Single Clad Research Articles

Porosity Reduction in 15CDV6 Steel Manufactured by L-DED

The Laser Directed Energy Deposition (L-DED) is an Additive Manufacturing process based on the direct injection of the filler material into the desired areas of a substrate. Damaged components can be repaired or coated in order to enhance their properties and increase their lifespan. However, this process is highly material dependent and to assure the quality of the deposited material, the process parameters need to be optimised. In the present work, a novel material for the L-DED is developed, the 15CDV6 aeronautical steel. The material was atomized ad hoc and the obtained powder was characterized (particle shape, size distribution, and chemical composition) in order to ensure its quality. Once the powder was analysed, the suitability of the 15CDV6 steel for the L-DED process was studied through a methodology consisting of three sequential steps: single clad tests, layer deposition and wall construction. The main process parameters (laser power, feed rate and powder feed rate) were controlled during these tests. Nevertheless, the initial tests showed high levels of porosity, which required considering additional process parameters to reduce them, such as the carrier and shielding gas flows, preheating, or the laser beam diameter. Consequently, the porosity formation mechanisms were identified and the most relevant process parameters established, which for the 15CDV6 steel were the gas flows. The effect of the shielding gas flow in the powder distribution below the nozzle was studied experimentally by digital image analysis to better interpret the obtained results and determine the optimum process parameters for achieving defect free parts. The quality of the deposited material was studied through metallographic analysis and an Acicular Ferrite structure was observed, ensuring good mechanical properties. To summarise, this research work proves the viability of employing 15CDV6 steel in the L-DED process and has determined the main process parameters to obtain porosity-free parts.

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.

10-µJ-level femtosecond pulse generation in the erbium CPA fiber source with microstructured hollow-core fiber assisted delivery and nonlinear frequency conversion.

We report on the development of a chirped pulse amplification (CPA) designed erbium fiber source with a hybrid high-power amplifier, which is composed of erbium-doped and erbium/ytterbium-co-doped double-clad large-mode-area fibers. Stretched pulses from the high-power amplifier with up to 21.9µJ energy and 198.5kHz repetition rate are dechirped in the transmission grating pair-based compressor with 73% efficiency, yielding as short as 742fs duration with 15.8µJ energy and ≈13M W peak power (maximum average power up to 3.14W) at the central wavelength of 1.56µm. Compressed pulses are coupled into microstructured negative-curvature hollow-core fibers with a single row capillary cladding and different core sizes of 34µm and 75µm in order to realize femtosecond pulse delivery with a diffraction-limited output beam (M 2≤1.09) and demonstrate ∼200n J Stokes pulse generation at 1712nm via rotational SRS in pressurized hydrogen (H 2). We believe that the developed system may be a prospect for high-precision material processing and other high-energy and high-peak-power laser applications.

Experimental and Analytical Investigation of the Re-Melting Effect in the Manufacturing of 316L by Direct Energy Deposition (DED) Method

In this study, the effects of the laser power (2000 W, 2250 W, 2500 W), scanning speed (0.6, 0.8, 1 m/min), and powder feed rate (10, 12.5, 15 g/min) on material structures and their mechanical properties were investigated in the production of 316L stainless steels through Direct Energy Deposition (DED). In addition, changes in the microstructure caused by the re-melting process were also investigated. Optimized process parameters were modeled using the CFD software (FLOW 3D V3.0). In order to see the effects on the density and mechanical properties, the sample production was repeated as a build and by applying the re-melting process between the layers. When the energy density and powder feed rate are considered together, it has been determined that the deposition rate increases in direct proportion to the energy density and tends to decrease inversely with the powder feed rate. When the experimental and analysis results of the single clad height are compared, it is seen that the values obtained are very approximate. It has been observed that the most important parameters affecting the formation of porosity are the energy density and powder feed density. Re-melting slightly affects the microstructure of the material and causes grain growth. Changes in the impact strength of the re-melted samples were observed depending on the energy density.

Machine-agnostic energy density model for laser, powder-blown directed energy deposition

Due to a lack of standardization of process parameters, experimental results from different laser powder-blown directed energy deposition (DED) machines can be difficult to compare or repeat. A specific energy density model is presented that can describe the deposited clad geometry and can guide the choice of initial process parameters instead of using the typical guess-and-check method. Single clads built using a wide variety of process parameters are used to validate the model, and a comparison is made between data sets from two different machines. Two power laws are established that relate the clad shape and dilution state to specific energy density. This work ultimately enables the determination of the low bound of process parameters for a successful DED build using analytical equations and known material properties, the proper translation of process parameters between machines on which experimental results are collected, and the establishment of a theoretical base for process control of clad structure.

