Powder Feed Research Articles

Anomalous twin boundary formation in magnesium alloys by rapid solidification

The aim of this work is to investigate the formation of an anomalously high fraction of twin boundaries (TBs) during laser directed energy deposition (DED) of a Mg-3Al-1 Zn (wt.%) alloy. With that goal, single tracks are deposited using different combinations of scan speed and powder feed rate. The melt pool dimensions are related to the DED parameters. Irrespective of the processing conditions, the resulting microstructures are always formed by fine grains with a very weak texture. However, some DED parameter combinations give rise to a fraction of TBs that is significantly higher than that corresponding to a random texture. These TBs are characterized by an irregular morphology and by the presence of segregated atoms, solute clusters, and nanoparticles. Additionally, the lattice in the vicinity of the TBs is highly distorted and contains a high population of stacking faults. All these characteristics set them apart from conventional tensile TBs, which exhibit a large degree of coherency and limited segregation. Rapid solidification is thus presented here as a novel avenue to design TBs with unique properties in Mg alloys. This work paves the way for future studies on grain boundary design via additive manufacturing methods, a field that is still in its infancy.

Effect of Abnormal Powder Feeding on Mechanical Properties of Fabricated Part in Directed Energy Deposition

Effect of Abnormal Powder Feeding on Mechanical Properties of Fabricated Part in Directed Energy Deposition

Investigation of Deposition Parameters for Near-Beta Alloy Ti-55511 Fabricated by Directed Energy Deposition

The directed energy deposition (DED) parameters were determined for near-β alloy Ti-55511 by employing statistical design of experiments (DOEs) methods. Parameters resulting in fully dense freeform deposits were identified using two sequential DOEs. Single laser tracks were printed with several laser power, traverse rate, and powder feed rate settings in an initial DOE to identify promising build parameters. The capture efficiency and effective deposition rate were used to characterize and rank the single track deposits. The best parameters were then used to print a solid cube with various X–Y and Z overlaps (different hatch spacing, HS, and layer thickness, ZS) in a second DOE. Suitable deposition parameters were selected based on the cube density and microstructure and were used to fabricate larger tensile samples for mechanical testing. Multiple parameter sets were found to provide dense Ti-55511 deposits with acceptable mechanical properties and the parametric models showed statistical significance.

Influences of makiang (Syzygium nervosum) seed powder on growth performance, immunological response, antioxidant and immune related gene expression in juvenile Nile tilapia (Oreochromis niloticus)

A makiang seed powder (MSP) feeding trial was performed on Nile tilapia (Oreochromis niloticus) for eight weeks to evaluate the effects on growth performance, immune response, and gene expression. Three hundred fingerlings (13.20 ± 0.04 g) were fed five diets with various amounts of MSP at 0, 5, 10, 20 and 40 g kg−1. After four and eight weeks of the feeding trial, growth rates and immune responses were tested, while relative immune and antioxidant gene expression were performed after eight weeks of MSP feeding. Accordingly, the growth indices (SGR, WG) and immune activity (skin mucus and serum lysozyme, skin mucus and serum peroxidase, alternative complement, phagocytosis and respiratory burst activities) in Nile tilapia were significantly increased in the treated diets compared with the control diet (P < 0.05). The maximum (P ≤ 0.05) growth and immune activity values were noted in fish fed 5 g kg−1 MSP. IL1, IL8, LBP, GPX, GSTa and GSR gene expressions were also shown to be upregulated in fish on MSP diets, with the highest value reported in fish fed 5 g kg−1 MSP. Finally, MSP has the potential to be employed as a feed supplement in the biofloc system for the cultivation of Nile tilapia.

