Cladding Speed Research Articles

Powder catchment efficiency in laser cladding (directed energy deposition). An investigation into standard laser cladding and the ABA cladding technique

This paper investigates the efficiency of powder catchment in blown powder laser cladding (a directed energy deposition technique). A comparison is made between standard “track by overlapping track” cladding (“AAA” cladding) and “ABA” cladding, where the gaps left between an initial set of widely spaced tracks (“A” tracks), are filled in by subsequent “B” tracks. In both these techniques, the melt pool surface is the collection area for the cladding powder, and the shape of this pool can be affected by several parameters including cladding speed, intertrack spacing, and type of cladding technique. The results presented here are derived from of an analysis of high-speed videos taken during processing and cross sections of the resultant clad tracks. The results show that the first track in AAA cladding has a different melt pool shape to subsequent tracks, and that the asymmetry of the subsequent track melt pools results in a reduction in the powder catchment efficiency. In contrast to this, the geometry of the “B” track melt pools between their adjacent “A” tracks results in an enhanced powder catchment efficiency.

Surface quality optimization of laser cladding based on surface response and genetic neural network model

The model was established to optimize the laser cladding process parameters, the coating surface topography can be predicted and controlled. Taguchi and Box-Behnken (BBD) experiments were used to carry out the experimental design of laser cladding multi-channel lap. 316 L stainless steel coating was cladded on the surface of 45 steel substrate. The genetic algorithm-back propagation (GA-BP) neural network and response surface methodology (RSM) models were established respectively. The prediction accuracy of the two models was compared. The coupling effect between cladding process and multi-channel lap forming quality was analyzed. The relationship between cladding process parameters, such as laser power, feeding speed, scanning speed and overlap ratio, and surface roughness of coating was studied. The experimental results show that: The root mean square error (RMSE) and absolute mean deviation (AAD) of the GA-BP model are smaller than those of the RSM model. The coefficient of determination R2 of the GA-BP model is closer to 1 than that of the RSM model. The minimum roughness predicted by GA-BP model is 20.89 μm, which is lower than that of RSM model (35.67 μm). The final findings: in the optimization of process parameters of laser cladding, overlap ratio and scanning speed has significant effects on coating surface roughness. The GA-BP model of the coating surface roughness prediction accuracy is better than the RSM model. The prediction and control of the coating surface roughness are realized by GA-BP model, for the precise forming of the laser cladding coating surface, which provides theoretical basis and technological direction.

Effect of laser cladding speed on microstructure and properties of titanium alloy coating on low carbon steel

Titanium and its alloys have excellent corrosion resistance in the marine environment, but their applications are limited by the high cost of raw materials and manufacturing difficulties. In this work, we successfully prepared a thin titanium alloy coating on the low carbon steel surface by a laser cladding method. With a systematical study on the cladding process, the laser cladding speed is found to be the crucial parameter to tune the coating performance. On the one hand, the corrosion resistance is determined by the laser cladding speed. The higher laser cladding speed leads to a thinner coating thickness, and the melted titanium powder is less resulting in a high dilution rate. The increase of the dilution rate is more likely to cause surface cracks, and the corrosion resistance decreases due to these cracks and the formation of the Fe-Ti intermetallic compounds on the coating surface. When the laser cladding speed is 6 mm/s, the sample possesses the lowest dilution rate of 9.9 % and the best corrosion resistance (Ecorr of −0.247 V and Icorr of 1.526 × 10−8 A·cm−2). Therefore, the critical dilution rate D (9.9 %) can be proposed as the optimization goal for the laser cladding speed. When the dilution rate is equal to or lower than the D, the corresponding laser cladding process can guarantee sufficient corrosion resistance of the titanium alloy coating. On the other hand, the laser cladding speed can also influence the coating hardness and the interfacial adhesion strength between the coating and substrate. When the laser cladding speed is slow, the coating hardness decreases to a certain extent, while the interfacial adhesion strength slightly descends. Therefore, this work can expedite the effective applications of titanium alloys in marine engineering equipment, with a greatly reduced cost and ensured performance.

