Laser Cladding Process Research Articles

Microstructure and performance enhancement of the TiN/Fe-based cladding layer induced by mechanical vibration assisted underwater wet laser cladding

It is challenging to obtain the underwater wet laser cladding layer with excellent properties while maintaining formability. In this paper, the method of using synchronous mechanical vibration assisted in the underwater wet laser cladding process of TiN/Fe-based cladding layer was introduced. The effect of mechanical vibration frequency on the dilution rate, microstructure, corrosion resistance, tribo-corrosion behavior of the cladding layer was studied. The result displayed that with increase of mechanical vibration frequency, the dilution effect of the substrate was obviously weakened and the phase changed from ferrite to ferrite and austenite, and TiN particles were evenly distributed. In addition, the grain size of the cladding layer showed a tendency to decrease first and then increase. When the mechanical vibration frequency was 400 Hz, the grain refinement phenomenon was the most obvious and the average grain size was 8.39 μm. Based on the effect of dispersion strengthening and fine grain strengthening, the microhardness and wear resistance of the cladding layer assisted at 400 Hz were improved, and the wear rate was 1.17 × 10−15m3N−1 m−1. While the cladding layer assisted at 400 Hz exhibited better corrosion resistance by forming a dense passivation film. In addition, the mechanism of mechanical vibration on microstructure evolution and performance enhancement of the cladding layer was also analyzed. This study provided the theoretical support for the formability of the underwater laser wet cladding assisted by mechanical vibration.

A novel approach to the deposition of Co-Mo-Cr-Si coating on Haynes 282 by laser fusion and laser remelting

This paper presents a novel hybrid method of the crack-free fusion of CoMoCrSi, which is a cobalt-based alloy with molybdenum additions with the composition analogous to Tribaloy® T400, on Haynes 282 for parts where extreme wear is problematic with high temperatures and corrosive media, such as industrial turbine applications, commercial jet engines, and rocket engines. To alleviate cracking of the coating during laser surface deposition/coating, previous attempts relied on preheating of the substrate to reduce cracks to alleviate a thermal mismatch between the substrate and molten powder. The primary aim of this work is accomplished by fusing crack free CoMoCrSi layers using a novel hybrid process of combining laser cladding and laser remelting processes. The optimal process conditions of coating crack-free CoMoCrSi on Haynes 282 were determined for both the laser powderbed fusion and remelting processes. Microhardness and chemical compositions of the coating layers produced using optimal process parameters with and without remelting the substrate were compared. The chemical compositions of different phases present in the coating layer were analyzed by Energy Dispersive X-ray Spectroscopy (EDS). The remelting process yielded no dilution at the surface, resulting in the preservation of the original CoMoCrSi coating properties.

Influence of Powder Mass Flow Rates on Wear Resistance and Impact Toughness of Inconel 718 Surface Coatings

Optimum laser cladding processing parameters were obtained based on the study of various powder mass flow rates for the repair of 27SiMn steel parts using Inconel 718 powder. In this study, fusion coating process parameters were set according to the influence of powder mass flow rates on fusion coating properties. The cross-sectional microstructure, X-ray diffraction patterns, micro-hardness distribution, friction, wear properties, impact properties, and fracture morphology of the clad layers were investigated for the various process parameters. The results indicate that the volume fraction for the Ni3Fe phase increases and then decreases as the powder mass flow rate increases. The micro-hardness, friction properties, and impact properties of the samples followed the same trend as those of Ni3Fe. At powder mass flow rates up to 20 g/min, microstructures in the cladding layer tended to be uniform with microstructures with fine grains, and micro-hardness and impact toughness reached maximum values of 328.2 HV0.5 and 45.4 J/cm2, respectively, which show better mechanical properties and wear resistance.

Residual stresses in circular steel tubular columns repaired by laser-cladding additive manufacturing

