Laser Heating Research Articles

Hydrogenation of calcite and change in chemical bonding at high pressure: Diamond formation above 100 GPa

Synchrotron X-ray diffraction (XRD) and Raman spectroscopy in laser heated diamond anvil cells and first principles molecular dynamics (FPMD) calculations have been used to investigate the reactivity of calcite and molecular hydrogen (H2) at high pressures up to 120 GPa. We find that hydrogen reacts with calcite starting below 0.5 GPa at room temperature forming chemical bonds with carbon and oxygen. This results in the unit cell volume expansion; the hydrogenation level is much higher for powdered samples. Single-crystal XRD measurements at 8–24 GPa reveal the presence of previously reported III, IIIb, and VI calcite phases; some crystallites show up to 4% expansion, which is consistent with the incorporation of ≤ 1 hydrogen atom per formula unit. At 40–102 GPa XRD patterns of hydrogenated calcite demonstrate broadened features consistent with the calcite VI structure with incorporated hydrogen atoms. Above 80 GPa, the CO stretching mode of calcite splits suggesting a change in the coordination of CO bonds. Laser heating at 110 GPa results in the formation of CC bonds manifested in the crystallization of diamond recorded by in situ XRD at 300 K and 110 GPa and by Raman spectroscopy on recovered samples commenced with C13 calcite. We explored several theoretical models, which show that incorporation of atomic hydrogen results in local distortions of CO3 groups, formation of corner-shared CO polyhedra, and chemical bonding of H to C and O, which leads to the lattice expansion and vibrational features consistent with the experiments. The experimental and theoretical results support recent reports on tetrahedral C coordination in high-pressure carbonate glasses and suggest a possible source of the origin of ultradeep diamonds.

Thermophoresis-Induced Polymer-Driven Destabilization of Gold Nanoparticles for Optically Directed Assembly at Interfaces.

The limitations of conventional template-based methods for the deposition of nanoparticle assemblies into defined patterns on solid substrates call for the development of techniques that do not require templates or lithographic masks. The use of optically-induced thermal gradients to drive the migration of colloids toward or away from a laser spot, known as opto-thermophoresis, has shown promise for the low-power trapping and optical manipulation of a variety of colloidal species. However, the printing of colloids using this technique has so far not been established. Herein, a method for the optically directed printing of noble metal nanoparticles, specifically gold nanospheres is reported. The thermophoresis of the polymer polyvinylpyrrolidone and gold nanospheres toward a laser spot led to the deposition of nanoparticle aggregates, capable of serving as surface-enhanced Raman scattering substrates. The influence of heating laser power and the concentrations of polymer, salt, and surfactant on the nanoparticle deposition rate and structure of the printed pattern are studied, showing that a variety of conditions can permit printing, suggesting facile generalization to different nanoparticle compositions, sizes, and shapes. These findings will greatly benefit future efforts for directed nanoparticle assembly, and drive applications in sensing, photothermal heating, and relevant applications in biomedicine and devices.

Weld Defect Inspection of Cylindrical Secondary Batteries Based on Active Thermographic Measurement with Thermal Magnification

This paper presents an active thermographic measurement-based inspection tech-nique for detecting weld defects in the battery cap region of cylindrical secondary batteries. As the proliferation of electric vehicles continues, safety issues related to secondary batteries have become prominent. In this study, a defect detection algorithm was developed by aligning visual images and active thermographic im-ages of the cylindrical secondary battery cap region. Lock-in amplitude images during the heating-cooling process using a laser were extracted to measure the difference in temperature patterns arising from internal structural variations. Ad-ditionally, to minimize the influence of surface conditions and temperature varia-tions other than laser-induced, a 10Hz periodic heating was employed, and ther-mal magnification in the heating frequency was achieved through data processing. This approach allowed the measurement of temperature changes induced by laser heating and cooling while minimizing the impact of surface conditions and tem-perature variations unrelated to the laser. A dataset of 1000 specimens was con-structed by aligning thermographic data with vision images acquired through this method. defective samples. Using this thermographic-vision alignment dataset, a defect detection algorithm was trained to achieve a more accurate and faster in-spection performance compared to existing non-destructive testing technologies.

