Laser Spot Research Articles

Size effect of femtosecond laser helical drilling on nickel-based single crystal superalloy

Femtosecond laser has gradually become a reliable tool for processing high-quality film cooling holes (FCHs) of turbine blades in recent years. However, in the case of turbine blades with a variety of aperture drilling requirements, the influence of aperture on drilling quality and its internal causes are ignored. In this paper, the “size effect” of different aperture holes prepared by femtosecond laser helical drilling method was analyzed and compared in terms of geometric features, machining efficiency, hole wall ablation and drilling evolution process, and the formation mechanism of the “size effect” were revealed from the aspects of removal efficiency, laser spot overlap rate, energy shielding effect and residues discharge capacity. The results show that with the increase of laser scanning diameter D, the taper of the hole increases, the drilling efficiency increases first and then decreases, and the surface of hole wall is transformed from microvoids, microcracks and adhesive oxide residues into a regular nanostripes. The increase of D makes the radial spot overlap rate Pr decrease significantly, and Pr seriously affects the removal efficiency and thermal effect on the hole wall, which should be adjusted according to different apertures. Thermal accumulation and laser energy utilization rate attenuation caused by the energy shielding effect are the most important factors that deteriorate the processing quality and reduce the processing efficiency during femtosecond helical drilling. Therefore, for smaller aperture drilling, the strategy of process adjustment is to increase residues discharge capacity.

Physics guided heat source for quantitative prediction of IN718 laser additive manufacturing processes

Challenge 3 of the 2022 NIST additive manufacturing benchmark (AM Bench) experiments asked modelers to submit predictions for solid cooling rate, liquid cooling rate, time above melt, and melt pool geometry for single and multiple track laser powder bed fusion process using moving lasers. An in-house developed Additive Manufacturing Computational Fluid Dynamics code (AM-CFD) combined with a cylindrical heat source is implemented to accurately predict these experiments. Heuristic heat source calibration is proposed relating volumetric energy density (ψ) based on experiments available in the literature. The parameters of the heat source of the computational model are initially calibrated based on a Higher Order Proper Generalized Decomposition- (HOPGD) based surrogate model. The prediction using the calibrated heat source agrees quantitatively with NIST measurements for different process conditions (laser spot diameter, laser power, and scan speed). A scaling law based on keyhole formation is also utilized in calibrating the parameters of the cylindrical heat source and predicting the challenge experiments. In addition, an improvement on the heat source model is proposed to relate the Volumetric Energy Density (VEDσ) to the melt pool aspect ratio. The model shows further improvement in the prediction of the experimental measurements for the melt pool, including cases at higher VEDσ. Overall, it is concluded that the appropriate selection of laser heat source parameterization scheme along with the heat source model is crucial in the accurate prediction of melt pool geometry and thermal measurements while bypassing the expensive computational simulations that consider increased physics equations.

ND:YAG Laser Vitreolysis as The Management of Occluded Tube After Glaucoma Drainage Device Implantation (GDD)

Introduction : Glaucoma Drainage Devices (GDD) implantation surgery can be an alternative therapy for patients with uncontrolled IOP after trabeculectomy. However, tube occlusion is a common complication of GDD implantation. Management of tube occlusion can be done using laser or with surgery. This case presents the management of vitreous occlusion of tube implant using ND:YAG laser-vitreolysis.
 Case Illustration : A 63 year-old male patient came with chief complaint of pain in his right eye. The patient had a history of cataract surgery on the right eye and was diagnosed with glaucoma. An examination showed IOP in the right eye was increased, vitreous in COA and lens was aphakic with posterior capsule rupture. The patient had undergone trabeculectomy, but IOP remained high, so an Aurolab Aqueous Drainage Implant (AADI) GDD implantation was performed. However, six weeks after the procedure, the IOP still increased, and an examination revealed vitreous occlusion of the GDD tube (Figure 1) . The patient underwent Zeiss ND-YAG laser-vitreolysis on his right eye (Figure 2) with laser spot size of 50?m and power of 2.1 MJ. Post laser IOP was decreased.
 Discussion : GDD implantation is a surgical option for primary or secondary therapy, but tube occlusion can cause implantation failure. Laser-vitreolysis is a non- invasive modality to treat tube occlusion caused by vitreous.
 Conclusion : GDD occlusion can occur due to various etiologies, but laser-vitreolysis is a non-invasive treatment option aimed at restoring tube patency and aqueous outflow.

