High Power Pulsed Magnetron Sputtering Research Articles

Influence of Cr + Si content variation on cutting behavior of TiAlCrSiN HPPMS coatings

As high power pulse magnetron sputtering (HPPMS) technology is becoming popular in cutting tool industry, the development of nanocomposite coating systems such as TiAlCrSiN with this technology presents a new research avenue. Here, the combined effect of Cr and Si contents on properties and cutting behavior of high Al content TiAlCrSiN HPPMS coatings needs further investigation. For this purpose, three HPPMS coatings with Al/Ti ratio x = 1.4–1.5 and varying Cr + Si content, namely (Ti28Al40Cr16Si16)N, (Ti30Al43Cr17Si10)N and (Ti36Al54Cr5Si5)N, were deposited on cemented carbide substrates. In addition to basic characterization, the fracture behavior of the coatings was characterized by scratch tests. The cutting behavior of the coated inserts was exemplarily investigated during dry cutting of normalized medium carbon steel C45 with cutting speed vc = 80 m/min, feed rate f = 0.12 mm and cutting depth ap = 0.8 mm. The tool damage over the cutting time of tc = 35–40 min, as per the tool condition, was observed using light microscopy. Moreover, the damage mechanisms were analyzed in detail at the end of the cutting test using scanning electron microscopy. All coatings showed comparable indentation hardness HIT and indentation modulus EIT. However, an increased Cr + Si content amplified the brittle fracture of the coating under sliding load of scratch test. Moreover, the workpiece material C45 showed a higher adhesion tendency to cutting insert with high Cr + Si content TiAlCrSiN coatings during cutting tests. The tool wear and built-up edge formation increased due to the combined effect of workpiece adhesions and amplified brittle fracture of the coating at considered cutting speed. On the other hand, the inserts with low Cr + Si content coating exhibited better cutting performance and reduced built-up edge formation based on the improved fracture behavior of the coating and lower adhesion tendency of workpiece material to the corresponding coated insert.

Cutting performance of TiAlN-based thin films in micromilling high-speed steel AISI M3:2

Micromilling high-speed steel offers high precision in shape and geometry. However, the service life greatly depends on the wear resistance of protective thin films. In comparison to TiAlN, TiAlSiN and TiAlTaN thin films offer enhanced wear resistance for difficult-to-machine materials. Employing a hybrid process that combines direct current magnetron sputtering (dcMS) and high power pulsed magnetron sputtering (HiPIMS) enhances the properties of these films. In cutting tests, it is demonstrated that TiAlSiN and TiAlTaN outperform TiAlN in micromilling of high-speed steel AISI M3:2. Notably, dcMS/HiPIMS-TiAlSiN stands out by having the lowest reduction in cutting forces combined with reduced wear.

Correction: Li et al. Dry Friction Performances of MoNx Coatings Deposited by High–Power Pulsed Magnetron Sputtering. Magnetochemistry 2023, 9, 60

In the original publication [...]

High power pulsed magnetron sputtering tailored low temperature CrAlN + MoWS coatings for dry tribological contacts

Gears are used in a variety of applications, for example, in automotive and aerospace industries. In these applications, gears are exposed to harsh conditions such as high Hertzian pressures. In many cases, lubricants are used to achieve a reduction in the coefficient of friction and, thus, in the wear of the components. Nevertheless, in some applications, the use of a lubricant is difficult, for example, in vacuum environments. One promising approach is the application of solid lubricants by using triboactive elements. The present study shows the potential of a process combining high power pulsed magnetron sputtering (HPPMS) and direct current magnetron sputtering (dcMS) for the deposition of CrAlN + MoWS coatings. In HPPMS/dcMS processes, especially, the share of HPPMS leads to higher ionization of the coating plasma and, therefore, to higher coating thicknesses on the teeth of gears. One major challenge in coating processes is the adjustment of the deposition temperature, since steels used for gear applications are temperature sensitive. Therefore, starting from an established coating process with a high coating temperature, the coating process was adjusted by reducing the number of used cathodes. By reducing the count of used dcMS cathodes, the share of HPPMS cathodes within the coating process was increased. Furthermore, segments of gears were coated in order to determine the coating thickness at different distances from the head of the gear tooth. A sufficient coating thickness distribution on the flank of the gear tooth is crucial for friction reduction and wear protection when used in gearboxes. The reduction of used cathodes led to a decrease in the coating temperature from a maximum coating temperature of Tmax = 281 °C to Tmax = 214 and 197 °C. It was shown by nanoindentation measurements that the effect of soft annealing was eliminated by reducing the coating temperature. At the same time, coatings deposited with increased HPPMS fraction led to a reduced coefficient of friction as well as lower wear volumes for pin-on-disk measurements in a dry tribological contact with an uncoated 100Cr6 counterpart. Moreover, these processes exhibited a good coatability of the gear tooth with a relatively high coating thickness even near the gear tooth root. The present study shows the potential of increasing the share of HPPMS during the deposition of coatings for dry-running applications. By increasing the HPPMS content, the tribological behavior as well as the coating thickness distribution on gears can be significantly improved.

