Scanning Speed Research Articles

Effect of laser parameters and shielding gas flow on co-axial photodiode-based melt pool monitoring signals in laser powder bed fusion

Melt pool monitoring using co-axial photodiodes is increasingly used for online quality monitoring in PBF-LB AM. However, the fundamental correlations between different processing conditions and the co-axial photodiode signals are not well understood. In this study the impact of laser parameters and the shielding gas flow speed on co-axial photodiode-based melt pool monitoring signals is established. It is shown that laser power has positive linear correlation with the photodiode signal, while the correlation with scanning speed is non-linear in the form of y=ax–b. The focal point position, scanning orientation and shielding gas flow speed have highly non-linear response on the photodiode signal, depending on the combinatorial effects of the parameters. These underlying physical correlations should be carefully assessed and taken into consideration when trying to establish correlations between photodiode-based melt pool monitoring signal and defect formation in the PBF-LB process.

Optimizing dose parameters for enhanced maskless lithography in MoS2-based devices

Maskless lithography simplifies the fabrication process and reduces costs compared to electron beam (E-beam) lithography, making it a more efficient choice for patterning nano-devices. Maskless lithography presents a promising avenue for expediting device fabrication by eliminating the need for masks. This technique can streamline the production of basic electronic devices, offering an efficient and low-cost alternative to traditional lithographic methods, like E-beam lithography. This study utilized a 405 nm photodiode to achieve pattern-writing with a minimum linewidth of 1 μm. Exploring optimal parameters includes adjustments in beam intensity, scan speed, and step size. Maskless lithography was applied to 2D transition metal dichalcogenides (TMDCs) material, MoS2, to investigate their electrical transport characteristics. The fabricated device exhibits an ON/OFF ratio of ∼1.7 × 106 and a mobility of ∼0.833 cm2/V·s, indicating a high switching efficiency. The results demonstrate optimized maskless lithography's potential for swift and cost-effective fabrication, offering intermediate-resolution patterning capabilities.

High-efficiency surface defect detection based on laser ultrasonic state space embedding and compressive sensing

Abstract The laser nonlinear wave modulation spectroscopy(LNWMS) technique has gained considerable attention due to its high sensitivity in detecting small surface defects and its ultra-fast scanning speed. This paper proposes a novel method for synthesizing intact wavefield reference, significantly enhancing the accuracy of surface defect imaging. Moreover, considering the potential for parallel processing of the nonlinearity calculation of ultrasonic signals at scanning points, we incorporate compressive sensing technology to accelerate this process. This innovative approach reduces the computational load to 10% of the original, thereby substantially increasing the imaging speed. The paper validates the method’s superior accuracy and efficiency in defect detection through conducting experiments using a high-speed laser ultrasonic scanning system on aluminum plates and turbine blade, and by comparing with local wavenumber estimation, demonstrating the promising potential of this technology for surface defect analysis.

Bimodal structure formation and texture transition mechanism in laser remelted Mg–Al-based alloy

Texture inheritance, texture weakening, and a complete texture transition within different solidified molten pool (MP) have been achieved by manipulating various processing parameters of conduction mode in laser remelted magnesium-aluminum (Mg–Al)-based AZ31 alloy. At a low laser power (P = 100 W), restricted number of temperature gradient directions on moving solid/liquid (S/L) interfaces within small MP leads to strong texture inheritance. Tilting angles 20°–45° away from building direction (B.D.) in {0001} plane is a preferential growth direction of texture inheritance. In contrast, spontaneous texture weakening has occurred due to frequently varied temperature gradient directions within increasing MP size in higher P cases. Meanwhile, increasing scanning speed V has a significant effect on weakening the texture as well as refining grains in the solidified MP. Furthermore, fine grains formation with random orientations in MP bottom at both high P (400 W) and high V (20, 30, and 50 mm/s) leads to the occurrence of a bimodal structure, which is affected by solidification characteristics as well as thermal convection. For the case of the highest P and the highest V, a texture transition has occurred as tilting angles of 45°–90° away from B.D. in {0001} plane within MP, compared to 0°–45° texture of base material for the Mg–Al-based alloy in the study.

