Optical Emission Monitoring Research Articles

Investigation of properties of novel multilayer Cr/CrN/CrTiN/CrTiAlN hard coating with four bilayers

A novel multilayer Cr/CrN/CrTiN/CrTiAlN hard coating with four bilayers was developed by reactive closed field unbalanced magnetron sputtering (CFUBMS). The substrate temperature was kept in the range of 170 °C to 200 °C. The reactive gas flow was controlled by Optical Emission Monitoring. A thickness of 1.8 μm was determined using a calotester. The morphology and chemical composition were studied by electron microscopy (SEM and EDS). Nanohardness of 34.1 GPa and a modulus of elasticity of 386 GPa were determined using the nanoindentation technique. The scratch test against a diamond Rockwell indenter did not show features indicating poor adhesion. The reciprocating wear test revealed strong resistance to wear, and a coefficient of friction of 0.19 was determined. The developed multilayered hard coating showed optimal mechanical properties for industrial applications on instruments of low-temperature materials.

Matrix-Assisted Processes in CH4-Doped Ar Ices Irradiated with an Electron Beam

The relaxation processes induced by exposure of the Ar matrices doped with CH4 (0.1–10%) to an electron beam were studied with a focus on the dynamics of radiolysis products—H atoms, H2 molecules, CH radicals, and energy transfer processes. Three channels of energy transfer to dopant and radiolysis products were discussed, including free charge carriers, free excitons and photons from the “intrinsic source” provided by the emission of the self-trapped excitons. Radiolysis products along with the total yield of desorbing particles were monitored in a correlated manner. Analysis of methane transformation reactions induced by free excitons showed that the CH radical can be considered a marker of the CH3 species. The competition between exciton self-trapping and energy transfer to the dopant and radiolysis products has been demonstrated. A nonlinear concentration behavior of the H atoms in doped Ar matrices has been established. Real-time correlated monitoring of optical emissions (H atom and CH3 radicals), particle ejection, and temperature revealed a nonmonotonic behavior of optical yields with a strong luminescence flash after almost an hour of exposure, which correlated with the explosive pulse of particle ejection and temperature. The connection of this phenomenon with the processes of energy transfer and recombination reactions has been established. It is shown that the delayed explosive ejection of particles is driven by both the recombination of H atoms and CH3 radicals. This occurs after their accumulation to a critical concentration in matrices at a CH4 content C ≥ 1%.

Signatures of r-process Enrichment in Supernovae from Collapsars

Despite recent progress, the astrophysical channels responsible for rapid neutron capture (r-process) nucleosynthesis remain an unsettled question. Observations of the kilonova following the gravitational-wave-detected neutron star merger GW170817 established mergers as one site of the r-process, but additional sources may be needed to fully explain r-process enrichment in the universe. One intriguing possibility is that rapidly rotating massive stars undergoing core collapse launch r-process-rich outflows off the accretion disks formed from their infalling matter. In this scenario, r-process winds are one component of the supernova (SN) ejecta produced by “collapsar” explosions. We present the first systematic study of the effects of r-process enrichment on the emission from collapsar-generated SNe. We semianalytically model r-process SN emission from explosion out to late times and determine its distinguishing features. The ease with which r-process SNe can be identified depends on how effectively wind material mixes into the initially r-process-free outer layers of the ejecta. In many cases, enrichment produces a near-infrared (NIR) excess that can be detected within ∼75 days of explosion. We also discuss optimal targets and observing strategies for testing the r-process collapsar theory, and find that frequent monitoring of optical and NIR emission from high-velocity SNe in the first few months after explosion offers a reasonable chance of success while respecting finite observing resources. Such early identification of r-process collapsar candidates also lays the foundation for nebular-phase spectroscopic follow-up in the NIR and mid-infrared, for example, with the James Webb Space Telescope.