Friction riveting of FR4 substrates for printed circuit boards: Influence of process parameters on process temperature development and joint properties

This work investigates the influence of Friction Riveting processing conditions on FR4-PCB substrate/AA2024 rivet joints in terms of process temperature evolution, joint formation, and joint physical-chemical and mechanical properties. The joints were manufactured using 4 mm diameter AA-2024-T3 rivets and FR4 laminates of 1.5 mm thickness with single or double copper-clad layers. The evolution of process temperature evolution was recorded on the FR4 substrate surface and correlated with the resulting joint formation. Most joints obtained with double copper clad layers developed process temperatures above 300 °C, whereas joints produced with a single copper clad presented slightly lower temperatures, but still above 250 °C. Rivet anchoring was achieved for both FR4 material combinations in the configuration of a single-base laminate, as well as two and even three overlapped laminates. Thermogravimetric analyses revealed that above 300 °C intensive thermal degradation occurs on FR4 materials (with 30% mass change), followed by decomposition, resulting in non-uniform heat distribution throughout the thickness. The joint ultimate tensile force was higher for double copper-clad layers and the joints achieved within more than one laminate, showing higher anchoring efficiency.

Theoretical analysis of mode evolution in a tapered double clad fiber based on the coupled local mode theory

Mode characteristics of a tapered double clad fiber should be analyzed based on three-layer waveguide model, so it is more complicated than that of a single clad fiber. In this paper, a method based on coupled local mode theory is introduced to calculate the mode evolution process in a tapered double clad fiber. Mode field characteristics of double clad fiber are calculated analytically with weak guidance approximation, and the expression of mode coupling coefficient is derived. Based on this, the local mode characteristics and mode coupling characteristics in a tapered double clad fiber are analyzed. The mode evolution characteristics of tapered double clad fibers with different parameters are simulated. As an example, the structure optimization process of a tapered double clad fiber is introduced. High efficiency coupling with a six-mode single clad fiber is realized, and the theoretical transmission loss is less than 0.3 dB.

Single optical fiber based forward-viewing all-optical ultrasound self-transceiving probe.

All-optical ultrasound probes with fully integrated ultrasound generation and detection functions demonstrate some unique advantages over traditional electroacoustic counterparts. However, due to the lack of an effective solution, the most commonly used method is to assemble two separate functional optical fibers together for ultrasound generation and detection, respectively. In this Letter, an innovative strategy, to the best of our knowledge, is developed to integrate the photoacoustic effect based ultrasound generation and the Fabry-Pérot (FP) interference based ultrasound detection structures together at the end of a single double clad optical fiber (DCF), so as to make a compact forward-viewing ultrasound self-transceiving probe (1-mm diameter). From the experiment results, the as-fabricated probe can generate an ultrasound signal with an amplitude of 2.36 MPa at 2.25 mm in the transmitting mode, and its peak frequency and -6-dB bandwidth are measured to be 10.64 MHz and 22.93 MHz, respectively. When being operated under the receiving mode, the probe has a detection sensitivity of 208.4 mV/MPa for ultrasound signals with the peak frequency of 8.24 MHz, and the noise equivalent pressure (NEP) is 76.8 kPa. In addition, the forward-viewing format ultrasound self-transceiving experiment is also performed and the pulse-echo signal varying with the transmission distance is successfully captured for the first time.

Investigation on the relationships among process parameters, molten pool characteristics, and fabrication quality of Ti-10V-2Fe-3Al by laser direct energy deposition

Ti-10 V-2Fe-3Al (Ti-1023) titanium alloy is a metastable high-strength β titanium alloy. Defects such as spatters, pores, and poor surface quality tend to occur during the laser direct energy deposition (LDED) of Ti-1023 titanium alloys, prohibiting its large-scale engineering application. Therefore, to obtain high-quality LDED of Ti-1023 titanium alloy, this study used a regression analysis model to investigate the relationship between key process parameters and the geometrical characteristics of single clad tracks to obtain the forming process map. In addition, an off-axis high-speed camera was used to monitor the forming process of the Ti-1023 titanium alloy single clad tracks, and the correlation between the forming quality of the three types of forming conditions—namely incomplete melting, normal melting, and over-melting—and the characteristics of the molten pool was analyzed. Finally, this study established a simplified relationship between the process parameters, the molten pool characteristics, and fabrication quality of LDED of Ti-1023 titanium alloy, which is expected to improve development for the online monitoring and increase the application of LDED Ti-1023 titanium alloy.

