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In laser powder bed fusion (LPBF) additive manufacturing, melt pool characterization is one of the potential approaches toward rapid process qualification and efficient non-destructive evaluation of printed parts. Especially melt pool width measurement is crucial for understanding the print process regimes, estimating the solidified melt pool depth, and identifying any process anomalies, among other attributes of interest. While existing works focus on monitoring melt pools of single scan tracks or single layer prints, melt pool characterization for a multi-track multi-layer (MTML) LPBF print has not been extensively studied. In this work, we employ our lab-designed coaxial single-camera two-wavelength imaging pyrometry (STWIP) system to monitor in-situ melt pool properties during a MTML LPBF process. The STWIP-measured melt pool widths are validated using a serial sectioning machine (Robo-Met, UES). The in-situ STWIP and ex-situ Robo-Met measurement data are in close agreement with each other, having a mean absolute error and root mean squared error of 9.83 μm and 16.53 μm, respectively. Furthermore, we demonstrate the successful mapping of melt pool location and melt pool size on the printed MTML part. In sum, this work demonstrates the capability and the applicability of STWIP for accurate large-scale melt pool monitoring during LPBF processing of practical parts, thereby facilitating the development of LPBF process models and control strategies.

This work is devoted to the study of the processes that take place in the welding gap during explosive welding (EW). In the welding gap, when plates collide, a shock-compressed gas (SCG) region is formed, which moves at supersonic speed and has a high temperature that can affect the quality of the weld joint. Therefore, this work focuses on a detailed study of the parameters of the SCG. A complex method of determining the SCG parameters included: determination of the detonation velocity using electrical contact probes, ceramic probes, and an oscilloscope; calculation of the SCG parameters; high-speed photography of the SCG region; measurement of the SCG temperature using optical pyrometry. As a result, it was found that the head front of the SCG region moved ahead of the collision point at a velocity of 3000 ± 100 m/s, while the collision point moved with a velocity of 2500 m/s. The calculation of the SCG temperature showed that the gas was heated up to 2832 K by the shock compression, while the measured temperature was in the range of 4100–4400 K. This is presumably due to the fact that small metal particles that broke off from the welded surfaces transferred their heat to the SCG region. Thus, the results of this study can be used to optimize the EW parameters and improve the weld joint quality.

A possibility of using non-monochromatic photodetectors registering radiation in a wide range of wavelengths as sensors of the brightness channel in spectral-brightness pyrometry is considered. A definition of the effective wavelength for a pyrometer is introduced based on a dependence of the registered signal on the temperature of thermal radiation source. Experimental results on determining the effective wavelength of the photodetector with the sensitivity in the interval of wavelength 400–1100 nm for recording the temperature lamp radiation in the temperature range from 1557 to 2494 K are reported.

Real-time closed-loop control of metallurgical processes is still in its infancy, mostly based on simple models and limited sensor data and challenged by extreme temperature and harsh process conditions. Contact-free thermal imaging-based measurement approaches thus appear to be particularly suitable for process monitoring. With the potential to generate vast amounts of accurate data in real time and combined with artificial intelligence methods to enable real-time analysis and integration of expert knowledge, thermal spectral imaging is identified as a promising method offering more robust and accurate identification of key parameters, such as surface temperature, morphology, composition, and flow rate.

Under high electrical current, some materials can emit electromagnetic radiation beyond incandescence. This phenomenon, referred to as electroluminescence, leads to the efficient emission of visible photons and is the basis of domestic lighting devices (for example, light-emitting diodes) 1 , 2 . In principle, electroluminescence can lead to mid-infrared emission of confined light–matter excitations called phonon polaritons 3 , 4 , resulting from the coupling of photons with crystal lattice vibrations (optical phonons). In particular, phonon polaritons arising in the van der Waals crystal hexagonal boron nitride (hBN) present hyperbolic dispersion, which enhances light–matter coupling 5 , 6 . For this reason, electroluminescence of hyperbolic phonon polaritons (HPhPs) has been proposed as an explanation for the peculiar radiative energy transfer within hBN-encapsulated graphene transistors 7 , 8 . However, as HPhPs are locally confined, they are inaccessible in the far field, and as such, any hint of electroluminescence has been based on indirect electronic signatures and has yet to be confirmed by direct observation. Here we demonstrate far-field mid-infrared (wavelength approximately 6.5 μm) electroluminescence of HPhPs excited by strongly biased high-mobility graphene within a van der Waals heterostructure, and we quantify the associated radiative energy transfer through the material. The presence of HPhPs is revealed by far-field mid-infrared spectroscopy owing to their elastic scattering at discontinuities in the heterostructure. The resulting radiative flux is quantified by mid-infrared pyrometry of the substrate receiving the energy. This radiative energy transfer is also shown to be reduced in hBN with nanoscale inhomogeneities, demonstrating the central role of the electromagnetic environment in this process. Far-field mid-infrared spectroscopy reveals both the electroluminescence of hyperbolic phonon polaritons of hexagonal boron nitride excited by strongly biased graphene, and the associated radiative energy transfer through the material.