Process parameter optimization for laser powder directed energy deposition of Inconel 738LC

Processing nickel-based superalloys is one of the major challenges in the additive manufacturing (AM) field. Nickel-based superalloys consist of several alloying elements, which make them prone to the formation of undesired phases and cracking due to the complex thermodynamics during the metal AM processes. In order to produce defect-free parts from nickel-based superalloys via metal AM processes, optimization of process parameters is required. In this study, the effect of laser powder directed energy deposition (LP-DED) process parameters on the geometrical properties and porosity ratio of Inconel 738 LC (low carbon) is investigated. Geometrical specifications, including the track height, width, and wetting angle are the major factors that indicate the quality of the final product. The analysis of variance (ANOVA) and response surface methodology (RSM) were developed in order to predict the geometrical specifications of single tracks from the key process parameters, namely laser power, scan speed, and powder feed rate. An optimum set of process parameters was obtained through multi-objective optimization by minimizing the porosity ratio, crack formation and maximizing the deposition rate. The results were verified and a good agreement with the experimental measurements was achieved. The produced bulk sample showed less than one percent porosity content, which indicates the effectiveness of single-track optimization prior to bulk sample production. The overall microstructure of the bulk sample showed a high content of MC carbides resulting from the abundance of alloying elements.

Incremental Feeding of Perovskite Powders: Angstrom‐Precision Growth for Single‐Source Solar Cell Fabrication

Vacuum‐based deposition of halide perovskites receives a lot of attention for its proven scalability and conformal depositions. Co‐evaporation has remarkable success, but efficiencies continue to lag behind their solution‐based counterparts. This is in part attributed to the complex sublimation behavior of some organic ammonium precursor salts and the increased complexity of the absorber materials, requiring the use of four or more sources in a conventional co‐evaporation setup. The latter has driven work into single‐source methods with flash evaporation presented as one such method. However, flash evaporation processes typically evaporate all material in a single batch, leading to short deposition times at high temperatures. Particle sputtering effects seen at these high temperatures drive processes toward low temperatures where prolonged exposure causes degradation. Here, a pulse‐driven incremental powder feeding system is presented. This method is capable of stable flash evaporation rates for &gt;1 h, with controlled rates as low as 1.5 Å per pulse (±0.89). The feasibility of this method is demonstrated for three different perovskite compositions: FAPbBr3, MAPbI3, and FA1−xMAxPbSnI3:SnF2. Furthermore, FAPbBr3 and MAPbI3 are integrated into all vacuum‐processed thin‐film solar cells leading to power conversion efficiencies (PCE) of ~4% and 10%, respectively.

Mechanical Behavior and Shape‐Memory Effects of NixTi1−x Alloys with Tunable Mixing of Ni/Ti Powders by Laser‐Directed Energy Deposition

As it is known, controlling NiTi alloy's microstructure is an urgent problem in additive manufacturing, which directly affects the mechanical properties of the alloy. In laser‐directed energy deposition (LDED) technology, the simultaneous powder feeding equipment with double powder barrels can effectively control the material ratio and realize the generation of NixTi1−x alloys with different atomic ratios. First, the performance differences of NiTi alloy under different thermal treatments are explored. Based on this, the optimal thermal treatment process is used to adjust the microstructure of NiTi alloy fabricated by LDED by changing the Ni/Ti atomic ratio to improve mechanical properties. The results indicate that Ni4Ti3 precipitates can induce the R phase, change the phase transition, and improve the mechanical properties in Ni‐rich NiTi alloys. Besides, the mechanical properties of NixTi1−x alloy can be enhanced by adjusting the Ni/Ti atomic ratio to change the content of Ni4Ti3 precipitates. Ni52Ti48 alloy has a tensile strength of 771 MPa, an elongation of 11.6%, and a recovery rate of 95.2%.