Transient heating of Pd nanoparticles studied by x-ray diffraction with time of arrival photon detection.

Pulsed laser heating of an ensemble of Pd nanoparticles, supported by a MgO substrate, is studied by x-ray diffraction. By time-resolved Bragg peak shift measurements due to thermal lattice expansion, the transient temperature of the Pd nanoparticles is determined, which quickly rises by at least 100 K upon laser excitation and then decays within 90 ns. The diffraction experiments were carried out using a Cu x-ray tube, giving continuous radiation, and the hybrid pixel detector Timepix3 operating with single photon counting in a time-of-arrival mode. This type of detection scheme does not require time-consuming scanning of the pump-probe delay. The experimental time resolution is estimated at 15 ± 5 ns, which is very close to the detector's limit and matches with the 7 ns laser pulse duration. Compared to bulk metal single crystals, it is discussed that the maximum temperature reached by the Pd nanoparticles is higher and their cooling rate is lower. These effects are explained by the oxide support having a lower heat conductivity.

Local augmentation of phonon transport at GaInN/GaN heterointerface by introducing a graded variation of InN mole fraction

The pump and probe technique in Raman spectroscopy of the E2 (high) mode is exploited to uncover the enhancing factor of the phonon transport across Ga1−xInxN/GaN interfaces. Two samples are investigated: one with a uniform x of 0.09 and another one with a graded variation in x from 0.17 to 0 along the depth direction. Lateral phonon transport is obtained by scanning the 532-nm probing laser from the irradiation position of the 325-nm heating laser. No difference in the lateral diffusion length is observed between the two samples, while the transport probability across the interface is higher for the sample with the graded variation in x than the sample with the uniform x of 0.09. The microscopic images of the decrease in the mode energy or the increase in temperature of the GaN layer reveal that the local phonon transport across the heterointerface is enhanced in regions with low differences in the phonon mode energy between the GaN and GaInN rather than the difference in crystal quality.

Finite Element Modeling of Ring and Gaussian Dual Laser Heat Sources for Aluminum Butt Welding

Aluminum alloys have been used extensively for automotive industries for the structural applications with their high specific strength and corrosion resistance. In order to use aluminum alloys for automotive components, laser welding has been used due to the advantage of being capable to weld thick products due to its deep penetration depth. In this regard, a dual laser heat source combining an outer ring laser beam with a centrally focused Gaussian laser beam was proposed to compensate for insufficient melting caused by laser reflection of aluminum alloy. The purpose of this study is to develop a simulation model that can consider heat input from the dual laser beams individually, for analyzing melting and heat distribution behavior during the laser welding. Two different heat source models were proposed. One model used 3D Gaussian distribution of heat input for the centrally focused laser while the other model utilized Gaussian cylinder heat input. The proposed heat input models were implemented by finite element analyses, and the results were compared with aluminum butt welding experiments. It was shown that Gaussian cylinder heat input for the centrally focused laser beam reproduced much better the experimentally observed melting behavior in comparison to the 3D Gaussian distribution.

Modeling and validation of hydrogen porosity formation in aluminum laser welding

Laser welding is used to weld aluminum alloy 1100 for battery cell manufacturing in the automotive industry. However, these welds can have porosity that can decrease their performance in the battery packs. One type of porosity is gas porosity, commonly understood to be due to hydrogen entrapment in the weld during solidification. Hydrogen is dissolved in the molten aluminum at elevated temperatures during laser heating and can be entrapped in the weld pool upon solidification. When welding anodized aluminum, the amount of hydrogen porosity is increased because the anodized oxide layer is broken up and the broken-up oxide can act as heterogeneous nucleation sites for hydrogen pores. A cellular automaton model has been developed to predict the nucleation and growth of hydrogen porosity during laser welding. This model has been validated with microstructure analysis, LECO® hydrogen analysis, and X-ray micro-computed tomography. This model can be used by welding engineers to reduce porosity and control weld quality during laser welding of aluminum alloys.