Effect of laser parameters on microstructure and mechanical properties of Al–Ni–Sc–Zr alloys fabricated by laser powder bed fusion

The processability, microstructure and mechanical properties of a near eutectic AlNiScZr alloy fabricated by laser powder bed fusion (LPBF) are investigated. The optimal processing windows for the LPBF alloy are determined. The results indicate that laser power exerts a predominant influence on the relative density of the as-built alloy. Elevated laser power can lead to increased relative density. Laser scanning speed exerts a significant impact on the microstructure and mechanical properties of the as-built alloys. An increase in the laser scanning speed can facilitate the growth of coarse columnar grains in the coarse grain region and suppress the formation of ultrafine equiaxed grain bands. Furthermore, the increase in the laser scanning speed can result in a reduction in the size of the cells, which in turn leads to an enhancement in the strength of the alloys. This study examines the evolution of the microstructure and mechanical properties of the as-built alloy as a function of laser scanning speed. By elucidating the relationship between laser parameters, microstructure and mechanical properties, the objective is to provide fundamental guidance for tuning the solidification structures and mechanical properties of LPBF AlNiScZr alloys by selecting appropriate laser parameters.

Study on forming process and performance of nano-La2O3 reinforced tungsten-based composites by selective laser melting

In this study, La2O3 nanoparticles were incorporated into a tungsten (W) matrix to enhance the microstructure and properties of pure W. The selective laser melting (SLM) process for W-2wt% La2O3 was optimized, and the influence of SLM processing parameters on the relative density and internal defects of the samples was examined. Challenges such as uneven powder layering and layer-by-layer thickening during the SLM process were addressed by incorporating a homogeneous material support formed with low laser energy density beneath the sample. This approach widened the process window for sample formation, resulting in a 2.38 % increase in the average relative density of supported samples compared to unsupported ones.With optimized parameters of 240W laser power, 200 mm/s scanning speed, and 80 μm hatch spacing, the sample achieved a relative density of 98.32 % with minimal internal pores, though some microcracks remained. Further investigation revealed that surface roughness decreased with increasing laser power and scanning speed. High laser power combined with low scanning speed yielded good surface quality. Under conditions of high relative density (over 96 %), samples processed with low laser power and high scanning speed (200W, 200 mm/s) exhibited fine and uniform grain morphology, few internal defects, and excellent mechanical properties, with a microhardness of 474HV and a compressive strength of 2237 MPa.

Morphological Characterization and Tribological Properties of TiCoNi Alloy Coatings on Ti–6Al–4V Alloy via Laser Deposition

The goal of this work is to improve the Ti–6Al–4V alloy's hardness and tribological behavior. Coaxial laser surface cladding was used to develop intermetallic layers of nickel (Ni), cobalt (Co), and titanium (Ti). Laser power of 900 W, beam spot size of 3 mm, powder feed rate of 1.0 g/min, and gas flow rate of 1.2 L/min are the optimized parameters used for laser depositions. The laser scan speeds were adjusted between 0.6 and 1.2 m/min. Investigations were conducted into the effects of powder admixture and laser parameters on the fabricated coatings' microstructure, tribological behavior and hardness. X-ray diffractometry (XRD), energy dispersive spectroscopy (EDS) with Scanning electron microscopy (SEM) was employed for the characterization of the microstructural evolution and phase identification, respectively. Additionally, the tribological experiment was conducted via UMT-2 –CETR reciprocating tribometer, and the coatings’ micro-hardness characteristics were examined using EmcoTEST DURASCAN. The micrographs exhibit no signs of porousness, cracks, or stress introduction, according to the results. For every manufactured sample, good metallurgical adhesion was obtained. By comparing the hardness of the ternary coating (Co–Ni–10Ti deposited at a scan speed of 1.2 m/min, with a hardness of 980 HV) to the substrate (Ti–6Al–4V, with a hardness of 330 HV), a hardness increase of approximately 2.96 times was observed. Furthermore, the Co–Ni–10Ti coating, deposited at a scan speed of 1.2 m/min, demonstrated a 51.1% reduction in the coefficient of friction (COF) compared to the base alloy, indicating superior anti-wear performance. The enhanced properties are attributed to the formation of hard intermetallic compounds such as Ti–Co, Co2Ti, Al5Co2, and Ni3Ti, along with their uniform distribution and finely tuned grain sizes.