Surface modification of AZ61 Magnesium Alloy with Stelcar Alloy Powder Using Laser Cladding Technique

Objective: To examine the tribological and mechanical characteristics of the AZ61 alloy reinforced with Stelcar alloy powder by surface modification through laser cladding. Methods: Surface modification was done by using a laser cladding machine, where the input parameters including Scanning Speed (SS), Laser Power (LP) and Powder Feed Rate (PFR) were adjusted. Experimental design followed a L9 Taguchi approach, and optimization of input parameters for the surface modified AZ61 alloy reinforced with Stelcar alloy particles was achieved using Grey Relational Analysis (GRA). Output responses, namely wear volume and micro hardness were measured to assess the effectiveness of the optimization process. Findings: From the results obtained through the experiments, powder feed rate contributes to 82.81% of the variability in wear volume, whereas the laser power mostly impacts micro hardness; influencing it by 89.46% confirmed with ANOVA. In order to determine the optimal processing parameters among various objectives, this research applies the grey relational method. The results showed that the wear volume and micro hardness of the composite were significantly affected by the Stelcar reinforcement. Employing Grey relational analysis combined with several optimization objectives into a transparent method, resulting in a clad material with the lower wear volume and higher micro hardness. The optimized processing parameters predicted grey relational grades with an error rate of 1.39% and a significant contribution of 63.60% from laser power. This study confirmed that multi-objective optimization could enhance laser-cladded surface mechanical characteristics and laid out the theoretical foundation for this approach. Novelty: This study introduces an innovative approach to surface modification by employing the laser cladding technique to reinforce Stelcar alloy particles, thereby creating a dense coating on the substrate. Keywords: Laser Cladding, AZ61 magnesium alloy, Stelcar alloy, Coating, Optimization

EXPLORING EPITAXIAL GRAIN GROWTH AND MARANGONI-INDUCED CONVERSION IN COLUMNAR DENDRITES: A STUDY OF INCONEL 718 ADDITIVE MANUFACTURING VIA DIRECT LASER ENERGY DEPOSITION

This study characterizes the microstructure changes of Inconel 718 (IN718) by laser cladding (LC). Well-bonded pore-free, crack-free, single-layer, and multi-layer (overlapped) LC was done on IN718 with the same powder. The basic microstructure illustrates the presence of [Formula: see text], [Formula: see text], and [Formula: see text] -phases. The precipitation of an irregularly shaped laves phase was observed with dendritic grains in the top and bottom regions of the single-track LC. Further, the epitaxial grain growth of columnar dendrites was observed in the interdendritic region along the laves phase. High leveraging of quick-dissolving behaviors of the laves phase in multi-track LC enhances the high-temperature mechanical performance. Modified grain morphology of the multi-track LC in terms of size, shape, and orientation is reported. Columnar dendrites (short and long) are the most common grains, with varied sizes and orientations reported in line with the Marangoni effect. The microhardness at the top layer of single and multi-track exhibited a higher value of 490.6[Formula: see text]HV and 500.7[Formula: see text]HV, respectively, which is comparatively lower than the bottom layer of single and multi-track samples. The influencing process parameter over clad width is scan speed, and over clad height is powder feed. The nonlinear mathematical model is proposed with a reliability of 99.22% and 99.52% for clad width and height, respectively.

Comparative assessment of supervised machine learning algorithms for predicting geometric characteristics of laser cladded inconel 718

Laser cladding, an innovative surface modification and coating preparation process, has emerged as a research hotspot in material surface modification and green remanufacturing domains. In the laser cladding process, the interaction between laser light, powder particles, and the substrate results in a complicated mapping connection between process parameters and clad layer quality. This work aims to shed light on this mapping using fast evolving machine learning algorithms. A full factorial experimental design was employed to clad Inconel 718 powder on an A286 substrate comprising 64 groups. Analysis of variance, contour plots, and surface plots were used to explore the effects of laser power, powder feeding rate, and scanning speed on the width, height, and dilution rate of the cladding. The performance of the predictive models was evaluated using the index of merit (IM), which includes mean square error (MSE), mean absolute error (MAE), and coefficient of determination (R2). By comparing the performance of the models, it was found that the Extra Trees, Random forest regression, Decision tree regression, and XGBoost algorithms exhibited the highest predictive accuracy. Specifically, the Extra Trees algorithm outperformed other machine learning models in predicting the cladding width, while the RFR algorithm excelled in predicting the associated height. The DTR algorithm demonstrated the best performance in predicting the cladding dilution rate. The R2 values for width, height, and dilution rate were found to be 0.949, 0.954, and 0.912, respectively, for these three models.