A Comparative Study on Microstructure and Properties of Ultra-High-Speed Laser Cladding and Traditional Laser Cladding of Inconel625 Coatings.

In this study, ultra-high-speed laser cladding (UHSLC) and traditional low-speed laser cladding (LSLC) were employed to prepare high-quality Inconel625 coatings on 27SiMn substrates. UHSLC has cladding speeds of 30 m/min, which are 15 times faster than those of LSLC, and it produces a much greater cladding efficiency, which is 13.9 times greater than LSLC. The microstructure of the Inconel625 coatings was investigated in detail utilizing field emission scanning electron microscopy (FESEM) and electron probe microanalyzer (EPMA). According to the FESEM results, UHSLC Inconel625 coatings have more refined crystals than LSLC Inconel625 coatings. Nevertheless, the EPMA results indicate that the UHSLC Inconel625 coatings exhibit much more severe elemental segregation. Moreover, the hardness, wear and corrosion resistance of Inconel625 coatings are significantly enhanced by increasing the laser cladding speed. Furthermore, the reasons for the differences in microstructure and properties of Inconel625 coatings prepared by UHSLC and LSLC were clarified by finite element simulation. UHSLC technique is, therefore, more suitable for preparing Inconel625 coatings on 27SiMn steel surfaces than LSLC.

Microstructure and corrosion behavior of Al-Ti-TiC-CNTs/AZ31 magnesium matrix composites prepared using laser cladding and high speed friction stir processing

Al-Ti-TiC-CNTs/AZ31 magnesium matrix composites (MMCs) were prepared using laser cladding (LC) and high speed friction stir processing (HS-FSP). The surface microstructure, phase composition, microhardness distribution and corrosion resistance of the MMCs were studied using scanning electron microscope (SEM), X-ray diffraction (XRD), microhardness tester and electrochemical workstation. The composite layers were composed of phases with different geometric morphology and distribution characteristics identified as α-Mg, Al12Mg17 and TiC phases. A defect-free LC composite layer with refined microstructure and a sound metallurgical bonding interface between the LC composite layer and the matrix were observed. In addition to maintaining the sound metallurgical bonding interface, the microstructure of the LC composite layer was significantly refined and densified after being subjected to HS-FSP. The surface microhardness and self-corrosion potential of the MMCs prepared using LC was obviously enhanced due to the formation of a large number of Al12Mg17 and TiC phases, but they show a decreasing trend with decreasing the Al12Mg17 and TiC phases. The MMCs produced using HS-FSP exhibited higher surface microhardness and better corrosion properties than those of the LC due to the formation of finer and denser microstructure and higher numbers of Al12Mg17 and TiC phases in the composite layers.

Microstructure and corrosion resistance of TiC/Inconel 625 composite coatings by extreme high speed laser cladding

Extreme high speed laser cladding technology (EHLA) can break the efficiency bottleneck of coating production and provide an effective access to prepare high quality coating. In this study, TiC/Inconel 625 composite coating was produced on AISI 1045 substrates by EHLA and conventional laser cladding (CLA), respectively. The microstructure, elements distribution, XRD pattern and corrosion morphology of the coating under different cladding speeds were characterized. The potentiodynamic polarization and electrochemical impedance spectroscopic were implemented for further investigating the corrosion behaviors of the coating. The results indicated that the microstructure of the both coatings exhibited the same growth pattern, changing from cellular crystals or primary columnar crystals to equiaxed crystals. High cladding speed was accompanied by dendrite refinement and uniform elements distribution. The refiner microstructure benefitting from the high cooling rate contributed to the improvement of the coating corrosion resistance. In the process of EHLA, the incorporation of TiC facilitated the formation of interdendritic carbides playing a role of precipitation strengthening. Many dislocation lines and dislocation tangles formed in EHLA coating are conducive to building a dense passive film on the coating surface. Corrosion tests showed that EHLA coating performed superior corrosion resistance compared to CLA coating.

