Laser Processing Parameters Research Articles

Quantifying laser irradiation-induced temperature field of particle reinforced metal matrix composites

While particle-reinforced metal matrix composites (PMMCs) are composed of particles and matrix with distinctly different thermomechanical properties, the thermal differences and coupled interactions between individual phases greatly determine the thermal characteristics of PMMCs under laser irradiation. In this work, we quantify the temperature evolution characteristics within SiCp/Al under laser irradiation by microstructural thermal finite element simulations and experimental investigation. Specifically, a 2D thermophysical FE model of laser-SiCp/Al interaction for the two-phase PMMCs material under laser irradiation is developed, which incorporates the temperature-dependent thermophysical properties of particles, matrix and interfaces, along with the considerations of the shape and distribution characteristics of particles, as well as the comprehensive thermal conditions. Furthermore, a 3D equivalent thermal FE model for experimental validation of predicted laser-induced temperature of SiCp/Al is developed, based on the derived equivalent properties. Meanwhile, an in-situ temperature measurement system is constructed for exploring temperature evolution characteristics during the on-going laser irradiation process, which validates a derivation of 1.7 % of predicted temperature by the equivalent thermal FE model. Finally, the impact of laser processing parameters on the temperature field of SiCp/Al is addressed. These findings provide valuable insights for understanding the thermal mechanisms of PMMCs under laser irradiation, and also the parameter optimization for laser processing of PMMCs.

Wettability Behaviour of Metal Surfaces after Sequential Nanosecond and Picosecond Laser Texturing.

This study examines the wettability behaviour of 304 stainless steel (304SS) and Ti-6Al-4V (Ti64) surfaces after sequential nanosecond (ns) and picosecond (ps) laser texturing; in particular, how the multi-scale surface structures created influence the lifecycle of surface hydrophobicity. The effect of different post-process treatments is also examined. Surfaces were analysed using Scanning Electron Microscopy (SEM), a white light interferometer optical profiler, and Energy Dispersive X-ray (EDX) spectroscopy. Wettability was assessed through sessile drop contact angle (CA) measurements, conducted at regular intervals over periods of up to 12 months, while EDX scans monitored elemental chemical changes. The results show that sequential (ns + ps) laser processing produced multi-scale surface texture with laser-induced periodic surface structures (LIPSS). Compared to the ns laser case, the (ns + ps) laser processed surfaces transitioned more rapidly to a hydrophobic state and maintained this property for much longer, especially when the single post-process treatment was ultrasonic cleaning. Some interesting features in CA development over these extended timescales are revealed. For 304SS, hydrophobicity was reached in 1-2 days, with the CA then remaining in the range of 120 to 140° for up to 180 days; whereas the ns laser-processed surfaces took longer to reach hydrophobicity and only maintained the condition for up to 30 days. Similar results were found for the case of Ti64. The findings show that such multi-scale structured metal surfaces can offer relatively stable hydrophobic properties, the lifetime of which can be extended significantly through the appropriate selection of laser process parameters and post-process treatment. The addition of LIPSS appears to help extend the longevity of the hydrophobic property. In seeking to identify other factors influencing wettability, from our EDX results, we observed a significant and steady rate of increase in the carbon content at the surface over the study period.

Transformations in laser track microstructures for a quasicrystal-reinforced Al-Cu-Fe-Cr alloy

Aluminum-quasicrystal composites are attractive candidate alloys for additive manufacturing, but the cost of evaluating such systems can be prohibitive. Recently, surface laser glazing studies have been used to show that desirable composite microstructures can be formed in an Al85Cu6Fe3Cr6 alloy under a wide range of laser processing parameters. Here the thermal stability of these laser track microstructures has been evaluated by performing in situ scanning transmission electron microscopy heating experiments on specimens produced by focused ion beam milling from the center of the tracks. The initial track microstructures exhibited a uniform phase mixture with 70 % by volume of I-phase quasicrystalline dispersoids in a FCC Al matrix with a film of Al2Cu at the interface. Preliminary ramped heating experiments were used to identify the temperatures at which transformations occurred and then isothermal experiments on fresh samples were used to monitor the progress of these processes. For temperatures of up to 450 °C the only significant changes were a redistribution and coarsening of the Al2Cu phase with a gradual increase in the Fe content of the phase. At higher temperatures, the I-phase decomposed to form a mixture of crystalline ω-Al7Cu2Fe and μ-Al4Cr phases. The I-phase decomposition proceeded by ejection of Cu and Fe with the remaining Cr-rich regions transforming to the Al4Cr approximant phase. The implications of these phenomena for use of the alloy in additive manufacturing are discussed.