This paper presents a study that investigates the magnitude and distribution of residual stress (RS) in laser cladding (LC) repaired circular steel tubular columns. The study involves experimental tests and numerical simulation. The familiar blind-hole method is employed in the experimental investigation for two RS measurement tests, while the finite element method is used for numerical thermal-mechanical analysis to obtain the temperature field and RS field. The results indicate the presence of residual tensile stress in the LC sheet and its surrounding area. The RS in the LC sheet area and in the vicinity of the LC sheet-substrate boundary is much greater than that in the substrate area located far away from the LC sheet. Additionally, the RS in the LC sheet along the scanning direction is larger than that perpendicular to the scanning direction. Nevertheless, the RS values in both the LC sheet and substrate are less than their respective yield strength values. The temperature-time cooling curves obtained from the finite element analysis, which simulate the laser cladding process for repairing the circular steel tubular column, are used to develop a theoretical model for predicting the RS in the LC sheet. A simplified RS model is proposed based on the thermal-mechanical theory, utilising the linear-exponential two-stage cooling curve. Comparisons between the experimental results and the theoretical results that are predicted using the proposed simplified RS model show both results to be in good agreement. Therefore, the simplified RS model proposed in this paper is suitable for efficiently and accurately predicting the RS in LC sheet for circular steel tubular columns repaired by LC.

Epitaxial growth of single crystal superalloy by a novel spot-cutting laser cladding method

A spot-cutting laser cladding process was proposed to repair the thin wall single crystal superalloy in this paper. The effects of spot cutting and its gap width on the dimensions and microstructure of cladding layers were studied. The results demonstrate that the cladding layers exhibit directionally epitaxial dendrites throughout the layer, reducing the formation of “stray grains” and significantly decreasing the machining allowance compared to samples without spot cutting. By optimizing the parameters, continuous epitaxial grains were achieved in the cladding layer, reaching a height of 1173 μm. The layer dimensions increased initially with weld height, but then decreased with a flattening morphology as the base metal width increased.

Application of the ABA cladding technique to a wire based laser cladding process

In this study, the application of the ABA cladding strategy in coaxial wire-based cladding processes is investigated. Individual weld seams (A) are first welded on the substrate and additional weld seams (B) are deposited into the intermediate spaces in the second step. Thereby, two different seam geometries are present in the cladding. Unidirectional AAA and ABA claddings are generated using laser hot-wire cladding and analyzed with respect to the quality criteria height, waviness, degree of dilution, and defects. Three different welding parameter sets are used to consider the effect of the contact angle on the applicability of the ABA cladding strategy. When the same process parameters and seam-to-seam offsets are used for the ABA cladding, as for the AAA cladding, the B weld seams are higher than the A weld seams and an uneven ridged cladding surface is present. Two approaches to solving this problem are considered. The cross-sectional area of the B weld seams is reduced by adjusting the welding speeds or an increase in the seam-to-seam offset. Both measures result in a significant reduction in waviness of 30%–58% compared to the AAA cladding. However, lack of fusion defects occurs more frequently at the deposition regime of the B weld seams. It was, therefore, necessary to adjust the process parameters for weld seam B.

Optimization of the Forming Quality of a Laser-Cladded AlCrFeNiW0.2 High-Entropy Alloy Coating

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 AlCrFeNiW0.2 high-entropy alloy coating with an excellent forming quality. It was found that as the laser power increased from 300 to 1800 W, the AlCrFeNiW0.2 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 AlCrFeNiW0.2 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.

Coaxial Laser Wire Deposition of AISI 316L steel - research on influence of processing parameters

Laser cladding technology is a well-established process, commonly used for deposition of improved-property coatings, repair of machine parts and additive manufacturing. Currently, in terms of application of laser cladding, the method based on powder deposition is much more common, as the use of an adapted nozzle allows the coaxial and direction-independent feeding of additional material into the weld pool. However, laser cladding with powder also has some significant drawbacks, e.g., limited powder feeding and melting efficiency, lower productivity and the resulting dust that poses a health risk to operators. The solution to these limitations is the use of additional material in the form of wire. To maintain the ability to coaxially feed the wire to the laser beam interaction point, a specialized cladding head is necessary. In mentioned system the laser beam, while being passed through the optical system, is divided into three separate beams that are focused on the substrate on the working point of the head. In this study, the COAXwire cladding head was integrated into the robot station and laser cladding process was carried out to determine the influence of the processing parameters on the deposition results. The parameters of the cladding system were identified, including the measurement of laser beam caustic. The experimental trials were carried out using AISI 316L wire deposited on S420MC substrate. The effect of the processing parameters on the geometry of the clad was determined with particular emphasis on the wire feeding.

