Parameters Including Laser Power Research Articles

Influence of processing parameters on the thermal history, microstructure and tensile properties of Inconel 738 produced by laser directed energy deposition

In this paper, laser directed energy deposition (LDED) technology was applied to produce non-weldable Inconel 738 parts. The influence of processing parameters including laser power, scanning speed and powder feeding rate on the thermal history of molten pool and the morphology of single track was evaluated. Considering the surface quality and deposition efficiency, the appropriate processing parameters for multilayer deposition were selected. Then the impact of laser power on the microstructure evolution and tensile properties of IN738 thin-wall parts was investigated. The research results show that increasing the laser power could increase the peak temperature and molten pool lifetime, but decrease the cooling rate. Increasing the scanning speed significantly increased the cooling rate but had little effect on the peak temperature. The thermal history was hardly affected by the powder feeding rate, but a too high powder feeding rate caused the particle adhesion and decline of surface quality. The microstructure of LDED-manufactured IN738 was composed of dense and fine dendrites. The higher laser powers of 800 W and 1000 W created higher temperature gradient within the molten pool, which promoted the epitaxial growth of dendrites. However, the long dendrites were prone to be torn apart under the transverse tensile stress, which was detrimental to the elongation and ductility. By comparison, when the laser power was 600 W, the growth direction of dendrites between adjacent layers was different and exhibited the best ductility.

Large-Scale Fabrication of Customized, Tunable, Ultrathin, and Flexible Metamaterial Absorbers Based on Laser-induced Graphene

Developing various 3D graphene microwave absorbers is a hotspot strategy to address the issue of continuous electromagnetic pollution, but remains great challenges in realizing high-performance microwave absorption capability at thin thickness. Herein, a series of flexible metamaterial absorbers (MAs) composed of periodical laser-induced graphene (LIG) surface, dielectric substrate and metallic ground fabric from top to bottom are fabricated. The LIG meta-surface is customized by means of regulating parameters including laser power density (LPD), laser engraving rate (LER) and input patterns to well balance impedance matching and electromagnetic loss. LIG MAs exhibit minimum reflection loss (RL) of −39.7 dB (with effective absorption bandwidth (EAB) of 5.5 GHz) and maximum EBA of 12.1 GHz (with RL of −18.9 dB) at thickness less than 1.1 mm, and the simulated and experimental results are highly consistent. In addition, radar cross section (RCS) simulation of LIG MA with multi-angles endows its potential for prospective applications in in-orbit satellites electromagnetic protection.

An experimental investigation of selective laser melting parameters effects on ferromagnetic properties of pure iron in both the as-built and annealed conditions

In this study, the effect of selective laser melting (SLM) parameters on the magnetic properties of pure iron has been experimentally extracted both in the as-built (A-Built) and stress-relieved (H-Treat) conditions, and the optimum levels of the parameters have been determined for optimum magnetic properties. The SLM process parameters include laser power, scanning speed, and hatch spacing, and the design of experiments was done by the Taguchi method. After manufacturing and preparing the specimens, their hysteresis curves were measured using vibrating-sample magnetometer (VSM), and the magnetic properties of the SLMed pure iron were calculated. Signal-to-noise analysis was used to determine the optimal levels of parameters for achieving the best magnetic properties. For samples’ permeability and coercivity, the best possible regression equations were extracted, and SOBOL sensitivity analysis was used to determine the most contributing input variable to the outputs. The results indicate that the laser power parameter has the most significant impact on the magnetic properties of the produced parts. Two of samples were annealed at 820 °C for 1 h, and then magnetic properties were remeasured. Although there was not a significant change in permeability, and magnetization saturation of the samples, coercive force has decreased approximately 60 %. This reduction in annealing is desirable for some AC electrical devices.

