Single Clad Tracks Research Articles

Numerical simulation and experimental research of molten pool flow field and temperature field by hollow-laser direct energy deposition

Hollow-laser Direct Energy Deposition (HL-DED) significantly surpasses traditional Laser Directed Energy Deposition (L-DED) methods, marked by its superior adjustability of energy density, exacting control of energy distribution, and versatility in creating cladding layers of varied geometries. This novel technique ensures a markedly uniform and stable melt path. In this paper, the HL-DED process was systematically analyzed by combining numerical simulation and experimental research. A novel three-dimensional transient computational fluid dynamics (CFD) simulation model is established based on the Flow 3D software to study the flow and heat and mass transfer behaviors. At the optimized processing parameters, the single-track and multi-track cladding layer processes were carried out respectively. Results show that the model can well predict and explain the flow of the molten pool and the morphology of the cladding layer in the HL-DED process. In the initial stage of single-track cladding, the molten pool exhibits a symmetrical bimodal distribution configuration characterized by the peak flow rate of 0.09 m/s, with temperatures being higher at the periphery and lower at the center. In the stabilization phase, the dynamics of the molten pool are primarily influenced by gas-powder momentum transfer, showing increased peak flow rates up to 0.26 m/s. Concurrently, the peripheral temperatures rise from 2001 K to 2122 K (0.06 % increase), but central temperatures ascend from 1400 K to 1800 K (0.29 % increase). The flow and temperature distribution patterns in multi-track cladding closely mirror those observed in single-track layers, maintaining a symmetrical bimodal temperature distribution with peak flow rates reaching 0.105 m/s. The temperature distribution evolves from a unimodal to a bimodal pattern, with the left peak approximately 100 K higher than the right, before reverting to a unimodal configuration. Simulation outcomes closely align with experimental findings, offering valuable insights for refining the experimental adjustment of the internal optical coaxial powder feeding process.

Process optimization and microstructure of Ti3Zr1.5NbVAl0.25 high entropy alloy produced by directed energy deposition

As an emerging materials preparation method, directed energy deposition (DED) has its unique advantages in the preparation of high entropy alloys (HEAs). However, improper process parameters can lead to numerous defects, affecting material properties. In this study, a Ti3Zr1.5NbVAl0.25 HEA was produced by DED. The effects of process parameters on single track cladding layer (STCL) were studied by response surface methodology (RSM), and the parameters were optimized accordingly. It is indicated that the microstructure of the STCL is composed of columnar and equiaxed crystals and the grain growth is parallel to the heat flux direction. 〈001〉//BD (building direction), 〈111〉//SD (scanning direction) and {100}〈001〉 textures were observed in molten pool. The microhardness of the molten pool measures 299.99 HV0.2, while the estimated Young's modulus and yield stress are 87.66 GPa and 945 MPa, respectively. This work provides unique insights into optimizing the DED process parameters of HEAs, further obtaining the solidification microstructure and mechanical properties of STCL.

Optimization model of overlap rate of laser cladding based on Gaussian function and top tangent model

As an important characterization of surface quality, the surface morphology of laser cladding coating directly affects the choice and difficulty of subsequent processing technology. The laser cladding coating is made of multi-track cladding layers, and the variation and optimization of overlap rate directly affect the quality of surface morphology. Firstly, the height, width and wetting angle of single-track cladding layer are substituted into the Gaussian function to obtain the characterization curve of single-track cladding layer, which can accurately characterize the profile curve of the single-track cladding layer. Then, by analyzing dual-track overlapping experiments with the varied overlap rates, it was found that the contour of the filled area is approximately a quadratic function curve. The area ratio of the filled area to the overlapping area first decreases and then increases with the increase of the overlap rate, reaching about 0.5 near the optimal overlap rate. Finally, a top-tangent overlapping model is developed based on the single-track characterization model of the Gaussian function and the forming characteristics of multi-track cladding layers. Experimental results show that the model can well characterize the multi-track cladding layers, and it is of great significance for optimizing the overlap rate of laser cladding and obtaining high-quality cladding layers.