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.

Study on Laser Transmission Welding Technology of TC4 Titanium Alloy and High-Borosilicate Glass.

As the demand for high-performance dissimilar material joining continues to increase in fields such as aerospace, biomedical engineering, and electronics, the welding technology of dissimilar materials has become a focus of research. However, due to the differences in material properties, particularly in the welding between metals and non-metals, numerous challenges arise. The formation and quality of the weld seam are strongly influenced by laser process parameters. In this study, successful welding of high-borosilicate glass to a TC4 titanium alloy, which was treated with high-temperature oxidation, was achieved using a millisecond pulsed laser. A series of process parameter comparison experiments were designed, and the laser welding behavior of the titanium alloy and glass under different process parameters was investigated using scanning electron microscopy (SEM) and a universal testing machine as the primary analysis and testing equipment. The results revealed that changes in process parameters significantly affect the energy input and accumulation during the welding process. The maximum joint strength of 60.67 N was obtained at a laser power of 180 W, a welding speed of 3 mm/s, a defocus distance of 0 mm, and a frequency of 10 Hz. Under the action of the laser, the two materials mixed and penetrated into the molten pool, thus achieving a connection. A phase, Ti5Si3, was detected at the fracture site, indicating that both mechanical bonding and chemical bonding reactions occurred between the high-borosilicate glass and the TC4 titanium alloy during the laser welding process.

Optimization of the Femtosecond Laser Machining Process for Single Crystal Diamond Using Response Surface Methodology

Femtosecond laser machining offers high precision and minimal thermal impact, making it a promising technique for processing hard and brittle materials like single-crystal diamonds (SCDs). In this study, the femtosecond laser machining process for SCD material was systematically optimized to improve both machining efficiency and quality. Initial single-factor experiments were conducted to explore the effects of key process parameters—laser power, scanning speed, and number of scans—on machining performance. Subsequently, response surface methodology (RSM)-based experiments designed using the Box–Behnken method were employed to comprehensively refine the process. A regression model was developed to analyze the data, and the interaction effects of the parameters were thoroughly evaluated. The validated model identified an optimal set of parameters, resulting in a significant improvement in machining performance. This research provides a comprehensive framework for optimizing femtosecond laser machining processes, offering valuable insights critical for the production of advanced lightweight components in industries such as aerospace, optical instruments, and high-performance electronics.

Targeted Microforming of Borosilicate Glass Induced by a Laser‐Ablation‐Free Process Using Femtosecond Pulses

AbstractThe use of ultrashort pulse lasers opens up a wide range of possibilities for processing dielectric materials. The present study focuses on the investigation of the ablation‐free microscopic surface modification of borosilicate glass using femtosecond laser radiation (350 fs at 515 nm wavelength) in a scanning machining process. Furthermore, its aim is to analyze the relationship between the laser process parameters and the microscopic changes in the surface topography observed. The characteristic of the generated surface structure, which takes place below the ablation threshold, shows both elevations and depressions within the irradiated field (2 × 2 mm2). The realized structures reach a profile height Peak‐to‐Valley (PV) of up to 10 µm. The amount of surface deformation depends on the selected parameters such as laser fluence, number of passes, and scanning strategy. The microdeformation is detected on both the top and bottom sides of the processed glass material with a thickness ≤1 mm. The influence of the temporal and spatial energy distribution on the material modification is discussed, demonstrating the possibilities of microforming of silicate glasses using ultrashort pulsed laser radiation.