Cracking mechanism of brittle FeCoNiCrAl HEA coating using extreme high-speed laser cladding

FeCoNiCrAl high entropy alloys (HEAs) are regarded as promising coating materials for traditional steel. However, the brittle nature always contributes to the cracking of the equiatomic FeCoNiCrAl HEA coating. In this work, FeCoNiCrAl coatings on C45 carbon steel and 304 stainless steel (304SS) pipes were fabricated using extreme high-speed laser cladding (EHLA) with a cladding speed of 50 m/min. The results showed the high-hardness character of the two coatings on C45 and 304SS substrates. The C45 substrate showed a remarkable effect on the cracking of the coating. The martensitic transformation of the heat-affected zone (HAZ) of the C45 substrate was considered the main factor contributing to cracking of the coating. The finite element method showed that the martensite transformation of C45 expanded the volume and increased the hardness of the HAZ. This restricted the plastic deformation of the substrate and increased the tensile stress and cracking tendency of the coating. As a martensitic transformation did not occur in 304SS, the low-hardness substrate effectively relieved the tensile stress in the coating and avoided cracking. • The MT of HAZ of C45 contributed the cracking of EHLA HEA coating • MT increased the volume and hardness of HAZ of C45 substrate. • Volume expansion and hardening of HAZ restricted the interfacial plastic deformation. • High interfacial stress of coating resulted in the crack initiation.

Influence of the Laser Cladding Parameters on the Morphology, Wear and Corrosion Resistance of WC-Co/NiCrBSi Composite Coatings.

To enhance the sliding wear and corrosion behavior of steels with low carbon content, cermet composite coatings are usually deposited on their surface by various deposition processes. Laser cladding, compared to other deposition techniques such as electroplating, arc welding, and thermal spraying, has numerous advantages to produce such protective coatings. The paper presents the optimization of laser cladding deposition speed versus energy density in order to obtain WC-Co/NiCrBSi coatings with Ni-Al addition free of defects and reduced porosity deposited on low carbon steel substrate. The microstructure and chemical composition were investigated by SEM combined with EDX analysis while XRD was performed in order to examinate the phases within the coatings. In order to investigate the cladding speed influence on the coatings, hardness measurements, POD (pin on disk) wear tests and corrosion tests in 3.5% NaCl solution were carried out. The results showed that an optimal cladding speed has a crucial impact on the microstructure, composition, and hardness. It was found out that optimizing the cladding deposition speed proved to be effective in enhancing the sliding wear resistance and corrosion behavior by controlling the iron content within the coatings.

Influence of Process Parameters on Microstructure of Reaction Plasma Cladding TiC-Fe-Cr Coating

In order to improve the quality and properties of the coating, a certain amount of Ti was added to the plasma cladding Fe-Cr-C coating in the early stage. And Fe-Cr-C-Ti composite powder was prepared by precursor carbonization-composition process. In situ synthesized TiC-Fe-Cr coatings were fabricated on substrate of Q235 steel by plasma cladding process with Fe-Cr-C-Ti composite powder. Microstructure of the coating with different process parameters, including cladding current, cladding speed, number of overlapping cladding layers, were analyzed by scanning electron microscope (SEM). The results show that the structure of the TiC-Fe-Cr coating is greatly affected by the fusion current, the cladding speed and the overlapping cladding process. In this test, when the cladding current of 300A and the cladding process parameter of the cladding speed of 50 mm/min are clad with three layers, a well-formed and well-structured TiC-Fe-Cr coating can be obtained. Which are the best synthetic process parameters in this test.