Observing molten pool surface oscillations during keyhole processing in laser powder bed fusion as a novel method to estimate the penetration depth

Various in-situ monitoring techniques have been developed for the detection of process drifts in the Laser Powder Bed Fusion (LPBF) process. Currently, optical emission monitoring can retrieve information regarding molten pool characteristics, such as temperature, width, length and area which provide substantial process signatures. Nonetheless, a fundamental indicator for the retrieval of a complete set of spatially distributed information is missing: the molten pool depth. Within the present investigation, a system for the estimation of the penetration depth based on the detection of molten pool surface oscillations is reported. Initially, the fundamentals of the monitoring technique are presented. The principle relies upon the observation of molten pool surface ripples through the measurement of probe light reflections in the melt area. Proof of concept testing of the sensing principle was conducted through an experimental investigation on a prototypal platform. A monitoring system (consisting of a high-speed camera and a secondary illumination light) was employed to view the process while realising both bead-on-plate material remelting and single track powder bed fusion depositions of AISI316L at different levels of laser emission power. Oscillation frequencies were extracted from the high-speed imaging acquisitions after image processing and signal analysis. The surface wave oscillations were measured to be in the range of 3.5–5.5 kHz in keyhole conditions. Metallographic cross-sections allowed to observe the effective molten pool penetration depth and cross-sectional area and were correlated to oscillation frequencies. Higher values of oscillation indicated shallower penetration and consequently a smaller mass of molten material.

Monitoring of optical emissions in laser cladding of 316L stainless steel.

Laser cladding is so complex that small disturbances may cause defects. Developing on-line monitoring technology for laser cladding is thus a priority task. Compared with expensive spectrometers and high-speed cameras, an economical optical sensing system based on two different photodiodes was established to optimize laser parameters and help monitor abnormal working conditions. In order to find optimal parameters, a series of experiments was carried out under different operating parameters such as laser power, scanning speed, and powder feeding rate. A practical rule is summarized to optimize process parameters by analyzing the time domain characteristics of the optical signal. Several experiments under different working conditions were performed to detect abnormal working conditions. Not only can an abnormal situation be recognized, but its type can also be distinguished by analyzing optical signals in the time and frequency domains. The optical sensing system provides a better understanding and accurate evaluation of laser cladding.

Nanostructured molybdenum nitride-based coatings: Effect of nitrogen concentration on microstructure and mechanical properties

Molybdenum nitride (MoNx) coatings were deposited onto AISI M2 tool steel substrates (hardened to HRC 60) by magnetron sputtering. The nitrogen content was controlled by means of a closed-loop optical emission monitor. The coating microstructure was examined by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. This showed that the increased nitrogen content led to a transformation from body-centered cubic α-Mo phase to γ-Mo2N phase (NaCl-B1 type) and then to a face-centered cubic MoN phase. The mechanical and tribological properties of these coatings were evaluated by nano-indentation, wear and scratch testing. The γ-Mo2N coating showed the highest hardness and the highest values of H (hardness)/E* (effective elastic modulus) and H3/E* ratio. During scratch and wear tests, the γ-Mo2N coating exhibited the best resistance to deformation and the lowest wear rate.

Contemporary Methods of Detecting Heavy Metals in Waste Waters (Review)

The necessity of monitoring the quality of waste waters and their specific features require the presence, development, and improvement of an instrumental analytic base, as well as the implementation of methods of detecting pollutants, including heavy metals. This review article characterizes methods of elemental atomic absorption, optical emission, and mass-spectral ecoanalytical monitoring of waste waters, which are of greatest practical interest. Particular attention is paid to methods using operations on separating and concentrating trace heavy metals.