Explainable machine learning for hardness prediction of laser powder bed fused Ti-6Al-4V and assisting in understanding effects of process parameters

Rapid fabrication of the Ti-6Al-4 V alloy with the target hardness via laser powder bed fusion (LPBF) is essential to meet the requirements of specific applications. Herein, the explainable machine learning (xML) models were employed to predict the hardness of LPBF-ed parts and to provide insights into the mechanisms linking process-microstructure-hardness. Results indicate that gradient boosting decision tree (GBDT) model outperforms others on test set, achieving an R square (R2) of 0.963, a mean absolute error (MAE) of 2.059 HV, and a root mean squared error (RMSE) of 3.844 HV. The contributions of process parameters were evaluated using SHapley Additive exPlanations (SHAP) values. The results demonstrate that the scanning speed (v) has the most significant influence on hardness, with the mean |SHAP value| accounting for approximately 51.2 % of the overall value, and shows an overall positive correlation with hardness. Experimental validation is consistent with the prediction results that S6 fabricated under the high v displayed a high hardness of 404.58 HV. The high v results in a large number of dislocations in as-built S6, impeding dislocation slip during loading and thus increasing resistance to deformation. The {10—11}<—1012> compression twins, nano-stacking faults and numerous fine α’-colonies provide extra grain boundary strengthening. Furthermore, the substantial volume fractions of interfaces between randomly oriented α’ martensite act as a strong barrier to dislocation slip transmission, thereby offering effective strengthening. This work offers guidance for predicting properties and exploring the underlying mechanisms of process parameters on material properties.

Development and Validation of a One‐Dimensional Finite Difference Simulation Scheme for Polymer Laser Powder Bed Fusion with Application to the Effect of the Inter Layer Time

The division of the polymer laser powder bed fusion process polymers (PBF‐LB/P) into temporal regimes originating from laser motion, thermal diffusion, viscous flow, crystallization kinetics, and powder application is exploited by considering only the building direction. The reduction of dimensionality enables fast simulations which are used to investigate the influence of the inter layer time on the final part density. Numerical simulation results are validated by experiments using polyamide 12 (PA 12) with good agreement in terms of part density. It is shown that an inter layer time of 90 s leads to nearly dense PA 12 parts while a time of 45 s leads to less dense parts. The cooling effect of the applied powder is identified as a cause for insufficient densification of the previous layer. The simulation tool is quantitatively validated against experimental results for the surface temperature of PA 12 as function of scan speed and hatch distance, for the melt pool depth of polyamide 6 as function of scan speed and for the melt pool depth of polyetherketoneketone as function of laser power. The presented simulation method enables rapid process parameter adjustment for new polymer materials in the PBF‐LB/P process.

Structure and Wet-Sliding Characterization of a Laser Powder Bed Fusion Ti-6Al-4V Biomedical Alloy: Effect of Laser Surface Modification

The effect of laser modification on the structure and wet (Simulated Body Fluid)-sliding behaviour of a Laser Powder Bed Fusion alloy Ti-6Al-4V was studied. The scanning of 400 W fiber laser with a speed of 10 mms –1 led to a surface melting with an increase in hardness (780–820 HV) and 20%-decrease in wear. Under the scanning speeds of 40–60 mms –1 the surface was refined almost without melting to provide a 7–8% increase in hardness/wear resistance accompanied by a decrease in the friction coefficient

CFRTP single-lap adhesive bonding and its mechanical performance enhanced by laser surface treatment: Finite element simulation and experimental validation