Selective laser melting and mechanical behavior of Mo-coated diamond particle reinforced metal matrix composites

Defects, such as pores, microcracks, and thermal damage, pose significant challenges in the selective laser melting (SLM) process of diamond reinforced metal matrix composites. To address these issues, this study utilizes Mo-coated diamond particles prepared via salt bath plating for SLM processing of CoCr-diamond composites. The SLM process parameters including laser power, scanning speed, and hatch spacing were systematically optimized using the response surface method (RSM). Subsequently, the microstructure and mechanical properties of the SLMed CoCr-diamond composites were thoroughly investigated. Notably, a protective layer of Mo2C is formed on the surface of diamond particles during the salt bath plating process. When compared to the SLMed CoCr-15 vol% Mo-uncoated diamond composite, the Mo coating significantly enhances the compressive strength by 69 % and flexural strength by an impressive 345 % for the CoCr-15 vol% Mo-coated diamond composite.

Enhancing powder bed fusion of alumina ceramic material: a comprehensive study from powder tailoring to mechanical performance evaluation

Powder bed fusion (PBF) is an additive manufacturing (AM) technique that holds a great promise for alumina ceramic materials to be processed in a one step. To ensure an effective outcome, the powder material should be thoroughly tailored, and the process parameters should be appropriately investigated. These process parameters include laser power, scanning speed, hatching space, and scanning strategies. The alumina powder has been tailored and modified to be appropriately used for PBF using the spray-drying technique, and the process parameters have been predicted and selected using a developed numerical model. Different scanning speeds of 100, 200, 300, and 400 mm/s have been considered, and the other parameters have been numerically predicted. The results demonstrated that spray drying is an effective technique for tailoring the characteristics of alumina powder, such as particle shape, particle size distribution, flowability, and absorptivity, making it ideally suited for PBF processing. Furthermore, the developed numerical model demonstrated outstanding reliability in predicting the most effective laser power and hatching space for different scanning speeds, resulting in significant cost and time savings when compared to relying solely on experimental trials. Employing a scanning speed of 400 mm/s yielded a significant improvement in relative density and quality of the printed samples surpassing other scanning speeds. Moreover, this speed effectively addressed various challenges encountered by other scanning speeds. Following the optimization of process parameters, it was determined that a relative density of 94.5% could be achieved by utilizing a scanning speed of 400 mm/s, a laser power of 210 W, and a hatching space of 30 µm. However, the evaluation of mechanical performance revealed that while the microhardness of the printed alumina samples matched the values reported in the literature, the attained compressive strength fell significantly below the values reported in the literature.

The influence of hatch distance on the surface roughness, microhardness, residual stress, and density of inconel 625 specimens in the laser powder bed fusion process

ABSTRACT The main goal of the laser powder bed fusion process is to produce high-quality parts with the required mechanical properties. Achieving this requires the proper selection of the key process parameters including laser power, scanning speed, layer thickness and hatch distance. In the present article, the effect of hatch distance parameter on the surface integrity issues i.e. surface roughness, residual stress, microhardness, and also density of Inconel 625 specimens has been studied using experimental approach. By using the non-destructive X-ray diffraction technique, residual stresses were measured in the different portion of the samples whose cross section changes. According to the results, as the hatch distance increases the microhardness decreases. The hatch distance has inverse effect on the residual stresses which its effect is less at the lower sections. It can be stated generally that the hatch distance increment reduces the microhardness, residual stress, and surface roughness but increases the specimen’s density.

A Superhydrophobic Surface on a Superalloy Substrate with Properties of High Mechanical Strength and Self-Cleaning of Carbon Deposition.

Laser processing is an efficient method for fabricating a superhydrophobic surface and has attracted much attention due to its multifunctionality. However, excessive laser processing, such as laser beam overlap and multiple scans, generates both a thick, brittle recast layer and a thin material thickness, thereby greatly reducing the mechanical strength of the substrate. In addition, there is no report on fabricating a superhydrophobic surface on a superalloy substrate whose application includes a self-cleaning property. This work proposes the fabrication of a superhydrophobic surface on a superalloy substrate with high mechanical strength by optimizing the laser processing parameters including laser power, scanning speed, line spacing, and number of scans. We found that the microstructures required by superhydrophobicity could be constructed with a single laser scan. which could guarantee a minimal loss of the mechanical strength. The fabricated superhydrophobic surface on the superalloy substrate exhibited excellent self-cleaning of carbon deposition, showing good application potential in the aero engine field.