Polarization‐Modulated Patterned Laser Sculpturing of Optical Functional Hierarchical Micro/Nanostructures

AbstractHierarchical micro/nanostructures have garnered considerable attention for their capabilities in light modulation, but the flexible fabrication of designed optical functional structures at both micro and nano scales remains challenging. Here, a polarization‐modulated patterned laser ablation method complemented by flowing liquid is proposed to fabricate hierarchical microgrooves featuring tunable cross‐sections and engraved surface nanostructures with controllable periods and orientations. The liquid‐assisted ablation counters the shielding effect of ablation debris through laser‐induced microjets, ensuring accurate control of the microgroove's shape by modulating the laser pattern in the focal plane. Simultaneously, the absence of debris also permits the consistent formation of laser‐induced periodic surface structures (LIPSS) across the microgrooves. The LIPSS's period and orientation can be finely adjusted by manipulating the pulse energy and polarization within the patterned laser spot, facilitating the adaptable creation of hierarchical micro/nanostructures for optical application needs. As a demonstration, blazed gratings featuring orientation‐customized LIPSS are fabricated, which exhibit polarization‐dependent diffraction efficiency. The laser fabrication technique offers a highly versatile solution for sculpturing shape‐controllable hierarchical gratings on hard‐to‐machine materials, paving the way for the swift production of customized optical elements.

Experimental study of laser spot tracking for underwater optical wireless communication.

In this paper, a novel laser spot tracking algorithm that incorporates the Kalman filter with the continuously adaptive Meanshift algorithm (Cam-Kalm) is proposed and employed in an underwater optical wireless communication (UOWC) system. Since the Kalman filter has the advantage of predicting the state information of the target spot based on its spatial motion features, the proposed algorithm can improve the accuracy and stability of the moving laser spot tracking. A 2 m optical wireless communication experimental system with auto-tracking based on a green laser diode (LD) is built to evaluate the tracking performance of different algorithms. Experimental results verify that the proposed algorithm outperforms conventional tracking algorithms in aspects of tracking accuracy, interference resistance, and response time. With the proposed Cam-Kalm algorithm, the experimental system can establish an effective communication link, while the maximum tracking speed is 20 mm/s given the forward-error-correction (FEC) threshold.

Safety and therapeutic efficacy of 577 nm yellow solid krypton laser for retinopathy of prematurity; A prospective pilot study.

To evaluate the outcome of 577 nm yellow solid krypton laser as an independent treatment modality for Retinopathy of Prematurity. Prospective, non-comparative, non-randomized, interventional. A prospective pilot study was conducted on 30 treatment eyes with retinopathy of prematurity (ROP) who underwent treatment with a 577 nm yellow solid state krypton laser. 3nethraNEO pediatric retinal imaging system was used to screen these infants born between March to August 2022. Pre procedure data such as gestational age (weeks), birth weight (g), and exposure to risk factors were recorded. Power (mW), exposure duration (msec), and number of laser spots administered were noted. Pain was assessed using the Neonatal Pain/Agitation and Sedation Scale (N-PASS). Post procedure data such as regression, persistence or reactivation of disease, and adverse effects were looked for. All eyes were followed up for a period of 3 months. Chi-square test, Fisher's exact test. Out of 30 eyes, 09 (30%) had type I and 21 (70%) had non-type I ROP. In type I disease, the mean power used was 88+/-10 mW with exposure duration of 130+/-27 msec and an average number of 890+/-260 burns were administered. In non-type I disease, the mean power used was 87+/-10 mW with an exposure duration of 150 ms and an average number of 900+/-290 burns were administered. The mean pain score calculated was 5 in type I and 6 in non-type I ROP. All eyes showed regression of disease after treatment. 577 nm yellow solid krypton laser was safe and effective in treating retinopathy of prematurity disease.