The Deposition and Properties of Titanium Films Prepared by High Power Pulsed Magnetron Sputtering

The Deposition and Properties of Titanium Films Prepared by High Power Pulsed Magnetron Sputtering

Effects of duty cycle and nitrogen flow rate on the mechanical properties of (V,Mo)N coatings deposited by high-power pulsed magnetron sputtering

(V,Mo)N is theoretically predicted to have high hardness and fracture toughness and is a promising material for the application on protective hard coatings. However, the toughness enhancement of (V,Mo)N coatings deposited by dc-unbalanced magnetron sputtering (dc-UBMS) was not as remarkable as expected. The issue could be due to insufficient energy delivery to the plasma species in the deposition process such that nitrogen and metal atoms were not fully reacted and led to the degradation of coating quality. Since high-power pulsed magnetron sputtering (HPPMS) can provide high peak power density, the method was selected to deposit (V,Mo)N coatings in this research. The objective of this study was to investigate the effects of duty cycle and nitrogen flow rate on the microstructure and mechanical properties of (V,Mo)N coatings deposited on Si substrates by HPPMS. Four sets of (V,Mo)N coatings were deposited by HPPMS at different durations with two duty cycles, 5% and 3%, and two nitrogen flow rates, 6.0 and 12.0 SCCM. The results showed that the N/metal ratio was mainly affected by the nitrogen flow rate, ranging from 0.70 to 0.96 with increasing nitrogen flow rate. The lattice parameter of the samples linearly increased with the N/metal ratio. The x-ray diffraction (XRD) patterns revealed that all samples tended to approach (200)-preferred orientation with increasing deposition duration. The glancing incident XRD patterns indicated that the samples deposited at 6 SCCM nitrogen flow rate and 3% duty cycle have multiphases. Transmission electron microscopy analysis confirmed that phase separation from (V,Mo)N to (V-rich,Mo)N and (V,Mo-rich)N occurred in those samples. The hardness of the (V,Mo)N coatings decreased with increasing N/metal ratio, which may be related to the N-vacancy hardening effect. The sample deposited at 6 SCCM nitrogen flow rate and 3% duty cycle for 36 h showed the highest hardness of 28.4 GPa, which was possibly associated with the phase separation, and hence plastic deformation became difficult. The fracture toughness (Gc) of the (V,Mo)N coatings was evaluated using the internal energy-induced cracking method. The resultant Gc of the (V,Mo)N coatings, ranging from 36.1 to 43.7 J/m2, was higher than that of the coatings deposited by dc-UBMS in our previous study. The toughness enhancement could be caused by a higher fraction of Mo–N bonding due to the adequate reaction energy provided by the HPPMS process.

HiPIMS deposition of CuNiTiNbCr high - entropy alloy films: Influence of the pulse width on structure and properties

In the process of high power pulsed magnetron sputtering, optimizing the ionization rate of plasma plays a pivotal role in enhancing the properties of films. Altering the pulse width can impact the ionization rate and particle energy in HiPIMS. In this study, we prepared the CuNiTiNbCr high-entropy alloy films by HiPIMS under different pulse widths. The influence of pulse width on target discharge and plasma ionization rate was investigated, followed by a comprehensive discussion of the films' structure and properties under various pulse widths. The film deposited at various pulse widths consisted of high-entropy alloy amorphous phase and Cu-rich FCC phase. Decreasing the pulse width resulted in an increase in the peak power of the target, elevating the ionization rate of sputtered particles and leading to higher compressive stress and a denser film structure. These increased compressive stress and dense structure make the film have higher toughness and better wear resistance. Notably, the film deposited with a pulse width of 200 μs displayed the best corrosion resistance due to its high content of the passivating element Cr and its dense structure. Consequently, adjusting the pulse width can effectively modify the ionization rate of sputtered particles and enhance the performance of the film.

