Conventional Direct Current Magnetron Sputtering Research Articles

Structure and Mechanical Properties of Ti-Al-Ta-N Coatings Deposited by Direct Current and Middle-Frequency Magnetron Sputtering

Ti-Al-Ta-N coatings are characterized by attractive mechanical properties, thermal stability and oxidation resistance, which are superior to ternary compositions, such as Ti-Al-N. However, because of their open columnar microstructure, the Ti-Al-Ta-N coatings deposited by conventional direct current magnetron sputtering (DCMS) exhibit insufficient wear resistance. This work is focused on obtaining the Ti-Al-Ta-N coatings with improved microstructure and mechanical and tribological properties by middle-frequency magnetron sputtering (MFMS). The coatings are deposited by the co-sputtering of two separate targets (Ti-Al and Ta) using pure DCMS and MFMS modes as well as hybrid modes. It is found that the MFMS coating has a denser microstructure consisting of fragmented columnar grains interspersed with equiaxed grains and a smaller grain size than the DCMS coating, which is characterized by a fully columnar microstructure. The modification of the microstructure of the MFMS coating results in the simultaneous enhancement of its hardness, toughness and adhesion. As a result, the wear rate of the MFMS coating is less than half of that of the DCMS coating.

Radio-frequency magnetron sputter deposition of ultrathick boron carbide films

The deposition of thick B4C films with low residual stress by conventional direct-current magnetron sputtering is accompanied by the formation of dust particulates contaminating the target, chamber, and substrates and leading to the formation of nodular defects in films. Here, we demonstrate that the formation of particulates is greatly reduced during radio-frequency magnetron sputtering (RFMS). We systematically study properties of B4C films deposited by RFMS with a substrate temperature of 330 °C, a target-to-substrate distance of 10 cm, Ar working gas pressure in the range of 4.5–12.0 mTorr (0.6–1.6 Pa), and substrate tilt angles of 0°–80°. All films are x-ray amorphous. A columnar structure develops with increasing either Ar pressure or substrate tilt. For columnar films, the column tilt angle decreases with increasing Ar pressure, which we attribute to a corresponding increase in the width of the distribution of impact angles of deposition flux. In contrast to the Keller–Simmons rule, the deposition rate increases with increasing Ar pressure, which suggests a better coupling of the RF energy to the plasma processes that lead to target sputtering at higher pressures. There is a critical substrate tilt angle above which the total residual stress is close to zero. This critical substrate tilt angle is ∼0° for an Ar pressure of 12 mTorr (1.6 Pa). The lower residual stress state, necessary for depositing ultrathick films, is characterized by a larger concentration of nanoscale inhomogeneities and decreased mechanical properties. Based on these results, RFMS deposition of 60-μm-thick B4C films is demonstrated.

A-phase tantalum film deposition using bipolar high-power impulse magnetron sputtering technique

In this study, a method for forming a highly adhesive and ductile α-phase tantalum film on 304 stainless steel using the bipolar high-power impulse magnetron sputtering (bipolar HiPIMS) technique was investigated. The growth of brittle β-phase tantalum, which is commonly formed when using conventional direct current magnetron sputtering methods (DCMS) at room temperature, was prevented by the high-energy ions directed toward the growing films. The results showed the formation of an extremely thin (<70 nm) α-phase tantalum film without any additional processes, such as substrate biasing or heating. In addition, a high adhesion strength exceeding 45 MPa, broadened intermixed layer, and nanocrystalline microstructure were achieved by the effect of positive voltage. These results indicate that the bipolar HiPIMS technique is a facile deposition method for modifying the substrate surface and forming high-quality crystalline films. Our tantalum films are optimized to protect substrates against corrosion in severely harsh mechanical, chemical, and thermal environments. To confirm the superiority of the bipolar HiPIMS technique over HiPIMS and DCMS, the properties of the films formed using the three methods were analyzed via X-ray diffraction, Auger electron spectroscopy, atomic force microscopy, scanning electron microscopy, and pull-off adhesion testing.

Enhanced Electrical Properties of Copper Nitride Films Deposited via High Power Impulse Magnetron Sputtering.

High Power Impulse Magnetron Sputtering (HiPIMS) has generated a great deal of interest by offering significant advantages such as high target ionization rate, high plasma density, and the smooth surface of the sputtered films. This study discusses the deposition of copper nitride thin films via HiPIMS at different deposition pressures and then examines the impact of the deposition pressure on the structural and electrical properties of Cu3N films. At low deposition pressure, Cu-rich Cu3N films were obtained, which results in the n-type semiconductor behavior of the films. When the deposition pressure is increased to above 15 mtorr, Cu3N phase forms, leading to a change in the conductivity type of the film from n-type to p-type. According to our analysis, the Cu3N film deposited at 15 mtorr shows p-type conduction with the lowest resistivity of 0.024 Ω·cm and the highest carrier concentration of 1.43 × 1020 cm−3. Furthermore, compared to the properties of Cu3N films deposited via conventional direct current magnetron sputtering (DCMS), the films deposited via HiPIMS show better conductivity due to the higher ionization rate of HiPIMS. These results enhance the potential of Cu3N films’ use in smart futuristic devices such as photodetection, photovoltaic absorbers, lithium-ion batteries, etc.