The effectiveness of low-level laser therapy and low-intensity pulsed ultrasound in reducing pain induced by orthodontic separation: a randomized controlled trial

BackgroundThe low-level laser therapy (LLLT) and low-intensity pulsed ultrasound (LIPUS) have been recently applied to control pain during orthodontic treatment.ObjectiveTo evaluate and compare the effectiveness of LLLT and LIPUS in reducing pain induced by orthodontic separation.Study designA single-blinded randomized controlled trial.MethodsOne hundred and fifty patients were randomly assigned into three groups; LLLT group, LIPUS group, and control group. After 5 min from the separators’ placement, the first dose of the laser or the ultrasound was applied, the second dose was applied after 24 h, and the third dose was applied after 48 h on both maxillary and mandibular first molars. The exposure of laser was for 20 s at each point (maxillary and mandibular first molars), with an 810-nm aluminum-gallium-arsenide (AlGaAs) diode laser on continuous mode. The output power set at 150 mW, the energy density of 4 J/cm2, and a laser spot diameter of 7 mm were applied. Whereas the frequency of ultrasonic toothbrush was 1.6 MHz; and average output intensity was 0.2 W/cm2. The application was for 20 min (5 min on each first molar). The control group received the separators without another intervention. A Visual Analog Scale (VAS 100 mm) was used to assess pain intensity at several time intervals during the first four days after the separators’ placement.ResultsA total of 145 patients were assessed. There was a significant difference in pain perception among the three groups after 5 min (P = .002). The maximum pain level was reached after 24 h. However, the laser group and the ultrasound group showed a statistically significant decrease in pain scores compared to the control group at all the assessment time points (P < .001). Whereas there was no difference between the laser group and the ultrasound group in reducing the pain scores (P > .05).ConclusionsThe LLLT and the LIPUS effectively reduce the separation pain when applied in multiple doses without differences between them.Trial registrationThis trial was registered with the German Clinical Trials Register (DRKS). (https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID= DRKS00029991). Date of registration: 26/08/2022.

Pose Control of Millimeter-Scale Objects in a Laser-Powered Thermocapillary Manipulation Platform

The miniaturization of technological components requires tools capable of manipulating them. Noncontact micromanipulation has recently gained popularity since it minimizes component damage and adhesion problems. However, the simultaneous position and orientation (pose) control using noncontact tools remains an open challenge. In this work, we propose the pose control of millimeter-scale structures at the air–water interface using laser-powered thermocapillary flows. We achieve autonomous pose control by steering two laser spots around the structure in a closed-loop manner. The controller consists of a linear pose controller and a model inversion. The pose controller defines the required force and torque to reach the target. The model inversion defines the required laser positions to obtain said force and torque. This inversion is performed with an optimization algorithm, without any prescribed strategy. The pose stabilization was validated experimentally, obtaining a position and orientation precision of 0.15 body lengths and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2^{\circ }$</tex-math></inline-formula> , respectively. Additionally, we show the experimental path-following with independent orientation control, obtaining a similar position precision.

Ability to Simulate Absorption and Melt Pool Dynamics for Laser Melting of Bare Aluminum Plate: Results and Insights from the 2022 Asynchronous AM-Bench Challenge

The 2022 Asynchronous AM-Bench challenge was designed to test the ability of simulations to accurately predict laser power absorption as well as various melt pool behaviors (width, depth, and solidification) during laser melting of solid metal during stationary and scanned laser illumination. In this challenge, participants were asked to predict a series of experimental outcomes. Experimental data were obtained from a series of experiments performed at the Advanced Photon Source at Argonne National Laboratories in 2019. These experiments combined integrating sphere radiometry with high-speed X-ray imaging, allowing for the simultaneous recording of absolute laser power absorption and two-dimensional, projected images of the melt pool. All challenge problems were based on experiments using bare aluminum solid metal. Participants were provided with pertinent experimental information like laser power, scan speed, laser spot size, and material composition. Additionally, participants were given absorptance and X-ray imaging data from stationary and scanned laser experiments on solid Ti–6Al–4V that could be used for testing their models before attempting challenge problems. In total, this challenge received 56 submissions from eight different research groups for eight individual challenge problems. The data for this challenge, and associated information, are available for download from the NIST Public Data Repository. This paper summarizes the results from the 2022 Asynchronous AM-Bench challenge as well as discusses the lessons learned to help inform future challenges.