Direct selective laser sintering of silicon carbide: Realizing the full potential through process parameter optimization

Direct-Selective Laser Sintering (D-SLS) is a promising Additive Manufacturing (AM) technology for Silicon Carbide (SiC). The appropriate values for the process parameters should be employed to achieve considerable success in the D-SLS of SiC. These process parameters include laser power, scanning speed, layer thickness, hatching space, and compaction ratio. A numerical model has been developed to determine the optimal process parameters for the D-SLS of SiC to be used as a guide during the experimental research. SiC samples were successfully printed using the estimated parameters from the numerical model, proving the reliability of the developed numerical model. With varying layer thicknesses of 22, 30, and 40 μm, the scanning speed at various values, including 100, 250, and 500 mm/s, was investigated. It was possible to print SiC samples with a relative density of 82% directly on a metallic base plate using low scanning speeds and layer thicknesses as low as 22 and 30 μm. This result was the first study to print SiC directly on a metallic baseplate. This remarkable finding will enable many applications that previously required metallic and ceramic materials to adhere together during SLS/M-based 3D printing. The process parameters were optimized to achieve a relative density of 87%, resulting in a laser power of 45 W, a scanning speed of 100 mm/s, and a hatching space of 40 μm. The evaluation of mechanical performance should be considered a future study.

A comprehensive study on the influence of the scan pattern in two porosity levels and surface roughness on the fatigue behavior of laser powder bed fusion manufactured specimens made of steel H13

As a developing and immature technique, additive manufacturing (AM) shows some limitations: depending on material and process parameters so far, it usually results in parts with residual porosity, high residual stresses and a surface with a certain level of roughness. Due to its weaknesses and high production costs, AM is more preferably used when the fabricated parts have a high geometry complexity, the material used is very expensive, or the parts can offer additional performance. In order to allocate AM further in industry, a better understanding of the not well-investigated fatigue behavior is necessary. This work focuses on the influences of some general process parameters including laser power, scan speed, scan pattern and postmachining on the resulting fatigue properties of H13 tool steel specimens generated through powder bed fusion (PBF) technique. Results reveal that scan patterns influence fatigue properties by affecting the largest porous defect size and microstructure thus matrix strength. The degree of porosity or roughness resulting from the energy input and postmachining has a significant inferior impact on the fatigue strength. Neither porosity nor tensile properties show a single direct mathematic correlation with the fatigue properties.

Surface Quality and Material Removal Rate in Fabricating Microtexture on Tungsten Carbide via Femtosecond Laser.

Tungsten carbide is currently the most widely used tool material for machining difficult-to-machine materials, such as titanium alloys and nickel-based super alloys. In order to improve the performance of tungsten carbide tools, surface microtexturing, a novel technology that can effectively reduce cutting forces and cutting temperatures and improve wear resistance, has been applied in metalworking processes. However, when fabricating the micro-textures such as micro-grooves or micro-holes on tool surfaces, the significant decrease in material removal rate is a major obstacle. In this study, a straight-groove-array microtexture was fabricated on the surface of tungsten carbide tools via a femtosecond laser with different machining parameters including laser power, laser frequency, and scanning speed. The material removal rate, surface roughness, and the laser-induced periodic surface structure were analyzed. It was found that the increase in the scanning speed decreased the material removal rate, whereas increasing the laser power and laser frequency had the opposite effects on the material removal rate. The laser-induced periodic surface structure was found to have a significant influence on the material removal rate, and the destruction of the laser-induced periodic surface structure was the reason for the reduction in the material removal rate. The results of the study revealed the fundamental mechanisms of the efficient machining method for the fabrication of microtextures on ultrahard materials with an ultrashort laser.

