Laser Cladding Research Articles

Effects of heat input on microstructure evolution and corrosion resistance of underwater laser cladding high-strength low-alloy steel coating

The effects of heat input on the microstructure evolution and corrosion resistance of the high-strength low-alloy (HSLA) steel coating obtained by wire-feed underwater laser cladding were studied. Optical digital microscope, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscope (TEM), electron back-scattered diffraction (EBSD), electrochemical tests, laser microscope and other characterization methods were used. As the heat input increased, the smoothness of the underwater cladding coating improved, with little changes in elemental distribution and phase composition. However, the content of acicular ferrite increased, while the amounts of lath bainite, lath martensite, and granular bainite decreased. As the heat input increased from 0.4 to 0.55 kJ/mm, the grain size increased from 25.3 to 55.9 μm, the proportion of low-angle grain boundaries rose from 61.3 % to 69.1 %, and the texture intensity of the (110) crystal plane increased from 16.22 to 23.83. Meanwhile, the dislocation density decreased from 4.9 × 1014 to 4.1 × 1014 m−2. These changes enhanced the corrosion resistance of underwater coating. As the heat input increased from 0.4 to 0.55 kJ/mm, the corrosion current density decreased from 2.13 × 10−5 to 3.35 × 10−6 A/cm2, and the corrosion potential increased from −0.823 to −0.529 V. Additionally, the depth-to-width ratio of the corrosion pits decreased from 0.255 to 0.053. This study laid the foundation for high-quality in-situ underwater repairs of ships and submarines made of high-strength steel.

Investigation of the microstructure and tribological properties of laser cladding 5%Ti3SiC2 reinforced Co-based composite coatings under different loads over the wide temperature range

In order to improve the mechanical properties of SUS 304 in practical engineering application, Co-5%Ti3SiC2 coating was successfully prepared on SUS 304 by laser technology. The microstructure of Co-5%Ti3SiC2 coating was characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD) to evaluate the tribological properties in detail. The relevant wear mechanism of the substrate and Co-5%Ti3SiC2 coating under different loads (2, 5 and 8 N) in isothermal tribological experiments (25 and 600 °C) were systematically explored. The results show that the Co-5%Ti3SiC2 coating is mainly composed of continuous matrix γ-Co solid solution, ceramic Fe2C, Cr7C3 and TiC, and lubricating phase Ti3SiC2. The average micro-hardness of Co-5%Ti3SiC2 coating is 358.61 HV0.5, which is significantly higher than that of SUS 304 (239.32 HV0.5). In all isothermal tribological experiments, the wear rate of Co-5%Ti3SiC2 coating decreases with the increase of load, and its coefficient of friction (COF) also decreases with the increase of load.

Influence of Heat Treatment on Microstructure and Mechanical Properties of Laser Cladding Coatings

This study investigates the influence of various heat treatment processes on the microstructure and properties of laser cladding Fe314 coatings. The microstructure, phases, and impact fracture morphology of the cladding layer were observed using X-ray diffraction and scanning electron microscopy, among other methods. The hardness and impact performance of the cladding layer were also tested. The results indicated that there was compositional segregation and non-equilibrium microstructure in the untreated cladding layer, with an average microhardness of 368.67 HV and an impact toughness of 27 J, exhibiting quasi-cleavage fracture. The stress-relief annealing treatment resulted in a uniform distribution of M23C6 carbides inside the cladding layer. The pinning effect generated by M23C6 reduced the microhardness by 16.26% and increased the impact toughness to 54 J. The impact fracture surface exhibited ductile fracture. After secondary normalizing and annealing, the microstructure of the cladding layer transformed into a fine single-phase austenite structure, and fine M7C3 carbides precipitated at the grain boundaries. Under the effects of fine grain strengthening and dispersion strengthening, the microhardness of the cladding layer decreased by 38.14%, and the average impact absorbed energy of the specimen was 64 J, showing complete ductile fracture.

Effect of laser remelting on microstructure evolution and high-temperature fretting wear resistance in a laser-cladding self-lubricating composite coating on titanium alloy substrate

TC21 titanium alloy possesses the advantage including high strength, low density, and great resistance to damage. Combining it with surface modification technology, it is expected to improve the performance of aviation structural components. This work applied laser remelting technology to realize surface modification, and the hardness and fretting wear properties of the coating were investigated. This research has found that laser remelting technology can effectively refine grain size and improve the performance of coatings. By exploring different laser remelting powers (600 W, 900 W, 1200 W) and the different diameters of laser beam (3 mm, 6 mm), the optimal laser process was obtained with laser power and spot diameter of 600 W and 6 mm, respectively. The average grain size is 2.1 μm. The laser remelting coating has an average microhardness about 980 HV0.2, and it is 2.5 times and 1.3 times higher than the substrate and laser cladding hardness, respectively. A minimum coefficient of friction (COF) about 0.5 was obtained by the laser remelting coating, and the wear rate reaches the lowest of 1.87 × 10−6 mm3/(N·m) at fretting temperature with 500 °C. The abrasive wear and adhesive wear were the main wear mechanisms, and accompanied by oxidative wear. This study provides important reference for improving the performance of high-strength titanium alloy to obtain low defect, high-performance coatings with stable quality.