Акустика кипения с недогревом на лазерном нагревательном элементе

We study acoustic signals arising during cavitation initiated by laser heating of water in the vicinity of the end of an optical fiber immersed in water. It is shown that the growth and collapse of the vapor phase in the vicinity of the end of the optical fiber (laser heating element), along which laser radiation propagates, generate acoustic signals characteristic of the elementary act of boiling, which precede the appearance of large-amplitude signals. It has been established that large amplitude signals are caused by shock waves that arise during the collapse of the main bubble and secondary bubbles - “rebounds”.

Determination of residual stress field in laser cladding using finite element updating method driven by contour deformation

Laser cladding is a cutting-edge technology widely used in additive manufacturing and surface modification. This process entails rapid melting and solidification driven by laser heating, which induces residual stress within the material. This study presents a data-driven approach to refine the numerical model of laser cladding, simultaneously emphasizing both the temperature characteristics and residual stress distribution within the thermomechanical coupling process. After integrating the residual stress distribution data obtained through the contour method with the molten pool morphology shaped by the thermal effects of laser cladding, a Levenberg-Marquardt optimization algorithm based finite element model updating scheme is proposed to efficiently identify the parameters of double ellipsoid heat source model, which employs parallel computing to reduce the computational time for iterations. The effectiveness of the proposed method is validated using experimental data. Moreover, this approach is adaptable, unaffected by the specimen size and shape, and can accurately predict the residual stress distribution characteristics. Therefore, it offers a robust framework for simulating the mechanisms of residual stress generation in titanium alloy laser cladding.

Laser Powder Bed Fusion and Heat Treatment of the Martensitic Age‐Hardenable Steel (1.2709)

The primary objective of this study is to clarify the fundamental question of whether, in principle, it is possible to dispense with a prior solution annealing process in favor of a direct aging heat treatment for specimens of maraging stainless steel grade X3NiCoMoTi18‐9‐5 (1.2709) produced by laser powder bed fusion (LPBF). The waiver of a solution annealing process would significantly increase the process efficiency and thus support a sustainable and resource‐friendly production of such components. Therefore, the hardness, microstructure, and the present phases of specimens in as‐built + aged condition (AB + A) and solution‐annealed + aged (SOL + A) are examined during this study. Initially, an extended parameter study is performed using a Renishaw AM 250 LPBF system equipped with a pulsed mode laser system to achieve the highest possible apparent density. As test specimens, small cubes are produced for parameter study and are analyzed for porosity by means of optical microscopy. To investigate the relationship between microstructure and hardness in different material states, one series of specimens is aged directly after LPBF processing in the as‐built state (AB + A). For comparison, the other series was solution annealed at 820 °C for 60 min, quenched in water and then aged (SOL + A). A maximum hardness value of 614 HV1.0 is achieved for specimen aged at 490 °C for 120 min in as built condition (AB + A), while 624 HV1.0 was measured for specimen aged at 490 °C for 180 min in conventionally solution annealed + aged (SOL + A) condition. Significant austenite reversion is not observed at aging temperature of 490 °C in both cases. Aging of specimens at temperatures of 540 and 600 °C resulted in reduction of specimen hardness due to higher percentage of austenite reversion. No significant difference between the hardness values of AB + A and SOL + A specimens is observed. It can therefore be concluded that, in principle, conventional solution annealing and ageing can be dispensed with in favor of direct aging. However, as the results are based on small sized specimens, further investigations into the scalability are needed.

Multiphysics modeling femtosecond laser ablation of Ti6Al4V with material transient properties

Femtosecond laser ablation associates with a series of multiphysics phenomena (electron thermalization, electron thermal conduction, electron-phonon coupled energy transport, melting, vaporization and phase explosion) and the instant variation of material transient properties, which impacts the laser energy absorption and the subsequent material removal. In this work, a multiphysics model with material transient properties is developed to study the femtosecond laser ablation of Ti6Al4V. A two-dimensional axisymmetric simulation is performed. The predicted ablation depth and ablation diameter with material transient properties show good agreements with the experimental data. The necessity of material transient properties for femtosecond laser ablation is demonstrated. Besides analyzing the roles of material transient properties on femtosecond laser ablation, the ablation thresholds of Ti6Al4V are probed for different pulse durations. In addition, the impact of pulse duration on femtosecond laser heat affected zone is studied. This work contributes to understand roles of material transient properties in femtosecond laser ablation.