Large-area deposition of protective (Ti,Al)N coatings onto polycarbonate

Polycarbonate (PC) and protective (Ti,Al)N coatings exhibit extremely different material properties, specifically crystal structure, thermal stability, and elastic and plastic behavior, as well as thermal expansion coefficients. These differences present formidable challenges for the deposition process development as low-temperature synthesis routes have to be explored to avoid a thermal overload of the polymer substrate. Here, a large-area sputtering process is developed to address the challenges by systematically adjusting target peak power density and duty cycle. Adhering (Ti,Al)N coatings with a critical residual tensile stress of 2.2 ± 0.2 GPa are obtained in the pulsed direct current magnetron sputtering range, whereas depositions at higher target peak power densities, realized by high power pulsed magnetron sputtering, lead to stress-induced adhesive and/or cohesive failure. The stress-optimized (Ti,Al)N coatings deposited onto PC with a target peak power density of 0.036 kW cm−2 and a duty cycle of 5.3% were investigated by the cross-cut test, confirming adhesion. By investigating the bond formation at the PC|(Ti,Al)N interface, mostly interfacial CNx bonds and a small fraction of (C−O)−(Ti,Al) bonds are identified by x-ray photoelectron spectroscopy, indicating reactions at the hydrocarbon and the carbonate groups during deposition. Nanoindentation reveals an elastic modulus of 296 ± 18 GPa for the (Ti,Al)N coating, while a Ti–Al–O layer is formed during electrochemical impedance spectroscopy in a borate buffer solution, indicating protective passivation. This work demonstrates that the challenge posed by the extremely different material properties at the interface of soft polymer substrates and hard coatings can be addressed by the systematical variation in the pulsing parameters to reduce the residual film stress.

The influence of microstructural orientation on fracture toughness in (V, Al)N and (V, Al)(O, N) coatings as measured by microcantilever bending

Since protective transition metal (oxy)nitride coatings are widely used, understanding of the mechanisms linking microstructure to their fracture behaviour is required to optimise wear resistance, while maintaining fracture toughness. To assess this interconnection, beam bending was performed using microcantilevers oriented parallel and at 90° to the growth direction. Furthermore, the tests were applied to favour normal bending and shear fracture. Coatings were synthesised by both direct current magnetron sputtering (DCMS) as well as high power pulsed magnetron sputtering (HPPMS). Here, we show that the fracture toughness depends on the alignment of the grains and loading directions. Furthermore, an improved fracture toughness was found in coatings produced by HPPMS, when microstructural defects, such as underdense regions in DCMS deposited coatings can be excluded. We propose indices based on fracture and mechanical properties to rank those coatings. Here, the HPPMS deposited oxynitride showed the best combination of mechanical properties and fracture toughness.Graphical abstractPrinciple of measuring the effects of microstructure and process route on the fracture toughness via microcantilever bending.

Oxidation and wear behavior of CrAlMoN with varied Mo-content for cutting Ti6Al4V

The cutting of difficult to machine materials such as titanium alloys is challenging for the machining industry. In case of the titanium alloy Ti6Al4V, the properties of the material cause high temperatures, mechanical loads as well as high frequency vibrations at the cutting edge, leading to premature tool failure. The use of uncoated carbide tools is very common for machining of Ti based alloys. However, temperature active, self-lubricating physical vapor deposition (PVD) coatings like CrAlMoN showed promising results to reduce friction and wear during turning of Ti6Al4V. In the present study, self-lubricating (Cr34Al41Mo25)N, (Cr29Al36Mo35)N and (Cr25Al31Mo44)N coatings were investigated on cemented carbide tools. These were deposited by a hybrid process combining direct current Magnetron Sputtering and High Power Pulsed Magnetron Sputtering. Coating morphology, thickness, chemical composition, indentation hardness and modulus at ϑ = 20 °C, ϑ = 200 °C, ϑ = 400 °C and ϑ = 600 °C as well as the oxidation behavior were analyzed. Moreover, wear development after cutting tests using a CNC-lathe was investigated. Independent of Mo-content, all coating variants possessed a dense morphology and a smooth surface topography, as well as a coating adhesion class of HF1 to the cemented carbide substrate in Rockwell indentation tests according to DIN 4856. With an increasing amount of Mo, heat treatment temperature and time, more self-lubricating molybdenum oxides such as MoO3 and Mo4O11 were detected by Raman spectroscopy. Therefore, the coating with the highest amount of Mo possessed the highest amount of molybdenum oxides. After cutting tests, molybdenum oxides were also found on the tool flank face by Raman spectroscopy. The level of flank wear land width decreased with increasing amount of Mo.