Measuring the temperature and deformation synchronously at elevated temperatures is technically challenging and has become a major concern in the evaluation of mechanical properties. In this study, a simple, easy-to-implement, yet effective monochromatic pyrometry is established for non-contact and full-field temperature measurements, which can significantly reduce the error caused by the camera’s channel crosstalk that commonly occurs in the existing improved two-color method. In addition, high-temperature digital image correlation, combined with band-pass filtering and monochromatic illumination, is applied for deformation measurement. Subsequently, an experimental system was set up to validate the accuracy of the proposed method, which consists of a CCD camera for image capturing, a blue bandpass filter for radiation suppression, blue light irradiation for light compensation, and an infrared pyrometer for temperature recording. The results of the thermal heating experiment on the C/SiC sample proved that the selection of camera channel R in monochromatic pyrometry can reduce the error by channel crosstalk, and the proposed method is applicable for synchronous measurement of temperature and deformation.

Volumetric multi-kHz laser irradiation can affect the measurements on soot particles. The severity of the influence causing local alteration of the particle and flame properties are investigated on a laminar diffusion flame. The aim is to identify a practical fluence threshold for which no or only minor influence on soot particles due to volumetric multiple laser irradiation occurs. To this end, the three quantities of interest (QoI) of particle temperature, soot volume fraction and primary particle size are measured and evaluated via 3D-two-color-pyrometry (3D-2CP) and 3D time-resolved laser-induced incandescence (3D-TiRe-LII). As laser source, a high repetition-rate burst-mode Nd:YAG pulse laser is employed. The progression of the three QoI is investigated for different fluences (up to ~ 160 mJ/cm 2 ) and repetition rates (up to 5 kHz) for selected individual pulses within a pulse train. For the determination of practical fluence limits, a maximum change of 25% in soot volume fraction is applied as a threshold. The fluence limit is highly dependent on laser repetition rate and flow velocity of the object of interest. For irradiation with eight laser pulses with 5 kHz, a fluence limit of ~ 60 mJ/cm 2 is identified.

This work presents a characterisation model for the temperature distribution at different substrate depths during the atmospheric plasma spray (APS) coating process. The torch heat flow in this model is simulated as forced convection defined by a surface, a temperature profile, and a convection coefficient. The simulation model considers three plasma temperature profiles of the Al2O3 coating on a 5 mm thickness flat aluminium substrate. The simple and low-cost experimental procedure, based on a thermocouple, measures the plasma plume temperature distribution of the APS coating system, and their results are used to obtain the parameter values of each of the three proposed plasma temperature profiles. The experimental method for in situ non-contact temperature measurements inside the substrate is based on an infrared pyrometry technique and validates the simulation results. The Gaussian temperature profile shows excellent accuracy with the measured temperatures. The Gaussian approach could be a powerful tool for predicting residual stress through a coupled one-way thermal-mechanical analysis of the APS process.

Liquid-Metal (LM) divertor configurations are being explored to identify potential solutions to develop more resilient Plasma Facing Components for harsh environments characterized by nominal and transient power loads that can seriously compromise the feasibility of conventional tungsten elements. In this work, tin (Sn) plasmoids generated in front of a LM filled Capillary Porous System target exposed to ITER-Intra edge localized mode (ELM) energy range (20–33 keV) particle beams (H0 and H0-H+ mixtures), are investigated at the OLMAT High-Heat Flux facility. Local characterization of plasmoids, including absolute quantification of the ionic species densities and their non-stationary evolution with target surface temperature, are conducted using a novel configuration consisting of a single Langmuir Probe (LP) directly embedded in the target while also employing a solid Titanium-Zirconium-Molybdenum alloy target for LP measurement benchmarking. Optical Emission Spectroscopy provides additional plasma characterization while infrared pyrometry monitors target thermal response. The temporal dynamic evolution of Sn plasmoids is described by four phases that depend on target temperature, parameter that determine the net eroded Sn flux and eventually Sn plasma content and global plasma build-up. The final phase, initiated at target temperature of 1600 K, is associated with the first stages of a thermal shielding state with partial mitigation of incoming heat fluxes. The thermal shielding and heat-flux mitigation fraction characteristics are inferred by studying deviations of target thermal response against a simple 1-D heat conduction model. Finally, the main Sn erosion mechanisms (thermal sputtering and evaporation) and atomic collisional processes (charge-exchange, electron/high-energy neutral-ion impact and recombination processes of Sn atoms) involving keV-range energy particles (neutrals, protons) as contributions to plasma build-up and heat flux mitigation characteristics are considered, these being questions of importance when considering detached LM divertor configurations operating in ELM-containing regimes.

In this work, the overall activation energy of the combustion of lean hydrogen–methane–air mixtures (equivalence ratio φ = 0.7−1.0 and hydrogen fraction in methane α=0, 2, 4) is experimentally determined using thin-filament pyrometry of flames stabilised on a flat porous burner under normal conditions (p=1 bar, T = 20 °C). The experimental data are compared with numerical calculations within the detailed reaction mechanism GRI3.0 and both approaches confirm the linear correlation between mass flow rate and inverse flame temperature predicted in the theory. An analysis of the numerical and experimental data shows that, in the limit of lean hydrogen–methane–air mixtures, the activation energy approaches a constant value, which is not sensitive to the addition of hydrogen to methane. The mass flow rate for a freely propagating flame and, thus, the laminar burning velocity, are measured for mixtures with different hydrogen contents. This mass flow rate, scaled over the characteristic temperature dependence of the laminar burning velocity for a one-step reaction mechanism, is found and it can also be used in order to estimate the parameters of the overall reaction mechanisms. Such reaction mechanisms will find implementation in the numerical simulation of practical combustion devices with complex flows and geometries.