Effects of laser welding parameters on the porosity and acicular phase in SiCp/6092 aluminum matrix composite welded joints

Al matrix composites (AMCs) are preferred engineering materials for aerospace and automotive industries owing to their high specific strength, superior wear resistance and low thermal expansion. It is a challenge to achieve high-quality fusion welded joints of AMCs because of the occurrence of defects such as pores, particles segregation and acicular phases. In this study, the effects of laser welding parameters including laser power, welding speed and laser incident angle on the formation of porosity and acicular phase were investigated in SiCp/6092 aluminum matrix composite welded joints using orthogonal experimental method. Range analysis of the orthogonal test results showed that the laser power and the welding speed had the greatest influence on the porosity and acicular phase size during the laser welding of aluminum matrix composites. At a heat input of 60 J/mm, the porosity in the weld was only 1.6% while that at 190 J/mm was 15.2%. Higher heat input produced a much larger size of brittle Al4C3 phases. The size of the acicular phase Al4C3 at the top and bottom of the weld was larger than that in the middle. Active Ti was added to the weld zone to mitigate the adverse effect of Al4C3 brittle phase and porosity on mechanical properties. The ultimate tensile strength increased from 115 MPa in direct laser welding to 148 MPa for the laser welding process employing the Ti interlayer. This work will provide referenceable data for designing high-quality AMC welded joints for aerospace and automotive industries.

The regulation of ethanol in reaction medium on the properties of nanogels prepared by photopolymerization at 532 nm

Nanogels with a unique three-dimensional structure have wide applications in tissue engineering and drug delivery. In this study, polyethylene glycol diacrylate (PEGDA) nanogels were prepared by photopolymerization under the irradiation of 532 nm laser using a mixture of ethanol and water as the solvent. The reaction parameters including laser power and stirring speed were systematically investigated. Since the amphiphilic PEGDA self-emulsifies to form micelles in water, the regulation of ethanol content in reaction medium can tune the size and morphology of nanogels. Based on these, the photopolymerization mechanism of PEGDA in aqueous solution of ethanol was proposed.

Study of residual stresses and distortions from the Ti6Al4V based thin-walled geometries built using LPBF process

The current paper focuses on the prediction of residual stresses and distortions in the Laser Powder Bed Fusion (LPBF) built Ti6Al4V thin-walled geometries using Ansys Additive Print (AAP) software which employs a layer-by-layer accumulation of inherent strain to calculate the deformations. Isotropic and anisotropic strain scaling factors were calibrated initially within the APP software for the Ti6Al4V based single cantilever beam geometry. Subsequently, the numerical simulations were performed in APP software and computed the residual stresses and distortions for the varied process parameters including laser power, scan speed and hatch distance while maintaining the layer thickness constant for all the design iterations. The numerical predictions were compared; they were found to match reasonably well with the XRD measurements within the calibrated regime.

Force enhanced wire laser additive manufacturing of aluminum and titanium alloys

Brittle intermetallic compound formation is typically difficult to avoid during fusion joining of dissimilar metals. In this paper, a new approach called force enhanced wire laser additive manufacturing is proposed to join aluminum and titanium alloys. Ti6Al4V titanium alloy single track was additively fabricated on AA7075 plate successfully, through two liquid pools of the wire and the substrate, separated by a buckled unmelted part of the wire, leading to a mechanically interlocked interface. The effects of manufacturing parameters including laser power, wire feeding speed, scanning speed and initial contact force between wire and substrate on the surface morphology, internal interface microstructure and formation of intermetallic compounds were investigated through high-speed camera, spectrometer, laser topography, optical imaging, SEM imaging, XRD characterizations along with numerical simulations at different scales. And the maximum tensile strength reached 380 MPa in the tensile test. The experimental and numerical results indicate that the thermal modulation approach can effectively control the formation of brittle compounds between titanium and aluminum alloys and that the initial contact force ensures a good bond between the two metals.