Numerical simulation and surface morphology of laser cladding of nickel-based C276 alloy coatings on AerMet100 steel surface

In order to rationally characterize the laser cladding process and effectively predict the processing results, the temperature field and convective heat transfer at the solid-liquid interface were simulated using ANSYS software. Under the selected process parameters, C276 nickel alloy powder was clad on the surface of AerMet100 steel by laser cladding technology, and the microstructure of the cladding layer was observed to investigate the effects of laser power and scanning speed on the laser results. The effect of laser power and scanning speed on the laser results was investigated. The results show that the best coating performance is obtained when the laser power is 1400 W and the scanning speed is 14 mm/s. When the laser power is 1400 W, the scanning speed is increased from 12 mm/s to 16 mm/s, the dilution rate of the coating is increased from 0.385 to 0.423, and the height of the coating is decreased from 0.706 mm to 0.428 mm. When the scanning speed is 14 mm/s, the laser power is increased from 1000 W to 1600 W, the dilution rate of the coating is increased from 0.375 to 0.511, and the height of the coating is increased from 0.393 mm to 0.662 mm. The laser power has a large effect on the height, width, depth and dilution of the coating, while the scanning speed has a large effect on the average particle size of the coating.

Temperature Gradient and Solidification Rate Simulation Model of the Microstructure of Laser-Cladded 27SiMn

In this study, 27SiMn was selected as a substrate, and the powder was a self-made iron-based alloy. Further, the thermophysical properties of the material were predicted by the CALPHAD phase diagram algorithm. In order to verify the accuracy of the numerical model, 10 sets of experiments were set up. The agreement between the results from the model calculations and the experimental results was 92%. Through the study of energy distribution in the laser cladding process, it was found that about 10% of the laser energy was used to heat the substrate to form a melt pool, and at least 53% of the energy was radiated into the environment. Finally, the effects of the temperature gradient and solidification rate on the microstructure of the cladding layer were explored. The numerical simulation results are helpful in predicting the solidification rate, temperature distribution and microstructure of the melt pool, thereby reducing the cost of testing as well as the time for the experimental method of trial–error.

Leveraging machine learning for predicting and monitoring clogging in laser cladding processes: An exploration of neural sensors

This study addresses the development of smart neural sensors to predict the powder mass flow and track clogging in real time during laser cladding. The challenges posed by powder granulometry and challenging environmental conditions that can lead to delivery failures are considered. An extensive experimental setup was conducted that included manipulation of key factors, such as laser power, travel speed, Z-step, N-layers, nozzle-to-substrate distance, and two types of process patterns. The mass flow rate of the powder was used as an independent variable to evaluate the predictive ability of the neural sensor with respect to the mass flow rate. Several models were trained and evaluated with different datasets and images of the cladding equipment. The model that integrated all data and images showed the best accuracy and precision also showed a strong predictive power for real-time estimation of the powder mass flow rate. Considering two practical rules—an error detection time of no more than one second and a confidence interval of less than 1.8 g/min—two strategies were proposed to meet these criteria. The first recommends the use of the comprehensive “all-features” model, while the second proposes a simplified model (with Z-step, N-slices, and the external camera as inputs) for efficient real-time error detection. The study provides an understanding of powder clogging prediction in laser cladding and suggests strategies for leaders in the field. Future research should validate these results and test these models in different environments to predict complex cladding properties and support the development of stand-alone laser cladding systems.

Influence of Bioactive Glass Addition on TC4 Laser Cladding Coatings: Microstructure and Electrochemical Properties

There is a growing interest in enhancing the bioactivity of TC4-based metallic biomaterials, which are known for their excellent biocompatibility. Bioactive glass (BG) has been recognized for its high potential in promoting bioactivity, particularly in osteo tissue engineering. This study focuses on investigating the influence of BG addition on the microstructure and electrochemical properties of TC4 coatings. The TC4/BG composite coatings were fabricated through laser cladding, and their microstructure was characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrochemical properties of the coatings were assessed through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in three different solutions. The results revealed that the incorporation of BG had a significant impact on the microstructure of the TC4 coatings, leading to the formation of a well-defined interface between the TC4 matrix and the BG aggregates. The distribution of BG aggregates within the TC4 matrix coating was found to be random and unrelated to the specific regions of the coating. The metallographic microstructure variations were attributed to different heat dissipation conditions during the laser cladding process. Furthermore, the electrochemical corrosion behavior of TC4/BG composite coatings reveals that they exhibit stability similar to that of passive films and good resistance against media corrosion compared to TC4, while also showing enhanced corrosion resistance in 3.5 wt% NaCl and Dulbecco’s modified Eagle medium (DMEM) solutions, indicating their potential for biomedical applications; however, the corrosion resistance decreases gradually in all solutions, potentially due to the elevated Cl− concentration. Further research can explore bioactivity enhancement of TC4/BG composite coatings and investigate the long-term stability and biological response of these coatings in diverse physiological environments.

