High Power Pulsed Magnetron Sputtering Research Articles

High power pulsed magnetron sputtering: a game changer or an overrated technology?

High power pulsed magnetron sputtering: a game changer or an overrated technology?

Influence of the deposition process and substrate on microstructure, phase composition, and residual stress state on as-deposited Cr-Al-C coatings

This paper focuses on the influence of the High Power Pulsed Magnetron Sputtering (HPPMS) and Direct Current Magnetron Sputtering (DCMS) coating deposition processes, the bias voltage, deposition temperature, and substrate on various properties of the as-deposited state of Cr-Al-C thin films. Three substrates with different coefficients of thermal expansion and electrical conductivity were used. To investigate the microstructure, phase composition, residual stress state, and mechanical properties, ex-situ and in situ synchrotron experiments were conducted accompanied by electron microscopy and nanoindentation. As-deposited Cr-Al-C coatings consisted of amorphous and crystalline areas, with the ratio highly dependent on the deposition process and substrate. The crystalline phase was identified as metastable (Cr,Al)2C. The highest crystallinity was determined for DCMS coatings. Increasing temperature and decreasing bias voltage increased coating crystallinity for HPPMS coatings. The influence of the deposition process and bias voltage was highly reduced for the substrate with low electrical conductivity. In-situ investigations of the stress state of amorphous areas revealed, that those were acting as a residual stress buffer. The hardness and Young’s modulus of the coatings were found to increase with crystallinity and were slightly increased for crystalline HPPMS coatings compared to DCMS coatings.

Influence of the deposition process on the Cr2AlC phase formation during heat treatment of Cr-Al-C thin films

This paper focuses on the Cr2AlC phase formation during annealing post-treatment, with amorphous Cr-Al-C and (Cr,Al)2C as initial phases in the as-deposited state. The influence of the deposition process on the Cr2AlC formation, texture, and phase composition is investigated and an in-depth discussion of the intermediate phase is carried out. Cr-Al-C thin films were deposited by Direct Current Magnetron Sputtering and High Power Pulsed Magnetron Sputtering with the variation of the deposition temperature. To investigate the microstructure, phase composition, and texture, in situ synchrotron and high-temperature X-ray diffraction experiments were conducted and accompanied by electron microscopy. The Cr2AlC formation can be described as a temperature and time-dependent process with one intermediate state characterized by the formation of the disordered-Cr2AlC phase. Disordered-Cr2AlC shows a similar unit cell to Cr2AlC with an increased c/a ratio. The ratio decreases during the phase formation resulting from an ordering process. Formation temperatures depend on the initial phase, with a decreased formation temperature for (Cr,Al)2C, and the deposition process. While the (002) fiber texture of (Cr,Al)2C inherited to Cr2AlC, Cr2AlC originated from amorphous Cr-Al-C showed no preferred orientation. The coatings contained Cr7C3 as an additional phase, dependent on the deposition process and initial phases.

Effect of the bias-graded increment on the tribological and electrochemical corrosion properties of DLC films

Diamond-like carbon (DLC) films with bias-graded increments of 5 V, 10 V, and 20 V were prepared by adjusting the substrate bias voltage in a high-power pulsed magnetron sputtering system (HPPMS). The microstructural, mechanical, tribological, and electrochemical corrosion properties of DLC films were systematically investigated. In this work, the sp 3 content in the DLC film with a constant bias of −200 V was the highest, and the sp 3 content in the bias-graded DLC film exhibited a gradient increasing trend. Bias-graded DLC films had lower hardness, elastic modulus and residual stress than DLC film with a constant bias of −200 V. With a decrease in bias-graded increment, the ratio of hardness to elastic modulus increased. Friction and wear tests demonstrated that the wear resistance of the DLC film was related to the hardness, residual stress and ratio of the hardness to the elastic modulus. The wear rate decreased with decreasing bias-graded increment, and the DLC film with a bias-graded increment of 5 V had the lowest friction coefficient and wear rate, which were 0.077 and 6.74 × 10 −7 mm 3 /Nm, respectively. The polarization curve results revealed that the DLC film with constant bias had the highest corrosion potential and corrosion current density. As the bias-graded increment increased, the corrosion potential and corrosion current density showed an increasing trend. Combined with the electrochemical impedance spectroscopy results, the bias-graded DLC films with bias-graded increments of 5 V and 10 V exhibited better corrosion resistances. • Bias-graded DLC films were prepared in HPPMS system. • Gradient structure achieved the balance between the residual stress and the content of sp 3 . • Coating DLC film can significantly improve the tribological and electrochemical corrosion properties of the substrate.