Study of the mechanical properties of Ti-and Cr-based multicomponent hard coatings

TiCrAlN and CrTiAlN multicomponent coatings have been developed using closed-field unbalanced magnetron sputtering technique (CFUBMS) in a gas mixture of Ar + N2. The nitrogen level was varied by using the feedback control of plasma optical emission monitor (OEM). An investigation into the effect of the CFUBMS process parameters on the properties of the coatings was undertaken. The main coatings parameters such as thickness, surface morphology, nanohardness, strength of adhesion and wear resistance were studied by means of ball-cratering method, atomic force microscopy, scanning electron microscopy, scratch tests and nanoindentation measurements. The study revealed strong dependency of the mechanical properties on the nitrogen flow rate. Analysis of the experimental results showed that Cr-based multicomponent coatings possess better mechanical properties than Ti-based coatings at a nitrogen flow rate of 21 sccm: higher value of hardness (≤ 31GPa) and higher scratch resistance (> 30 N).

Correlation between stoichiometry and properties of scandium oxide films prepared by reactive magnetron sputtering

Scandium oxide films were deposited on fused silica substrates by reactive pulsed DC magnetron sputtering. The use of feed-back optical emission monitoring enabled high-rate reactive deposition of films with tunable stoichiometry and properties. The under-stoichiometric, stoichiometric and over-stoichiometric scandium oxide films were prepared. The compressive stress in films was between 235 and 530MPa. We showed that phase structure, density, surface roughness and optical properties of the scandium oxide are affected by the film stoichiometry and deposition conditions. Transparent scandium oxide films were slightly hydrophobic (94±3°), homogeneous with a crystallite size of 20±5nm. The lowest extinction coefficient 0.7×10−3, the highest refractive index 2.08 (both quantities at the wavelength of 355nm) and the highest density 4.1±0.1g cm−3 exhibited film prepared with the stoichiometric composition. Stoichiometric scandium oxide can be used in various optical applications as high refractive index and wide bandgap material. Transitions to under- or over-stoichiometry lead to a decrease of film density, refractive index and increase of the extinction coefficient.

Optical emission monitoring for defocusing laser percussion drilling

This paper presents a novel method for controlling the laser-drilling process for a hole by monitoring induced plasma emission. The variation of light brightness from laser-induced plasma is used as an indicator to control laser percussion drilling. Through on-line plasma emission acquisition and analysis, we obtain the positive association between the increased depth and the optical signal output. A coaxial photodiode is used to estimate the brightness levels of laser-induced plasma. The above constitute an inexpensive and practical on-line feedback system that can be easily implemented in the laser systems. All of the processing work is performed in air under standard atmospheric conditions without gas assist. The acquired signal for drilling could also be used as an input to a focus point process control scheme. Moreover, the technology demonstrates the feasibility to develop an automated laser micromachining system. Experimental results show that drilling efficiency was increased 47% by applying the proposed defocusing laser percussion drilling.

Multilayered TiAlN films on Ti6Al4V alloy for biomedical applications by closed field unbalanced magnetron sputter ion plating process

Ti6Al4V alloy has been widely used as a suitable material for surgical implants such as artificial hip joints. In this study, a series of multilayered gradient TiAlN coatings were deposited on Ti6Al4V substrate using closed field unbalanced magnetron sputter ion plating (CFUBMSIP) process. Taguchi design of experiment approach was used to reveal the influence of depositing parameters to the film composition and performance of TiAlN coatings. The phase structure and chemical composition of the TiAlN films were characterized by X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). Mechanical properties, including hardness, Young's modulus, friction coefficient, wear rate and adhesion strength were systematically evaluated. Potentiodynamic tests were conducted to evaluate the corrosion resistance of the coated samples in Ringer's solution at 37°C to simulate human body environment. Comprehensive performance of TiAlN films was evaluated by assigning different weight according to the application environment. S8, deposited by Ti target current of 8A, Al target current of 6A, bias voltage of −60V and nitrogen content with OEM (optical emission monitor) value of 45%, was found to achieve best performance in orthogonal experiments. Depositing parameters of S8 might be practically applied for commercialization of surgical implants.