Investigation of corrosion resistance offered by the Fe-based clad layer under salt spray and electrochemical workstations

The present work aims to evaluate the electrochemical characteristics of the Fe–based alloy coating formed on the 27SiMn steel substrate under neutral salt spray and 3.5 wt% NaCl environments. By adopting the high-speed laser cladding technique, the Fe-based clad layer was fabricated to perform microstructural and electrochemical characterizations. The microstructure and phase of the coating were analyzed using a scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD), and its corrosion performance was also discussed using the salt spray corrosion chamber and the electrochemical workstation. The results show that the microstructure of the coating surface contains equiaxed crystals and long dendritic crystals which arise due to the higher solidification rate after the cladding process. The Fe–based coating was rich in FeCr phase throughout its microstructure without the formation of the intermetallic compounds. Compared to the substrate, the corroded surface of the coating tends to be compact containing a few corrosion pits after different corrosion times, which is attributed to the formation of Cr oxide on it. The electrochemical tests on the potentiodynamic polarization curve (PPC) and electrochemical impedance spectrum (EIS) indicate that the corrosion resistance of the coating is superior to the substrate, presenting a higher corrosion potential (−0.298 V), lower passive current density (1.36 × 10−6 A•cm2), and higher charge transfer resistance (8.23 × 106 Ω·cm2). Additionally, the corrosion mechanism of coating in salt spray and electrochemical tests is the local pitting corrosion due to the autocatalytic effect on the localized region, which facilitates Cl− ions penetrating the coating and leads to the dissolution of Fe and Cr oxides.

Study on fabrication of multi-phase reinforcement coatings on Ti6Al4V by laser cladding for enhanced tribological performance

In order to improve the wear resistance, the multi-phase reinforcements coating with high hardness were fabricated on the surface of Ti6Al4V by laser cladding. In this study, Cr3C2 and Ti6Al4V powders, along with continuous fiber laser cladding in a protective gas of N2 atmosphere, were used to prepare a stepwise-solidifying-point multiphase composite coating (TiC, TiN, and CrN) on the surface of Ti6Al4V. The results showed that the crack-free coating with a coating depth of 1.24 mm and a maximum hardness of 1155.52 HV can be prepared on laser power of 900 W. As the laser power increases from 900 W to 1400 W, the combined effect of the soft α-Ti phase and the in-situ synthesized hard TiN phase on hardness results in a decrease in the maximum surface hardness at 1400 `W. And the surface hardness of Ti6Al4V after laser cladding increased by 2.80–2.68 times, and the wear rate decreased by 0.74–0.86 times. Due to the soft phase α-Ti and in-situ synthesized TiC-TiN secondary dendrites serve as the hard phase, which also serve as the supporting skeleton of the oxide film, and the coatings is enriched with TiO2 oxide film. Additionally, the wear mechanisms of Ti6Al4V include abrasive wear, adhesive wear, and oxidation wear. In contrast, the coatings primarily exhibit abrasive wear and oxidation wear.

Microstructure, Hardness and High-Temperature Corrosion Behaviors in Sulfur-Containing Environment of Laser Cladding Y2O3/IN625 Composite Coating.

Water-cooled wall tubes are susceptible to high-temperature corrosion during service. Applying high-performance coatings via laser cladding on the tube surfaces can significantly enhance corrosion resistance and extend the service life of the tubes, providing substantial economic advantages. This paper prepared Y2O3/IN625 composite coating by means of high-speed laser cladding. Furthermore, the effects of Y2O3 addition on the microstructure evolution, hardness, as well as the high-temperature corrosion behaviors have been systematically investigated. The results show that Y2O3 addition can effectively refine the microstructure of the Inconel 625 coating, but the phase composition has little change. The coating's hardness can also be improved by about 7.7%, reaching about 300 HV. Compared to Inconel 625 coating, the Y2O3-added composited coating shows superior high-temperature corrosion resistance, with the corrosion mass gain decreased by about 36.6%. The denser and tightly bonded Cr-rich oxides layer can be formed adjacent to the coating surface, which plays a predominant role in improving the coating corrosion resistance.