Adhesion Enhancement on a Duplex DLC HiPIMS Positive Pulse Coating Performed by Active Screen Plasma Nitriding Pretreatment on 316L Stainless Steel Substrate

Diamond-like carbon (DLC) coatings have been the object of research interest due to properties such as excellent wear resistance, low coefficient of friction, high hardness, high elastic modulus, and biocompatibility. Despite this, DLC has poor adhesion properties, which makes it challenging to use in industrial applications. The application of DLC using the high-power pulse magnetron sputtering (HiPIMS) technique with positive pulses has been studied. Seeking greater DLC coating adherence, the application of a nitriding pretreatment prior to the DLC coating has been studied to improve its adhesion to AISI316L stainless steel soft metal substrates, employing active screen plasma nitriding (ASPN). The influence of the different pretreatment temperatures to reach the maximum levels of adhesion has been analyzed. Scratch methods have been employed to assess adhesion. The elemental composition, morphology, and roughness of the samples have been studied, as well as the behavior of resistance to wear and friction. The results show an improvement in DCL adhesion. Critical loads (LC3) increase at higher pretreatment temperatures, from 48 N for the DLC to 82 N for the ASPN + DLC. Pretreatment has also been shown to be effective in maintaining excellent dry wear resistance properties and a low coefficient of friction.

Structure optimization of Spindt-type emitter fabricated by triode high power pulsed magnetron sputtering

Spindt-type emitters were fabricated with cavities made of Al/Mo/SiO2 using the triode high power pulsed magnetron sputtering method. We explored the process parameters (gas pressure and voltage of the additional cap electrode) to optimize the sharpness of the emitter shape. We found that the intermediate pressure and voltage were suited to obtain sharp emitters. Further, we elucidated the crucial effect of the cavity dimensions, such as the cavity depth and hole diameter in the cavity ceiling, on the emitter shape. At a cavity depth of 480 nm, the aspect ratio (AR) of the emitter increased monotonously with an increase in the hole diameter. With a large hole diameter (900 nm) and even shallower cavity (380 nm depth), we attempted to reoptimize the process parameters. Consequently, a very sharp emitter cone structure with an AR exceeding 1.3 was obtained. The cap voltage that produced the optimum AR was found to decrease for the larger-hole and shallower-depth cavities. Finally, the applicability of the process for preparing a working emitter is discussed.

DLC-Coated Thermoplastics: Tribological Analyses under Lubricated Rolling-Sliding Conditions

The goal of this work is to evaluate the potential of diamond-like carbon (DLC) coatings on thermoplastic polymers for friction and wear reduction in highly stressed rolling–sliding contacts. Therefore, hydrogen-containing DLC coatings were deposited on the polymer surface by a low-temperature high power pulsed magnetron sputtering (HPPMS) physical vapor deposition (PVD) process. The rolling-sliding contact between coated polyamide 66 (PA66) or coated polyether ether ketone (PEEK) against case-hardened steel 16MnCr5 is investigated in a twin-disk tribometer at normal loads up to FN = 1,000 N, sum velocities between 1 m/s ≤ vΣ ≤ 16 m/s and slip ratios up to s = 50%. Results show a friction reduction with the application of DLC on the considered polymers compared to uncoated polymers under specific lubrication conditions. High solid losses caused by the polymer’s internal damping properties dominate the temperature behavior of the polymer, even when coated with DLC. Regarding the wear behavior, DLC coatings show potential especially under severe mixed lubrication conditions with high-solid load portion and sliding. The knowledge gained about coated polymers can be used to improve the overall tribological performance in terms of friction and wear of thermoplastic machine elements like gears.

