Laser Heating Research Articles

Numerical simulation of temperature profile during laser cladding of nickel powder for in situ repairing

A 3-D Finite Element (FE) model was established to simulate the laser cladding of nickel powder for in situ repairing AISI 410 stainless steel. The temperature distribution field was estimated at six different points using low laser power of 450 W and a scanning speed of 2 mm/s. This study used a moving laser heat source in COMSOL to simulate the laser cladding process. The proposed FE model investigated the temperature field in two cases: (1) in situ repairing the defect by laser cladding without preheating and (2) in situ repairing the defect by laser cladding technique after preheating the cavity made on the substrate. A time-temperature profile was obtained after the simulation in both cases. The results of both cases were compared and analyzed. When the cladding material is poured into the preheated cavity, its temperature rises due to the heating effect obtained from the cavity, resulting in a higher maximum temperature after the cladding process. It was observed that after the cladding process, the maximum temperature was higher in the case of laser cladding after preheating the substrate (2400.49 K) compared to the maximum temperature in cladding without preheating the substrate (1770 K). Therefore, a molten pool is formed, solidifying rapidly to form a clad coating with better metallurgical bonding and enhanced surface properties.

Ultrafast laser triggered electron emission from ultrananocrystalline diamond pyramid tip cathode

Nitrogen-incorporated ultrananocrystalline diamond [(N)UNCD] pyramid tip cathode has been considered as a next-generation high peak current electron source for dielectric laser accelerators as well as other high peak current particle accelerator applications. In this work, we study non-linear photoemission from an (N)UNCD pyramid tip cathode using an ultrafast laser with the pulse length of 150 fs with the central wavelength of 800 nm in the peak intensity range of 109–1010W/cm2. We demonstrated that as the incident laser intensity increases, the current emitted from the nano-tip first increases as a power function with an exponent of about 5 and then starts to roll over to an exponent of 3. This roll over is attributed to the Coulomb interaction between electrons emitted from the tip also known as the space charge. We also measured the photoemission electron energy spectra that show electrons with energies as high as ∼10 eV. Based on the shape of the electron energy spectra, we conclude that the high-energy electrons are thermally emitted electrons due to ultrafast laser heating at the tip of the (N)UNCD pyramid tip cathode.

A computational model to understand the interaction of nanosecond pulsed laser with ultra-thin SiN[formula omitted] layer-coated silicon substrate

Nanosecond lasers can be used for the selective ablation of ultra-thin SiNx layer (80–100 nm) coated on a silicon substrate with applications in the fabrication of PERC solar cells. Experiments reveal that the ablation process can occur in different regimes with material removal in solid, liquid, vapor, and explosion forms. This study investigates the different regimes for single pulse ablation through a physics-based model developed using the finite volume method in Ansys Fluent. The model accounts for various physical phenomena, including laser heating, melting, thermal expansion, thermal decomposition, Marangoni convection, vaporization, plasma formation, melt expulsion, and phase explosion. Experiments were conducted using Nd: YVO4 laser (λ=532 nm, pulse duration = 50 ns), and the measured single pulse crater profiles are in excellent agreement with the model predictions over a broad range of laser fluence. Results show that the SiNx layer breaks due to the thermal expansion of the underlying silicon at lower fluences (3.05–3.35 J/cm2) in a very narrow range. Above this fluence range lies another narrow range (3.35–5.55 J/cm2) wherein the SiNx layer is thermally decomposed into silicon and nitrogen, and craters are formed due to Marangoni convection in the melt pool formed. Ablation due to vaporization occurs in a broad fluence range (5.55–8.4 J/cm2), causing deeper ablation depths and material deposition at the crater edge. At higher fluences (¿8.4 J/cm2), explosive boiling occurs due to homogeneous nucleation, resulting in much higher ablation depths (¿1.6μm), broader crater widths, and poor surface finish. This model provides an understanding of different material removal regimes in laser ablation of SiNx-coated silicon.