Multi-Objective Optimization of Process Parameters in Laser DED Ni-Based Powder on Steel Rail Using Response Surface Design

With the rise of global industrialization, the requirements for the operating speed and carrying capacity of high-speed trains are increasingly higher. Because the wear and tear of rails gradually increases during the running of high-speed trains, strengthening or repairing rail surfaces is of paramount significance. Laser-directed energy deposition (DED) exhibits significant advantages in improving surface hardness, corrosion resistance, and abrasion resistance. Because of the multiple interacting optimization objectives, the development of a multi-objective optimization method for process parameters is significant for improving DED deposition quality. Response surface design employs multivariate quadratic regression equations to fit the functional relationship between the factors and the responses, which can be employed to find the optimal process parameters and solve multivariate problems. This study develops a multi-objective optimization model with response surface design and 2D process mappings to visually analyze the effects of scanning speed, laser power, and powder feed rate on aspect ratio, dilution rate, and microhardness. The optimal combination of process parameters for Ni-based alloys on U71Mn rail is a laser power of 431 W, a scanning speed of 5.34 mm/s, and a powder feed rate of 1.03 r/min. In addition, a multi-physics field finite element model is developed to analyze the evolution mechanism of the microstructure from the bottom to the top of the single track. This study can provide theoretical and technical support for the surface strengthening or repair of U71Mn rail.

Effect of Process Parameters on the Microstructure and Wear Resistance of Fe3Al/Cr3C2 Composites

In this paper, a brake cylinder coating comprising a composite material of an Fe3Al and Cr3C2 mixed powder was prepared by adding laser cladding onto carbon structural steel. We studied the influence of process parameters on the microstructure and tribological properties of the cladding materials using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and 3D white light interferometer and wear tests. The influence of different processes on the morphology of the carbide strengthening phase was found to be relatively small with a Cr3C2 content of 15 wt.%. The carbides mainly exhibited a network structure in each group of cladding layers. The area of the network strengthening phase varied under different processes. Of the cladding layers formed with different processes, the scanning speed of the 0.003 m/s cladding layer had the lowest wear rate. When the laser power was too low or the powder feed rate was too high, unmelted Cr3C2 particles could be found in the cladding layer. During the wear process, the particles peeled off, causing severe abrasive wear. When the powder feeding rate was too low, more materials in the base material entered the cladding layer. This made the composition of the cladding layer similar to that of the grinding material, resulting in severe adhesive wear.

Process parameter optimization for laser directed energy deposition (LDED) of Ti6Al4V using single-track experiments with small laser spot size

Single-track experiments are routinely used in the optimization of process parameters in additive manufacturing processes. Most of the process parameter optimization studies use a laser spot size of 1 mm or more. Since laser spot size affects the input energy density and in turn the efficiency of the deposition process, it is important to develop process maps every time a laser of different spot sizes is used. In this work, we determine the process maps for a laser of 0.6 mm spot size. By combining the process maps and the metallographic inspection, we estimate the optimum process parameters (laser power, scan speed, powder feed rate) for building Ti6Al4V components using powder-based laser-directed energy deposition(LDED). Single-tracks corresponding to 64 different parameter combinations are deposited. After eliminating the process parameter combinations resulting in defective tracks, the optimum process parameters of 300 W laser power and 720 mm min−1 scan speed is established by considering the relationship between the process parameters and the geometrical features of the deposit. The experimental results are then used to calibrate the modeling parameters of a three-dimensional finite element model for simulating the deposition process.

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.