Effect of bias voltage on the structure and properties of CuNiTiNbCr dual-phase high entropy alloy films

The dual-phase structure has been proved to overcome the effect of strength-ductility trade-off of high-entropy alloys. However, most of the high entropy alloy films with larger atomic size difference tend to form a single amorphous structure under non-equilibrium deposition conditions such as magnetron sputtering. In this study, the dual-phase CuNiTiNbCr high entropy alloy film containing the Cu-rich FCC alloy phase and amorphous phase were synthesized by high-power pulsed magnetron sputtering at different bias voltages. The poor affinity of copper with other elements led to the segregation and enrichment of copper to form a Cu-rich FCC phase. The effects of substrate bias voltage on the microstructure, mechanical and corrosion properties of the films were investigated. With the increase of bias voltage, the content of copper in the film decreased, the stress state of the film changed significantly, and the compactness of the structure was improved. The hardness of all films was higher than that of most other high entropy alloy film systems. The films deposited under low bias voltage have better toughness. The film deposited at －50 V showed the best wear resistance due to a combination of high hardness and good toughness. The film deposited at －150 V showed the best corrosion resistance since it had the lowest self-corrosion current density (6.1 ×10−8 A/cm2), which was due to its compact structure and lower impurity content.

Oxidation stability of chromium aluminum oxynitride hard coatings

Hard coatings like CrAlN deposited by physical vapor deposition are state of the art for wear and oxidation protection of cutting tools. Conducting direct current magnetron sputtering (dcMS)/High power pulsed magnetron sputtering (HPPMS) hybrid processes combines the advantages of HPPMS, like denser structures and smoother surfaces, with the high deposition rates of dcMS. The current study aims to increase the aluminum content in the reaction layer of CrAlON coatings by incorporating oxygen in CrAlN and therefore achieve an enhanced oxidation stability. For this purpose, CrAlON coatings with different oxygen contents were deposited by dcMS/HPPMS hybrid processes. The morphology of the coatings was investigated by scanning electron microscopy. The chemical composition of the bulk was measured by electron probe micro analysis and of the reaction layer by X-ray photoelectron spectroscopy. The phase composition of the coatings was investigated by X-ray diffraction and the elastic-static properties by nanoindentation. Furthermore, the coated cemented carbide samples were heat treated at T = 900 °C and T = 1000 °C for t = 0.5 h in ambient atmosphere. A low oxygen content of x(O) = 6.9 at.% of the oxynitride coating increased the aluminum content of the reaction layer to x(Al) = 17.8 at.% compared to x(Al) = 8.5 at.% for the nitride coating and to x(Al) ≤ 9.6 at.% for the oxynitride coatings with higher oxygen contents of x(O) ≥ 18.2 at.%. As shown by XRD, this enhanced the oxidation stability of the coating with a low oxygen content of x(O) = 6.9 at.% from T = 900 °C to T ≥ 1000 °C for t = 0.5 h.

Enhanced tribological and corrosion properties of DLC/CrN multilayer films deposited by HPPMS

Diamond-like carbon (DLC)/CrN multilayer composite films with different modulation ratios were prepared by high power pulsed magnetron sputtering (HPPMS). The strengthening mechanism of tribological properties and corrosion resistance of multilayer DLC films were detailedly discussed. The results showed that the single layer DLC film peeled off after 25 min of friction, while the DLC/CrN multilayer films exhibited good wear resistance. The furrow phenomenon of wear track weaken, the depth of wear track decreased, and the wear resistance of the film enhanced with the increase of modulation ratio. The wear resistance of DLC film is directly related to its hardness, plastic deformation resistance and residual internal stress, and the DLC/CrN multilayer film with modulation ratio of 2:1 had the best wear resistance. Electrochemical experiments show that improving the density of the film, inhibiting the formation of corrosion ion diffusion channel and forming passive film at the interface are important factors to enhance the corrosion performance, and the DLC/CrN multilayer film with modulation ratio of 1:1 film had the best corrosion properties.