A method for predicting the morphology of single-track laser cladding layer based on SO-LSSVR

The morphology of the cladding layer is directly affected by the process parameters of laser cladding. To improve the morphology of single-track cladding layer, it is necessary to accurately reveal the nonlinear relationship between the morphology and process parameters of laser cladding. Firstly, the single-track Ni60/10%WC cladding layer was preparate on the surface of 35CrMoV substrate, and the effects law of process parameters such as laser power, scanning speed and powder feed rate on the morphology of single-track cladding layers were investigated through single factor experiment. Then, the prediction model for predicting the morphology of single-track laser cladding layer was established by the SO-LSSVR. At the same, the prediction models based on ternary quadratic regression, SVR, and LSSVR were established for comparative analysis. Finally, the prediction results show that the MAPE, RMSE and R2 of the SO-LSSVR prediction model are better than the prediction results of the remaining three models. The proposed SO-LSSVR prediction model can accurately describe the nonlinear relationship between the process parameters and morphology of single-track cladding layer, which lays a foundation for the subsequent process parameter optimization to improve the morphology of cladding layer.

Multi-objective optimization of key process parameters in laser cladding Stellite12 cobalt-based alloy powder

Laser cladding (LC) process parameters have a substantial influence on coating morphology and mechanical characteristics; it is necessary to optimize key parameters for laser processing. In this study, Stellite12 cobalt-based alloy powder with excellent corrosion and wear resistance was selected as the cladding material. The multi-objective optimization model of the LC process was established by response surface methodology, laser power, scanning speed, and powder feeding rate as input factors, and the target response variables involve dilution, aspect ratio, and microhardness of the single-track cladding. Combined with variance analysis (ANOVA), the multi-objective optimization of laser power, scanning speed, and powder feeding rate was conducted. A single-track cladding layer with a dilution of 18.29%, an aspect ratio of 3.88, and a microhardness of 634.67 HV0.2 was obtained using the optimized process parameters. Errors between the predicted and actual values of single-track cladding dilution, aspect ratio, and microhardness were less than 8%, which verified the accuracy of the established model.

Laser cladding: A high-speed-imaging examination of powder catchment efficiency as a function of the melt pool geometry and its position under the powder stream

This paper provides quantitative information about the paths taken by blown powder particles during laser cladding. A proportion of the powder is “wasted” by bouncing off the solid areas surrounding the melt pool. This wastage reduces the productivity and profitability of the process. In this paper, specially developed software was used to analyze high-speed imaging videos of the cladding process, to monitor the directions of powder particle flight toward and away from the melt pool area. This information has been correlated to the geometry and position of the melt pool zone for three different cladding techniques: single track cladding (A tracks), standard overlapping track cladding (AAA cladding), and a recently developed technique called ABA cladding. The results show that the melt pool geometry, and particularly the overlap between the melt pool and the incoming powder stream, has a strong influence on powder catchment efficiency. ABA cladding was found to have considerably better powder catchment efficiency than standard AAA cladding and this improvement can be explained by consideration of the geometries and positions of the melt pools and surrounding solid material in each case. As powder costs are an important factor in industrial laser cladding, the adaption of the ABA technique, and/or control of pool/powder stream overlap (e.g., by making the powder stream not coaxial with the laser beam), could improve the profitability of the process.