Laser metal deposition of TiB/Ti6Al4V composites with first-scale network microstructure

This study investigated the effect of in-situ alloying of Ti6Al4V and TiB2 during laser metal deposition for microstructure, hardness and tensile properties enhancement. It was found that the addition of TiB2 at powder feed rates of range 0.1–0.3 rpm resulted in the formation of TiB whiskers with columnar and equiaxed network morphologies, in a lamella α + β matrix. By increasing TiB2 at 0.4–0.5 rpm, a complete dissolution of the equiaxed and columnar network morphologies were achieved. The dissolution led to a random distribution of formed TiB whiskers, resulting in enhanced hardness and ultimate tensile strength (UTS), with the 0.5 rpm giving the highest hardness and UTS values of 511 ± 13 HV and 1745 MPa, respectively.

Parameters optimization for laser-cladding CoCrFeNiMn high-entropy alloy layer based on GRNN and NSGA-II

In order to improve the bonding strength of FeCoCrNiMn cladding layer, laser power, scanning speed and powder feeding rate were selected as the optimization variables; the aspect ratio, dilution rate and heat affected zone depth of the cladding layer were selected as the optimization indicators; a three-factor three-level full-factor experiment was designed; a nonlinear model of cladding parameters and cladding performance was established by generalized regression neural network algorithm (GRNN), while the error of prediction value and experimental results was less than 10%. A set of optimal Pareto frontiers were obtained by the Non-Dominance Ordering Genetic Algorithm (NSGA-II), and the optimal individuals were obtained based on the equal weights, and the optimal cladding parameters were as follows: laser power 2.33 kW, scanning speed 2.90 m/min, and powder feeding rate 12.46 g/min. The cladding layer prepared under the optimal parameters has a dense cross-section with no defects such as cracks and porosity. The joint optimization using the GRNN neural network and the NSGA-II genetic algorithm can obtain excellent results, and the relative error between the experimental and predicted values can be controlled within 10%. The application of optimized laser process parameters can significantly improve defects such as poor adhesion, cracks and porosity on the surface of the cladding layer, and also improve the surface hardness and wear resistance. The experimental results show that the wear rate of the cladding layer prepared by the optimized parameters is 3.21×10−5 mm3/N·m, which is 1.5 times higher than that of the cladding layer prepared by P=2.1 kW, V=3 m/min and C=9 g/min. The wear mechanism mainly includes abrasive wear, plastic deformation and oxidative wear.

Studies on high power laser cladding Stellite 6 alloy coatings: Metallurgical quality and mechanical performances

The present study systematically investigates the effect of powder feeding rates (Vp) on the quality of Stellite 6 alloy coatings with a 20 kW fiber laser. The results demonstrate that the hot cracks in the Stellite 6 coatings can be effectively eliminated by increasing the Vp without preheating substrate or adding buffer layers. It is possible to achieve a single-track coating with a thickness of 2.34 mm, width of 20 mm and dilution rate of 17.3 % with crack-free and densely microstructure when Vp is 90 g/min. Moreover, the build rate (172 mm3/s) surpasses the maximum build rate (133 mm3/s) of low power laser cladding. The heat accumulation of multi-track and double-layer (5.6 mm) under high power laser results in the formation of ε-Co through phase transformation from part of γ-Co. Consequently, the dendrite region primarily consists of γ-Co while a small amount of ε-Co and Cr23C6 dominate in the inter-dendritic region. Although the heat accumulation effect also tends to coarsen the grains in bottom region of the coatings, leading to a slight reduction in mechanical properties, both hardness (485 HV–523 HV) and tensile strength (1131 MPa–1250 MPa) are comparable to those achieved by low power laser cladding, and the break elongation (6.9 %–8.1 %) has significantly surpassed the current level of 3 %. High power laser cladding processes may play a significant role in enhancing the effectiveness of surface modification or remanufacturing for large workpieces, such as the runner of hydroelectric generator set.