Synthesis and thermal characterization of pulsed laser deposited molybdenum on aluminium nitride substrates for heat sink applications

Thin films of molybdenum (Mo) were grown on aluminium nitride (AlN) substrates by pulsed laser deposition for heat sink applications. The effect of experimental growth parameters on the films’ structural properties were investigated by Scanning Electron Microscopy, X-Ray Diffraction and Atomic Force Microscopy. Thermal characterization was achieved by measuring the in-plane thermal diffusivity of the grown layers by means of a photothermal beam deflection technique using an IR heating laser. Within the experimental parameters studied in this work, a substrate temperature of 600 ˚C and an ambient argon gas pressure of 10 mTorr were identified as the optimal growth conditions for the synthesis of smooth and well-crystallized Mo layers. Concurrently, the thermal diffusivity of the films is significantly affected by film growth parameters. Under the optimal growth conditions, a thermal diffusivity value as high as 5.42x10-5 m2/s was measured, a value that is very close to that of bulk Mo, and which would be a result of the synthesis of polycrystalline Mo films whose grains’ size is greater than the heat carriers mean free path, namely the free electrons. The temperature dependence of the thermal diffusivity was also investigated, and the films were found to be stable up to an operating temperature of 200 °C. Beyond this temperature, photothermal beam deflection imaging shows the onset of film delamination from the underlying substrate.

Coupling influence of laser-Nb interlayer on microstructure and performance of Ti/Al joint

Laser fusion welding of TC4 titanium (Ti) alloy and aviation 7075 aluminum (Al) alloy was conducted with the assistance of a niobium (Nb) interlayer. The effect of laser heat input and the alloying effect of Nb on the interfacial layer was analyzed. The study also investigated the coupling influence of the laser-Nb interlayer on the microstructure and performance of the Ti/Al joint. By utilizing a 0.1 mm-thick Nb interlayer and a welding velocity of 1800 mm/min, the results reveal an initial increase in tensile-shear force followed by a decline with the increase of laser power. The tensile-shear force reached a peak of 1663 N at 1.2 kW, representing a 36.76 % improvement over the 1 kW levels. Under appropriate laser power, the enhancement in joint performance is dominated by the controlled heat input and the effective Nb-alloying effect, which reduce the thickness and brittleness of the interfacial intermetallic layer, respectively. However, metallurgical regulation of Nb will be restricted by the insufficient Nb melting amount resulting from the low laser power, leading to a decrease in joint properties. Excessive laser power can lead to the formation of hot cracks and an excessive amount of Ti-Al intermetallic compounds, which can decrease the Nb content, thereby restricting the metallurgical regulation of Nb and the overall joint performance.

A Gaussian Process-Based extended Goldak heat source model for finite element simulation of laser powder bed fusion additive manufacturing process

Laser powder bed fusion (L-PBF) additive manufacturing (AM) is a key enabling technology to manufacture highly complex and integrated metallic structures. In L-PBF AM process, the melting of the metal powders and the layers underneath can be governed by either “conduction mode” or “keyhole mode”, with the keyhole mode reportedly leading to porosity and decreased strength and ductility by many studies. In part scale simulations, finite element (FE) model is often used to study the temperature distribution during printing and to predict the residual stress, where a volumetric heat flux with a Gaussian or a double ellipsoidal (Goldak) distribution is often applied as the laser heat source. However, the above heat source models can only capture the melt pool shape in the conduction mode, and fail to capture the transition to keyhole melting mode when the process parameters change. To overcome this inaccuracy, an extended Goldak heat source model is proposed by introducing a laser penetration term as a function of laser parameters obtained from a Gaussian-Process (GP) model. The model is validated by “2D pad” AlSi10Mg L-PBF experiments under a wide range of laser power, scan speed, and laser focus offset, and the results show the model successfully captures the measured melt pool shape in all conditions.