Effect of Plasma Cladding Speed on the Microstructure and Properties of ZrC-ZrB2/NiAl Coating

NiAl composite coating strengthened by ZrC and ZrB2 phases is synthesized by the plasma cladding process. The influence of cladding speed on microstructrue and properties of coatings is studied. The main phases of coatings are NiAl, γ-(Fe,Ni), ZrC and ZrB2 phases. ZrC is in the shape of points and small blocks, ZrB2 shows long strips and needle bar. The slower the cladding speed, the larger the size of the reinforcing phases. With the increase of cladding speed, the wear resistance of the coatings improves. Coating with the cladding speed of 10mm/s has excellent wear-resistance property owing to high hardness and low friction coefficient. ZrC and ZrB2 strengthening phases play an important role. The main wear mechanism of NiAl composite coating is adhesive wear.

A comparative study on microstructure and properties of traditional laser cladding and high-speed laser cladding of Ni45 alloy coatings

High-speed laser cladding technology can significantly improve the efficiency of coating preparation and effectively widen the application range of laser cladding. In this study, the Ni45 powders were deposited on steel substrate by traditional low speed laser cladding and high-speed laser cladding process, respectively. The cladding efficiency, surface forming, cross-sectional microstructure, microhardness, wear and corrosion resistance properties of the traditional and high-speed laser cladded Ni45 alloy coatings were compared. It can be seen that the thickness of the high-speed laser cladding coating was much thinner than that of the traditional laser cladding coating. Compared with traditional laser cladding, high-speed laser cladding could achieve a cladding speed of 76.86 m/min and a cladding efficiency of 156.79 cm2/min. The microstructure of the two kinds of coatings shows the same growth law, but the microstructure in high-speed laser cladding was smaller and denser, and the columnar crystal interval was narrower, only about 6 μm. It is found that the cooling rate of the traditional laser cladding coating was smaller than that of the high-speed laser cladding, and as the cladding speed increased, the cooling rate became higher and higher. The cross-section microhardness of the traditional laser cladding coating was relatively uniform of 337 HV0.2, while the microhardness of high-speed laser cladding surface increased to about 543 HV0.2. In addition, the wear and corrosion resistance of high-speed laser cladded coatings were better than that of traditional laser cladded coatings. As the cladding speed increased, the wear and corrosion resistance of the cladded coatings became better.

Process optimization for directed energy deposition of SS316L components

Directed energy deposition (DED), also known as laser cladding, is a metal additive manufacturing process in which a high-power laser combined with a coaxial powder delivery system is used to additively manufacture a three-dimensional metal component layer-by-layer. Due to its convenience and superior quality, DED has gained popularity in recent years. However, despite many advantages, it has low deposition efficiency and produces parts with poor surface evenness, high porosity, and poor mechanical properties. This study performs one-factor-at-a-time experiments to valuate five DED processing parameters, namely the laser and powder focus point positions, laser head raising height (Z-offset), laser power, powder feed rate, and laser scanning speed. The laser and powder focus point positions and the Z-offset are first adjusted to maximize the surface evenness and deposition efficiency. Several experiments are then performed to investigate the effects of laser power, powder feed rate, and laser cladding speed on the porosity and dilution of DED-built parts. Finally, a mathematical model is proposed to predict the quality (i.e., dilution) of DED-built parts as a function of DED processing parameters. Based on the results, the optimal focus point positions and Z-offset are found. The variations of porosity and dilution with three processing parameters are shown. The proposed model can be used to set up DED processing parameters to produce higher quality parts on the first attempt.