Research on Geometrical Features of FGH95 Nickel-based Superalloy by Coaxial Single Track Laser Cladding

FGH95 nickel-base superalloy powders were coated on GH4169 nickel-base superalloy by coaxial single-track laser cladding. The effects of process parameters on cladding width and cladding height were studied based on the three-factor and three-level orthogonal experiment. The experimental results are nonlinearly fitted by MATLAB software, and the mathematical model between the geometrical features and the process parameters is set up. The results show that the effect factor on the clad width is in the order of first power, followed by feeding rate, and scanning speed. However, the influence on the clad height is in the order of first scanning speed, followed by laser power, and feeding rate. The average prediction error of cladding width and height is less than 7%. The model can accurately forecast the geometrical features of the cladding coating and can offer some references for the optimization of laser cladding.

Cooling rate measurement in directed energy deposition using photodiode-based planck thermometry (PDPT)

• A novel method for measuring cooling rates during solidification was developed. • The developed method can measure solidification cooling rates above 5,000 °C/s. • Liquidus and solidus temperatures can be predicted from the second derivative of average melt pool temperature. • The cooling rate is inversely proportional to energy density and clad volume. • Considering the actual clad dimension is important to estimate accurate cooling rates by simulation. A novel method to measure cooling rates during solidification in Directed Energy Deposition (DED) using on-axis photodiode-based Planck thermometry (PDPT) was developed. The proposed method can monitor the average in-situ melt pool temperature at a 100 kHz acquisition rate. This is much faster than other thermal imaging methods, such as an IR (50 ∼ 200 Hz) or melt pool camera (25 ∼ 100 Hz), due to the use of photodiode single-pixel measurements. PDPT measures the average melt pool temperature by detecting two visible wavelengths from a coaxial, top-down field of view (FOV) of the melt pool through the cladding nozzle. To investigate the viability of the proposed method, single clads of Inconel 718 were manufactured with various energy densities (20 ∼ 90 J/mm 2 ) and characterized in terms of cooling rates and dimensions. Cooling rates measured from an off-axis IR camera as well as FEM simulations were compared with the cooling rates from the proposed method to verify the method. The measured solidification cooling rate values from PDPT were consistent with the reported values in the literature (800 °C/s ∼ 5,000 °C/s), which validated the proposed approach. Furthermore, the developed method can measure rapid solidification cooling rates over 5,000 °C/s, beyond the current limit of IR cameras in industrial applications and at a fraction of the cost. The findings indicate that solidification cooling rates can be monitored with respect to processing conditions, ultimately enabling a connection between process parameters and the resulting local microstructure. This opens possibilities for effective certification or for tailoring desired mechanical properties through closed-loop control.

L-DED numerical model for sensor embedding

Sensor integration is one of the drivers in modern industry for obtaining real-time data and enabling transition to Industry 4.0. Sensor integration on production systems and tooling is one of the key points for data acquisition. Although several techniques can be applied for sensor integration, Laser Directed Energy Deposition (L-DED) is becoming one of the most relevant, since the sensor can be placed into the manufactured layer-by-layer structure. However, the thermal nature of the L-DED poses a challenge when heat-sensitive parts, such as thermocouples, are to be embedded. In order to ease parametrization and anticipate the behavior of the L-DED process, modeling is an interesting tool that has attracted the attention of academia in the last years. Nevertheless, most models are highly complex and focused on a very local scale or include symmetry assumptions that restrict their use for real applications. In view of this need, in the present research work a thermal model that considers material addition and determines the clad geometry is developed. The model includes an automatic meshing algorithm that adapts the element size by refining the mesh where required. Besides, the model enables 5 axis L-DED, in-process variation of the machine feed rate, and allows to switch on and off the laser to simulate not only the material deposition, but also the idle movements. The model is validated in two steps: single clad deposition on a flat surface and single clads on a 0.3 mm thick thermocouple sheath. Finally, the validated model is used for defining the maximum laser power for embedding virtually a 3 mm diameter K-type thermocouple with a 0.3 mm thick sheath. The results of the simulation are also corroborated by experimental integration of the same thermocouple, which functionality is tested afterwards. Therefore, the L-DED modeling is proven to be an effective tool for manufacturing complex parts on the first try.