XANES and XRR study on phase evolution of TiO2 films developed using HiPIMS

High power impulse magnetron sputtering (HiPIMS) is one of the recent advanced techniques for the development of high quality TiO2 thin films. Due to the formation of high energetic ions in the discharge, HiPIMS can produce various crystalline phases of TiO2 (anatase and rutile) with low roughness as compared to conventional direct current magnetron sputtering (DCMS). This work emphasizes on the effect of oxygen partial pressure in the evolution of phases and oxidation states of TiO2 films deposited using HiPIMS along with a comparative study against DCMS grown films under similar oxygen environment. TiO2 thin films were prepared with DCMS and HiPIMS, as a function of oxygen content in the sputter gas flow. Thickness, density and roughness were calculated using XRR fitting and analysis. It was observed that HiPIMS deposited films were smoother and denser than DCMS grown films. Crystallite sizes of HiPIMS deposited films were significantly lower than DCMS. Phase growth analyses were performed using X-ray diffraction (XRD), Raman and XANES (X-ray absorption near-edge spectroscopy of the Ti L2,3 and O K-edges) spectroscopy. In HiPIMS grown films, the increase in O2 partial pressure changed the phase from rutile to mixed and then to anatase phase whereas only rutile and mixed phases were detected in DCMS grown film under similar oxygen environment. HiPIMS developed films were smooth, uniform free from cracks as observed in FESEM and Atomic Force microscope (AFM) morphological images. Lognormal crystallite size distribution values decreased with increasing O2 partial pressure. Crystal field splitting values of (Δo) between ∼1.9 and 2.2 eV indicate crystalline phase formation by XANES Ti L2,3-edge analysis. These findings point to better crystalline growth TiO2 thin films as compared to DC-MS. HiPIMS grown films shows phase transformation of rutile into mix phase and anatase with increase in oxygen partial pressure.

Bipolar high‐power impulse magnetron sputtering synthesis of high‐entropy carbides

AbstractIn this study, we report high‐entropy carbides synthesis with reactive bipolar high‐power impulse magnetron sputtering (HiPIMS). Uncontrolled microstructure and stoichiometry development with reactive gas flow rate are major limitations of conventional direct current (DC) and radio frequency (RF) magnetron sputtering of multicomponent carbides. With HiPIMS these chemically disordered crystals structurally and compositionally transform from a carbon‐deficient metallic (C/M &lt; 1), to a stoichiometric ceramic zone (C/M ∼ 1), and to a nanocomposite embodiment (C/M &gt; 1), as a function of the carbon content during HiPIMS deposition. X‐ray diffraction, X‐ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and nanoindentation hardness measurements are combined to demonstrate the three regions of synthesis domain. HiPIMS provides access to metallic, ceramic, and composite carbides with great control over the microstructure and stoichiometry, which is elusive in case of conventional DC and RF magnetron sputtering. Notably, the stoichiometric ceramic zone maintains a constant carbon to metal ratio (C/M ∼ 1) over an extended amount of methane flow before transitioning to a nanocomposite microstructure (C/M &gt; 1). The transition zone breadth depends on materials affinity for carbon that correlates with valence electron concentration (VEC). As such, synthesis conditions for new high‐entropy carbides can be understood and predicted based on VEC.

Microstructure of titanium coatings controlled by pulse sequence in multipulse HiPIMS

The deposition rate, as well as the structure of a coating for a given magnetron sputtered material are determined by the plasma properties which are significantly dependent on the type of plasma generation. Single-pulse high power impulse magnetron sputtering (s-HiPIMS), multipulse HiPIMS (m-HiPIMS) with the same energy per pulse sequence and conventional direct current magnetron sputtering (DC-MS) were employed to deposit metallic Ti coatings. Varying the number of pulses in one pulse sequence in multipulse HiPIMS operation enables us to influence the ion fluxes on the substrate and the ionisation of the sputtered titanium. The grain size for the HiPIMS-deposited coatings was in the range of 5 to 25 nm depending on the number of pulses in the pulse sequence, whereas it was 15 nm for the coating prepared by the DC-MS. By the use of multipulse HiPIMS, it was also possible to achieve coatings with a smoother surface morphology and lower roughness as well rougher coatings with larger asperities and higher roughness compared to DC-MS. The texture and the deposition rate were significantly affected by the number of pulses, too.