Composition optimization of multilayered chromium-nitride–carbon film on 316L stainless steel as bipolar plates for proton exchange membrane fuel cells

The composition of multilayered chromium-nitride-carbon (Cr-N-C) film has great influence on the performance of coated 316L stainless steel (SS316L) as bipolar plates for proton exchange membrane fuel cells (PEMFCs). In this study, five films with different composition are deposited by closed field unbalanced magnetron sputter ion plating (CFUBMSIP) and the influence of nitrogen content adjusted by a closed-loop optical emission monitor (OEM) is evaluated. The phase structure and chemical composition of the films are characterized by X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). Interfacial contact resistance (ICR) between coated samples and gas diffusion layer (GDL) is measured. Potentiodynamic and potentiostatic tests are conducted to evaluate the corrosion resistance of coated samples. Experimental results show that Cr-N-C film with OEM setting of 60% presents the best performance, i.e. the ICR reduces to 2.11 mΩ cm2 under a compaction pressure of 1.4 MPa, and the corrosion current density reaches 0.308 μA cm−2 in the PEMFCs cathodic environment (0.5 M H2SO4 + 5 ppm HF solution at 70 °C, 0.6 V vs. SCE). Therefore, this study indicates that Cr-N-C film with OEM setting of 60% achieves optimal film composition and may be practically applied for commercialization of PEMFCs technology.

Detection of Acoustic Emission (AE) from Zinc Emibrittlement Cracking During Welding Using Optical Fiber AE Monitoring System

We have developed an optical fiber acoustic emission (AE) monitoring system equipped with phase and polarization control systems. The phase control system has an integration-type feedback loop with a phase lead process that maintains the phase difference between the sensing and the reference beam at π/2 and compensates for environment noise in the frequency range of less than one hundred hertz. Additionally, we controlled the polarization of the sensing beam corresponding with the reference beam to keep the system highly sensitive. We applied the developed system to the detection of zinc embrittlement cracking in an AISI type 304 plate during a simulated welding process (melt-run) at elevated temperatures. We succeeded in detecting a significant amount of AE from the cracking during welding process.

Deposition of nano-scaled CrTiAlN multilayer coatings with different negative bias voltage on Mg alloy by unbalanced magnetron sputtering

In a magnetron sputtering system, the negative substrate bias voltage has been used as a basic process parameter to modify the deposition structure and properties of coatings. In this paper we report the effect of bias voltage ranging from −40 V to −90 V on nano-scaled CrN/TiN/CrN/AlN (CrTiAlN) multilayer coatings synthesized on a Mg alloy by a closed-field unbalanced magnetron sputtering ion plating system in a gas mixture of Ar + N 2. The technological temperature and atomic concentration in the multilayer coatings were controlled by adjusting the current density of different metal magnetron targets and the plasma optical emission monitor. The composition, crystallographic structure, deposition model and friction coefficient of multilayer coatings were characterized by X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and ball-on-disc testing. The experimental results show that the deposition model and friction coefficient of nano-scaled CrTiAlN multilayer coatings were significantly affected by the negative bias voltage ( V b). The nitride species in multilayer coatings mainly involve CrN, AlN and TiN, and XRD analysis shows that the crystallographic structure was face-centered cubic. Under different bias voltage conditions, the multilayer coating composition shows a fluctuation, and the Al and Cr concentrations respond in the opposite sense to the bias voltage, attaining their greatest values at V b = −70 V. The surface and cross-sectional morphology shows deposition model change from a columnar model into non-columnar model with the increase in negative bias voltage. The friction coefficient of the nano-scaled multilayer coatings at V b = −55 V stabilize after 10 000 cycles.