Structure, mechanical properties and tribocorrosion behaviours of superhard TiSiCN nanocomposite coatings

Superhard coatings are no longer very difficult to obtain, but the direct observation and prediction of their failure are still a challenge. 3D tomography of the microcracks in coating failure offers lots of new information on the geometric shape, size, and spatial structure relationship of microcracks which was not available up to now. Hence, in this work, cross-scale visualization analysis of the microcrack network in superhard yet toughness TiSiCN coatings around indentations was achieved through advanced 3D tomography combined with HRTEM characterization. TiSiCN nanocomposite coatings were deposited by high-power pulsed magnetron sputtering. Superhard TiSiCN coatings exhibit a simultaneous superhardness of 48 ± 6.99 GPa and favorable toughness due to fully dense microstructure and smooth surface morphology. Due to the excellent crack initiation resistance and super-high hardness, superhard TiSiCN coatings show enhanced tribocorrosion performance in 3.5 wt% NaCl aqueous solution, with a low coefficient of friction of 0.11 and low specific wear rates of 3.23 × 10−6 mm−3N−1m−1.

Erosion Performance of TiAlSiN Coatings Prepared by High-Power Pulsed Magnetron Sputtering

Erosion seriously threatens the safety of high-speed rotating mechanical components in very harsh service environments, particularly for lightweight titanium alloy matrix material. In order to improve the erosion resistance of titanium alloy, TiAlSiN coatings with different phase compositions are deposited on TC6 titanium alloy using a high-power pulse magnetron sputtering discharge (HPPMS) system under various discharge voltages. The componential and microstructural evolution as well as mechanical properties of the TiAlSiN coatings are evaluated by X-ray diffraction, scanning electron microscopy, and nanoindentation, respectively. The erosion performance relative to titanium alloy is investigated by a sand blasting tester. With the increase in discharge voltage from −500 to −600 V, the peak of discharge current increases from 105 to 225 A. The prepared TiAlSiN coatings show a shift of the preferred crystallographic orientation from (220) to (200), but all of them have a dense nanocomposite structure. Their hardness (H) and elastic modulus (E) gradually increase before decreasing, arriving at maximum values of 35.34 and 360.5 GPa at −570 V. The erosion resistance of the TiAlSiN coatings dependent on the discharge voltage is consistent with the H/E ratio change. The TiAlSiN coatings prepared at −560 V exhibit the optimal erosion resistance, which is 15 times that of the TC6 substrate. The erosion behavior of the coatings is positively correlated with their hardness and toughness. Adjusting the discharge voltage of the HPPMS pulse is finally proved to be an effective way of tailoring the coating phase compositions to improve the erosion resistance of titanium alloy.

Hydrogen-free DLC films fabricated using superimposed HiPIMS-DCMS deposition system: Bias voltage effects

Diamond-like carbon (DLC) films were grown using a superimposed high-power pulse magnetron sputtering and direct current magnetron sputtering (HiPIMS-DCMS) deposition system at various bias voltages from 0 to −350 V. The microstructure, mechanical and tribological properties of the films were studied in relation to bias voltage. The results suggested that the deposition rate of DLC films decreased gradually with the enhancement of bias voltages. The surface roughness of DLC films decreased from 2.81 nm to 0.54 nm. The values of ID/IG of DLC films decreased first and increased later with the enhancement of bias voltages, and the value of ID/IG was the minimum at −150 V. Therefore, the highest sp3 CC fraction of DLC film was obtained when deposited at −150 V. Moreover, the hardness and internal stress of DLC films also show the law of increasing first and decreasing later. DLC film obtained the maximum hardness and highest internal stress of 32.0 GPa and − 2.08 GPa at −150 V. Finally, the friction test suggested that the films had excellent tribological performance. In particular, the film deposited at −150 V had excellent tribological properties, including low friction coefficient (0.095) and low wear rate (1.36 × 10−7 mm3/N·m).