Laser powder bed fusion of a non-equiatomic FeNiCoAl-based high-entropy alloy: Printability, microstructure, and mechanical properties

In this work, the laser powder bed fusion (LPBF) process has been applied to fabricate the FeCoNiAlTaB (NCATB) high entropy alloys. The influence of process parameters including laser power and scanning speed on the relative density and microstructure were investigated. A sample with relative density of 99.8% can be achieved by optimal process parameters with laser power of 120 W and scanning speed of 800 mm/s. It can be found that the NCATB alloy maintains the FCC single-phase structure at different parameters, which is consistent with the pre-alloyed powder. According to the tensile test results, samples fabricated with different direction show similarity in strength and anisotropy in plasticity. Therefore, the causes of mechanical property anisotropy are discussed in terms of strengthening mechanism, texture and defects, separately. Compare to the as-cast samples, the printed samples show a substantial improvement in mechanical properties, which was contribute to the grain refinement, fine cellular morphology and high dislocation density.

An Optimization of Manufacturing Process of SS304L Using Direct Energy Deposition Method

The direct energy deposition (DED) method is an emerging manufacturing technique that has been recently highlighted due to its capabilities to coat materials with complex geometry for high temperature and highly corrosive environmental applications, such as steam turbine blade. Amongst metallic materials, SS304L has been reported to have superior corrosion resistance in such environments. Therefore, 3D printing of complex-shaped parts using SS304 maybe a promising strategy to introduce 3D printing techniques for nuclear industry application. To obtain robust and stable products that can withstand extreme environments, optimization of the SS304 manufacturing process conditions is required. This study investigated the effects of process parameters including laser power, scan speed, coaxial gas flow, and feeder rate using the DED method with a 4 way nozzle. It was found that laser power has an effect on grain growth behaviors. If the other variables are fixed and the scan speed is above a certain value, then the scan speed does not affect surface oxidation. The feeder rate is related to height. As the feeder rate increases, the height increases. Coaxial gas works to prevent oxidation and damage to the optic components and is not a critical factor in determining the size of the deposited material. These results can be utilized in future studies to accelerate the process design time of other 3D printed materials and future applications using SS304L

Study on microstructures and mechanical performance of laser transmission welding of poly-ether-ether-ketone (PEEK) and carbon fiber reinforced PEEK (CFR-PEEK)

The reliable assembly of poly-ether-ether-ketone (PEEK) and carbon fiber-reinforced PEEK (CFR-PEEK) is crucial to effective load transfer within lightweight and high-stiffness structures, which are commonly demanded in aeronautical, automobile, and medical industries. In this work, laser transmission welding of PEEK and CFR-PEEK has been performed by using a 1070 nm Nd:YAG fiber laser. The effects of process parameters including laser power, laser scanning speed, and clamping pressure on joining quality have been investigated via mechanical, morphological, and thermal characterization. Results show that strong bonds have been formed by entanglements of polymer chains at the joining interface and the mechanical embedment between carbon fibers and PEEK. The formation mechanisms of bubble defects have been classified into three types. One of them was eliminated by scanning the joints twice, which significantly improved joints' mechanical performance and hermeticity with the maximum joining strength reaching 11.6 MPa. Also, a comparative study between PEEK/PEEK and PEEK/CFR-PEEK joints shows that the existence of carbon fibers within the CFR-PEEK significantly increased joints' decomposition threshold, joining region, and strength due to their great thermal conductivity. Besides, the influence of the welding process on the crystallinity of PEEK was analyzed, which was then improved from 11.7% to 34.1% through annealing.