Deviations between film and target compositions induced by backscattered Ar during sputtering from M2-Al-C (M = Cr, Zr, and Hf) composite targets

M-Al-C (M = Cr, Zr, and Hf) thin films are deposited from stoichiometric M2AlC composite targets by direct current magnetron sputtering (DCMS) and high power pulsed magnetron sputtering (HPPMS) in an industrial coater. Using DCMS it is observed that the composition of the Cr-Al-C film is close to stoichiometric, while the Al concentration in the Zr-Al-C and Hf-Al-C films is significantly reduced compared to the Al concentration in the targets. It is evident that the magnitude of the difference in Al concentration between the target and the corresponding film composition is strongly dependent on the atomic mass of the transition metal. Zr and Hf atoms are 1.8 and 3.4 times heavier than Cr. In HPPMS, the target potential is approximately 1.6 times larger than that in DCMS, which can result in the film compositions deviating even stronger from the target composition as compared to DCMS. The Zr-Al-C thin film deposited by HPPMS exhibits a larger Al-deficiency than the film deposited by DCMS.The energy distributions of backscattered Ar neutrals are simulated by utilizing a two-body collision model and the Transport of Ions in Matter (TRIM) code. Based on the simulation results the experimentally observed Al-deficient film compositions can be readily explained: As the mass of the transition metal in the target is increased, both, energy and flux of the (at the target) reflected Ar is increased causing preferential re-sputtering of Al in the films. As stoichiometric compositions are a prerequisite for the formation of single-phase compound thin films it is evident that composite targets with a transition metal mass-dependent Al-overstoichiometry are required to compensate the Al-loss induced by the energetic Ar neutrals.

Effect of Negative Bias of HiPIMS and AIP Hybrid Deposition on Microstructure, Mechanical and Anti-Corrosive Properties of Cr2N/TiN Multilayer Coatings

Multi-layered nitride coatings have been widely applied to improve the mechanical and anti-corrosive of metals and/or alloys. Cr2N/TiN multilayer coatings were prepared by the combination of high-power pulsed magnetron sputtering (HiPIMS) and arc ion plating (AIP). The Cr2N layer was co-deposited by HiPIMS and AIP, while the TiN layer was deposited by a single HiPIMS. With increasing the negative bias voltage (Vs) on substrate up to −100 V, the number and size of the droplets decreased; the average grain size of the coatings decreased from 9.4 to 7.5 nm and the hardness increased from 21.5 to 25.1 GPa, and the level of the adhesion of the coatings has reached HF1. The coatings obtained at Vs = −100 V present the best corrosion resistance in NaCl aqueous solution based on the anodic polarization curves and EIS spectroscopy.

From cathode to substrate: Plasma diagnostics on high power pulsed magnetron sputtering deposition of titanium nitride

The present study focuses on an approach to measure the plasma properties from cathode to substrate parallel at three different positions in the coating chamber with activated substrate bias. High power pulsed magnetron sputtering is a powerful tool for the application in various coating systems with advantageous properties. For this reason it was investigated by countless studies during the last years. Several of these studies focusing on investigating the coating and plasma properties. Moreover, they investigated the plasma properties either at a high distance from the target or at different points in time at different chamber positions. The investigated positions were in front of the substrate, in front of the target and between both of them. After the plasma diagnostic measurements by optical emission spectroscopy, titanium nitride coatings were deposited. The coating thickness and deposition rate were investigated by scanning electron microscope. The indentation modulus EIT, the indentation hardness HIT as well as the plastic Wpl and elastic work Wel were investigated by nanoindentation. The chemical composition of the coatings was investigated by glow discharge optical emission spectroscopy (GDOES). For a pulse-on time ton variation of the cathode pulse, the relative deviation between the optical emission spectroscopy and GDOES results was determined for the different chamber positions. The best fit between the optical emission spectroscopy and GDOES results were found for the optical emission spectroscopy measurements conducted closest to the substrate. The present study shows that optical emission spectroscopy measurements close to the substrate are more suitable for the prediction of coating properties than optical emission spectroscopy measurements in front of the cathode.