Forming characteristics analysis of variable-process alternated overlapping strategy based on contour description for laser melting deposition

To predict the geometric characteristics and improve the forming quality and macro-micro defects of multi-track overlapping cladding layer effectively, the experimental research of laser melting deposition single-track Co-based alloy on 42CrMo substrate was carried out. The influence trends of laser process parameters on the single-track cladding height and cladding width were analyzed, and the regression prediction models were established. A variable-process alternated overlapping strategy was proposed using the geometric functions to fit the single-track profile. The surface forming quality and macro-micro defect of different overlapping cladding layers were compared and evaluated. The results showed that the cladding height and cladding width regression models established by an improved optimization algorithm had an excellent prediction effect. The variable-process alternated overlapping cladding layer prepared by the parabolic function had a flat surface, and the fluctuation distance was 81.56 μm, which was significantly improved compared with other overlapping strategies. The surface flatness of the continuous overlapping cladding layer was the worst and the spheroidization defect was the most unsatisfied. The internal defects of the constant-process alternated overlapping cladding layer were the most terrible, with more non-fusion and cracks caused by oxides. The variable-process alternated overlapping strategy proposed in this study can effectively prepare a multi-track cladding layer with a smooth surface and dense interior, which provides essential theoretical guidance for the near-net forming of component surface deposition and repair.

Prediction of single track clad quality in laser metal deposition using dissimilar materials: Comparison of machine learning-based approaches

Powder-based laser metal deposition (LMD) offers a promising additive manufacturing process, given the large number of available materials for cladding or generative applications. In laser cladding of dissimilar materials, it is necessary to control the mixing of substrate and additive in the interaction zone to ensure safe metallurgical bonding while avoiding critical chemical compositions that lead to undesired phase precipitation. However, the generation of empirical data for LMD process development is very challenging and time-consuming. In this context, different machine learning models are examined to identify whether they can converge with a small amount of empirical data. In this work, the prediction accuracy of back propagation neural network (BPNN), long short-term memory (LSTM), and extreme gradient boosting (XGBoost) was compared using mean squared error (MSE) and mean absolute percentage error (MAPE). A hyperparameter optimization was performed for each model. The materials used are 316L as the substrate and VDM Alloy 780 as the additive. The dataset used consists of 40 empirically determined values. The input parameters are laser power, feed rate, and powder mass flow rate. The quality characteristics of height, width, dilution, Fe-amount, and seam contour are defined as outputs. As a result, the predictions were compared with retained validation data and described as MSE and MAPE to determine the prediction accuracy for the models. BPNN achieved a prediction accuracy of 0.0072 MSE and 4.37% MAPE and XGBoost of 0.0084 MSE and 6.34% MAPE. The most accurate prediction was achieved by LSTM with 0.0053 MSE and 3.75% MAPE.

Optimization on laser cladding parameters for preparing Ni60 coating along with its friction and wear properties

Ni60 coating was prepared on Q235 substrate by using laser cladding method, and the optimization of processing parameters was performed based on response surface methodology. Laser power, scanning speed and powder feeding rate were considered as input variables, while dilution ratio, ratio of width to height, and hardness were considered as output responses. Then, the influence of processing parameters on cladding quality was studied by single track cladding experiments, and the optimal parameters were obtained by regression analysis. Subsequently, Ni60 coating was successfully prepared and its friction and wear properties were investigated. Results show that the optimal parameters are: laser power 540 W, scanning speed 30 mm/s, powder feeding rate 0.2 r/min and overlapping step 0.4 mm. The microhardness of coating is 499.4 HV0.5, which is 5 times higher than that of the substrate. Correspondingly, the wear loss of the coating is 68.3% and 82.1% lower than that of Q235 substrate at room temperature and 400 °C respectively, indicating that the Ni60 coating can improve the wear resistance of Q235 steel significantly.

Parameters optimization for single-track laser cladding based on MPA-SVR and A-NSGA-III

Laser cladding as an emerging surface modification technology, the morphology of the single-track cladding layer is directly affected by the process parameters. To obtain the ideal cladding layer morphology, it is necessary to build the mapping relationship between the process parameters and the morphology and optimize the process parameters. A method for predicting the morphology of the single-track cladding layer is proposed by using the support vector regression optimized by the marine predators algorithm. Then, the adaptive non-dominated sorting genetic algorithm III is used for process parameter optimization to determine the optimal process parameters of laser cladding. The results of the validation experiments show that the aspect ratio of the optimized cladding layer has been improved by 41.78%, the dilution rate has been improved by 22.30%, and the wetting angle has been reduced by 35.20%. The proposed process parameters optimization method of laser cladding can significantly improve the morphology of the cladding layer.