Experimental and numerical investigation of laser-assisted electrodeposition based on amorphous forming: Laser-electrodeposition correlation and explanation of enhancing mechanism

In this study, the laser parameters including laser power, scanning rate, scanning line distance, pulse width, frequency, and scanning area were used as the influencing factors, and the temperature, current density, and force impact effect were used as the response indexes to discuss the correlation between laser irradiation and electrochemical deposition (ECD) amorphous-forming process. The results show that in the preparation area ranges of 5 × 5, 10 × 10, and 20 × 20 mm, the laser power, scanning rate, and scanning line distance are the most significant parameters affecting the ECD process performance. The laser power affects the rising range and vibration amplitude of the current density, whereas the scanning rate and line distance influence the rising range, vibration amplitude, and variation period. The current density and force signal change periodically and stably over the suitable processing range. Compared with ECD NiP coating, the comprehensive performance of the coating prepared by the representative parameters selected according to the optimized parameter range are better. This study can provide ideas for the parameter optimization of the laser-enhanced ECD for different materials and processing sizes. In the future work, the influence of laser parameters on the ECD reduction process from a microscopic perspective will be discussed for establishing the correlation between laser parameters and coating performance. Moreover, the periodic current waveform formed by the laser is expected to prepare multilayer gradient structures with alternating grain sizes.

The Study on Resolution Factors of LPBF Technology for Manufacturing Superelastic NiTi Endodontic Files

Laser Powder Bed Fusion (LPBF) technology is a new trend in manufacturing complex geometric structures from metals. This technology allows producing topologically optimized parts for aerospace, medical and industrial sectors where a high performance-to-weight ratio is required. Commonly the feature size for such applications is higher than 300–400 microns. However, for several possible applications of LPBF technology, for example, microfluidic devices, stents for coronary vessels, porous filters, dentistry, etc., a significant increase in the resolution is required. This work is aimed to study the resolution factors of LPBF technology for the manufacturing of superelastic instruments for endodontic treatment, namely Self-Adjusting Files (SAF). Samples of thin walls with different incline angles and SAF samples were manufactured from Nickel-Titanium pre-alloyed powder with a 15–45 μm fraction. The printing procedure was done using an LPBF set-up equipped with a conventional ytterbium fiber laser with a nominal laser spot diameter of 55 microns. The results reveal physical, apparatus, and software factors limiting the resolution of the LPBF technology. Additionally, XRD and DSC tests were done to study the effect of single track based scanning mode manufacturing on the phase composition and phase transformation temperatures. Found combination of optimal process parameters including laser power of 100 W, scanning speed of 850 mm/s, and layer thickness of 20 μm was suitable for manufacturing SAF files with the required resolution. The results will be helpful for the production of NiTi micro objects based on periodic structures both by the LPBF and μLPBF methods.

Surface texture characterization for thin-wall NASA HR-1 Fe–Ni–Cr alloy using laser powder directed energy deposition (LP-DED)

Additive Manufacturing (AM) offers new design and manufacturing opportunities of thin-wall microchannel heat exchangers for aerospace and industrial applications. Laser Powder Directed Energy Deposition (LP-DED) is an AM process providing large scale manufacturing of thin-wall microchannel heat exchangers. Successful industrialization of the LP-DED process requires critical quantification and understanding of the metallurgical, geometric, and process limitations. Specifically, understanding the as-built surface texture, inclusive of roughness and waviness, is significant due to its effects on the friction factor and pressure drop within a heat exchanger. This experimental study completed a design of experiments (DOE) to determine the critical build parameters that impact surface texture for enclosed thin-wall samples. This study summarizes the characterization work of the LP-DED process for 1 mm enclosed walls with an Fe–Ni–Cr (NASA HR-1) alloy. The LP-DED parameters including laser power, powder feedrate, travel speed, layer height, and rotary atomized powder feedstock were modified in the experiment. An evaluation of the DOE samples and resulting surface texture is provided along with conclusions from these experiments. Results indicate that 3D areal and 2D profile (directional) surface texture is estimated by 2x the powder diameter that becomes captured or partially melted on the trailing edge of the melt pool. The fine powder showed a higher sensitivity to parameter changes but resulted in a higher density material and 23% reduction in roughness. Surface texture was also shown to vary between closed channel shapes (internal) due to ricochets, recirculation, and higher volume of powder available to bond compared to external (outer) surfaces. The understanding of the LP-DED process as-built surface texture is essential to fluid flow applications such as heat exchanges and can modify performance for enhanced heat transfer or can be a detriment to pressure drop.