Enhancing biocompatibility, mechanical properties, and corrosion resistance of laser cladding β-TiNb coatings

β-type TiNb biomedical alloys have received quite significant attention rooted in their excellent comprehensive performance. Nevertheless, their practical application is hampered by relatively poor performance and biological toxicity. Herein, TixNb alloy coatings were fabricated on the surface of Ti6Al4V (TC4) by laser cladding to evade the property-toxicity trade-off. Biocompatibility and mechanical properties, as well as the corrosion resistance of the TixNb alloy coatings, were discussed. The results show that the microstructure is composed of β grains and a small amount of the α″ martensite phase uniformly precipitated around them. The rapid melting process of laser cladding promotes the formation of the β phase, which improves the microhardness and wear resistance of the coating. However, the corrosion resistance was significantly improved due to the formation of the densification and stabilization of the passive films formed on the coating’s surface. Benefiting from the superior wettability and the biologically active sites of Ti and Nb on the alloy surface, MG-63 cells adhered to the coating’s surfaces in spindle shape and proliferated rapidly in cell experiments, denoting that the coatings have better biocompatibility than TC4. Hereby, the obtained TixNb laser cladding coatings with excellent mechanical properties and biocompatibility have extensive application prospects in the field of orthopedic biomaterials.

Effect of WC Content on the Wear and Corrosion Properties of Oscillating Laser-Cladding-Produced Nickel-Based Coating

Pneumatic conveying pipe is an important part of the coal industry. Its working environment is harsh, and it is mainly affected by serious wear and corrosion, which affects its operating life. Studying a method of strengthening the pipe wall of pneumatic conveying pipe is of great significance. In this paper, nickel-based alloy coatings with different WC (tungsten carbide) contents were prepared using an oscillating laser-cladding process, and the micro-characterization characteristics, wear resistance and corrosion resistance of the laser-cladded layer were discussed. The main conclusions are as follows: The microstructure of the laser-cladded layer gradually grows from the plane crystals and cellular crystals at the bottom to the relatively coarse columnar crystals in the middle, and finally to a large number of equiaxed crystals in the upper part. Moreover, with an increase in WC content, more fine equiaxed crystals are formed, mainly due to the decrease in temperature gradient with the increase in distance from the fusion line. Also, with an increase in WC content, the hardness and wear resistance of the nickel-based alloy are improved. When 20% WC is added, the laser-cladded layer shows the best corrosion resistance in 3.5 wt.% NaCl solution, and its polarization resistance is 16% lower than that when 10% WC is added. This study provides a technical reference for improving the operating life of pneumatic conveying pipelines.

Molten pool image processing and quality monitoring of laser cladding process based on coaxial vision

Aiming at the problems of the traditional detection method of cladding quality in laser cladding process, which relies on experience, has low accuracy and long recognition time, a method based on the image area of molten pool is proposed to detect cladding quality. Firstly, the median filter algorithm with dynamic adjustment of filter window is used to reduce noise and the iterative threshold segmentation algorithm is used to separate the molten pool from the boundary, then the edge of the molten pool is extracted by Canny algorithm which can adaptively change the high and low thresholds and finally the area value of the molten pool is obtained according to the correspondence between the pixel value and the actual value. The relationship between three key factors (nozzle angle, scanning speed and laser power) and molten pool area is analyzed to achieve favorable cladding quality. The results show that the influence of nozzle angle on the molten pool area is anisotropic. And the molten pool area decreases monotonically with the increase of scanning speed, while the higher velocity will destroy the formation of the molten pool. In addition, with the increase of laser power, the expansion of molten pool area is intensified. At the same time, the analysis of the change of molten pool area over time can quickly and accurately detect the three defects (protrusion, depression, and slag inclusion) in the process of cladding.

Advances in Surface Laser Cladding Remanufacturing of Shaft Parts

This paper provides an overview of the commonly used processes and equipment for laser cladding, including pre-set powder feeding, simultaneous powder feeding, wire feeding cladding, and coaxial cladding nozzles. By comparing the above processes and related nozzles, the coating characteristics are summarized for the selection of appropriate methods and equipment in different working environments. Meanwhile, the morphology and properties of the clad layers of shaft parts processed with different process parameters (e.g. laser power, scanning speed, lap rate, powder feed rate) and the influence of the combined parameters are overviewed. The changes and mechanisms of metals, ceramics, and metal-ceramic composites in terms of hardness, wear resistance, metallurgical bonding, and microstructure are analyzed. In addition, the application of numerical simulation techniques to simulate the temperature and stress fields and to plan the melting trajectory when laser cladding processing is performed on the surface of shaft parts are reviewed. Finally, the problems in the current research on laser cladding of shaft parts are summarized and the development directions are discussed.