Characterization of TiC particle reinforced magnesium matrix composites (MMCs) prepared by laser cladding based on element evaporation

In this study, we report the preparation of AZ31/TiC composites by laser cladding based on elemental vaporization and supplementation and investigate the effects of laser process parameters and mixed powder ratio on the vaporization and spattering. It was found that the capillary pressure generated by using TiC could effectively suppress the molten pool sputtering during laser cladding. In addition, TiC particles promoted the recrystallisation behavior of the molten pool, and the grains were significantly refined from 61.58 μm to 6.46 μm. The random orientation of the recrystallized grains led to a weaker texture, decrease from 12.349 to 1.964. The microhardness of the composites higher than AZ31 from 46 to 86.2 HV0.2, and the average wear rate was reduced by 21.9%.

Near-full density enabled excellent dynamic mechanical behavior in additively manufactured 316L stainless steels

Mechanical properties of additively manufactured alloys are momentously affected by the fabrication defects, thus limiting their applications in extreme conditions. Here we report on a near fully dense 316L stainless steel via optimized laser processing parameters. The results reveal that the dynamic mechanical response exhibits much greater sensitivity to defects than the quasi-static one. The densest specimen (porosity < 0.01 %, 260W-316L) exhibits superior spall strength of 3.87 GPa and negligible damage fraction of 0.03 % at peak stress of 4.8 GPa, which are 12 % higher and 92 % smaller than those of 0.18 % porosity specimen (300W-316L). For both horizontal and vertical impacts, hardly any anisotropy of spall strength is observed in 260W-316L, demonstrating the crucial role of the pore defects on the dynamical behavior. Moreover, dislocation slip dominated spallation mechanisms have been observed in the additively manufactured 316L specimens, accompanied by a small amount of deformation twinning and martensitic transitions. This comprehensive understanding of the defect-dependent spallation behavior and deformation mechanisms provides valuable insights for optimizing the dynamic mechanical properties of additively manufactured metals and alloys.

Influence of Mg Content on Microstructure Coarsening, Molten Pool Size, and Hardness of Laser Remelted Al(-x)-Mg-Sc Alloys.

Investigations leading to high-quality surfaces and optimized properties in laser remelted Al-Mg-Sc alloys remain scarce. Laser surface remelting (LSR) has been used for the final treatment of these alloys processed through additive manufacturing. However, the direct microstructure responses of the treated cast surfaces have not yet been investigated. In the present research, Al-3, 5, and 10 wt %-Mg-0.1 wt %-Sc alloys plates were processed using LSR to study the effects of local melting and rapid solidification. The morphology of the α-Al phase, microstructure coarsening, and hardness were mapped from the bottom to the top of the molten pools, varying with local Mg content and laser heat input (2.5 J/mm, 5 J/mm, and 10 J/mm). This study aimed to create a comprehensive map of the microstructures, hardness, and molten pool sizes under various conditions. The findings may help to optimize these alloys through understanding laser processing parameters. Methods used included CALPHAD computations, optical microscopy, SEM, EDS, image analysis, hardness tests, and heat flow models. The results obtained showed α-Al cell growth with bands in all alloys with hardness changes correlating with cell spacing and heat input. Higher Mg content resulted in more refined cells and a higher fraction of bands. Increased Mg content decreased the thermal diffusivity and enthalpy of melting, enlarging the molten pool size. Hardness increased with decreasing heat input and higher Mg content in the tested alloys, especially in the Al-10 wt %-Mg-0.1 wt %-Sc alloy as the heat input was varied.