Effect of the auxiliary cathode on the thickness of the HiPIMS TiAlN coating deposited on the inner surface of the tube

The paper is focused on influencing the thickness of the TiAlN layer deposited using the high power pulse magnetron sputtering (HiPIMS) method on the inner surface of the tube. The HiPIMS method makes it possible to deposit layers at temperatures up to 400°C. An auxiliary cathode placed in the axis of the coated tube was used. The auxiliary cathode made it possible to deposit an AlTiN layer with a thickness in the center of the coated tube up to 45% higher compared to the thickness of the layer deposited without an auxiliary cathode.The layer thickness was measured to be from 1.5 µm to 2.2 µm for the layer deposited without an auxiliary cathode and 1.05 µm to 1.95 µm for the layer deposited with the wire as the cathode in the axis of the coated tube. Adhesion of the evaluated layers showed the degree of HF2 at the measured thickness points.

Effect of pulse width on deposition of diamond-like carbon on high-power pulsed magnetron sputtering

A diamond-like carbon (DLC) film was deposited using high-power pulsed magnetron sputtering. The effect of pulse width on the deposition of DLC film was investigated under constant peak power density or average power density to clarify the densification mechanism of DLC film. The maximum hardness of 25 GPa analyzed by nanoindentation was obtained using Ar gas without negative substrate bias voltage at pulse width 30 μs and a peak power density of 1.5 kW cm−2. The flux and energy of C+ and Ar+ incident to the DLC film was evaluated by using energy-resolved and time-resolved mass spectrometry to clarify the relation between the input power to the target and the behavior of produced ions. The change in hardness is well correlated with the ion flux ratio C+/Ar+. This result indicates that a flux and energy of Ar+ as well as C+ is a key parameter to characterize the microstructure of DLC film.

A new TiAlSiN coated tool and its machining performance evaluation for milling difficult-to-machining materials under MQL conditions

In this study, the Si and Al contents in a coating composition were improved, and a new TiAlSiN-coated tool was fabricated using high-power pulsed magnetron sputtering (HiPIMS). For comparison purposes, four types of coated tools, typically used in the market, were selected to mill 304 stainless steel in a minimum quantity lubrication environment. To evaluate the machining performance of the tools, the criteria of tool wear, workpiece surface roughness, and milling force were considered. The machining performance of the TiAlSiN-coated tools remained stable for all four working conditions, and it had the smallest compound milling force and tool wear in the experiment. The primary wear forms of the tools were coating peeling, oxidation wear, and adhesive wear. Under working conditions 1 and 2, due to the lower initial surface friction coefficient and thermal barrier effect, the workpiece surface roughness of the TiN-coated tools was the smallest, followed by that of the TiAlSiN. However, under inadequate working conditions, because of the good wear resistance of the TiAlSiN coating, it was not rapidly worn. This resulted in a lower average friction coefficient during processing and the workpiece surface exhibited the minimum surface roughness. A comparative analysis of the processing state of the five coatings under four groups of parameters indicated that the TiAlSiN coating had good processing stability, wear resistance, and a low surface friction value. The TiAlSiN-coated tools had better machining performance than the other four commercial-coated tools for 304 stainless steel machining, especially under working conditions 3 and 4.

Prediction of OES intensity ratios based on coating unit data in HPPMS processes by ANN

High power pulse magnetron sputtering (HPPMS) processes are characterized by high peak powers and peak voltages. This results in a high fraction of ionized metal ions within the coating plasma. In order to analyze the correlations between parameters of the coating unit and the intensities of the excited and ionized plasma species, optical emission spectroscopy (OES) can be used. In those experiments, several process parameters are varied in a single coating process. Currently, the prediction of plasma parameters based on coating unit data follows deterministic models which cannot describe the complexity in total. Therefore, not all correlations can be fully understood. Artificial neural networks (ANN) can be used to identify correlations between process parameters and plasma species. This enables prediction of OES data based on data of the coating machine. In the present study different coating processes containing the elements Al, Cr, Ti, N and O were investigated. Current and voltages of the cathodes, substrate bias, chamber pressure, gas flows and the target compositions were used as input parameter of the ANN. Time resolved OES data of metal and gas species were used as output data. To determine the most appropriate training algorithm for the current predictions, multiple algorithms were employed. A good prediction accuracy of OES intensity ratios based on coating unit data for industrial scale coating processes for TiAlN was obtained. For CrAlON the prediction of the intensity ratios of the gas species showed good results. Nowadays a high amount of coating machine parameter variations in physical vapor deposition processes is needed in order to achieve tailored coating parameters. By using plasma diagnostics, such as OES, cost intensive coating deposition processes can be reduced significantly. A further shortening of process development time is possible by using ANN, since plasma compositions can be determined based on coating unit data.