Mechanical properties of amorphous and crystalline CrN/CrAlSiN multilayer coating fabricated using HPPMS

In this study, CrN/CrAlSiN multilayer coatings were prepared on Si wafer, high-speed steel and 304 stainless steel substrates via high-power pulsed magnetron sputtering with targets of metallurgical Cr30Al60Si10 and Cr. The structural characteristics of the coatings were modulated by performing deposition under a fixed rotation speed while varying the nitrogen-argon flow ratio. FE-SEM revealed that increasing the nitrogen content decreased the grain size and thickness of the coatings. GIXRD analysis revealed that the crystallinity of the multilayer changed from an amorphous phase to crystalline structures as a function of N2 gas flow conditions. Improvements were exhibited in the hardness (from 13.3 to 26.8 GPa) and Young's modulus (from 261 to 402.2 GPa) with a period of modulation of 12 nm and crystal transformations. The adhesion strength of the multilayer improved from 17.2 to 66.6 N.

A study of the phase transformation of low temperature deposited tantalum thin films using high power impulse magnetron sputtering and pulsed DC magnetron sputtering

In this study, tantalum thin films were deposited on silicon substrates using high power impulse magnetron sputtering (HiPIMS) and pulsed DC magnetron sputtering (pulsed DC), investigating the texture transformation behavior of α-Ta and β-Ta tantalum films by changing the duty cycle of tantalum targets from 5% to 88% at the power of 150 W and 50 W. The surface, microstructure, and texture of sputtered tantalum films were measured by scanning electron microscopy (SEM), atomic force microscope (AFM) and X-ray diffraction spectroscopy (XRD). The hardness and resistivity were measured by nanoindentation and a four-point probe. The results reveal that the impulse power and voltage of the Ta target were increased because of the lower duty cycle. The higher the ion energy, resulting in a more efficient atomic mobility, the texture phase of tantalum film gradually changes from β-Ta-dominated to α-Ta-dominated, hardness and resistivity shift from β-Ta to the α-Ta property with the decreasing duty cycle. By adjusting the duty cycle and controlling the power, the texture transformation of tantalum film occurs. Different from the previously complicated transformation process, the tantalum thin film structure with high density and high quality deposited using this approach provides a broader range of applications.

Ab initio-guided X-ray photoelectron spectroscopy quantification of Ti vacancies in [formula omitted] thin films

Ab initio calculations were employed to investigate the effect of oxygen concentration dependent Ti vacancies formation on the core electron binding energy shifts in cubic titanium oxynitride (Ti1−δOxN1−x). It was shown, that the presence of a Ti vacancy reduces the 1s core electron binding energy of the first N neighbors by ∼0.6 eV and that this effect is additive with respect to the number of vacancies. Hence it is predicted that the Ti vacancy concentration can be revealed from the intensity of the shifted components in the N 1s core spectra region. This notion was critically appraised by fitting the N 1s region obtained via X-ray photoelectron spectroscopy (XPS) measurements of Ti1−δOxN1−x thin films deposited by high power pulsed magnetron sputtering. A model to quantify the Ti vacancy concentration based on the intensity ratio between the N 1s signal components, corresponding to N atoms with locally different Ti vacancy concentration, was developed. Herein a random vacancy distribution was assumed and the influence of surface oxidation from atmospheric exposure after deposition was considered. The so estimated vacancy concentrations are consistent with a model calculating the vacancy concentration based on the O concentrations determined by elastic recoil detection analysis and text book oxidation states and hence electroneutrality. Thus, we have unequivocally established that the formation and population of Ti vacancies in cubic Ti1−δOxN1−x thin films can be quantified by XPS measurements from N 1s core electron binding energy shifts.

Ag Surface and Bulk Segregations in Sputtered ZrCuAlNi Metallic Glass Thin Films.

We report on the formation of Ag-containing ZrCuAlNi thin film metallic glass (nano)composites by a hybrid direct-current magnetron sputtering and high-power pulsed magnetron sputtering process. The effects of Ag content, substrate temperature and substrate bias potential on the phase formation and morphology of the nanocomposites were investigated. While applying a substrate bias potential did not strongly affect the morphological evolution of the films, the Ag content dictated the size and distribution of Ag surface segregations. The films deposited at low temperatures were characterized by strong surface segregations, formed by coalescence and Ostwald ripening, while the volume of the films remained featureless. At higher deposition temperature, elongated Ag segregations were observed in the bulk and a continuous Ag layer was formed at the surface as a result of thermally enhanced surface diffusion. While microstructural observations have allowed identifying both surface and bulk segregations, an indirect method for detecting the presence of Ag segregations is proposed, by measuring the electrical resistivity of the films.