Effect of energy density on quality and properties of 18Ni300 laser clad layers by laser cladding

By preparing the 18Ni300 laser clad layers at different energy densities, the pores of the laser clad layers were measured and analyzed by using the image method, and the effect of energy density on the porosity was explored by combining the experimental data. The experimental results show that the cross-sectional pores of the laser clad layers are regular in shape and do not intersect with each other, and most of the pores are gathered at the top edge of the fused cladding layer. The influence of process parameters on the morphology of the laser clad layer is obvious. The study shows that the influence of process parameters on porosity is in the order of laser power, scanning speed, and powder feeding voltage; combined with the analysis of variance table and response surface diagram, the interaction between the parameters is obvious, and combined with the change, it can achieve the purpose of reducing porosity. Porosity first increases and then decreases with the increase in the energy density, and the distribution of the energy density and porosity is divided into regions, and larger porosity can be avoided by selecting the regions. The hardness of the laser clad layer can be increased by the choice of energy density. The laser clad layer with good test results was observed to contain Co, α-Fe, and Fe7Ni3 intermetallic compounds. The microstructure is transformed from fine grains at the top to columnar dendrites at the bottom.

Deposition characteristics, sintering and CMAS corrosion resistance, and mechanical properties of thermal barrier coatings by atmospheric plasma spraying

Atmospheric plasma spraying (APS) was used to fabricate 4.5 mol% Y2O3 stabilized ZrO2 (YSZ) and 4.0 mol% Yb2O3 and 0.5 mol% Y2O3 co-stabilized ZrO2 (YbYSZ) series coatings with different spraying parameters. This study presents the effects of particle size of feed powder and substrate temperature on the microstructure and performance of thermal barrier coatings. Single-pass and multi-pass experiments were conducted to explore the relationship between the splat and the coatings. The experimental results indicate that adjusting particle size of feed powders and deposition temperature can alter the splat behaviour and microstructure, improve anti-corrosion and anti-sintering abilities, and enhance the hardness and elastic modulus. Changes in parameters can cause changes in the microstructure of as-sprayed coatings. Lower substrate temperatures can lead to vertical cracks, finer powders can introduce more microdefects, and conventional sized powders can form larger pores. A coating deposited using a conventional feed powder at a substrate temperature of 800 °C shows excellent sintering resistance. A coating deposited using a fine feed powder on 800 °C substrate exhibits the best calcium‑magnesium-alumina-silicate (CMAS) corrosion resistance.

Influence of the laser-beam intensity distribution on the performance of directed energy deposition of an axially fed metal powder

This paper investigates the influence of laser-beam intensity distribution (LBID) on the performance of the annular laser-beam directed energy deposition (DED) process with axial powder delivery. Three different LBIDs: Gaussian-like (G-LBID), top-hat-like (TH-LBID) and ring (R-LBID) at two LBID diameters were used. The process performance was characterised qualitatively in terms of the melt-pool shape and the process stability and quantitatively by powder-catchment efficiency, selected geometrical and metallurgical properties of the clad. The observed influence of LBID on process performance, as determined by the relationship between LBID and powder stream density distribution (PSDD), decreased with increasing mean surface-energy density and was more significant at larger LBID diameter. The highest powder-catchment efficiencies (90% and 87%) were achieved with the G-LBID and TH-LBID, whose high-intensity centre is aligned with the peak of the Gaussian-like PSDD. A lower powder-catchment efficiency of 77% was achieved with the R-LBID, whose high-intensity region is located at the edge of the melt pool with minimum powder density. However, this also results in the highest and most uniform dilution, the highest metallurgical bond ratio and the lowest lack of fusion porosity at the clad-substrate interface. In addition, the process was stable at the lower values of mean surface-energy density with R-LBID, while balling instability was observed with G-LBID and TH-LBID. It can be concluded that the use of R-LBID at lower values of mean surface-energy density improves the performance of the DED process with axial powder feed in terms of process stability and metallurgical properties of the clad.