Wear Behavior and Machining Performance of TiAlSiN-Coated Tools Obtained by dc MS and HiPIMS: A Comparative Study.

Duplex stainless steels are being used on applications that require high corrosion resistance and excellent mechanical properties, such as the naval and oil-gas exploration industry. The components employed in these industries are usually obtained by machining; however, these alloys have low machinability when compared to conventional stainless steels, usually requiring the employment of tool coatings. In the present work, a comparative study of TiAlSiN coating performance obtained by these two techniques in the milling of duplex stainless-steel alloy LDX 2101 was carried out. These coatings were obtained by the conventional direct current magnetron sputtering (dc MS) and the novel high power impulse magnetron sputtering (HiPIMS). The coatings were analyzed and characterized, determining mechanical properties for both coatings, registering slightly higher mechanical properties for the HiPIMS-obtained coating. Machining tests were performed with varying cutting length and feed-rate, while maintaining constant values for axial and radial depth of cut and cutting speed. The surface roughness of the material after machining was assessed, as well as the wear sustained by each of the tool types, identifying the wear mechanisms and behavior of these tools, as well as registering the flank wear values presented for each of the tested tools. The HiPIMS-obtained coating exhibited a very similar behavior when compared to the other, producing similar surface roughness quality. However, the HiPIMS coating exhibited less wear for higher cutting lengths, proving to be a better choice in this case, especially regarding tool life.

On the relationship between the plasma characteristics, the microstructure and the optical properties of reactively sputtered TiO2 thin films

A titanium target was reactively sputtered in an Ar/O2 atmosphere by (i) conventional direct current magnetron sputtering (DCMS), (ii) high-power impulse magnetron sputtering (HiPIMS), and (iii) bipolar HiPIMS (BPH) discharges for the deposition of titanium dioxide thin films without intentional heating and biasing. In the HiPIMS and BPH cases, the peak current density was set to either 0.32 A cm−2 or 0.86 A cm−2. The time-averaged power density delivered to the plasma was set to ≈1.2 W cm−2 in each case. For the BPH discharge, a positive pulse of +300 V was applied after the negative pulse to accelerate the positive ions toward the substrate. Energy-resolved mass spectrometry analysis has shown a low-energy peak for DCMS while a high energy tail extending in the range of several tens of eV was observed with HiPIMS. In the BPH discharge, the energy reached ≈300 eV for Ti+ ions, which is in agreement with the applied positive potential. According to the x-ray diffraction patterns, amorphous coatings were obtained with DCMS, while rutile TiO2 was obtained with both HiPIMS and BPH. However, in the BPH case, diffractograms were characterized by more intense high-angle diffraction peaks highlighting a modification of the growth process for these conditions. Rutherford backscattering spectrometry analysis has shown that a higher amount of argon atoms were incorporated into the TiO2 films which are found to be slightly understoichiometric for the BPH discharge. It was also found that the refractive index, n, varied as a function of the sputtering regime with the highest value obtained in the HiPIMS case (n = 2.73 at 550 nm). Finally, the experimentally determined optical data were compared to the ones extracted from NASCAM simulations which are found in good agreement except for the BPH case.

Mechanical Properties and Diffusion Barrier Performance of CrWN Coatings Fabricated through Hybrid HiPIMS/RFMS

CrWN coatings were fabricated through a hybrid high-power impulse magnetron sputtering/radio-frequency magnetron sputtering technique. The phase structures, mechanical properties, and tribological characteristics of CrWN coatings prepared with various nitrogen flow ratios (fN2s) were investigated. The results indicated that the CrWN coatings prepared at fN2 levels of 0.1 and 0.2 exhibited a Cr2N phase, whereas the coatings prepared at fN2 levels of 0.3 and 0.4 exhibited a CrN phase. These CrWN coatings exhibited hardness values of 16.7–20.2 GPa and Young’s modulus levels of 268–296 GPa, which indicated higher mechanical properties than those of coatings with similar residual stresses prepared through conventional direct current magnetron sputtering. Face-centered cubic (fcc) Cr51W2N47 coatings with a residual stress of −0.53 GPa exhibited the highest wear and scratch resistance. Furthermore, the diffusion barrier performance of fcc CrWN films on Cu metallization was explored, and they exhibited excellent barrier characteristics up to 650 °C.