Investigation on Accelerated Initiation of Oblique Detonation Wave Induced by Laser-Heating Hot-Spot

A reliable initiation of oblique detonation is critical in oblique detonation engines, especially for oblique detonation engines under extreme conditions such as a high altitude and low Mach number, which may lead to excessive length of the induction zone and even the phenomenon of extinction. In this paper, surface ignition was applied to the initiation of oblique detonation, and a high-temperature region was set on the wedge to simulate the presence of a hot-spot induced by the laser heating. The two-dimensional multi-component Navier–Stokes equations considering a detailed H2 combustion mechanism are solved, and the oblique detonation wave accelerated by a hot-spot is studied. In this paper, hot-spots in the induction zone on the wedge, are introduced to explore the possibility of hot-spot initiation, providing a potential method for initiation control. Results show that these methods can effectively promote the accelerated initiation of the oblique detonation. Furthermore, the hot-spot temperature, size and position are varied to analyze their effects on the initiation position. Increasing the temperature and size of the hot-spot both can accelerate initiation, but from the perspective of energy consumption, a small hot-spot at a high temperature is preferable for accelerating ODW initiation than a large hot-spot at a low temperature. The initiated position of the oblique detonation is sensitive to the position of the hot-spots; if a 2000 K hotspot is at the beginning of the wedge, then the ODW’s initiation distance will be reduced to about 30% of that without hotspot acceleration.

Structural Phase Transition and Decomposition of XeF2 under High Pressure and Its Formation of Xe-Xe Covalent Bonds.

Noble gases with inert chemical properties have rich bonding modes under high pressure. Interestingly, Xe and Xe form covalent bonds, originating from the theoretical simulation of the pressure-induced decomposition of XeF2, which has yet to be experimentally confirmed. Moreover, the structural phase transition and metallization of XeF2 under high pressure have always been controversial. Therefore, we conducted extensive experiments using a laser-heated diamond anvil cell technique to investigate the above issues of XeF2. We propose that XeF2 undergoes a structural phase transition and decomposition above 84.1 GPa after laser heating, and the decomposed product Xe2F contains Xe-Xe covalent bonds. Neither the pressure nor temperature alone could bring about these changes in XeF2. With our UV-vis absorption experiment, I4/mmm-XeF2 was metalized at 159 GPa. This work confirms the existence of Xe-Xe covalent bonds and provides insights into the controversy surrounding XeF2, enriching the research on noble gas chemistry under high pressure.

Robust inverse parameter fitting of thermal properties from the laser-based Ångstrom method in the presence of measurement noise using physics-informed neural networks (PINNs)

The two-dimensional laser-based Ångstrom method measures the in-plane thermal properties for anisotropic film-like materials. It involves periodic laser heating at the center of a suspended film sample and records its transient thermal response by infrared imaging. These spatiotemporal temperature data must be analyzed to extract the unknown thermal conductivity values in the orthotropic directions, an inverse parameter fitting problem. Previous demonstration of the metrology technique used a least-squares fitting method that relies on numerical differentiation to evaluate the second-order partial derivatives in the differential equation describing transient conduction in the physical system. This fitting approach is susceptible to measurement noise, introducing high uncertainty in the extracted properties when working with noisy data. For example, when noise of a signal-to-noise ratio of 10 is added to simulated amplitude and phase data, the error in the extracted thermal conductivity can exceed 80%. In this work, we introduce a new alternative inverse parameter fitting approach using physics-informed neural networks (PINNs) to increase the robustness of the measurement technique for noisy temperature data. We demonstrate the effectiveness of this approach even for scenarios with extreme levels of noise in the data. Specifically, the PINN-approach accurately extracts the properties to within 5% of the true values even for high noise levels (a signal-to-noise ratio of 1). This offers a promising avenue for improving the robustness and accuracy of advanced thermal metrology tools that rely on inverse parameter fitting of temperature data to extract thermal properties.