Effect of laser speed on neck formation in SS316L powder joining for LPBF

The objective of this study is to comprehend how changes in laser speed affect the behaviour and features of neck formation in SS316L during powder bed fusion. This study examines the impact of various laser speeds on the neck formation in the commonly used SS316L. Uniweld Laser 3000 was used for laser joining. A constant laser power of 15 W and laser scan speed of 25–150 mm/s were implemented, and powder joining within a single track was observed. Results show that neck size decreases with increasing laser scanning speed and no particle joining occurs at 150 mm/s scan speed, as it is considered too fast for sufficient heat absorption and melting. As laser speed decreases to 125 mm/s, neck starts to form because the particles absorb more heat, which facilitates melting and bonding. Surface diffusion occurs early at this stage because it requires only a small amount of energy to break atomic bonds on the surfaces of particles compared to those in the internal part. This process involves atoms moving along the surfaces of the particles, facilitating the initial stages of sintering by reducing surface energy and causing neck formation between particles. At 125 mm/s, the particle shape remains spherical, and the average neck size is 49 μm. At 100 μm, the powder average neck size is 62 μm. Moreover, the powder completely merges at 50 mm/s and 25 mm/s. The neck formed between particles considerably improves the product's mechanical strength by strengthening bonds between particles. Material density increases with neck quality, and stable neck growth can reduce the porosity of the final parts. Ensuring thermal stability in the laser powder bed fusion allows consistent heat to particles, ensuring even temperature in materials and ultimately facilitating stable neck growth. Thermal stability enables atoms in particles to migrate efficiently and prevents defects, such as bubbling, which increases porosity in printed parts. Therefore, a slow scanning speed allows particles to absorb more heat for melting, increasing the neck size of particles. This knowledge is useful for optimizing laser processing parameters in various industrial applications.

Characterization of Micro-Holes Drilled Using a UV Femtosecond Laser in Modified Polyimide Flexible Circuit Boards.

Modified polyimide (MPI) flexible printed circuits (FPCs) are used as chip carrier boards. The quality of the FPC directly affects the reliability of the integrated circuit. Furthermore, micro-holes are critical components of FPCs. In this study, an ultraviolet (UV) femtosecond laser is used to drill micro-holes in double-layer flexible circuit boards with MPI as the substrate. The morphology of the micro-hole wall in the copper foil and MPI layer is observed, and the effects of the laser processing parameters on the diameter and depth of the micro-holes are analyzed. The drilling process and mechanism of micro-holes obtained using a UV femtosecond laser in MPI FPCs are discussed. The results show that the morphology of femtosecond laser-machined copper is closely related to the laser energy, and a periodic structure is observed during the machining process. Copper, MPI, and copper oxides are the most common molten deposits in micro-holes during drilling. The depth of the micro-holes increases with an increase in the energy of a single pulse, scanning time, and scanning overlap rate of the laser beam. However, the diameter exhibits no discernible alteration. The material removal rate increased significantly when laser processing was applied to the MPI resin layer.

Finite element simulation and experimental verification of laser machining of nitinol tubes

Nitinol tubes are widely used to cut various biological stents, especially cardiovascular stents. However, stent fabrication defects, such as residual stress, microcracks, and heat-affected zones (HAZs) from the laser cutting, can lead to severe clinical complications. In this study, a multiphase flow coupling model for fiber laser cutting simulation is established by considering surface tension, gravity, and recoil pressure and combining the characteristics of fluid heat transfer with phase transition dynamics. The accuracy of the model is verified through the fiber laser cutting experiments. The simulation model is used to explore the influence of the key process parameters of laser cutting on the kerf width, stress, temperature distribution, and the HAZ. The microscopic removal mechanism of the material during the laser cutting is revealed, thus minimizing the problems generated during stent forming. The simulation model can provide an optimized process plan for fiber laser cutting.

Optical properties of transparent TiO2 films by sintering anatase nanoparticles with a CO2 laser