Laser-induced thermal runaway dynamics of cylindrical lithium-ion battery

Laser is a precise, remote, and non-invasive heating method that can initiate thermal runaway of lithium-ion batteries in safety tests. This study systemically explores the thermal runaway of cylindrical cells induced by constant laser irradiation up to 20 W and 1.6 MW m−2 within a 4-mm diameter spot. Results indicate that thermal runaway intensity is relatively insensitive to the laser power but controlled by the battery state of charge (SOC). The overall heating efficiency of the laser (78 ± 7 %) is higher than that of the oven and comparable to contact heating methods. As the battery SOC decreases from 100 % to 30 %, the minimum laser output power for thermal runaway increases from 9.5 W to 15 W, corresponding to the effective battery heating power rising from 6.7 W to 11.1 W. These critical values hold significance in evaluating the thermal hazards associated with localized hotspot failures. Finally, the strategy for applying the laser to trigger the battery thermal runaway is proposed based on a simplified heat transfer model. This work reveals the battery fire risk under high-intensity spot heating and provides a valuable scientific basis for using laser heating in battery safety test standards.

Phase transition kinetics revealed by in situ x-ray diffraction in laser-heated dynamic diamond anvil cells

We report successful coupling of dynamic loading in a diamond anvil cell and stable laser heating, which enables compression rates up to 500 GPa/s along high-temperature isotherms. Dynamic loading in a diamond-anvil cell allows exploration of a wider range of pathways in the pressure-temperature space compared to conventional dynamic compression techniques. By x-ray diffraction, we are able to characterize and monitor the structural transitions with the appropriate time resolution i.e., millisecond timescales. Using this method, we investigate the γ−ε phase transition of iron under dynamic compression, reaching compression rates of hundreds of GPa/s and temperatures of 2000 K. Our results demonstrate a distinct response of the γ−ε and α−ε transitions to the high compression rates achieved, possibly due to the different transition mechanisms. These findings open up new avenues to study tailored dynamic compression pathways in the pressure-temperature space and highlight the potential of this platform to capture kinetic effects (over ms time scales) in a diamond anvil cell. Published by the American Physical Society 2024

Thermal equation of state of rhodium to 191 GPa and 2700 K using double-sided flash laser heating in a diamond anvil cell

The phase behavior of rhodium (Rh) metal has been studied to 191 GPa and 2700 K using a combination of room-temperature isothermal compression and double-sided flash laser heating experiments. The isothermal compression data have been fitted with a second-order adapted polynomial of order L equation of state (EoS) with best-fitting parameters of V0=13.764(2)Å3/atom, K0=258(3)GPa, and K′=5.36(9). Two-dimensional maps of the uniaxial stress component t are presented for Rh at different pressures showing the spatial distribution of the local stress state of a relatively high-yield strength material encased in a Bi pressure medium. In addition, a simple, thermal pressure equation-of-state model, based on a single Einstein temperature, has been fitted to the high-pressure-temperature data up to 2700 K at 148 GPa and ambient-pressure thermal expansion data up to 1982 K. Also determined are the best-fitting parameters to reproduce the thermal EoS within the two-dimensional integration software. The optimized parameters are V0=13.764Å3/atom, K0=260.54GPa, K′=5.114, αT=2.99×10−5 K−1, ∂αT/∂T=1.27×10−9 K−2, ∂K0/∂T=−6.43×10−5GPa/K, and ∂K′/∂T=−9.3×10−10K−1. Published by the American Physical Society 2024

Optical properties optimization of carbon fiber reinforced thermoplastic tapes by micro surface texturing for enhanced laser heating efficiency and in-situ consolidation quality during AFP process

The laser-assisted automated fiber placement (L-AFP) process of carbon fiber-reinforced thermoplastic composites suffers from insufficient heating efficiency and in-situ consolidation quality caused by significant reflection on the tape surface. Here, we propose a novel strategy to increase the heating efficiency by refocusing the reflected light, initially scattered to the environment and wasted, onto the tapes for multiple and full absorptions. The method for laser concentration is first validated through light-tracing simulation. Then, three kinds of tapes with different micro textures on the surface are prepared by the hot-embossing process. The transverse V-grooved texture tapes and flat surface tapes absorb 25% more laser energy than the longitudinal V-grooved and commercial tapes due to the reduction in transverse scattering angle from 180° to 2.72°. This leads to a temperature increase of 130 °C at the nip point during the L-AFP process at the lay-down rate of 500 mm/s with 1 kW laser power. Improved in-situ consolidation quality leads to a significant increase in the flexural and shear strength of L-AFP-prepared carbon fiber reinforced polyetheretherketone (CF/PEEK) laminates, with a reduction in porosity to around 2%.