Laser-induced color reversal on metal surfaces in acetic acid solution

Laser coloring for decoration and visual attraction has been widely used in daily life. To fulfill the requirements of timely correction or modification of colors, color erasure has also become an important part in marking technology. The thickness of the oxide layer and the concentration of oxygen elements are key factors affecting the quality of color erasing. The conventional method is to erase the color in air, which is difficult to remove the oxide film. Acetic acid, as an environment-friendly solution, which provides a low oxygen environment and can undergo chemical reactions with titanium dioxide under laser heating, is selected as a liquid environment for laser-induced color erasure. Oxygen concentration in the erased area decreases from more than 50% to 10%. The color difference ΔEab* between the erased area and original metal surface is around 1.4, which shows almost no difference to the naked eyes. Furthermore, the color difference ΔEab* between laser re-coloring and laser coloring before the erasure is around 1.5, which means that the re-coloring under the same laser processing parameters after the erasure maintains a high level of consistency with the colors initially drawn. Here we successfully realize the reversal process from laser coloring to laser erasure and laser re-coloring on metal surfaces. This technology has considerable applications in the field of anti-counterfeiting and information storage. Meanwhile, acetic acid assisted laser color erasing as a safe and green method greatly improves the erasure quality and enhances the development of laser color marking technology.

Optimization of the Laser Drilling Processing Parameters for Carbon Steel Based on Multi-Physics Simulation

The laser drilling of carbon steel is always suffered from the formation of slag, the presence of cutting burrs, the generation of a significant quantity of spatter, and the incomplete penetration of the substrate. In order to avoid these defects formed during the laser drilling of carbon steel, the COMSOL multi-physics simulation method was used to model and optimize the laser drilling process. Considering the splash evolution of the material during the complex drilling process, the transient evolution of the temperature field, the flow of the molten fluid, the geometrical changes, and the absorption of the laser energy during the laser drilling process were investigated. The simulated borehole dimensions are consistent with the experimental results. The process parameters have a great influence on the fluid flow pattern and material slag splashing. The laser power has a significant effect on the laser processing compared with the process parameters. With the increase in laser power and the decrease in laser heat source radius, the time required for perforation is reduced, the flow of melt is accelerated, the perforation efficiency is increased, and the hole wall is smoother, but the degree of spattering is greater. The optimized process parameters were obtained: laser heat source radius of 0.3 mm, laser power of 3000 W. These findings can help reduce the machining defects in carbon steel with excellent mechanical properties by optimizing the laser drilling processing parameters.

Reduced Training Data for Laser Ultrasound Signal Interpretation by Neural Networks

The performance of machine learning algorithms is conditioned by the availability of training datasets, which is especially true for the field of nondestructive evaluation. Here we propose one reconfigurable specimen instead of numerous reference specimens with known, unchangeable defect properties, which are usually complicated to fabricate. It consist of a shape memory polymer foil with temperature-dependent Young’s modulus and ultrasound attenuation. This open a possibility to generate a reconfigurable defect by projecting a heating laser in the form of a short line on the specimen surface. Ultrasound is generated by a laser pulse at one fixed position and detected by a laser vibrometer at another fixed position for 64 different defect positions and 3 different configurations of the specimen. The obtained diversified datasets are used to optimize the neural network architecture for the interpretation of ultrasound signals. We study the performance of the model in cases of reduced and dissimilar training datasets. In our first study, we classify the specimen configurations with the defect position being the disturbing parameter. The model shows high performance on a dataset of signals obtained at all the defect positions, even if trained on a completely different dataset containing signals obtained at only few defect positions. In our second study, we perform precise defect localization. The model becomes robust to the changes in the specimen configuration when a reduced dataset, containing signals obtained at two different specimen configurations, is used for the training process. This work highlights the potential of the demonstrated machine learning algorithm for industrial quality control. High-volume products (simulated by a reconfigurable specimen in our work) can be rapidly tested on the production line using this single-point and contact-free laser ultrasonic method.