A novel CO2 laser additive manufacturing technique is reported in this paper for depositing transparent TiO2 films on quartz substrates using anatase TiO2 nanoparticles (NPs). Single- and double-layers of TiO2 films were prepared in two stages: (i) wet deposition using the spin-coating technique, and (ii) laser-assisted both drying of the wet layer and then sintering of the dried NPs to form a film. A theoretical model is presented to select and optimize the laser processing parameters. Scanning electron microscopy (SEM) revealed that the laser heating induces necking and coalescence of TiO2 NPs without cracking the sintered films or damaging the quartz substrate. An anti-reflection coating (ARC) model is utilized to select the film material and film thickness, aiming to reduce the reflectance and enhance the transmittance at certain wavelengths. UV/Vis spectrophotometry showed transmittance above ∼90% in the visible (Vis) range. The effect of laser power on the enhancement of transmittance is presented in this paper. Different concentrations of TiO2 NPs were used to optimize the film thickness. Single layer (∼110nm thick) and double layer films of the same total thickness as the single layer were analyzed to infer the effects of interface on the transmittance of TiO2 films. The transmittance of the single layer is higher, same as that of the double layer. Therefore, the difference in the transmittance of the single- and double-layer may be due to the effect of interface. The optical properties of the anti-reflection TiO2 coating in the UV–Vis ranges were investigated. X-ray diffraction (XRD) analysis showed that the thickness affects the crystallinity of the sintered TiO2 films.

A Machine Learning Framework for Melt-Pool Geometry Prediction and Process Parameter Optimization in the Laser Powder-Bed Fusion Process

Abstract This study presents a cost-effective and high-precision machine learning (ML) method for predicting the melt-pool geometry and optimizing the process parameters in the laser powder-bed fusion (LPBF) process with Ti-6Al-4V alloy. Unlike many ML models, the presented method incorporates five key features, including three process parameters (laser power, scanning speed, and spot size) and two material parameters (layer thickness and powder porosity). The target variables are the melt-pool width and depth that collectively define the melt-pool geometry and give insight into the melt-pool dynamics in LPBF. The dataset integrates information from an extensive literature survey, computational fluid dynamics (CFD) modeling, and laser melting experiments. Multiple ML regression methods are assessed to determine the best model to predict the melt-pool geometry. Tenfold cross-validation is applied to evaluate the model performance using five evaluation metrics. Several data pre-processing, augmentation, and feature engineering techniques are performed to improve the accuracy of the models. Results show that the “Extra Trees regression” and “Gaussian process regression” models yield the least errors for predicting melt-pool width and depth, respectively. The ML modeling results are compared with the experimental and CFD modeling results to validate the proposed ML models. The most influential parameter affecting the melt-pool geometry is also determined by the sensitivity analysis. The processing parameters are optimized using an iterative grid search method employing the trained ML models. The presented ML framework offers computational speed and simplicity, which can be implemented in other additive manufacturing techniques to comprehend the critical traits.

Processing correlations of laser direct energy deposited Inconel718 based on multi-field numerical simulation

Laser direct energy deposited (LDED) Inconel718 always have problems of non-uniform temperature distribution because of the complex flow of molten pool and layer-by-layer fabrication characterization which directly affected the microstructure and mechanical properties of materials. In this work, Inconel718 revealed a refined grains and a weave structure exhibiting excellent mechanical properties which were superior to those of the conventional casting process were successfully fabricated by adopt a high-precision and intelligent coaxial powder feeding system during the LDED processing. Moreover, based on multi-field numerical simulation method, a two-phase flow model and a transient thermal mechanical deformation model were established to simulate the LDED processing, while takes into account the evaporated mass loss of the inconel718 alloy. The morphology prediction of laser directed energy deposition by multi-physics numerical simulation, the relationship among the laser process parameters, i.e., the laser power, scanning speed and the amount of powder feeding, the temperature filed and the microstructure and mechanical properties of Inconel718 alloy during LDED were investigated and established. The simulated results consistent well with the experimental results. Results shown that the relative density of sample was sensitive to the laser power, the precision and stability of the powder feeding rate. With increasing laser power, the grain size of Inconel718 is refined, and the microhardness and tensile properties of the materials increased. The optimized LDED processing parameters were determined. Evaluating the mechanical properties of the materials LDEDed at a laser power of 600W and a scanning speed of 8.5mms-1 exhibited a high tensile strength of 944±5 MPa and a good elongation of 29 ± 0.5 %. This work suggests that the processing parameters can be optimized to prepare densified materials with excellent mechanical properties.