Detection of defects during laser-powder interaction by acoustic emission sensors and signal characteristics

Acoustic Emission (AE) sensing is an in-situ real-time nondestructive monitoring method proposed for Additive Manufacturing (AM) to detect defects such as cracks. Previous AE research in AM mainly focused on developing algorithms to automatically detect the defects from AE signals without understanding the physical mechanisms or the signal characteristics that could be used as identifiers. We study AE signals during a laser spot welding on a powder bed to clearly distinguish between different physical mechanisms using their signal characteristics. We identified specific signals associated with 1) tensile cracks from cooling, 2) a powder effect on the substrate, and 3) sudden thermal expansion of the substrate. We used the spectral ratio between high frequency (70–150 kHz) and low frequency (10–40 kHz) spectral amplitudes in the frequency domain to classify and differentiate the source types. We found that porosity due to insufficient energy density did not produce detectable AE signals. Using a ball drop calibration technique, we used AE signals to estimate the absolute sizes of the tensile cracks. Crack sizes ranged from 40 μm to 1 mm and were in general agreement with scanning electron microscope images of the fractures. We performed a line scanning test and successfully validated its potential for the application. Our findings provide a basic understanding of AE signal characteristics in AM, as well as the practical parameters used to separate the signal types.

Accurate Real-Time Laser Spot Locating Based on Template Correlation in Intersatellite Laser Communications

Accurate Real-Time Laser Spot Locating Based on Template Correlation in Intersatellite Laser Communications

Control of growth kinetics during remote epitaxy of complex oxides on graphene by pulsed laser deposition

Remote epitaxy through 2D materials opens new opportunities for research and application, overcoming some limitations of classical epitaxy and allowing the creation of freestanding layers. However, using graphene as a 2D interlayer for remote epitaxy of metal oxides is challenging, particularly when carried out by pulsed laser deposition (PLD). The graphene layer can be easily oxidized under the typically applied high oxygen pressures, and the impact of highly kinetic particles of the plasma plume can lead to severe damages. In this study, both aspects are addressed: Argon is introduced as an inert background gas in order to avoid oxidation and to reduce the kinetic impact of the plasma species on graphene. The laser spot size is minimized to control the plasma plume and particle flux. As a model system, strontium titanate (STO) is quasi-homoepitaxially grown on graphene buffered STO single crystals. Raman spectroscopy is performed to evaluate the 2D, G, and D band fingerprints of the graphene layer and to assess the defect structure of the interlayer after the deposition. Our results prove that control of the growth kinetics by reducing the laser spot size and by using high argon pressures provides a key strategy to conserve graphene with a low defect density during PLD while allowing a layer-by-layer growth of structurally coherent oxide layers. This strategy may be generalized for the PLD remote epitaxy of many complex oxides, opening the way for integrating 2D materials with complex oxides using widely accessible PLD processes.

Mass Transfer System of a Large Number of Small Objects Based on Conjunction of Triboelectric Nanogenerators and Photo‐Responsive Interface

AbstractMass transfer technology for large quantities of tiny substances, such as electronic chips and drug particles, plays a crucial role in many industries. This study proposes a transferring system for large quantities of small objects based on the synergism of triboelectric nanogenerators (TENGs) and photo‐responsive dielectric materials. TENG device can provide an output voltage of over 8 kV within a rotation time of 40 ms and the titanium oxide phthalocyanine (TiOPc) photoconductive films are fabricated as the photo‐responsive interface, in order to match the output impedance of TENG. The transfer system enables a maximum adsorption load of 98 mg mm−2, which is enough for handling all common electronics chips/wafers. Under the stimulation of laser light, the conductivity of the TiOPc interface can be increased by two orders of magnitude within 1 ms, which leads to the vanish of the surface potential on the laser spot and the release of patterned or pointed object. This photo‐responsive strategy can achieve both large quantity transfer of tiny objects and highly selective release of the element at designed position. This collaborative mechanism of electrostatic force and photoconductivity provides a different approach for realizing efficient and precise Mass transfer system of semiconductor and chip industry.

Sulfide compositions of young Chang’e-5 basalts and implications for sulfur isotopes in lunar basalt sources