Model predictive control for real-time microstructure control in laser heat treatment

Metals’ surface microstructure can be altered through controlled heating and cooling of the surface using the laser heat treatment (LHT) method. Lasers have the advantage in this process of being able to heat treat specific regions of the workpiece without affecting the whole product. However, because a laser is being used, this process is extremely sensitive to changes in the process inputs and disturbances, which results in changes in the thermal dynamics and alterations in the peak temperature and cooling rate, in particular. These alterations have a direct effect on the material and its mechanical characteristics, such as hardness and hardening depth. Since these variations are caused by complex metallurgical phenomena, it is important to control the thermal dynamics in real-time. Real-time control systems are usually error-based and do not have the ability to predict the effect of the control action on the system, deal with constraints, or correlate the mechanical and material properties of the processed materials to LHT process parameters. Hence, the development of accurate model-based controllers is required. Therefore, a Model Predictive Control (MPC) algorithm is developed in this paper to control the thermal dynamics during the LHT process, e.g., the peak temperature, in real-time. This controller uses a finite difference thermal model to find the optimal process speed that results in the desired peak temperature. Moreover, consistent hardness and hardening depth will be obtained by closed-loop peak temperature control.

Growth of β-Ga2O3 crystal with a diameter of 30 mm by laser-diode-heated floating zone (LDFZ) method

To investigate the effect of high-power laser heating on the floating zone (FZ) method, a crystal of β-Ga2O3 was grown by the LDFZ method using a newly developed optical system equipped with a 20-kW laser diode (LD) system as a heat source. The growth started from a twin-free seed crystal with a diameter of 7 mm and the diameter of the crystal was increased gradually up to 30 mm. With increasing the diameter of the crystal, three patterns of the beam intensity profile were switched to heat the whole of the molten zone locally and intensively. The intensity profile of the five beamlets irradiating the sample was adjusted with a combination of the zooming by the optical system and the partial blocking by the alumina cylinder. By the proper tuning of the beam profile and the proper selection of the diameter of the feed rod, the molten zone was kept stable against gravity. The obtained crystal has a layer texture without clear facets or cracks. It almost conserves the crystallographic direction of the seed crystal but is twinned except for a twin-free region near the seed crystal.

An Hsp70 promoter-based mouse for heat shock-induced gene modulation.

Physical therapy is extensively employed in clinical settings. Nevertheless, the absence of suitable animal models has resulted in an incomplete understanding of the in vivo mechanisms and cellular distribution that respond to physical stimuli. The objective of this research was to create a mouse model capable of indicating the cells affected by physical stimuli. In this study, we successfully established a mouse line based on the heat shock protein 70 (Hsp70) promoter, wherein the expression of CreERT2 can be induced by physical stimuli. Following stimulation of the mouse tail, ear, or cultured calvarias with heat shock (generated by heating, ultrasound, or laser), a distinct Cre-mediated excision was observed in cells stimulated by these physical factors with minimal occurrence of leaky reporter expression. The application of heat shock to Hsp70-CreERT2; FGFR2-P253R double transgenic mice or Hsp70-CreERT2 mice infected with AAV-BMP4 at calvarias induced the activation of Cre-dependent mutant FGFR2-P253R or BMP4 respectively, thereby facilitating the premature closure of cranial sutures or the repair of calvarial defects. This novel mouse line holds significant potential for investigating the underlying mechanisms of physical therapy, tissue repair and regeneration, lineage tracing, and targeted modulation of gene expression of cells in local tissue stimulated by physical factor at the interested time points. KEY MESSAGES: In the study, an Hsp70-CreERT2 transgenic mouse was generated for heat shock-induced gene modulation. Heat shock, ultrasound, and laser stimulation effectively activated Cre expression in Hsp70-CreERT2; reporter mice, which leads to deletion of floxed DNA sequence in the tail, ear, and cultured calvaria tissues of mice. Local laser stimuli on cultured calvarias effectively induce Fgfr2-P253R expression in Hsp70-mTmG-Fgfr2-P253R mice and result in accelerated premature closure of cranial suture. Heat shock activated AAV9-FLEX-BMP4 expression and subsequently promoted the repair of calvarial defect of Hsp70-CreERT2; Rosa26-mTmG mice.