Parametric optimization in co-axial laser powder deposition of cobalt-base alloys on DIN 1.2714 die steel

In this work, cobalt-based powders (Stellite 6 and Stellite 12) were deposited on the hot forging die steel (DIN 1.2714) by direct laser deposition using a 2 kW Yb-fiber laser. Single tracks were developed by varying process parameters—powder mass flow rate (25–35 g/min), laser power (800–1100 W), and scan speed (400–800 mm/min). Further, the influence of these process parameters on clad geometry and dilution rate was studied. Optimization of parameters was carried out using grey analysis, and the results were analyzed based on analysis of variance (ANOVA). It was observed that the optimal parameters for Stellite 6 cladding are a powder mass flow rate of 25 g/min, laser power of 1100 W, and a scan speed of 400 mm/min. In contrast, the optimal parameters for Stellite 12 are a powder mass flow rate of 35 g/min, laser power of 1100 W, and a scan speed of 800 mm/min. In addition, a correlation between input and output parameters was established using regression analysis. The micrographs of the single-track cladding developed under optimal parametric conditions consist of fine cellular structure at the clad-surface interface followed by course cellular dendrites and fine equiaxed grains at the surface of the cladding. Stellite 12 cladding exhibits higher hardness (545 ± 10 HV0.3) than Stellite 6 cladding (470 ± 10 HV0.3) due to the formation of more refined grains.

Investigation on the columnar-to-equiaxed transition and corrosion behavior in multi-track Stellite-6 coating fabricated by laser cladding

In this study, aiming to investigate the effect of secondary thermal effect on the structure and properties of coatings, multi-track Stellite-6 coating was successfully fabricated on 42CrMo steel by laser cladding technology. The results showed that, in the overlap zone, the ratio of temperature gradient and solidification rate of the melted pool was relatively low, which promoted the columnar-to-equiaxed transition (CET) behavior ahead of the single-track cladding. Electrochemical analysis displayed that the corrosion resistance of the overlap zone was higher than that of the non-overlap zone, which can be attributed to the dense passive film generated on the samples surface by the dendrite rich in Cr element. Meanwhile, the smaller equiaxed crystal provided more active sites for the generation of passive film (Cr2O3) and delayed the corrosion of Cl− to samples.

Prediction of molten pool temperature and processing quality in laser metal deposition based on back propagation neural network algorithm

Stability of molten pool temperature directly affects the dimensional accuracy, metallurgical defects, solidification microstructure and mechanical properties of formed parts manufactured by laser metal deposition technology. Therefore, the optimization of the macroscopic morphology and microstructure of the formed parts through the stable control of the molten pool temperature has been intensively studied. In this study, three models, based on the back propagation neural network (BPNN), random forest (RF) algorithms and response surface methodology (RSM) approach, respectively, were used to establish prediction relationships between the deposition input parameters and processing status parameters, geometric morphology and mechanical property parameters. Then, the processing temperature and molten pool characteristics of thirty groups of 316L stainless steel single-track cladding layers were analyzed. The prediction results show that the average prediction error (APE) of the prediction of molten pool temperature, track width, track height and micro-hardness of the deposited layer based on BPNN model are 0.5%, 1.3%, 2.9% and 0.1%, respectively, which are better than the prediction results of RF and RSM models. Then, BPNN model was further used to predict the molten pool temperature and processing quality of the deposited layer under the combination of five new process parameters groups. Objective of this study was to lay the foundation for the subsequent design of the molten pool temperature control system to improve the morphology accuracy and mechanical properties of formed parts.