Sulfides are accessory phases in lunar rocks butare important forunderstanding lunar interior processes as well as impacts on the lunar surface.Whether or not the lunar mantle had achieved sulfide saturation during magma ocean evolution and displays homogeneous sulfur isotopes remains under debate. TheChang’e-5 (CE-5) mission returned young (2.0 Ga) basalts from a mare terrain in thenorthern Oceanus Procellarum.Here we study chemical and sulfur isotopic compositions (δ34SV-CDT) of sulfides from CE-5 basaltic fragments and combine them with δ34S of other young (3.1–3.0 Ga) lunar low-Ti basalt (NWA 10597 and NWA 4734) and gabbro meteorites (NWA 6950) to compare them with Apollo low-Ti and high-Ti mare basalts. The sulfides in basaltic fragments of CE-5 are troilites (FeS) with lowabundances ofNi, Co, and Cu(e.g., Ni < 0.04 wt% and Ni/Co < 0.3). Textures and chemical compositions indicate that most troilites arelate-stage crystallization products fromthe highly evolvedCE-5 basalts. Several troilites occur in the matrices of impactite clasts and are intergrown with Fe–Ni metal(12–36 wt% Ni, Ni/Co of 12–39). These troilites are distinct from the major population of troilites withnoticeably higher Ni abundances (mostly > 0.2 wt% with Ni/Co of 1–3) andreconcile with the addition of meteoritic materials into the impact melts.The δ34SV-CDTof large troilite grains (>10 μm) from the CE-5 basaltic fragments and lunar meteorites were obtained by high-precision, high-spatial-resolution femtosecond laser ablation MC-ICP-MS which achieved external uncertainty (0.65 ‰, 2SD at 8-μm laser spots) like nano-SIMS. Sulfur degassing during surficial effusive lava flow likely led to a slightdecrease inδ34S (by ∼ 1 ‰) for some basaltic fragments; however, such effects were limited to the scale of bulk rock samples, consistent with previous results. The mean δ34Sof troilites in CE-5 basaltic fragments (0.35 ± 0.25 ‰, 2SE, n = 45) is similar to those of ancient (3.8–3.1 Ga old) Apollo low-Ti and high-Ti mare basalts and the young gabbro cumulate NWA 6950 (0.56 ± 0.21 ‰, 2SE, n = 10). The paired NWA 10597 and NWA 4734 show consistent δ34S, lower than most values by ∼ 0.5 ‰. Current data thus indicate that most mantle sources of lunar basalts would be homogeneous for δ34S(0.6 ± 0.3 ‰) and minor regions may be different. The overall homogenous δ34S from different mantle sources with variably low sulfur contents supports sulfide-undersaturated accumulation of the lunar magma ocean, which was inherited from strong volatile loss and evaporative fractionation during the formation of the Moon.

Laser beam shaping using a photoinduced azopolymer droplet-based mask.

The dewetting of an azopolymer droplet, followed by the photostructuration of the evaporated droplet, is employed to create an amplitude mask. This straightforward process yields a large area featuring periodic micro- and nanostructures. The resulting pattern is utilized to generate a nondiffracting beam. Starting with a Gaussian beam illuminating the amplitude mask, the critical aspect is the production of a bright, ring-shaped beam with a high radius-to-width ratio and symmetric central laser spots, each with the same intensity. This alternative approach to shaping a laser beam is demonstrated as a rapid and cost-effective fabrication technique.

A two-step laser-jet electrodeposition for the preparation of superhydrophobic surfaces on SUS304

A laser-jet electrodeposition step-by-step processing was used to fabricate a superhydrophobic surface with excellent performance on the SUS304 substrate. Firstly, different micro structures were obtained by laser texturing on the surface of the SUS304 substrate. Secondly, Ni-MoS2 composite coating was deposited on the SUS304 substrate with microstructure by jet electrodeposition. Previous research has shown that different sizes of microstructures can be processed on the substrate surface and exhibit different wettability if changing the scanning pitch of laser textures. Superhydrophobic surfaces with contact angles up to 156 ° and 151.5 ° were obtained when jet electrodeposited on the basis of laser scanning pitches with 1 and 1.5 times the laser spot diameter. Compared with hydrophobic surfaces only by the laser, the superhydrophobic surfaces have shown superior corrosion resistance and self-cleaning properties. In addition, the superhydrophobic surface produced by the two-step laser-jet electrodeposition still exhibits good superhydrophobicity after undergoing friction, which indicates that the superhydrophobic surface has excellent mechanical stability by two-step laser-jet electrodeposition.