Diverse high-pressure chemistry in Y-NH3BH3 and Y-paraffin oil systems.

The yttrium-hydrogen system has gained attention because of near-ambient temperature superconductivity reports in yttrium hydrides at high pressures. We conducted a study using synchrotron single-crystal x-ray diffraction (SCXRD) at 87 to 171 GPa, resulting in the discovery of known (two YH3 phases) and five previously unknown yttrium hydrides. These were synthesized in diamond anvil cells by laser heating yttrium with hydrogen-rich precursors-ammonia borane or paraffin oil. The arrangements of yttrium atoms in the crystal structures of new phases were determined on the basis of SCXRD, and the hydrogen content estimations based on empirical relations and ab initio calculations revealed the following compounds: Y3H11, Y2H9, Y4H23, Y13H75, and Y4H25. The study also uncovered a carbide (YC2) and two yttrium allotropes. Complex phase diversity, variable hydrogen content in yttrium hydrides, and their metallic nature, as revealed by ab initio calculations, underline the challenges in identifying superconducting phases and understanding electronic transitions in high-pressure synthesized materials.

Enhancement of the Microstructure and Fatigue Crack Growth Performance of Additive Manufactured Titanium Alloy Parts by Laser-Assisted Ultrasonic Vibration Processing

Post-processing techniques can efficiently improve the surface quality, address microstructural defects, and optimize mechanical properties in additively manufactured parts. Surface severe plastic deformation processes such as ultrasonic nanocrystal surface modification (UNSM) integrated with localized laser heating were explored to enhance the surface properties, microstructure as well as the fatigue crack growth properties (FCG) in both directions of built. We successfully induced greater plasticity flow and achieved beneficial refinement of the surface grain structure by precisely controlling the heat and impact energies during surface treatment process. The LA-UNSM process, with the parameters utilized in this study considerably decreased the FCG rates of treated samples, when compared to samples without surface treatment. Improved fatigue crack growth properties along vertical and horizontal orientations after the post-process treatment were attributed to the induced-microstructural changes, improved surface quality, induced compressive residual stresses through gradient structure deformation layer that was prepared on the surface of the material. The fractographic analysis revealed that the cracks mostly originated from the pores in the as-produced state. This observation shows a clear correlation between the surface treatment performed and a substantial improvement in fatigue crack growth resistance.

Reconstruction of laser-induced microstructures temperature profiles

Metallic microstructures are currently widely used in micro-optoelectronics, sensorics, microfluidics, and other applications. A promising direction in the creation of such microstructures is pulsed laser processing of thin metal films. To improve laser technologies and simulate ongoing processes, data on the temperature fields that arise during laser exposure are needed. The article shows that the temperature distribution on the surface of a material during pulsed laser heating can be obtained from optical, scanning electron or atomic force micrographs. The proposed approach opens up the possibility of estimating temperature fields from archival photographs of various microstructures.

