₂O₃ (31% oxidation mass gain compared to the substrate after 120-min exposure). Microstructural analysis reveals that the dense grain boundary network facilitates rapid surface diffusion of Al, promoting continuous Al₂O₃ protective film formation. Additionally, Y segregation at grain boundaries suppressed outward diffusion of Cr³⁺ cations, effectively inhibiting void formation at the oxide-coating interface and improving interfacial stability. The developed rare-earth-oxide-doped composite coating via extreme high-speed laser cladding process shows promising applications in surface-strengthening engineering for nuclear reactor Zr-4 alloy cladding tubes, providing both theoretical insights and technical references for the design of high-temperature oxidation-resistant coatings in nuclear industry. Full article

AlCoCrFeNi HEA powders were cladded onto AISI 1045 steel using EHLA and CLA, respectively. The phase composition, microstructure, micro/nanohardness, and corrosion resistance of the two coatings were compared and analyzed. The results show that the phase structure of AlCoCrFeNi HEA coatings prepared by EHLA and CLA was that of a BCC/B2 phase solid solution. From the bottom to the top, the EHLA-derived AlCoCrFeNi HEA coating experienced evolution in the microstructure of plane crystal, dendrite, and equiaxed crystal. The micro/nanohardness of EHLA-derived coating (~507 HV_0.2, 6.716 GPa) is higher than that of CLA-derived coating (~429 HV_0.2, 5.778 GPa). The electrochemical test results show that the E_corr of CLA is −0.527 V and the I_corr of CLA is 1.272 × 10⁻⁷ A/cm², while the E_corr of EHLA is −0.454 V and the I_corr of EHLA is 1.588 × 10⁻⁸ A/cm², which means that the corrosion resistance of EHLA is better. Full article

As a novel type of metal material emerging in recent years, high-entropy alloy boasts properties such as a simplified microstructure, high strength, high hardness and wear resistance. High-entropy alloys can use laser cladding to produce coatings that exhibit excellent metallurgical bonding with the substrate, thereby significantly improvement of the wear resistance of the material surface. In this paper, the research progress on improving the high-temperature wear resistance of high entropy alloy coatings (LC-HEACs) was mainly analyzed based on the effect of some added alloying elements and the presence of hard ceramic phases. Building on this foundation, the study primarily examines the impact of adding elements such as aluminum, titanium, copper, silicon, and molybdenum, along with hard ceramic particles like TiC, WC, and NbC, on the phase structure of coatings, high-temperature mechanisms, and the synergistic interactions between these elements. Additionally, it explores the potential of promising lubricating particles and introduces an innovative, highly efficient additive manufacturing technology known as extreme high-speed laser metal deposition (EHLMD). Finally, this paper summarizes the main difficulties involved in increasing the high-temperature wear resistance of LC-HEACs and some problems worthy of attention in the future development. Full article

Laser cladding is an effective surface strengthening method widely used in the surface treatment of extreme operating components such as gas turbines, aviation engines, and nuclear facilities. However, traditional cladding layers struggle to meet the diverse application needs of extreme working conditions due to their single cladding material and poor forming quality. Therefore, this article selected the new-type high-entropy alloy as the coating material and optimized its laser cladding process parameters in order to obtain an AlCrFeNiW_0.2 high-entropy alloy coating with an excellent forming quality. It was found that as the laser power increased from 300 to 1800 W, the AlCrFeNiW_0.2 high-entropy alloy coating transitioned from the incomplete or near-melted state to the fully and over-melted state gradually, while the coating showed the opposite trend of change as the laser scanning speed increased from 0.002 to 0.008 m/s. And when the laser power was 1000 W, the scanning speed was 0.005 m/s, and the spot diameter was 0.003 m, the AlCrFeNiW_0.2 high-entropy alloy coating with a low dilution rate (9.95%) had no defects such as pores and cracks, and achieved good metallurgical bonding with Q235 steel substrate, demonstrating excellent forming quality. These could provide valuable theoretical and technical guidance for optimizing the laser cladding process and forming quality of new-type high-entropy alloy coatings. Full article