Effect of Au Doping on ZnO Nanoporous Structure for H2S Gas Sensing

This research mainly constitutes the fabrication of semiconductor gas sensors using high Power pulse magnetron sputtering (HiPIMS) technology to deposit ZnO thin films. As a doping substance, different thicknesses of gold plating is deposited on the surface of ZnO thin films. Various thicknesses of gold used in the study are 3.3 nm, 6.6 nm, 10 nm, 13.3 nm and 16.6 nm. The structural properties of thin films were identified by X-ray- diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). EDS analysis conveyed that gold particles filled the pores of nanoporous ZnO structures, which increased the films surface area and enhancing the gas sensing response. Various concentrations of H2S gas is used to test the gas sensing properties and the results proved the Au doped ZnO thin film sensor has enhanced sensing than the pure ZnO thin film sensor. 10 nm thickness doped Au has prime sensing properties with the operating temperature of 300 °C. Other sensing properties such as repeatability, selectivity and effect of humidity are tested and presented the data which shows the Au doping ZnO superiority over pure ZnO thin films.

Machine learning based model for plasma prediction in high power pulsed magnetron sputtering processes

The coating development using physical vapor deposition (PVD) is time intensive and expensive. The coating processes are usually developed and improved based on the operator's experience. In order to improve the understanding of the processes during coating deposition, methods of plasma diagnostics can be used. However, this is time intensive and requires the installation of special diagnostics. The aim of the current study is to build a machine learning based model of PVD processes to predict the ionized to excited intensity ratio of the plasma species during the coating process. This enables a knowledge-based, cost-reduced process improvement. Based on measured data of different coating processes, the models were trained and tested in the current study. Therefore, a database was established by measuring process and plasma properties in hybrid processes of direct current magnetron sputtering and high power pulsed magnetron sputtering using an industrial coating unit. Different processes with variations of cathode powers and gas flows of the reactive gases oxygen and nitrogen were processed. The intensities of the ionized and excited species were measured using optical emission spectroscopy with six substrate side positioned collimators for spatial resolution to calculate the intensity ratios. The data was measured time resolved during the coating process. Compared to the measured data, the predictions show similar trends and values for the species within the coating chamber. The model was used to predict the influence of oxygen gas flow for CrAlON coating development. Furthermore, the models can be used for a more targeted process development. This can contribute to the application oriented adjustment of the coating processes and the coating properties.

Thermodynamic quasi-equilibria in high power magnetron discharges: a generalized Poisson–Boltzmann relation

The Poisson–Boltzmann (PB) equation is a nonlinear partial differential equation that describes the equilibria of conducting fluids. Using a thermodynamic variational principle based on the balances of particle number, entropy, and electromagnetic enthalpy, it can also be justified for a wide class of unmagnetized technological plasmas (Köhn et al 2021 Plasma Sources Sci. Technol. 30 105014). This study extends the variational principle and the resulting PB equation to high power magnetron discharges as used in planar high power pulsed magnetron sputtering. The example in focus is that of a circular high power magnetron. The discharge chamber and the magnetic field are assumed to be axisymmetric. The plasma dynamics need not share the symmetry. The domain is split into the ionization region close to the cathode where electrons are confined, i.e. can escape from their magnetic field lines only by slow processes such as drift and diffusion, and the outer region , where the electrons are largely free and the plasma is cold. With regard to the dynamics of the electrons and the electric field, a distinction is made between a fast thermodynamic and a slow dissipative temporal regime. The variational principle established for the thermodynamic regime is similar to its counterpart for unmagnetized plasmas but takes magnetic confinement explicitly into account by treating the infinitesimal flux tubes of as individual thermodynamic units. The obtained solutions satisfy a generalized PB relation and represent thermodynamic equilibria in the fast regime. However, in the slow regime, they must be interpreted as dissipative structures. The theoretical characterization of the dynamics is corroborated by experimental results on high power magnetrons published in the literature. These results are briefly discussed to provide additional support.