Designing High-Porosity Porous Structures with Complex Geometries for Enhanced Thermal Conductivity Using Selective Laser Melting and Heat Treatment

Designing High-Porosity Porous Structures with Complex Geometries for Enhanced Thermal Conductivity Using Selective Laser Melting and Heat Treatment

A novel numerical modeling of microsecond laser beam percussion micro-drilling of Hastelloy X: experimental validation and multi-objective optimization

The paper investigates the characteristics of the laser beam percussion micro-drilling (LBPMD) process in aerospace nickel-based superalloy Hastelloy X using microsecond pulses. The quality of the drilled hole is crucial in laser beam micromachining, and selecting appropriate process parameters significantly impacts the hole’s quality. The objective is to achieve predefined hole dimensions with minimal taper angles. Additionally, the study focuses on the alteration of pulse width, which is a combination of laser pulse frequency and duty cycle. Laser power (P), duty cycle % (D), focal plane position (FPP), and laser frequency (f) are considered input parameters, while geometric features such as inlet and outlet diameters, hole taper angle, and inlet circularity are examined as process responses. ANOVA is employed to establish significant relationships between process parameters and response variations based on experimental tests. Creating a precise simulation model that accurately accounts for the moving boundary of the target material’s receding surface is a crucial and challenging task in formulating the laser heat conduction problem. It is necessary to simultaneously capture the material’s dynamic front movement and update the boundary conditions of the laser source. To model the micro-drilled hole with LBPMD, the UMESHMOTION and DFLUX subroutines, along with the arbitrary Lagrangian-Eulerian (ALE) adaptive remesh algorithm in the Abaqus™ software, are utilized. Notably, no previous numerical study has predicted the geometry of micro-drilled holes using this technique. The proposed procedure is validated through the predictions of inlet and outlet hole diameters. Special emphasis is placed on the validation of models. Consequently, the numerical model and statistical model are compared as well as the need to define model applicability. The study demonstrates that all input parameters significantly influence the inlet hole diameter, while the pulse width notably affects the taper angle and circularity. The interaction between high laser frequency and low duty cycle results in reduced pulse duration. Multi-objective optimization is performed to determine the optimal process parameter settings for desired quality characteristics, considering minimum hole taper angle, precise inlet diameter, and maximum inlet circularity of the hole as optimization criteria. The findings show that with the optimized predicted results obtained from the optimal input variables, a composite desirability of 92% can be achieved.

Process stability in laser–MIG hybrid welding of aluminum alloys with various laser and arc distances

During laser–MIG hybrid welding process of aluminum alloys, the distance between laser and arc heat source (DLA) is one of the key factors which affect the welding process stability. Weld formation exhibited various penetration depths, since the interaction between laser and arc changed. Hybrid plasma morphology fluctuated significantly at DLA of 0 mm and hybrid plasma height decreased with the increase of DLA. Violent evaporation of droplet and spatters were generated at DLA of 0 mm. Moreover, keyhole fluctuated violently and significant downward flow of liquid metal was induced at the bottom zone of molten pool due to the impact action of droplet. Keyhole fluctuation was suppressed and molten pool stability was improved at DLA of 2 mm.

Minimum work associated with separating nitrogen from air: An exergy analysis

Background Nitrogen is essential for a variety of industries, including heat treatment, laser cutting, fire protection, and food packaging. Many companies in these industries obtain nitrogen via on-premises air separation processes. The three main processes for separating nitrogen from ambient air are cryogenic distillation, membrane separation, and pressure-swing adsorption (PSA). Improvements to these processes will likely focus on increasing efficiency, resulting in reduced environmental impact owing to less electrical power demand and opportunities for economic incentives. Regardless of the process utilized, a minimum theoretical amount of work input is required to obtain nitrogen gas at different pressures and concentrations compared to ambient conditions. Methods An equation was derived to evaluate the total exergy (including thermo-mechanical and chemical exergy) of product and exhaust mixtures resulting from air separation, indicating the minimum theoretical work input as a function of the product pressure, purity, and process recovery rate. This analysis considered an air separation system as a black box, with the input, output, and exhaust assumed to be ideal gas mixtures of nitrogen and oxygen at 15°C. The analysis applies to cryogenic distillation if the product and exhaust mixtures return to the gas phase. Results In general, the minimum required work input increases with product purity and recovery rate. Plots of minimum theoretical work versus product purity and recovery rate were made for two product pressures (atmospheric and 800 kPa) to show the behavior of the derived equation. Conclusions The analysis allows for direct efficiency (based on the second law of thermodynamics) comparisons between existing processes and future technological innovations in the field of air separation. Actual air separation systems have low efficiencies compared to ideal systems; actual PSA systems were estimated to have second law efficiencies of 5.5–11.2%. Therefore, there is great potential for improvements to current air separation systems.