Microstructure evolution in laser-based powder bed fusion of metals

Abstract Laser-based powder bed fusion (LPBF) of metals offers the unique possibility of creating the microstructure voxel-by-voxel. The minimum voxel size in each direction is dependent on material dosing accuracy coupled with laser processing parameters. The rapid solidification conditions during LPBF lead to material heterogeneity coupled with hierarchical and non-equilibrium microstructures. The current paper delves into two different pathways available currently to control microstructure in LPBF, namely: in-situ microstructure control through material distribution to form functionally graded components with complex interfaces; application of post-processing thermo-mechanical treatments to control the microstructure. Unlike traditional manufacturing methods, each voxel in LPBF can be further processed multiple times after the first fusion process. Such in-situ processing presents further opportunity for tailoring the microstructure of each voxel in 3D. A future perspective is thus offered on the opportunities to control and engineer LPBF microstructures in metals.

Surface quality evaluation through new optical imaging system-based objective speckle for additive manufactured titanium samples

Laser cladding is an effective additive manufacturing technology used for materials’ surface modification to enhance their surface and mechanical properties. Surface roughness is a crucial feature that affects the materials’ quality and lifespan. Additionally, it is a real indicator of hardness and wear resistance. Although the existing methods may precisely measure surface roughness, they require delicate adjustment, can damage surfaces, and have limited working distances. This study presents a novel optical imaging system to quantitatively estimate the quality modifications of additive manufacturing samples by measuring their surface roughness based on objective speckle and advanced multivariate analysis methods. The raw speckle patterns are generated from deposited layers on Ti6Al4V titanium alloys obtained at different laser processing parameters. The proposed analysis approach produces collections of local statistical matrices from which histogram features are extracted. Canonical correlation analysis (CCA) is then proposed to distinguish the most significant features. The correlation between the features (with and without applying CCA) and surface roughness is established by using two machine learning regression algorithms, nonlinear support vector regression (SVR), random forest regression (RF), and k-nearest neighbor regression (kNN). The results confirmed that combining RF and CCA provided a feasible regression model to estimate the surface roughness, with 0.998 for R2 in training samples and maximum values of 0.258, 0.484, and 4.593 %, respectively, for MAE, RMSE, and MAPE in test samples. This demonstrates that the proposed objective speckle imaging system is effective in estimating the quality modification of additive manufacturing samples by measuring their surface roughness.

Experimental study and parameter optimization of laser wire additive manufacturing of titanium alloy

In the single-pass multilayer deposition process of laser wire additive manufacturing, variations in process parameters significantly influence the morphology of the deposited layer. This study experimentally investigates how the main process parameters (laser power, scanning speed, and wire feeding speed) affect the morphology of the deposited layer. It was found that each parameter has distinct effects on the geometrical morphology of deposition. Simultaneously, aiming to enhance the surface topography of the deposited layer and its bonding with the substrate, three optimization objectives are defined. An optimization model is then constructed using experimental data to refine the process parameters. The optimal parameters are determined through experimentation, resulting in significant enhancement of the deposited layer’s topography.

A laser-induced superhydrophobic surface with multiple microstructures for stable drag reduction

To address the issue of water resistance in ship navigation, we developed a drag-reducing surface based on the microstructure of shark skin and a superhydrophobic coating. First, grooves with various microstructures were fabricated on the substrate surface using laser processing. Then, a mixture of octadecyltrichlorosilane, water, and silica solution was uniformly sprayed onto the grooved substrate surface to achieve superhydrophobicity. To enhance and stabilize the drag reduction effect, we optimized the width and spacing of the grooves by adjusting the laser processing parameters, achieving a high drag reduction rate under various flow conditions. In the Reynolds number range of 2 × 105 to 5 × 105, the drag reduction rate of the superhydrophobic coated surface with grooves reached over 66.57 %, which is an improvement of 7 % to 26.51 % compared to the superhydrophobic coated surface without grooves. Additionally, the oxides accumulated on the ribs after laser ablation can slow down the wear of the superhydrophobic coating, significantly enhancing the surface's mechanical durability. This simple and cost-effective surface provides a new approach for laser preparation of drag-reducing surfaces.