The outstanding mechanical properties of carbon fiber reinforced thermoplastic polymer (CFRTP) have led to its widespread application in many industrial sectors. In response to the engineering challenge of repairing large non-critical CFRTP structural components in situ, an infrared fiber laser surface cleaning technology is proposed to treat the bonding interface and enhance the tensile strength of polypropylene (PP)-based CFRTP single-lap bonded joints. Specifically, through single-factor and orthogonal experiments, the impact of different process parameters on the properties of the bonded joints was identified first. Then, online temperature monitoring was performed to elucidate the laser treatment mechanism of the CFRTP sample interface. Surface morphology of the laser-treated samples further indicates that when the temperature of the sample surface surpasses the resin decomposition temperature with extended holding time, the resin could be removed from the surface more thoroughly. Additionally, a novel three-dimensional woven finite element (FE) model, accounting for anisotropic heat transfer, was established to predict the surface temperature and cleaning quality of CFRTP. The FE model incorporates the anisotropic heat transfer characteristics of carbon fibers, thus accurately simulating the heat transfer behaviors between carbon fibers and the resin matrix. The laser ablation mechanism is elucidated by examining the surface ablation morphologies and peak surface temperatures. A comparison between experimental results and FE simulations demonstrated a notable coherence in the trend of surface morphology variations, with discrepancies in peak surface temperatures ranging from 3.29 % to 24.63 %. The experimental tests proved that the shear strength of single-lap bonded joints reaches its maximum value when the laser power is 35 W, the scanning speed is 2500 mm/s, and the number of scans is four. The enhancement of the mechanical properties of bonded joints can be attributed to the improved wettability and higher surface free energy of the laser-treated samples.

Prototyping Ti2Cu intermetallic grain growth heterogeneously in Ti6Al4V matrix through laser additive manufacturing

The Ti2Cu intermetallics compound possessing an ability to release Cu2+ ions has promising antibacterial properties. This research integrates experimental and computational techniques to delve into the interfacial intermetallic (IMC) formation within the Ti6Al4V/Cu system. Heat transfer analysis is performed to numerically outline the thermal history within the microstructure during laser surface alloying (power = 1000 W and scan speed = 200 mm/s), while the phase field method is employed to describe the Ti2Cu IMC grain growth in the Ti6Al4V matrix. As the IMC and the matrix phases respectively have free energy minima of -68.52 and -61.35 kJ/mol at Taverage=1250.0 K, the growth of Ti2Cu IMC grains at the Ti6Al4V matrix located around the depth of 5 μm from the top surface is thermodynamically favorable. Laser processing can cause the nucleation of IMC precipitates of irregular sizes and curvature profiles, in which case the curvature driven effects between the adjacent grains can additionally affect their growth kinetics. Furthermore, microbiological assays underscore the superior antibacterial efficacy of the Ti6Al4V+Ti2Cu heterostructures as compared to the control (Ti6Al4V) counterpart.

Understanding the regulation of protein synthesis under stress conditions

Protein synthesis regulation primarily occurs at translation initiation, the first step of gene translation. However, the regulation of translation initiation under various conditions is not fully understood. Specifically, the reason why protein production from certain mRNAs remains resistant to stress while others do not show such resilience. Moreover, why is protein production enhanced from a few transcripts under stress conditions, whereas it is decreased in the majority of transcripts? We address them by developing a Monte Carlo simulation model of protein synthesis and ribosome scanning. We find that mRNAs with strong Kozak contexts exhibit minimal reduction in translation initiation rate under stress conditions. Moreover, these transcripts exhibit even greater resilience to stress when the scanning speed of 43S ribosome subunit is slow, albeit at the cost of reduced initiation rate. This implies a trade-off between initiation rate and the ability of mRNA to withstand stress. We also show that mRNAs featuring an upstream ORF can act as a regulatory switch. This switch elevates protein production from the main ORF under stress conditions; however, minimal to no proteins are produced under the normal condition. Because, in stress, a larger fraction of 43S ribosomes bypasses the upstream ORF due to its weak Kozak context. This, in turn, increases the number of scanning ribosomes reaching the main ORF, whose strong Kozak context can convert them into 80S ribosomes, even under stress conditions. This switching allows an efficient use of cellular resources by producing proteins when they are required. Thus, our computational study provides valuable insights into our understanding of stress-responsive translation-initiation.

Ultra-fast Digital DPC Yielding High Spatio-temporal Resolution for Low-Dose Phase Characterization.

In the scanning transmission electron microscope, both phase imaging of beam-sensitive materials and characterization of a material's functional properties using in situ experiments are becoming more widely available. As the practicable scan speed of 4D-STEM detectors improves, so too does the temporal resolution achievable for both differential phase contrast (DPC) and ptychography. However, the read-out burden of pixelated detectors, and the size of the gigabyte to terabyte sized data sets, remain a challenge for both temporal resolution and their practical adoption. In this work, we combine ultra-fast scan coils and detector signal digitization to show that a high-fidelity DPC phase reconstruction can be achieved from an annular segmented detector. Unlike conventional analog data phase reconstructions from digitized DPC-segment images yield reliable data, even at the fastest scan speeds. Finally, dose fractionation by fast scanning and multi-framing allows for postprocess binning of frame streams to balance signal-to-noise ratio and temporal resolution for low-dose phase imaging for in situ experiments.

