Effects of Process Parameters on Microstructure and Hardness of Layers by Laser Cladding

Laser cladded NiCrBSi alloy coating was fabricated on the surface of a 42CrMo roll using a 6 kW fiber laser. The effects of the laser power, scanning speed and feeding rate on the cladding layer form, size, dilution rate, microstructure, and hardness of coating were studied by using optical microscopy (OM), scanning electron microscopy (SEM) and a microhardness tester. The results show that the microstructure, size, dilution rate and hardness of the cladding layer had changed with an increase in laser power, powder feeding rate and scanning speed. The appropriate parameters of the laser cladding experiment are as follows: the laser power is 2000 W, powder feed rate 20 g × min-1, the scanning speed 4 mm × s-1. The cladding layer and the substrate exhibit good metallurgical bonding under the above processing parameters. The microstructure of the cladding layer is fine, the dilution rate is 9.8 wt.-%, and the microhardness of the cladding layer is 710.7 HV.

Analysis and prediction of Cu-Sn-Ti alloy deposited on 316 L steel by coaxial laser cladding

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.

To study the surface morphology of laser cladding, Workbench simulated the influence of laser power and scanning speed on the width and height of the cladding layer numerically, as well as the temperature field change and residual stress distribution of the cladding layer. The simulation results reveal that the melting height and width of the cladding layer are inversely proportional to the scanning speed. When the scanning speed is from V = 3 mm/s to V = 5 mm/s, the Al cladding layer’s melting width and melting height are reduced by 15.59% and 20.8%, respectively. A positive correlation exists between the melting height and width of the cladding layer and the laser power. When the laser power changes from P = 23 w to P = 27 w, the welding width and height of the A1 cladding layer increase by 6.55% and 55.56%, respectively. The melting height and width of the second cladding layer are generally higher than those of the bottom cladding layer. The pre-experiment screening process parameters ranges are laser power P (23 w–27 w) and scanning speed (3 mm/s–8 mm/s). Based on the Minitab response surface central composite method, the most notable influence on the melting height and width is revealed to be the powder-feeding rate and laser power, respectively. The response surface analysis method establishes the regression prediction models of melting width and height. The predicted value of melting width was 95.68%, and the predicted value of melting height was 82.26%. The results show that the values of cladding width and height are within the 95% prediction interval, proving that the regression model is correct.

This paper aimed to establish a nonlinear relationship between laser cladding process parameters and the crack density of a high-hardness, nickel-based laser cladding layer, and to control the cracking of the cladding layer via an intelligent algorithm. By using three main process parameters (overlap rate, powder feed rate, and scanning speed), an orthogonal experiment was designed, and the experimental results were used as training and testing datasets for a neural network. A neural network prediction model between the laser cladding process parameters and coating crack density was established, and a genetic algorithm was used to optimize the prediction results. To improve their prediction accuracy, genetic algorithms were used to optimize the weights and thresholds of the neural networks. In addition, the performance of the neural network was tested. The results show that the order of influence on the coating crack sensitivity was as follows: overlap rate > powder feed rate > scanning speed. The relative error between the predicted value and the experimental value of the three-group test genetic algorithm-optimized neural network model was less than 9.8%. The genetic algorithm optimized the predicted results, and the technological parameters that resulted in the smallest crack density were as follows: powder feed rate of 15.0726 g/min, overlap rate of 49.797%, scanning speed of 5.9275 mm/s, crack density of 0.001272 mm/mm2. Therefore, the amount of crack generation was controlled by the optimization of the neural network and genetic algorithm process.

Effects of process parameters on properties of porous foams formed by laser-assisted melting of steel powder (AISI P21)/foaming agent (ZrH2) mixture

The aim of the present work is to establish the relationship between laser cladding (LC) process parameters (power, process speed, and powder feed rate) and AISI D2 tool steel metallurgical transformations, with the objective of optimizing the processing conditions during real reparation. It has been deposited H13 tool steel powder on some steel substrates with different initial metallurgical status (annealed or tempered) using a coaxial LC system. The microstructure of the laser clad layer and substrate heat-affected zone (HAZ) was characterized by optical microscopy, scanning electron microscopy, and electron backscattered diffraction. Results show that the process parameters (power, process speed, feed rate, etc.) determine the dimensions of the clad layer and are related to the microstructure formation. Although it is simple to obtain geometrically acceptable clads (with the right shape and dimensions) in many cases some harmful effects occur, such as carbide dilution and non-equilibrium phase formation, which modify the mechanical properties of the coating. Specifically, the presence of retained austenite in the substrate–coating interface is directly related to the cooling rate and implies a hardness diminution that must be avoided. It has been verified that initial metallurgical state of the substrate has a big influence in the final result of the deposition. Tempered substrates imply higher laser absorption and heat accumulation than the ones in annealed condition. This produces a bigger HAZ. For this reason, it is necessary to optimize the process conditions for each repair in order to improve the working behaviour of the component.