Laser Cladding of a Ti–Zr–Mo–Ta–Nb–B Composite Coating on Ti60 Alloy to Improve Wear Resistance

To improve the wear resistance of the Ti60 alloy, laser cladding was used to obtain a composite coating containing a high-entropy (Ti0.2Zr0.2Mo0.2Ta0.2Nb0.2)B2 boride phase, with Ti, Zr, Mo, Ta, Nb, and B powders as the raw materials. The microstructure and wear characteristics of the coating were studied using XRD, SEM, EDS, and the pin-on-disc friction wear technique. The results show that the coating mainly consists of six phases: (Ti0.2Zr0.2Mo0.2Ta0.2Nb0.2)B2, ZrB2, TiB, TiZr, Ti1.83 Zr0.17, and Ti0.67Zr0.67Nb0.67. The average microhardness of the coating was 1062.9 HV0.1 due to the occurrence of the high-entropy, high-hardness (Ti0.2Zr0.2Mo0.2Ta0.2Nb0.2)B2 boride phase, which was about 2.9 times that of the Ti60 alloy substrate. The coating significantly improved the wear resistance of the Ti60 alloy substrate, and the mass wear rate was about 1/11 that of the Ti60 alloy substrate. The main types of wear affecting the coating were abrasive, adhesive, and oxidation wear, while the main wear affecting the Ti60 alloy matrix was abrasive wear, accompanied by a small amount of adhesive and oxidation wear.

Numerical simulation of temperature field and stress field of laser cladding Stellite6

To comprehensively investigate the evolution of the stress field, a three-dimensional thermodynamic model of laser cladding was developed in this paper. By analyzing the physical process and constructing a mathematical model, the temperature transfer and stress distribution were calculated. The simulation examined the evolution and distribution of stress at various scanning speeds, discussing the interplay between the temperature field and the stress field during rapid heating and cooling. Residual stress was measured through X-ray diffraction in experiments, and the crack distribution within the cladding layer was observed. The findings indicated that the stress values calculated from the simulation model aligned well with the experimental results. By combining experimental data, we conducted a qualitative analysis of the distribution of residual stresses and the trends of crack initiation, leading to the proposal of an optimized processing scheme that significantly enhances the quality and reliability of the cladding layer.

Ultrasonic-Enhanced Laser Cladding: Improving Microstructure and Performance Through Synergistic Processing Techniques

Ultrasonic-Enhanced Laser Cladding: Improving Microstructure and Performance Through Synergistic Processing Techniques

Investigation on the interface microstructure and phase composition of laser cladding pure copper coating

Laser cladding is an efficient and clean method that can prepare a corrosion-resistant pure copper coating on the nuclear fuel container surface to ensure service safety. In this study, the single-layer and double-layer pure copper coatings were prepared on 20# steel tubes by laser cladding. The microstructure, elements distribution, phase composition, and interface structure, as well as strain distribution, were characterized by Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), and transmission kikuchi diffraction (TKD). The results show that the kernel average misorientation (KAM) and geometry necessary dislocation (GND) density at the coating/substrate interface in the double-layer Cu coating decrease compared to the single-layer Cu coating. Under the thermal action during laser cladding of double-layer coating, the phase composition in the substrate transforms completely from austenite, FeO, and ferrite to the entire ferrite. The Cu/Fe interface maintains certain orientation relationships, namely the Kurdjumov-Sachs (KS) and the Nishiyama-Wassermann (NW) relationships, with a mismatch of only 3.01 % for the coherent interface. Thus, the lattice distortion at the interface reduces, slightly alleviating the strain concentration.

Investigation on Microstucutres and properties of ion nitriding layer of Al0.5CoCrFeNiTi0.25 HEAs cladding coating