Enhanced Corrosion Protection of Printed Circuit Board Electronics using Cold Atmospheric Plasma-Assisted SiOx Coatings.

The miniaturization and widespread deployment of electronic devices across diverse environments have heightened their vulnerability to corrosion, particularly affecting copper traces within printed circuit boards (PCBs). Conventional protective methods, such as conformal coatings, face challenges including the necessity for a critical thickness to ensure effective barrier properties and the requirement for multiple steps of drying and curing to eliminate solvent entrapment within polymer coatings. This study investigates cold atmospheric plasma (CAP) as an innovative technique for directly depositing ultrathin silicon oxide (SiOx) coatings onto copper surfaces to enhance corrosion protection in PCBs. A systematic investigation was undertaken to examine how the scanning speed of the CAP deposition head impacts the film quality and corrosion resistance. The research aims to determine the optimal scanning speed of the CAP deposition head that achieves complete surface coverage while promoting effective cross-linking and minimizing unreacted precursor entrapment, resulting in superior electrical barrier and mechanical properties. The CAP coating process demonstrated the capability of depositing SiOx onto copper surfaces at various thicknesses ranging from 70 to 1110 nm through a single deposition process by simply adjusting the scanning speed of the plasma head (5-75 mm/s). Evaluation of material corrosion barrier characteristics revealed that scanning speeds of 45 mm/s of the plasma deposition head provided an effective coating thickness of 140 nm, exhibiting superior corrosion resistance (30-fold) compared to that of uncoated copper. As a proof of concept, the efficacy of CAP-deposited SiOx coatings was demonstrated by protecting an LED circuit in saltwater and by coating printed circuits for potential agricultural sensor applications. These CAP-deposited coatings offer performance comparable to or superior to traditional conformal polymeric coatings. This research presents CAP-deposited SiOx coatings as a promising approach for effective and scalable corrosion protection in miniaturized electronics.

Fabricating diamond bit by selective laser melting and its drilling performance evaluation

Diamond abrasive tools play an important role in efficient and precision machining of difficult-to-cut materials. As the traditional tool manufacturing process is difficult to meet the integrated molding preparation of complex structures, the use of selective laser melting (SLM) technology to manufacture diamond tools with functions and structures has become a research hotspot in recent years. In this paper, the feasibility and wear characteristics of diamond bits prepared by SLM using AlSi7Mg as metal matrix are investigated. The optimal parameter combination of diamond/AlSi7Mg mixture was obtained through orthogonal experiments, in which the powder layer thickness was 30 μm, the laser power was 300 W, the scanning speed was 3000 mm/s, and the scanning spacing was 120 μm. This parameter combination realized the improvement of the mechanical properties and the decrease of the porosity. Two types of bits with and without groove-structure (Labeled as Bit-G and Bit-N) were fabricated and their drilling performance were compared by processing BK7 optical glass. The results show that the Bit-G has more excellent machining performance, including lower drilling force, better hole quality and longer service life. According to the simulation results, the self-sharpening cycle of the Bit-G’s wear characteristics can be attributed to the groove structure that allows the coolant to be fully utilized in the bit/workpiece contacting area. This paper demonstrates the feasibility of the SLM process for the preparation of diamond tools and comprehensively analyzes the wear process, which provides reference value for further research on this process for the manufacturing of diamond abrasive tools.

Effect of the Laser Cladding Parameters on Microstructure and Elevated Temperature Wear of FeCrNiTiZr Coatings.