Influences of Pulse Shaping on Single-Track Clad of AISI316L Stainless Steel by Laser Material Deposition

As a very common type of laser additive manufacturing technology, laser material deposition (LMD) is widely used, having exceptional application advantages including surface enhancing, repairing damaged parts with high value-add, and building functionally graded material. At present, the continuous wave laser is a common laser mode used in the LMD process. The investigation of pulse shaping, which can add a degree of control over the thermal history, is limited. In this study, the effects of pulse shaping on the geometrical characteristics, microstructure, and microhardness were investigated through conducting single-track experiments with different laser shapes, including continuous, rectangular, ramp up, ramp down, and hybrid ramp. The results indicated that the clads created by continuous and ramp up laser shape presented the maximum and minimum dimensions of geometrical characteristics, respectively. The rectangular and hybrid ramp laser shape deposited the clads with similar dimensions. The continuous laser shape produced the clad with the coarsest microstructure and lowest hardness because of the lowest cooling rate. The smallest grain size and highest hardness presented in the clad were seen with the rectangular laser shape owing to the biggest cooling rate. The cooling rates in ramp up and ramp down were restrained by the gradual heating and gradual cooling, respectively.

Thermal study of a cladding layer of Inconel 625 in Directed Energy Deposition (DED) process using a phase-field model

In an effort to simulate the involved thermal physical effects that occur in Directed Energy Deposition (DED) a thermodynamically consistent phase-field method is developed. Two state parameters, characterizing phase change and consolidation, are used to allocate the proper material properties to each phase. The numerical transient solution is obtained via a finite element analysis. A set of experiments for single-track scanning were carried out to provide dimensional data of the deposited cladding lines. By relying on a regression analytical formulation to establish the link between process parameters and geometries of deposited layers from experiments, an activation of passive elements in the finite element discretization is considered. The single-track cladding of Inconel 625 powder on tempered steel 42CrMo4 was printed with different power, scanning speed, and feed rate to assess their effect on the morphology of the melt pool and the solidification cooling rate. The forecast capability of the developed model is assessed by comparison of the predicted dimensions of melt pools with experiments reported in the literature. In addition, this research correlated the used process parameter in the modeling of localized transient thermal with solidification parameters, namely, the thermal gradient (\(G\)) and the solidification rate (\(R\)). The numerical results report an inverse relationship between \(R\) with \(G\), and microstructure transition from the planar to dendrite by moving from the boundary to the interior of melt pool, which agree well with experimental measurements.

Microstructures and mechanical properties of Ti–Al–V–Nb alloys with cluster formula manufactured by laser additive manufacturing

Ti–Al–V–Nb alloys with the cluster formula, 12[Al–Ti12](AlTi2)+5[Al–Ti14](V,Nb)2Ti, were designed by replacing V with Nb based on the Ti–6Al–4V alloy. Single-track cladding layers and bulk samples of the alloys with Nb contents ranging from 0 to 6.96 wt.% were prepared by laser additive manufacturing to examine their formability, microstructure, and mechanical properties. For single-track cladding layers, the addition of Nb increased the surface roughness slightly and decreased the molten pool height to improve its spreadability. The alloy, Ti–5.96Al–1.94V– 3.54Nb (wt.%), exhibited better geometrical accuracy than the other alloys because its molten pool height was consistent with the spread layer thickness of the powder. The microstructures of the bulk samples contained similar columnar β-phase grains, regardless of Nb content. These grains grew epitaxially from the Ti substrate along the deposition direction, with basket-weave α-phase laths within the columnar grains. The α-phase size increased with increasing Nb contents, but its uniformity decreased. Along the deposition direction, the Vickers hardness increased from the substrate to the surface. The Ti–5.96Al–1.94V–3.54Nb alloy exhibited the highest Vickers hardness regardless of deposition position because of the optimal matching relationship between the α-phase size and its content among the designed alloys.