Investigations on dry sliding of laser cladded aluminum bronze

The aim of this study was to investigate the tribological behaviour of laser cladded aluminum bronze tool surfaces for dry metal forming. In a first part of this work a process window for cladding aluminum bronze on steel substrate was investigated to ensure a low dilution. Therefore, the cladding speed, the powder feed rate, the laser power and the distance between the process head and the substrate were varied. The target of the second part was to investigate the influence of different process parameters on the tribological behaviour of the cladded tracks. The laser claddings were carried out on both aluminum bronze and cold work tool steel as substrate materials. Two different particle sizes of the cladding powder material were used. The cladding speed was varied and a post-processing laser remelting treatment was applied. It is shown that the tribological behaviour of the surface in a dry oscillating ball-on-plate test is highly dependent on the substrate material. In the third part a deep drawing tool was additively manufactured by direct laser deposition. Furthermore, the tool was applied to form circular cups with and without lubrication.

Facile Fabrication and Microstructure of α‐Al2O3/TiC Composite Coating as Tritium Permeation Barrier

Well‐crystallized α‐Al2O3/TiC composite coating was synthesized on the surface of steel substrate by a facile laser‐assisted combustion synthesis technique without subsequent calcination. The effect of laser cladding speed on formation and microstructure of the coatings was studied. At 6 mm/s, α‐Al2O3/TiC coating with good quality was obtained without pores and cracks and was well bonded with the steel substrate. By adjusting the precoating thickness, the coating thickness was easily controlled. As a simple, environmentally friendly and energy‐saving technique, laser‐assisted combustion synthesis is expected to find applications in ceramic coating fabrication as tritium permeation barrier or wear‐ and corrosion‐resistance coatings.

Spectroscopic monitoring of metallic bonding in laser metal deposition

A new approach is presented in this paper to link optical emission spectrum analysis to the quality of clad layers produced with laser metal deposition (LMD). A Nd:YAG laser (λ=1.064μm) was used to produce clad tracks with Metco 42C powder on AISI 4140 steel substrate. The laser power was ramped in steps of 220W from 800W to 2780W focusing the laser beam into a 4.8mm diameter spot. A constant cladding speed of 10mms−1 is used with a powder feeding rate of 0.36gs−1. The extent of metallic bonding is evaluated from dilution data obtained by measuring the melt depth in the substrate from cross sections of the clads. The spectra generated during the deposition process were collected with an optical spectrometer attached to the laser head. The discrete spectral lines from the collected spectra were identified from the NIST database as Fe I and Cr I lines. Two different spectral analysis methods were used, namely the calculation of the electron temperature Te and the intensity ratio IR. The electron temperature Te is computed from four discrete Cr I lines at 526.415, 529.827, 532.834, and 534.044nm wavelength. The intensity ratio IR is a measure of the absorption of a discrete Fe I line at 588.91nm. The analysis of the collected spectra indicates that onset and extent of metallic bonding can be detected with a spectrometer during the deposition process. A sudden decrease of the IR signal during the LMD process indicates the onset of metallic bonding. A further increase of the laser power mainly contributes to an increase in melt depth, leading to a higher dilution. In this region, the Te signal shows a better correlation with the dilution.

Complex analysis of elaboration of steel–TiC composites by direct metal deposition

Development of composites with multifunctional properties is a challenging problem that could be solved by laser cladding. Robotic laser cladding with coaxial powder injection is often referred to as direct metal deposition (DMD). The objective of the present work is to demonstrate the advantages of the optical monitoring in optimizing the deposition of carbide-reinforced metal matrix composites (MMCs). A multiwavelength pyrometer and an infrared camera are applied to analyse high temperature heat and mass transfer in the DMD zone. The influence of the laser power, laser cladding speed, and powder feeding rate on the true temperature is studied. The thermal images of the molten pool obtained by the infrared camera for different TiC contents in the powder blend are analysed as well as the beads geometry, microstructure, and microhardness. It is found that MMC with the low TiC content (2.5 and 5 vol. %) has the highest microhardness (about 550 HV0.1) due to the formation of the supersaturated solid solution of TiC in α-Fe with a strong distortion of the crystal lattice. At the 10 vol. % TiC content, the material microhardness insignificantly exceeds the one of the pure laser-cladded steel (about 280 HV0.1) because of the nonequilibrium eutectic which is composed mainly of the ductile α-phase in the form of a rim around the TiCprim crystals.