Probing the onset of wurtzite phase formation in (V,Al)N thin films by transmission electron microscopy and atom probe tomography

Single-phase metastable cubic (V,Al)N thin films with columnar microstructure were grown by high power pulsed magnetron sputtering at 440 °C and the thermal decomposition mechanisms were systematically investigated by post-deposition vacuum annealing from 600 to 900 °C. The onset of spinodal decomposition into isostructural V- and Al-rich cubic nitride phases is demonstrated after cyclic vacuum annealing at 700 °C. Moreover, at this temperature, evidence for aluminum diffusion to grain boundaries and triple junctions is provided by correlation of transmission electron microscopy and atom probe tomography data. The formation of Al-rich regions can be understood by the more than 25% lower activation energy for bulk diffusion of aluminum compared to vanadium as obtained from ab initio calculations. It is reasonable to assume that these Al-rich regions are precursors for the formation of wurtzite AlN, which is unambiguously identified after annealing at 800 °C by microscopy and tomography. The significantly larger equilibrium volume of wurtzite AlN compared to the cubic phase explains its initial formation exclusively at triple junctions and grain boundaries. In contrast, twin boundaries are enriched in vanadium. Interestingly, the formation of the wurtzite phase at grain boundaries and triple junctions can be tracked by resistivity measurements, while X-ray diffraction and nanoindentation data do not support an unambiguous wurtzite phase formation claim for annealing temperatures <900 °C. Hence, it is evident that previously reported formation temperatures of wurtzite AlN in transition metal aluminum nitrides, determined by other characterization techniques than chemical and structural characterization at the nanometer scale and/or resistivity measurements, are overestimated.

Orientation dependence of the fracture mechanisms in (V,Al)N coatings determined by micropillar compression

Transition metal aluminium nitrides produced by physical vapour deposition are widely used as hard, protective coatings in the manufacturing industries. To optimise coatings wear resistance while maintaining fracture toughness, an understanding of the mechanisms linking the microstructure and the orientation-dependent fracture behaviour is required. (V,Al)N coatings were synthesised by direct current and high power pulsed magnetron sputtering. Uniaxial compression testing was performed using micropillars oriented between 0° and 90° with respect to the growth direction to assess the effect of microstructure on the fracture behaviour. We show here that different fracture mechanisms are active depending on the alignment of grains and loading direction. The fracture behaviour could be divided into three classes associated with column buckling, decohesion or shearing and no significant difference between the specimens induced by the deposition process could be observed.Graphical abstract

Microstructure, mechanical, and wettability properties of Al-doped diamond-like films deposited using a hybrid deposition technique: Bias voltage effects

In this study, Al-doped diamond-like carbon (DLC) films were prepared using a hybrid deposition technique combining high-power impulse magnetron sputtering and pulsed direct current magnetron sputtering. The influence of bias voltage effects on the microstructure and properties of films were investigated. The results showed that the deposition rate of the films decreased after increasing the bias voltage, and the Al content also slightly decreased in the films. All films exhibited a cauliflower-like surface morphology, which was independent of the bias voltage. The maximum values of sp2/sp3 and ID/IG were achieved without bias voltage; the ratios then monotonously decreased with an increase in the bias voltage from −100 V to −400 V, which indicates that the content of sp3-C bonds has improved in films. The mechanical properties and the wettability of the films were also evaluated. The results revealed that the hardness, elastic modulus and residual stress of the films increased with increasing bias voltage. The highest hardness occurred at −400 V, and the high sp3-C fraction and residual stress were beneficial to the hardness enhancement. All films exhibited a water contact angle greater than 100°, implying that the film possessed good hydrophobic performance. Specifically, when deposited at −300 V, the film presented a combination of superior properties, namely, a relatively high hardness and strong hydrophobic behavior.