To investigate the effect of ion nitriding on the microstructures and properties of high entropy alloy coatings, the Al0.5CoCrFeNiTi0.25 high entropy alloy coating was fabricated via laser cladding and subsequently subjected to ion nitriding treatment. A comparative analysis were conducted to investigate the phase compositions, microstructures and properties of cladding coatings and ion nitriding layer. Furthermore the formation mechanism of the nitriding layer was studied. XRD results revealed that Al0.5CoCrFeNiTi0.25 HEA coatings consisted of duplex FCC and BCC phases, whereas the nitriding layer was composed of high-nitrogen FCC solid solutions and nitrides such as AlN, CrN, Fe4N and TiN. Following ion nitriding, the surface morphology of nitriding layer presented “cauliflower-like” nitride particles, which became denser with the extended nitriding time. Notably, the microhardness of nitriding layer was approximately four times that of HEA coating, and the wear resistance and the corrosion resistance of cladding coating were improved significantly after ion nitriding. During ion nitriding process, N atoms reacted with the alloying elements to form nitrides, which preferentially deposited at grain boundaries and BCC phases and grew horizontally. As the deposition layer spread across the entire surface, the nitriding mechanism shifted from reaction -controlled to diffusion-controlled, with N atoms diffusing inward to form a diffusion layer with high nitrogen solid solutions. With the prolong of nitriding time from 1h to 12h, the thickness of the diffusion layer increased from 11.77 μm to 96.07 μm.

Study on the Influence of Laser Power on the Heat–Flow Multi-Field Coupling of Laser Cladding Incoloy 926 on Stainless Steel Surface

In order to explore the influence of laser power on the evolution of molten pool and convective heat transfer of laser cladding Incoloy 926 on stainless steel surface, a three-dimensional thermal fluid multi-field coupled laser cladding numerical model was established in this paper. The variation of latent heat during solid-liquid phase transformation was treated by apparent heat capacity method. The change in the gas–liquid interface was tracked using the mesh growth method in real time. The instantaneous evolution of temperature field and velocity flow field of laser cladding Incoloy 926 on a stainless steel surface under different laser power was discussed. The solidification characteristic parameters of the cladding layer were calculated based on the temperature-time variation curves at different nodes. The mechanism of the impact of laser power on the microstructure of the cladding layer was revealed. The experiment of laser cladding Incoloy 926 on 316L surface was carried out under different laser power. Combined with the numerical simulation results, the effects of laser power on the geometrical morphology, microstructure and element distribution of the cladding layer were compared and analyzed. The results show that with the increase in laser power, the peak temperature and flow velocity of the molten pool surface both increase significantly. The thermal influence of the molten pool center on the edge is enhanced. The temperature gradient, solidification rate, and cooling rate increased gradually. The microstructure parameters (G/R) are relatively small when the laser power is 1000 W. In the experimental range, the dilution rate and wetting angle of the cladding layer both increase with the increase in laser power. When the laser power is 1000 W, the alloying elements of the cladding layer are more evenly distributed and the microstructure is finer. The experimental results are in good agreement with the simulation results.

Microstructure evolution and high-temperature erosion behaviors of laser cladded AlxCoCrFeNi2.1 HEA coatings

High entropy alloys (HEAs) are anticipated to be candidates for high-temperature applications. In this work, high-speed laser cladding has prepared AlxCoCrFeNi2.1 (1≤x≤1.4) HEA coatings with high Al content. The effects of Al content on the microstructure, microhardness, and high-temperature erosion behaviors have been systematically investigated. With the increase of Al content, the coating’s microstructure transforms from the dual-phase structure of FCC and BCC to a single-phase BCC structure. Correspondingly, the microhardness of HEA coating gradually increases at room temperature due to the increment of BCC proportion. The Al1.4 HEA coating, consisting of a single BCC phase, exhibits the highest resistance to solid-particle erosion at 600℃, while Al1.0 coating with FCC and BCC dual-phase structure takes the second place. Ploughing, fracture, and spalling occurred during the high-temperature erosion process of AlxCoCrFeNi2.1 HEA coatings. The synergistic interaction between the FCC and BCC phases in dual-phase coatings primarily influences erosion behaviors. However, oxidation resistance is critical to erosion resistance for single-phase BCC coatings.

Effects of Scanning Speed on the Microstructure and Wear Properties of Rockit 606 Coating Layer by Disk Laser Cladding.

Improving the wear resistance and corrosion resistance of 60Si2Mn steel is an important issue in agricultural machinery. A Rockit 606 coating layer may exhibit excellent performance in wear resistance and corrosion resistance. However, there are very a few public reports and articles involving the topic of a Rockit 606 laser cladding layer on a steel 60Si2Mn surface. It is of great importance to research Rockit 606 laser cladding layers. This work focuses on studying the microstructure and properties of Rockit 606 coating layers with different scanning speeds by disk laser cladding. Firstly, the laser cladding platform was designed and set up. Secondly, the laser cladding parameters were designed, and then the laser cladding experiment was conducted, and the Rockit 606 coating layers were obtained. And finally, the microstructure, phase distribution, corrosion resistance, surface hardness, and wear resistance of the coating layers were measured and analyzed. A scanning electron microscope (SEM), X-ray diffractometer (XRD), electrochemical workstation, and microhardness tester were used in this work. It was found that the microstructure Rockit 606 alloy coating consists of γ-Fe, V8C7, and Cr7C3. The microhardness of the Rockit 606 alloy coatings decreased with an increase in the scanning speed. When the scanning speed was 4 mm/s, the highest microhardness value reached 867.2 HV, which is about three times of that of the substrate. The average coefficients of friction (COFs) of the coatings decreased with an increase in the scanning speed, which led to the corresponding decrease of the wear rate. When the scanning speed was 4 mm/s, the wear behavior of the coating was mainly oxidative wear and a small amount of adhesive wear. The self-corrosion current density of the coatings prepared by laser cladding in a 3.5 wt.% NaCl solution is one order of magnitude lower than that of the substrate, indicating that the coatings have better corrosion resistance properties.