Structural, mechanical and tribological properties of nanostructured CN x/TiN multilayers

Nanostructured CN x /TiN multilayers were deposited onto Si(1 0 0) and M42 high-speed steel substrates using closed-filed unbalanced magnetron sputtering. The deposition process was controlled by a closed-loop optical emission monitor (OEM) to regulate the flow of N 2 gas. Different carbon nitride Λ CN x layer thicknesses could be attained by varying the C target current (0.5–2.0 A). OEM settings and bilayer thickness periods (i.e. Λ CN x = 0.3 – 1.2 nm , while Λ TiN=3.0 nm) significantly affected the mechanical and tribological properties of CN x /TiN multilayer films. XPS analyses revealed that the chemical states, such as TiN, TiC, TiN x O y ???????????and TiO 2, existed in a TiN layer. The nanohardness of the film with bilayer thickness Λ TiN=3.0 nm and Λ CN x = 0.9 nm was ∼41.0 GPa. The residual compressive stress was found to be between 1.5 and 3.0 GPa. By the scratch test, the critical load value obtained was high ∼78 N. Rockwell-C adhesion tests exhibited the best adhesion and cohesive strength for multilayers with Λ TiN=3.0 nm, Λ CN x = 0.3 and 0.6 nm . The friction coefficient of a multilayer was found to be low 0.11. Lower frictional coefficients and wear rates were the consequences of the increase in Λ CN x , which provided a lubricating function in the multilayers.

Influence of deposition conditions on mechanical and tribological properties of nanostructured TiN/CN x multilayer films

Nanostructured TiN/CN x multilayer films were deposited onto Si (100) wafers and M42 high-speed-steel substrates using closed-filed unbalanced magnetron sputtering in which the deposition process was controlled by a closed loop optical emission monitor (OEM) to regulate the flow of N 2 gas. Multilayers with different carbon nitride (CN x ) layer thickness could be attained by varying the C target current (0.5 A to 2.0 A) during the deposition. It was found that the different bilayer thickness periods (i.e. the TiN layer thickness Λ TiN was fixed at 3.0 nm while the CN x layer thickness Λ CN x was varied from 0.3 to 1.2 nm) significantly affected the mechanical and tribological properties of TiN/CN x multilayer films. These multilayer films were characterized and analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), Rockwell-C adhesion test, scratch test, pin-on-disc tribometer, and nanoindentation measurements. XPS analyses revealed that the chemical states, such as TiN, TiC, TiN x O y and TiO 2, existed in a TiN layer. Nanoindentation results showed that the hardness was highly dependent on the bilayer thickness. A maximum hardness of ~ 41.0 GPa was observed in a multilayer film at bilayer thickness Λ TiN = 3.0 nm and Λ CN x = 0.9 nm. All multilayer films exhibited extreme elasticity with elastic recoveries as high as 80% at 5 mN maximum load. The compressive stresses in the films (in a range of 1.5–3.0 GPa) were strongly related to their microstructure, which depended mainly on the incorporation of nitrogen in the films. By scratch and Rockwell-C adhesion tests, the multilayer films with smaller bilayer thicknesses (Λ TiN = 3.0 nm, Λ CN x = 0.3 and 0.6 nm) exhibited the best adhesion and cohesive strength. The critical load value obtained was as high as ~ 78 N for the films with Λ TiN = 3.0 nm, Λ CN x = 0.9 nm. The friction coefficient value for a multilayer at Λ TiN = 3.0 nm and Λ CN x = 0.9 nm was found to be low 0.11. These adhesive properties and wear performance are also discussed on the basis of microstructure, mechanical properties and tribochemical wear mechanisms.

Structural and tribological properties of CrTiAlN coatings on Mg alloy by closed-field unbalanced magnetron sputtering ion plating

In this paper, a series of multi-layer hard coating system of CrTiAlN has been prepared by closed-field unbalanced magnetron sputtering ion plating (CFUBMSIP) technique in a gas mixture of Ar + N 2. The coatings were deposited onto AZ31 Mg alloy substrates. During deposition step, technological temperature and metallic atom concentration of coatings were controlled by adjusting the currents of different metal magnetron targets. The nitrogen level was varied by using the feedback control of plasma optical emission monitor (OEM). The structural, mechanical and tribological properties of coatings were characterized by means of X-ray photoelectron spectrometry, high-resolution transmission electron microscope, field emission scanning electron microscope (FESEM), micro-hardness tester, and scratch and ball-on-disc tester. The experimental results show that the N atomic concentration increases and the oxide on the top of coatings decreases; furthermore the modulation period and the friction coefficient decrease with the N 2 level increasing. The outstanding mechanical property can be acquired at medium N 2 level, and the CrTiAlN coatings on AZ31 Mg alloy substrates outperform the uncoated M42 high speed steel (HSS) and the uncoated 316 stainless steel (SS).