On the effect of small laser spot size on the mechanical behaviour of 316L stainless steel fabricated by L-PBF additive manufacturing

This research effort experimentally investigated the influence of small laser spot size (LSS – 50 µm and 100 µm) on the mechanical behaviour of additively manufactured 316 L Stainless Steel (SS) samples produced by laser-powder bed fusion on a single metal 3D printer. The effect of main process parameters including scanning speed (1400, 1700 and 2000 mm/min), layer thickness (30, 55, and 80 µm), build direction (0°, 15° and 30°, 90 ° or flat) and printing power (100, 200, and 350 W) was analysed. Tensile tests together with scanning electron microscopy were carried out to determine the mechanical behaviour and fractography pattern of the parts produced with different parameters. When changing the build direction, the results led to a nearly isotropic mechanical behaviour in combination with the manufacturing equipment. By employing small laser sport size, the melt pool depth was increased, which in turn led to an enhancement in the mechanical performance of the fabricated 316L SS. Printed specimens displayed ultimate tensile strength values of 165–550 MPa (LSS of 50 µm) and 147–519 MPa (LSS of 100 µm), yield strengths of 137–402 MPa (LSS of 50 µm) and 120–385 MPa (LSS of 100 µm), with an elongation at break of 5–64%.

Microstructure and properties of Al–Cu–Mg alloy welded by 14 μm single-mode laser small oscillation welding

In this paper, the 14 μm single-mode laser oscillation welding technique was adopted to achieve high-quality welding of 2A12 aluminum alloy. Specifically, its influence on the microstructure and mechanical properties of the joint and the formation mechanism were investigated. The results showed that the ultra-small spot laser (28 μm) was able to achieve sequential oscillation of the molten pool with small amplitude (0.1 mm). The increased frequency caused the average grain size to decrease and the grain boundary length increased in the fusion zone. Meanwhile, the average grain orientation difference increased, and the growth orientation was more dispersed and homogeneous. While reducing weld morphology defects and refining grain microstructure, there was little influence on the penetration and width morphology of the weld. Finally, successfully prepared welds with tensile strength up to 410.4 MPa and elongation simultaneously increased to 4.065 % at 200 Hz. Furthermore, the influence of keyhole oscillation on the molten pool flow at small amplitude was explained by high-speed camera observation, which explored the mechanism of grain growth in the oscillating joints and provided new ideas for the welding of 2xx aluminum alloys.

Laser-spot lock-in thermography with a non-research-grade thermal camera: From thermal diffusivity measurements to visualizing free convection

The widespread use of Lock-in Thermography (LIT) has been hindered by the high cost of the thermographic cameras available for such applications. We show that a low-cost thermographic camera (we used the QIANLI MEGA-IDEA Super iR Cam 2S) can be straightforwardly used in advanced applications, particularly for measuring the thermal diffusivity of solids using the Laser Spot LIT Technique and the Slope Method. The results of measurements performed in test samples were compared with those obtained using the FLIR SC5000 research-grade camera, whose usefulness for this kind of application has been demonstrated before. The Super iR Cam 2S is almost two orders of magnitude cheaper than the FLIR SC5000 but has an inferior performance. However, a good agreement between the thermal diffusivities of materials, with values between 10 and 100 mm2/s, obtained using both cameras and those reported in the literature demonstrates inexpensive instrumentation usefulness for conducting high-quality research work. The visualization of cracks between samples with different diffusivities was demonstrated too. For the first time, we also show the possibility of using Laser Spot LIT to directly observe a convective effect in a fluid layer closest to the sample’s surface.

Heat affected zone evolution in fine grained aluminum alloys during laser welding: Phase-field simulation and analytical investigation

One of the biggest challenges in the welding of strengthened alloys by grain refinement is the grain growth phenomenon in the heat-affected zone (HAZ), which would result in the degradation of mechanical properties. The goal of this study is to comprehend the HAZ evolution in the fine-grained aluminum alloy during laser welding as a low heat input process. Spot laser welding of fined grain 1050 aluminum alloy revealed that grain growth and HAZ formation occurred in samples with 4 µm grain size, but no grain growth occurred outside of the fusion line (FL) in larger grain samples. The microstructure of HAZ was simulated using the numerical phase-field technique. The numerical model's findings demonstrated that a critical grain size (Dcr) for the base metal can be established, above which grain growth would not occur outside FL. To predict grain size distribution outside FL, an analytical model was also used. According to both models, as grain size increases, the HAZ width decreases, and above a critical grain size, no HAZ will form outside of FL. In spot welding, Dcr was independent of power density but for continuous welding processes, Dcr has a direct relationship with heat input per unit length of weld. Moreover, HAZ grain growth mainly occurred in heating step for both types of processes.