Laser material deposition (LMD) is a widely used coating process in industry. However, to increase its economic appeal, higher process speeds are required. The solution to this challenge is an innovative modification known as extreme high-speed laser material deposition (EHLA). EHLA allows for an impressive increase in process speed from 2 m/min for conventional LMD to 500 m/min. With the ability to adjust process parameters, EHLA can generate tailor-made surface properties, expanding its potential application beyond current industrial uses. In this novel study, we explore the effects of relative positioning between tools (laser beam and powder–gas jet) and substrate on the surface properties of EHLA coatings. By laterally and axially offsetting the tools, the proportional energy coupling of the laser radiation into the powder–gas jet and substrate can be modified. Altering the position of the powder–gas jet can also affect the weld pool flow or number of particle attachments, thereby affecting surface properties. This approach allows for the adjustment of surface roughness over a wide range—from smooth, quasi-laser-polished surfaces to rough surfaces covered with particle adhesions. Full article

With the aim to improve cladding coating quality and prevent cracking, this paper established an extreme high-speed laser cladding thermo-mechanical coupling simulation model to study the evolution of the temperature field and the residual stress distribution. Process parameters that impacted the macroscopic morphology of single-pass coatings were investigated. Numerical calculations and temperature field simulations were performed based on the process parameter data to validate the effects of the temperature gradient and cooling rate on the coating structure and the residual stress distribution. The results showed that a good coating quality could be achieved using a laser power of 2400 W, a cladding speed of 20 m/min, and a powder feeding rate of 20.32 g/min. The coatings’ cross-sectional morphology corresponded well with the temperature distribution predicted by the numerical modeling of the melt pool. The microstructure of the molten coatings was affected by the temperature gradient and the cooling rate, which varied greatly from the bottom to the middle to the top. Maximum residual stress appeared between the bonding region of the coatings and the substrate, and the coatings themselves had significant residual stress in the form of tensile strains, that were mostly distributed in the direction of the laser cladding. Full article

This work aims to develop a novel method for on-line monitoring of coating quality during the Extreme High-speed Laser Cladding (EHLA) process. JG-11 coating was prepared by EHLA, and microstructure, microhardness, corrosion performance, and scratch resistance were investigated. To analyze the influences of fluctuations in processing parameters on coating quality, a single-factor experiment scheme was designed and an on-line monitoring system based on laser triangulation was built. Furthermore, a new forming method for the surface profile of EHLA coating was proposed, and a new comprehensive evaluation index of surface morphology was accordingly designed. Benefitting from the extremely high cooling rate, EHLA JG-11 coating had fine grains, high hardness, and better corrosion resistance and scratch resistance than those of Electroplating Hard Chromium (EHC). The results revealed that the surface morphologies presented different characteristics due to the fluctuations of process parameters, such as high surface flatness, deep pits, small peaks, poor directionality, etc. The comprehensive evaluation index composed of S_a, S_sk, and S_tr could effectively characterize the surface morphology of EHLA coating, which proved that the monitoring system and evaluation method could realize on-line monitoring of the process parameters during the EHLA process. Full article

In order to improve material service life under a fatigue and corrosion coupling environment, a high-velocity oxygen fuel (HVOF) Cr₃C₂–NiCr coating with a bonding layer was prepared. The objective was to obtain the optimum bonding layer for the HVOF Cr₃C₂–NiCr coating, which included a laser cladding (LC) Ni625 layer, extreme high-speed laser material deposition (EHLA) Ni625 layer and HVOF NiCr layer. Fatigue properties of the samples with various bonding layers were investigated by means of a four-point bending fatigue test. Electrochemical impedance spectroscopy (EIS) and the salt spray test were executed after the bending fatigue test to simulate the interactive effect of fatigue and corrosion atmosphere. Failure surfaces were characterized by scanning electron microscopy (SEM) and an energy-dispersive spectrometer (EDS) to indicate the details of corrosion products. Corrosive behaviors of samples were adequately demonstrated according to the results, which included the curves of potentiostatic polarization, impedance magnitude and phase degree, and corrosion products. The result showed that the cycles of perforative cracking for the sample with the EHLA Ni625 bonding layer was almost three times than that of the sample with the HVOF NiCr layer. The magnitude of EIS reduced from ~10⁵ to ~10³ for the sample after BFT. Eventually, the main improvement mechanism of the HVOF Cr₃C₂–NiCr coating with the EHLA Ni625 bonding layer was attributed to the grain refinement of the bonding layer and performed a good level of metallurgical bonding with the substrate. Full article