Structural, mechanical, and tribological studies of Cr–Ti–Al–N coating with different chemical compositions

In this paper, a multicomponent hard coating system of Cr–Ti–Al–N has been studied for its structural, mechanical and tribological properties under different chemical compositions. The coatings were deposited onto AISI M42 steel plates by closed-field unbalanced magnetron sputtering ion plating (CFUBMSIP) technique in a gas mixture of Ar + N 2. Three processing steps in deposition involved were plasma ion cleaning, buffer layer deposition, and multicomponent layer deposition. During the final deposition step, nitrogen concentration was controlled at ∼ 50 at.% by using the feedback control of metal plasma optical emission monitor (OEM). The metallic ratio of Cr, Ti, and Al was varied by adjusting the currents of different magnetron targets. The coatings were characterized by means of energy dispersive X-ray (EDX) analysis, X-ray photoelectron spectrometry (XPS), X-ray diffractometry (XRD), Rockwell-C indentation tester, microhardness tester, and pin-on-disc (POD) tribometer, in order to check their chemical composition, as well as to determine the structural, mechanical and tribological properties. The experimental results showed that the optimised quaternary Cr–Ti–Al–N coating performs better than the binary CrN as well as the ternary Cr–Ti–N and Cr–Al–N coatings in terms of hardness and wear resistance. The introduction of both Ti and Al elements into the CrN-based coatings enhances both of their mechanical and tribological performance.

Development of Heat Resistant AE Monitoring System Using Optical Fiber Sensor

We developed an advanced optical fiber Acoustic Emission (AE) monitoring system with a phase compensation feed back circuit. Two lasers transmitted through the reference and sensing arms are combined by a 2x2 coupler and detected by two photodiodes as the intensity change of the interfered laser. Outputs of the photodiodes are then combined in a differential amplifier which extracts error signal and improves the S/N ratio. The developed system was demonstrated to detect weak guided wave AE signals such as zero-th order longitudinal cylindrical wave (Lo-mode) with the S/N ratio higher than that of PZT sensor. This system was utilized to monitor the oxidation resistance of various alloys during thermal cycles from 300 K to 1273 K. We detected weak AE signals from micro fractures of growing oxide films of boiler tube and austenitic stainless steel, but no AE from Inconel 600 tubes. Here the optical fiber sensor was wound over the tube at 600 K. Both the AE counts and amplitudes during thermal cycles showed clear tendency depending on the oxidation resistances of the alloys.

Wear of CrC-coated carbide tools in dry machining

This paper discusses the tribological characteristics and cutting performance of chromium carbide (Cr x% C)-coated carbide tool inserts and micron-drills in dry machining. Cr x% C coatings have been deposited with different optical emission monitoring (OEM) set values, x%, of chromium target “poisoning” by unbalanced magnetron sputtering and OEM control. The microstructures and mechanical properties of Cr x% C coatings have been measured by the experiments of scanning electron microscope (SEM), nanoindentation and adhesion. Experimental results indicate that the coating microstructure, mechanical properties and wear resistance vary according to OEM set values. Cr 10%C-coated inserts showed the best wear resistance in AISI 1045 steel turning test. Cr 50%C-coated tools have performed exceptionally well in both copper turning and printed circuit board (PCB) through-hole drilling tests. The service life of Cr 50%C-coated tool is four times higher than that of an uncoated tool in the PCB through-hole drilling test.