Quantification of plasma enabled surface cooling by electron emission from high temperature materials

In this work, the potential for hypersonic leading edge cooling by electron emission is demonstrated. To overcome space charge limitations the experiments are carried out in an argon discharge at 1 Torr. Cooling is observed with time-resolved measurements of the electron emission current and surface temperature, taking advantage of well controlled laser heating of the emitting surface and time accurate surface pyrometry. For the ignited mode of the plasma discharge, surface cooling by the electron emission is directly observed, leading to an estimated cooling rate of 1.6±0.2 MW m−2. Higher cooling rates with self sustained plasmas for space charge mitigation are expected using cesium transpiration. A two-dimensional model of heat transfer has been developed, which reproduces well the experimentally observed cooling dynamics. Parametric tests of emitter materials with various work functions show that for effective surface cooling by electron emission, the optimal work function must be less than 3.0 eV. This result indicates that electron cooling can be a promising thermal protection method for leading edges of hypersonic vehicles in flight.

Effect of inclined magnetic field and chemical reaction on Casson fluid flow over a stretching surface with Cattaneo–Christov double diffusion

This investigation discusses the significance of studying the behavior of non-Newtonian fluids, specifically the Casson fluid, subjected to an electrically conducting and stretching sheet. The study also explores the effects of an aligned magnetic field, Cattaneo–Christov double diffusion, viscous dissipation and chemical reactions on heat and mass transfer, respectively. The partial differential equations governing the flow problem are transformed into ordinary differential equations through the utilization of similarity transformations. Furthermore, the shooting technique is implemented in MATLAB to solve the ODEs. The influence of physical parameters, such as the magnetic field parameter, Eckert number, Prandtl number and chemical reaction parameter, on the velocity profile, temperature distribution, concentration profile, skin friction coefficient, Nusselt number and Sherwood number is studied and presented in graphical and tabular forms. It is found that increasing the Prandtl number causes a drop in the temperature profile. Moreover, the presence of thermal radiation and the Eckert number significantly amplifies the temperature distribution. When the magnetic number undergoes a substantial increase, there is a notable decrease in the velocity profile, and simultaneously, the temperature profile experiences a noticeable rise. Additionally, increase in the chemical reaction parameters leads to a decrease in the concentration profile. The skin friction coefficient, local Nusselt number and Sherwood number exhibit significant reductions as the Casson parameter increases. Additionally, a MATLAB built-in function named bvp4c is incorporated to verify the computed results. The practical implications of the Cattaneo–Christov heat flux model include microelectronics, microfluidic devices, processes involving rapid heating or cooling, such as laser welding or pulsed laser ablation and heat transfer in biological tissues.

Stabilization of Pr4+ in Silicates─High-Pressure Synthesis of PrSi3O8 and Pr2Si7O18.

The reaction between PrO2 and SiO2 was investigated at various pressure points up to 29 GPa in a diamond anvil cell using laser heating and in situ single-crystal structure analysis. The pressure points at 5 and 10 GPa produced Pr2III(Si2O7), whereas Pr4IIISi3O12 and Pr2IV(O2)O3 were obtained at 15 GPa. Pr4IIISi3O12 can be interpreted as a high-pressure modification of the still unknown orthosilicate Pr4III(SiO4)3. PrIVSi3O8 and Pr2IVSi7O18 that contain praseodymium in its rare + IV oxidation state were identified at 29 GPa. After the pressure was released from the reaction chamber, the Pr(IV) silicates could be recovered, indicating that they are metastable at ambient pressure. Density functional theory calculations of the electronic structure corroborate the oxidation state of praseodymium in both PrIVSi3O8 and Pr2IVSi7O18. Both silicates are the first structurally characterized representatives of Pr4+-containing salts with oxoanions. All three silicates contain condensed networks of [SiO6] octahedra which is unprecedented in the rich chemistry of lanthanoid silicates.