In order to prepare coating with good friction and wear resistance at elevated temperature on the surface of hot-working tool steel, by using a CO2 laser, FeCrNiTiZr high-entropy alloy coating with different laser scanning speeds (360, 480 and 600 mm/min, respectively) was successfully fabricated by using laser cladding technology on the surface of H13 steel in this paper. Phase constitutions, microhardness, microstructure, and wear characteristics of FeCrNiTiZr coatings under different laser scanning speeds were analyzed. It was determined that 480 mm/min was the optimal laser scanning speed. The results showed that the coating at the scanning speed of 480 mm/min consists of a BCC phase with significant lattice distortion and high dislocation density; the crystal structure is cellular crystal and dendrite crystal. The coating demonstrates the highest microhardness (842 HV0.2), which is 4.2 times that of the substrate (200 HV0.2). Its average friction coefficients at room temperature and 823 K are approximately one-seventh and one-third of the substrate's, respectively, and its wear volume is reduced by about 98% and 81% under these conditions. Compared to the substrate, the coating underwent slight abrasive wear, adhesive wear, and oxidative wear at both room temperature and 823 K. In contrast, the substrate underwent severe abrasive wear, adhesive wear, oxidative wear, and even fatigue wear.

Laser heat conduction joining of polycarbonate and aluminum alloy

The present work demonstrates the laser heat conduction joining (LHCJ) of polycarbonate and aluminum alloy. The experiments are performed to examine the impact of scan speed and laser power on the joint’s strength and quality. The bonding between the substrates was assessed by examining the cross-section using a scanning electron microscope and conducting energy-dispersive X-ray spectroscopy. The fractured surfaces are inspected by an optical microscope to explore the bond morphology. A finite-element-based numerical model is developed for the estimation of interface temperature and validated with the experimental results. Results of lap shear tests show that the weld strength is significantly affected by the laser power, scan speed, interface temperature, and bubble area. Microscopic observations of the joint interface disclose bubble area and mechanical interlocking between polycarbonate and aluminum. Through X-ray photoelectron spectroscopy (XPS) analysis, it was discovered that the interface experiences chemical bonding facilitated by the formation of Al-O-C bonds, which effectively enhances the strength of the joint.

Shape Anisotropy of Grains Formed by Laser Melting of (CoCuFeZr)17Sm2

For permanent magnetic materials, anisotropic microstructures are crucial for maximizing remanence Jr and maximum energy product (BH)max. This also applies to additive manufacturing processes such as laser powder bed fusion (PBF-LB). In PBF-LB processing, the solidification behavior is determined by the crystal structure of the material, the substrate, and the melt-pool morphology, resulting from the laser power PL and scanning speed vs. To study the impact of these parameters on the textured growth of grains in the melt-pool, experiments were conducted using single laser tracks on (CoCuFeZr)17Sm2 sintered magnets. A method was developed to quantify this grain shape anisotropy from electron backscatter diffraction (EBSD) analysis. For all grains in the melt-pool, the grain shape aspect ratio (GSAR) is calculated to distinguish columnar (GSAR &lt; 0.5) and equiaxed (GSAR &gt; 0.5) grains. For columnar grains, the grain shape orientation (GSO) is determined. The GSO represents the preferred growth direction of each grain. This method can also be used to reconstruct the temperature gradients present during solidification in the melt-pool. A dependence of the melt-pool aspect ratio (depth/width) on energy input was observed, where increasing energy input (increasing PL, decreasing vs) led to higher aspect ratios. For aspect ratios around 0.3, an optimum for directional columnar growth (93% area fraction) with predominantly vertical growth direction (mean angular deviation of 23.1° from vertical) was observed. The resulting crystallographic orientation is beyond the scope of this publication and will be investigated in future work.

Surface Modification and Corrosion Performance of Laser Cladded Co–Ni on Ti–6Al–4 V in 0.5 M H2SO4 Environment

This study investigates the laser cladding of Co and Ni powders onto Ti–6Al–4 V substrates, varying the admixed percentages while adjusting laser processing parameters. The influence of nickel and cobalt contents on the microstructure, phase composition, and electrochemical behavior of the laser-clad Ti–6Al–4 V coatings were analyzed. Coating morphology and phases were characterized using scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS), and X-ray diffractometry (XRD), respectively. The corrosion resistance of Ti–6Al–4 V, both with and without Ni–Co additions, in 0.5 M H2SO4 was evaluated using potentiodynamic polarization technique. Results indicated that the coatings exhibited excellent metallurgical compatibility with the substrate. Additionally, the high scan speed laser-clad samples showed enhanced corrosion resistance compared to those processed at low speeds. The potentiodynamic polarization analysis revealed passive behavior in all specimens, with higher cobalt content notably enhancing passivity and corrosion resistance by suppressing the anodic reaction.