Structure and oxidation behavior of CoCrFeNiX (where X is Al, Cu, or Mn) coatings obtained by electron beam cladding in air atmosphere

High-entropy alloys (HEAs) are currently considered as promising materials for a wide range of applications, including high-temperature use. Since HEAs contain a large number of expensive elements, producing HEA-based coatings seems to be a reasonable approach from an economic point of view. In this study, non-vacuum electron beam cladding was used for the first time to produce CoCrFeNiX layers (where X = Al, Cu or Mn) on a surface of low-carbon steel. As-received coatings had a columnar grain structure with a 〈100〉 fiber texture. The CoCrFeNiCu cladding layer consisted of two fcc phases: Cu-enriched phase was observed in the interdendritic regions, and the Cu-depleted phase was found in dendrites. The CoCrFeNiMn coating had a single-phase fcc structure. CoCrFeNiAl alloy consisted of bcc and B2 phases. The hardness of the Cu and Mn-containing coatings was 190 and 186 HV, respectively. The hardness of the CoCrFeNiAl coating was 570 HV, which is 3.4 times higher compared to the material of the substrate. High-temperature oxidation tests carried out at 850 °C for 45 h revealed that oxide layers formed on the tested samples had a gradient structure that consisted of several different sublayers. The total mass gain due to high temperature oxidation was 2.29 mg/cm2, 2.04 mg/cm2, and 0.60 mg/cm2 for the CoCrFeNiCu, CoCrFeNiMn, and CoCrFeNiAl samples, respectively. The mass gain of the base material over the same period of time was 41.01 mg/cm2. The CoCrFeNiAl coating had the best oxidation resistance due to the formation of a dense Al2O3 scale. We show that non-vacuum electron beam cladding can be used to produce an HEA-based coating with a different chemical composition. The thickness of coatings in a single pass cladding can be as high as 1.8 mm. CoCrFeNiAl is a suitable coating for low-carbon steel in applications where high hardness and oxidation resistance are required.

Single Track Geometry Prediction of Laser Metal Deposited 316L-Si Via Multi-Physics Modelling and Regression Analysis with Experimental Validation

Laser metal deposition (LMD) is an additive manufacturing process used in manufacturing freeform geometries, repair applications, coating and surface modification, fabrication of functionally graded materials. It has a broad range of applications in various industries, including aviation, space, defence, automotive, tooling, etc. In this work, a multi-physics model of the LMD process was developed to rapidly predict the geometrical characteristics of the single clad track using the commercial software package Flow-3D. The volume of fluid (VOF) method was integrated to differentiate the interface between the metallic and gaseous cells. To validate the numerical model single bead tracks were deposited, and cross-sections of the beads were analysed. Mathematical formulae to predict different aspects of the single clad track (height, width, and depth) were derived using regression analysis. The influence of the process parameters on the geometrical characteristics of the single clad track was analysed in detail using analysis of variance (ANOVA). Both multi-physics model and mathematical regression model results were compared to the experimental measurements. The results were in good agreement with the experimental results.Graphical abstract

Advances in Multicore Fiber Grating Sensors

In recent years, multicore fiber (MCF) has attracted increasing interest for sensing applications, due to its unique fiber structure of multiple parallel cores in a single fiber cladding, which offers a flexible configurable platform to establish diverse functional fiber devices for sensing applications. So far, a variety of discrete fiber sensors using MCF have been developed, among which one of the major categories is the MCF grating sensors. The most distinct characteristic of MCF that differs from the normal single mode fibers is that the off-center cores of a MCF are sensitive to bending, which is caused by the bending induced tangential strain in off-center waveguides through either compression or stretching. The bending sensitivity has been widely developed for bending/curvature sensing or measuring physical parameters that are associated with bending. In this paper, we review the research progress on MCF-based fiber grating sensors. MCF-based diverse fiber grating sensors will be introduced, whose working principles will be discussed, and various types of applications of the MCF grating sensors will be summarized. Finally, the challenges and prospects of MCF grating for sensing applications will be presented.

Performance evaluation of TIG cladded in-situ TiC-TiB2 composite coating fabricated on AISI304 stainless steel

Tungsten inert gas (TIG) cladding is a surface modification technique used to deposit a coating with hard and resistance to wear material, which can improve the operational life of engineering components. In the present work, to improve the mechanical performance of AISI 304 stainless steel, in-situ TiC-TiB2 composite coating was fabricated through TIG cladding route by pre-placing Ti and B4C powder mixture at 3:1 wt ratio. The single line clad width and height was measured from the cross-sectional SEM images of the clad track. The microstructural analysis of the clad layer was accomplished through SEM images; however, EDS analysis was performed to study the distribution of different elements present in the clad layer. Almost a uniform clad layer with minor pores at the boundaries of the clad track was observed. The micro-hardness values variation towards the depth of the coating were evaluated for the clad layers deposited with different arc scanning speeds. Average value of micro-hardness was recorded between 800 and 1000 HV0.05, which was significantly higher than the substrate hardness.

Theoretical Investigation of the Influence of Wavelength on the Bandwidth in Multimode W-Type Plastic Optical Fibers with Graded-Index Core Distribution.