Multi-response optimization of Ni-based laser cladding via principal component analysis and grey relational analysis

Silicon carbide (SiC) microchannels show their promising merits in the applications of microchannel heat sink cooling systems, microsensor MOS devices, and UV photodiodes. The fabrication of SiC microchannels is critical for their wide applications. In this study, a laser micromilling method is utilized to process SiC microchannels. A series of SiC microchannels are fabricated using a pulsed fiber laser. Based on the SEM observations and 3D confocal microscope measurements, the formation of microchannels is analyzed. The effects of laser processing parameters, such as laser output power, scanning speed, and scanning times as well as the predetermined microchannel width, on the geometric dimension and surface morphology are systematically assessed. The common recast layer deposited around the laser-scanned areas in the laser micromilling of metallic structures was not found for the SiC microchannels. A transition between triangular and trapezoidal shapes occurred for the laser-micromilled microchannels depending on the processing parameters and predetermined width. The microchannel depth increased monotonically with the laser output power and laser scanning time but decreased with increasing scanning speed. On the contrary, the bottom width of microchannels presented an inverse trend. The surface roughness was dependent on the laser scanning speed, scanning time, as well as predetermined width.

Optimization of process parameters for laser cladding Stellite6 cobalt-based alloy

Influences of depositing materials, processing parameters and heating conditions on material characteristics of laser-cladded hypereutectoid rails

When laser cladding is used to repair parts, the interaction of parameters has a significant influence on equipment performance. In order to explore the process parameters and quality of Ni60PTA coating, the statistical relationship between the process parameters (laser power, scanning speed, and powder feeding rate) and the responses (dilution ratio, ratio of layer width to height, and contact angle) was established by experiments using the response surface method (RSM) and variance analysis. The results show that the laser power is the dominant factor affecting the dilution ratio. However, the scanning speed has the greatest influence on the ratio of layer width to height and contact angle. These experimental results show that the proposed model can predict the actual data. In addition, the microstructure and microhardness of the samples prepared with the optimum process parameters were characterized. The results show that the quality of the cladding layer is good without cracks, deformation, and pores. The microstructure of the cladding zone is mainly composed of γ (Ni), FeNi3, M (M = Fe, Ni, Cr)23C6, M7C3, and CrB. The average microhardness of the coating is about 620 HV0.2, which is about 3.1 times that of 45 steel substrate.

Grain size evolution under different cooling rate in laser additive manufacturing of superalloy

Selective laser melting (SLM), a significant branch of laser additive manufacturing (LAM) technology, has become a popular topic of research in engineering, materials and many other disciplines. SLM can transform metallic powders directly into 3D components, which allows SLM to offer the unique flexibility of manufacturing parts with complex structures. The quality of the product is closely related to the characteristics of the temperature field, as well as that of the molten pool. Because of the high localized temperatures and the rapid cycles of melting and solidification during SLM, it’s difficult to monitor the temperature field in real time. Hence, numerical simulation is often used to study the SLM process. In this work, the SLM process of ZL104 aluminum alloy was simulated using the CFD method, and the influences of processing parameters, including laser power and scan speed, on the temperature field and the characteristics of the molten pool have been investigated. Results showed that when the laser power increased, the peak temperature of the molten pool also mounted, however, the maximum temperature of the molten pool fell as the scan speed rose. The dimensions of heat affected zone (HAZ), including the width and depth, increased with growing laser power, but decreased with the increase of scan speed.

In order to achieve the restoration of the sprocket, it is significant to repair or modify the damaged sprocket by using an advanced surface treatment technique, such as the laser cladding process. In this paper, the Taguchi method was applied to conduct the experiment to optimize the process parameters for repairing a sprocket in the laser cladding process. The dilution was chosen to evaluate the quality of the cladding layer and the effect of the process parameters, such as the laser power, scanning speed, and powder feeding rate, with respect to the cladding layer geometry, and the dilution was investigated systematically. Then, using the optimized parameters, the sprocket was remanufactured and its surface profile characteristics, microstructure, and microhardness of the repaired sprocket were analyzed. The results show that the optimal process parameters (1000 W, 2.81 g/min, 1200 mm/min) obtained by the Taguchi method could realize the lower dilution. With the optimal parameters, the repair accuracy of the sprocket could reach 2.973 mm, which offers the machining allowance for machining of the sprocket. A white bright band observed at the interface shows that the metallurgical bonding was realized between the cladding zone and base metal. The microhardness of the cladding zone is higher than that of the heat-affected zone and base metal. Furthermore, the results reveal that the Taguchi method can effectively acquire the optimal combination of process parameters, and the laser cladding process exhibits good feasibility and effectiveness for repairing the machinery components with complex shapes.