Thermal fatigue mechanisms in laser cladding at varying elevation angles for metallurgical bearing seats

Thermal fatigue mechanisms in laser cladding at varying elevation angles for metallurgical bearing seats

Research on rapid prediction method of laser cladding deposited layer state based on molten pool texture sequence

A texture sequence feature combining texture statistical characteristics with time series is proposed for rapid prediction of the state of laser cladding deposited layer. Texture features in the molten pool images are extracted using high-order dense texture descriptor operators and transformed into probability sequences with the aid of multi-cell histograms. Texture features are screened based on the types of points of interest to improve the sequence, enhancing the prediction accuracy and speed for deposited layer. For different types of points of interest, the optimal texture sequence obtained achieves an improvement of more than 6% in prediction accuracy for deposited layer state compared to the full-texture sequence. The proposed texture sequence features, when compared with molten pool image features, exhibit an average improvement in prediction speed of more than 17 times across different deep learning models. Overall, the results indicate that this method significantly improves prediction speed while maintaining accuracy, satisfying the requirements of high-speed monitoring in laser cladding.

Substantial enhancement of AlCoCrFeNiTiWC high-entropy alloy coating performance under water cooling and pulsed laser

AlCoCrFeNiTiWC high-entropy alloy (HEA) coatings were prepared using laser cladding technology with continuous laser and air cooling, as well as pulsed laser with water cooling. The phase structures of the coatings were BCC, (Ti,W)C, and μ phase. The carbides and μ phase in the pulsed laser with water-cooled coating were refined, and the proportion of the μ phase decreased. The wear resistance of the pulsed laser with water-cooled coating significantly increased, which can be attributed to the reduction in the proportion of μ phase, the refinement of carbides, and the formation of a wear lubrication layer. The pulsed laser with water cooling enhanced the thickness and uniformity of the passivation film on the coating surface, thereby improving corrosion resistance.

Research Progress and Current Status of Gas-Solid Two-Phase Flow Technology in the Direction of Laser Cladding.

In the process of laser cladding, there are usually problems such as powder plugging and uneven delivery, which affect the quality of the final cladding layer. Therefore, powder convergence characteristics in laser cladding need to be further improved. Gas-solid two-phase flow technology has been widely used in the study of powder flow characteristics because it can precisely regulate the interaction between carrier air and powder flow. In this paper, we systematically review the current status of gas-solid two-phase flow in the field of laser cladding powder, deeply analyze the latest optimization progress of laser cladding nozzle design, and comprehensively explain the key progress of gas-solid two-phase flow technology in improving the uniformity and efficiency of powder field distribution. At the end of this paper, the research results are summarized and a series of prospective prospects are proposed, aiming to provide a valuable reference framework and directional guidance for the subsequent related research.

Effect of Ti and Mo content changes on microstructure and properties of laser cladding FeCoCrNiMn high entropy alloy coatings

The HEA coatings of FeCoCrNiMnTixMo1.5-x(x = 0.25, 0.5, 0.75, 1 and 1.25) were prepared by laser cladding. X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and scanning electron microscopy (SEM) were used to characterize the phase and crystal structure. The mechanical properties were tested. The results show that Ti is solidly dissolved in the FCC phase for solid solution strengthening. Mo is precipitated as the second phase σ phase for second phase dispersion strengthening. As x increases, the coating becomes the FCC+σ phase, and the σ phase disappears at x = 1.25. The microhardness and wear resistance of the coating are greatly improved by solution strengthening and second phase precipitation strengthening. The microhardness is up to 3.18 times of the substrate, and the wear resistance is up to 10.9 times of the substrate. Corrosion resistance of all coatings is better than that of 45# steel. With the increase of x, the corrosion resistance of the coating increases first and then decreases. When x = 1, the corrosion resistance of the coating is the best.