The bandwidth of multimode W-type plastic optical fibers (POFs) with graded-index (GI) core distribution is investigated by solving the time-dependent power flow equation. The multimode W-type GI POF is designed from a multimode single-clad (SC) GI POF fiber upon modification of the cladding layer of the latter. Results show how the bandwidth in W-type GI POFs can be enhanced by increasing the wavelength for different widths of the intermediate layer and refractive indices of the outer cladding. These fibers are characterized according to their apparent efficiency to reduce modal dispersion and increase bandwidth.

Microstructure and corrosion properties of the AISI 904L weld cladding obtained by the electro slag process

The AISI 904L steel is a superaustenitic stainless steel, which presents a good combination of properties like high strength, weldability, and good corrosion resistance. Despite its wide use in several industrial segments, the literature reporting the performance of claddings deposited with this alloy to improve the corrosion performance of equipment is limited. Based on this scenario, this work evaluates the microstructure and corrosion properties of the AISI 904L steel weld cladding obtained by the electroslag welding (ESW) deposited on a carbon steel ASTM A516 Grade 70. Single layer cladding was deposited on 50 × 400 × 400 mm steel plates with average welding energy of 11.7 kJ/mm to obtain the minimum thickness required. After welding, metallographic examination and corrosion tests were performed on samples removed at 1 and 3 mm parallel to the fusion line. Metallographic characterization was performed by optical and scanning electron microscopy. Cyclic polarization tests in 3.5% NaCl solution were performed at the same positions as the metallographic examinations. The results showed that the austenitic microstructure presenting a low volume fraction of secondary phases provided suitable corrosion results for all conditions studied. It evidences that single layer weld overlays obtained with the AISI 904L steel deposited by the ESW process may be considered an adequate alternative for overlay welding with reduced thicknesses because good results were observed at only 1.0 mm from the fusion line, and this could represent a significant cost reduction.

Novel investigation on tribological behavior of microwave synthesized functionally graded claddings

In this study, functional performance of Ni/Cr3C2 functionally graded claddings (FGCs) was investigated under dry sliding wear environment. The Ni/Cr3C2-based FGCs were produced by varying Cr3C2 fraction (Ni-XCr3C2) (X=10%–30% by weight) using microwave irradiation. The FGC layers were composed of cellular-structure with reinforced particles dispersed randomly inside Ni-based matrix. Variation of Cr3C2 particles inside Ni matrix exhibited significant impact on micro-structural and mechanical properties. The microhardness profile of the FGC layers showed an increase in hardness value with an increase in the amount of reinforced Cr3C2 particles. FGC top layers showed the maximum value of micro-hardness of 555 ± 34 HV. Functional performance of microwave processed FGCs was studied through the pin-on-disk tribometer under varying sliding velocity and sliding distances. For comprehension study, wear study was also carried out on microwave processed single layer clads with compositions corresponding to FGC layers. The FGC sample showed better wear resistance than all single clad layers and substrate material. The FGC sample exhibited 1.6 times less wear rate than the Ni-based + 30% Cr3C2 single layer clad. The worn-out surfaces of FGC and single-layer-clads showed presence of multiples cracks and grooves, which resulted in their weight loss during dry sliding contact. Material debonding and the formation of craters and cracks are the main phenomena responsible for the wear loss in the FGC surface.

Machine learning approaches for predicting geometric and mechanical characteristics for single P420 laser beads clad onto an AISI 1018 substrate

The final mechanical and physical properties should be predicted in tandem with the bead geometry characteristics for effective additive manufacturing (AM) solutions for processes such as directed energy deposition. Experimental approaches to investigate the final geometry and the mechanical properties are costly, and simulation solutions are time-consuming. Alternative artificial intelligent (AI) systems are explored as they are a powerful approach to predict such properties. In the present study, the geometrical properties as well as the mechanical properties (residual stress and hardness) for single bead clads are investigated. Experimental data is used to calibrate multi-physics finite element models, and both data sets are used to seed the AI models. The adaptive neuro-fuzzy inference system (ANFIS) and a feed-forward back-propagation artificial neural network (ANN) system are utilized to explore their effectiveness in the 1D (discrete values), 2D (bead cross-sections), and 3D (complete bead) domains. The prediction results are evaluated using the mean relative error measure. The ANFIS predictions are more precise than those from the ANN for the 1D and 2D domains, but the ANN had less error for the 3D scenario. These models are capable of predicting the geometrical and the mechanical properties values very well, including capturing the mechanical properties in transient regions; however, this research should be extended for multi-bead scenarios before a conclusive “best approach” strategy can be determined.