Study on Corrosion Resistance of Fe-based Amorphous Coating by Laser Cladding in Hydrochloric Acid

Abstract In this study, the Fe41Co7Cr15Mo14C15B6Y2 bulk amorphous alloy with high glass-forming ability was prepared using the arc- melting copper mold casting technique, and corresponding amorphous coating was obtained using the laser melt amorphous powders on the surface of carbon steel. The corrosion resistance performance of the laser cladding coating in hydrochloric acid was analyzed and tested in experiments under the conditions of different laser cladding speeds. The amorphous alloy coating with different fabrication parameters have the difference internal structure, which lead to the difference corrosion resistance in the same environment to some extent. The nature of amorphous alloy and the corrosion morphology were investigated using XRD and SEM method, respectively. The corrosion experiments showed that: when the laser power was 3300W, the corrosion resistance of four kinds of samples in hydrochloric acid from strong to weak as follows: as-cast sample > the coating with laser cladding speed 110 mm/min > the coating with laser cladding speed 120 mm/min > the coating with laser cladding speed 130 mm/min. The free corrosion current density of casting sample, sample 1, sample 2 and sample 3 is 3.304 × 10-6 A/cm2, 2.600×10-3 A/cm2, 2.030×10-3 A/cm2 and 3.396×10-4 A/cm2, respectively.

Optical Monitoring in Elaboration of Metal Matrix Composites by Direct Metal Deposition

Development of composites with multi-functional properties is a challenging problem that could be solved by laser cladding. The objective of the present work is to demonstrate the advantages of optical monitoring in optimizing deposition of carbide-reinforced metal matrix composites. Multi-wavelength pyrometer and infrared camera are applied to analyse high temperature heat – and mass transfer in the cladding zone. The influence of laser power, laser cladding speed and powder feeding rate on the brightness temperature are studied. The thermal images of the molten pool obtained by infrared camera for different TiC contents in the powder blend are analysed as well as the beads geometry, microstructure and microhardness.

Analytical modeling and experimental investigation of laser induction hybrid rapid cladding for Ni-based WC composite coatings

Laser induction hybrid rapid cladding (LIHRC) cannot only increase the cladding efficiency, but can also eliminate porosity and cracking of ceramic–metal composite coatings. In order to obtain a deep understanding of LIHRC with rapid cladding speed and high powder deposition rate, an analytical model of LIHRC for Ni-based WC composite coatings is proposed in the paper. The predictions of cladding height and powder efficiency obtained with this model are in good agreement with experimental results. Injection angles at which the attenuation rate of laser power is relatively low are identified and crack-free composite coatings with smooth surface, good profile and metallurgical bonding to substrate can be obtained. The calculated results for the temperature of the powder particles are compared to experimental data of the microhardness profiles and show a similar trend.

Optimization of Processing Parameters During Laser Cladding of ZE41A-T5 Magnesium Alloy Castings Using Taguchi Method

A continuous wave 4 kW Nd:YAG laser welding system was employed to clad single beads on machined 6.2-mm thick ZE41A-T5 aerospace magnesium alloy sand castings using nominal 1.6-mm filler rods of the parent metal. Based on the quality criterion of minimum dilution ratio, the Taguchi experimental method was used to optimize different process parameters and to identify the dominating factors. It was found that, for the process window investigated in this work, the optimal levels were 5.0 m/min for wire feed rate, 2.25 kW for laser power, and 2.5 m/min for cladding speed, with a minimum dilution ratio of 0.155. With 95% confidence, the wire feed rate is the dominating factor with the most significant influence on the dilution ratio. The dilution ratio usually decreases with increased wire feed rate while it increases with increased laser power. By contrast, the cladding speed appears to have insignificant influence on the dilution ratio over the cladding speed range used in this study.