Investigation on swinging arc plasma-cladded Ni60A coating on copper surface

To improve the manufacturing efficiency, a swing arc plasma cladding process was developed and successfully used to fabricate Ni60A coating on the copper surface. The cladding efficiency can reach 45 mm2/s, which is about 3 times that of single-track cladding. The coating (thickness of 2 mm) is free of crack defects and has a good metallurgical bonding with the copper substrate. Due to the rapid swing arc speed, there is no obvious difference in the microstructure between the overlapping zone and the non-overlapping zone, resulting in a uniform microhardness distribution. The average microhardness of the coating (635.6 HV) prepared by the swinging arc plasma cladding is about 8.2 times that of the copper substrate.

Process, microstructure and microhardness of GH3039 superalloy processed by laser metal wire deposition

Laser metal deposition has high build rate and it is suitable for fabricating parts with larger sizes. Using the metal wire as feedstock material in laser metal deposition is a potential and promising approach compared with other metal additive manufacturing technologies, due to the metal wire is with lower cost, higher material efficiency and less pollution to environment. However, the experience and development activities relevant to metal wire based additive manufacturing are relatively limited. In this work, laser metal wire deposition was conducted to fabricate single-track cladding layers of GH3039 superalloy at different processing parameters, the empirical models and correlations between the main processing parameters (laser power (P), laser scanning speed (V) and wire feeding rate (F)) and geometrical characteristics (clad width (W), clad height (H), penetration depth (h), dilution (D) and wetting angle (θ)) of the cladding layers were studied by employing the combined parameter PαVβFγ and regression analysis (RA) method, which provides the possibility of predicting the geometrical characteristics under the applied processing parameters. To verify the correctness of the empirical models and study the layer-by-layer problems, the multi-layer single-track thin wall of GH3039 superalloy was fabricated and investigated. Furthermore, the microstructure and the microhardness of the cladding layers which may be aid for facilitating the industrial applications of laser metal wire deposition were also studied.

Strategy Development for the Manufacturing of Multilayered Structures of Variable Thickness of Ni-Based Alloy 718 by Powder-Fed Directed Energy Deposition

In this study, a manufacturing strategy, and guidelines for inclined and multilayered structures of variable thickness are presented, which are based on the results of an own-developed geometrical model that obtains both the coating thickness and dilution. This model is developed for the powder-fed directed energy deposition process (DED) and it only uses the DED single-track cladding characteristics (height, width, area, and dilution depth), the overlap percentage, and the laser head tilting-angle as inputs. As outputs, it calculates both the cladding geometry and the dilution area of the coating. This model for the Ni-based alloy 718 was improved, based on previous studies of the single clad working both vertically and at an inclined angle, adding the equations of the single clad characteristics with respect to the main process parameters. The strategy proposed in this paper for multilayered cladding consisted of both adding an extra clad at the edges of the layer and using a variable value of the overlap percentage between clads for geometric adaptations. With this strategy, the material deposition is more accurate than otherwise, and it shows stable growth. Manufacturing a multilayered wall of wider thicknesses at higher heights was utilized to validate the strategy.

Multicomponent multiphase modeling of dissimilar laser cladding process with high-speed steel on medium carbon steel

During a laser cladding process, the transport phenomena in the molten pool, including rapid solidification, strong fluid convection, and species diffusion are complex, and determine the microstructure and composition of the cladding layer. In this study, a three-dimensional transient multicomponent multiphase model was proposed to simulate the dissimilar laser cladding process with T15 powder and T15/CeO2 mixed powder on 42CrMo substrate. The position and expression of the source terms on energy and mass were clearly defined. The model was validated by comparing the morphology of the cross section with single-track cladding experiments. The simulation results indicate that the molten pool is dominated by a strong Marangoni flow that results in a fully mixed cladding layer and a narrow transition zone at the bottom. The molten pool exhibits an inward flow pattern with pure T15 powder and an outward flow pattern with T15-CeO2 mixed powder. The content of the elements and the microstructure of the cladding layer were investigated by using an electron probe micro-analyzer and a scanning electron microscope. The microstructure evolves from planar to cellular, and to equiaxed dendrites from the substrate–clad interface to the top surface. The transition zone comprised of planar and cellular grains. The solidification characteristics calculated from the numerical model were associated to the grain morphology.