Investigating the relationship between mechanical properties and residual stress in the laser cladding process of Inconel 625 superalloy

In the present study, the tensile strength, fracture surface, hardness, and amount of residual stress in Inconel 625 super alloy cladded with direct metal deposition (DLD) process in the states before and after stress relief was studied. Residual stresses on the cladding layer surface were determined via XRD method. According to results, the yield strength of Am sample increased by 10% compared to thecast sample (reference sample). Although the yield strength experiebced an increase, the ductility followed an opposite trend falling from 42.5% to 26%. According to residual stress test outcomes, tensile residual stress of 361 MPa in the additive-manufactured sample. After stress relaxation heat treatment and almost complete removal of residual stress, the ductility reached 52.5%, the ultimate strength was also improved by 17% from cast sample. Also, after stress relaxation, the hardness of the sample and its fluctuations are reduced.

Numerical simulation and experimental investigation of the laser cladding processes of Ti6Al4V with coaxial shroud protection

Laser cladding with coaxial shroud protection offers the possibility to process reactive metals in an open environment. The numerical analysis was performed on the thermal field and dynamics of molten pool with the aim of clarifying the mechanism of the complex effects of the applied extra shielding gas on the resultant microstructure and surface quality of cladding layers of Ti6Al4V. A three-dimensional (3D) computational fluid dynamics (CFD) model was first developed to investigate the extra shielding gas effect on the molten pool. The simulation shows that the extra shielding gas influences both the surface and internal flow field characteristics of the molten pool. The predicted solidification parameters imply fully columnar microstructure in the entire cladding layer. Comparative analysis was then carried out between the numerical simulation and experiments. The electron backscattering diffraction (EBSD) examination reveals that the high cooling rate due to the extra shielding gas inhibits the formation of grain boundary α phase and simultaneously refines the microstructure. The extra shielding gas reduces the surface roughness of cladding layers, and its bunching effect improves the powder utilization. The multi-track cladding experiments reveal that the extra shielding gas can effectively suppress crack formation with a large overlap ratio. This study provides a better understanding of the effect of extra shielding gas flow on molten pool, which helps control and improve the quality of cladding layers.

Simulation of microstructure evolution process in the melt pool formed by laser cladding with a multi-scale model

The microstructure directly determines the alloys’ mechanical performance, therefore understanding the microstructure evolution process is essential to controlling the cladding layer’s mechanical performance. A multiscale model in three dimensions is developed to evaluate the complicated microstructure evolution in the melt pool formed during the laser cladding process. The model consists of two parts: the FVM to calculate the evolution of the melt pool at the macroscopic scale, and the simulation of the solidification of grains at the microscopic scale by the CA. The high consistency with the experimental results proves the accuracy of the multiscale model in three dimensions. Using the developed model, the solid-liquid phase transformation process of the whole melt pool is studied and the impact of the variations of scanning speed on the microstructure is analyzed. The grain size decreases and the “laser-grain angle” increases with an increase in scanning speed. This study explains the evolution of the microstructure, which helps to customize the cladding layer’s microstructure.

Numerical Simulation Analysis of Temperature Distribution of NbC-Reinforced Ti-Based Composite Coating by Laser Cladding

In this article, three-dimensional numerical modeling of the laser cladding process by Ansys was proposed. The three-dimensional Gaussian heat source model was used to simulate the actual laser heat source to analyze the temperature distribution of the molten pool. The temperature distribution of the molten pool of TiAlSi + NbC coatings within different process parameters was obtained by simulation. To obtain finer simulation results, the thermophysical properties of TiAlSi + NbC powder and TiAlSi + NbC alloy were investigated, respectively. The temperature selection judgment mechanism, which is used to distinguish the powder and alloy elements, was built. The results showed that the laser power and laser scanning speed play a vital role in the temperature distribution along with the track width and the depth of the molten pool. The simulation values of the width and depth of the cladding layer under different processing parameters were obtained by using the temperature selection judgment mechanism and fitting. The results showed that the track width and depth had a positive correlation with the laser power, whereas they had a negative correlation with the laser scanning speed.