Role of energetic ions in the growth of fcc and ω crystalline phases in Ti films deposited by HiPIMS

In this work, we show how to control the nucleation of fcc and hexagonal (ω) crystalline phases in Ti films by adding a proper Ti ion flux to the film-forming species. To this aim, films with different thicknesses are grown by High Power Impulse Magnetron Sputtering (HiPIMS) and conventional Direct Current Magnetron Sputtering (DCMS) as a reference. HiPIMS depositions with different substrate bias voltage US (0 V, −300 V and −500 V) are performed to investigate different ion energy ranges. Microstructure, morphology and residual stress of the deposited films, as well as the DCMS and HiPIMS plasma composition, are analysed with different characterization techniques. The DCMS samples, where the species are mostly atoms, exhibit the Ti α-phase only. As far as HiPIMS samples are concerned, films deposited in low energy ion conditions (US = 0 V) show the presence of the Ti fcc phase up to a maximum thickness of about 370 nm. Differently, films deposited under high energy conditions (US = −300 V and −500 V) show the nucleation of the Ti ω-phase for thicknesses greater than 260 and 330 nm, respectively. The formation of these unusual Ti phases is discussed considering the different deposition conditions.

ZrCuAlNi thin film metallic glass grown by high power impulse and direct current magnetron sputtering

Abstract High-power impulse magnetron sputtering (HiPIMS) is a thin film deposition technique that combines the advantages of energetic deposition methods with magnetron sputtering. HiPIMS has so far mostly been utilized for the growth of crystalline coatings. Here we offer a study devoted to metallic glasses, in which we compare Zr60Cu25Al10Ni5 (target composition) thin films deposited by conventional direct current magnetron sputtering (DC) and HiPIMS. Film microstructure is strongly dependent on the choice of the sputtering method. The DC layers show a columnar structure with intra-columnar porosity, which provides a pathway for oxygen diffusion into the film. In contrast, HiPIMS films are column-free and possess about 4% higher density, as revealed by X-ray reflectivity. Electron diffraction reveals a decrease in average atomic spacing for the latter film of about 12%. These differences in film properties and morphology can be attributed to an increase in ad-atom mobility during HiPIMS caused by an increase in ion energy and flux of the film-forming species enabling a more efficient energy and momentum transfer to the growing film surface. The relative contribution of metallic and hence film forming ions to the overall ion flux of the DC plasma compared to the HiPIMS plasma is 13% and 96%, respectively. Additionally, a substrate bias causes the ionized film forming species during HiPIMS to arrive close to the substrate normal reducing shadowing effects. Different microstructures have a direct effect on the average roughness values, which for DC and HiPIMS films are 1.4 nm and 0.2 nm, respectively. The indentation hardness H and Young's modulus E are higher for the HiPIMS sample, at 9.2 ± 0.3 GPa and 131.6 ± 3.6 GPa, respectively. The increase in hardness for the HiPIMS sample as compared to the DC sample (~35%) can be attributed to higher film density, compressive (HiPIMS) as opposed to tensile (DC) stress and the lack of a columnar structure.

Experimental evaluation of direct current magnetron sputtered and high-power impulse magnetron sputtered Cr coatings on SiC for light water reactor applications

Two types of physical vapor deposition Cr coatings were deposited on chemical vapor deposited SiC coupons using conventional direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) to mitigate the corrosion of SiC, an advanced fuel and structural material in light water nuclear reactor cores. Coating microstructure was characterized using scanning electron microscopy and scanning transmission election microscopy. X-ray diffraction analysis was conducted for phase identification and qualitative analysis of residual stresses. The mechanical integrity of the coatings was evaluated using scratch testing, micro-indentation, and nano-indentation tests. The microstructure of the DCMS coating consisted of fine columnar grains with nanoscale intercolumnar channels, while the HiPIMS microstructure was denser and free of any columnar defects. The DCMS coating showed a small tensile residual stress, while the HiPIMS coating was under compressive stress. Both types of coatings showed good mechanical integrity in terms of ductility and adhesion to the substrate. Corrosion performance of the coatings was assessed with a 30-day high temperature water autoclave test. Both types of coatings formed a protective Cr2O3 surface layer 20-30 nm thick during the autoclave test. In the DCMS coating, the columnar defects provided permeation pathways for water penetration resulting in oxide formation in the intercolumnar regions in the interior of the coating. Overall, both types of Cr coatings offer promise for the mitigation of hydrothermal corrosion of SiC in light water reactor operating environments.

Role of Energetic Ions in the Growth of fcc and ω Crystalline Phases in Ti Films Deposited by HiPIMS

Titanium (Ti), due to its excellent properties, is widely exploited in thin film technology that usually leads to the production of hcp (α-phase) Ti films. In this work, we show how to control the nucleation of fcc and hexagonal (ω-phase) crystalline phases in Ti films by adding a proper Ti ion flux to the film-forming species. To this aim, films with different thicknesses are grown by High Power Impulse Magnetron Sputtering (HiPIMS) and conventional Direct Current Magnetron Sputtering (DCMS) as a reference. Furthermore, HiPIMS depositions with different substrate bias voltage Us(0 V, -300 V and -500 V) are performed to investigate different ion energy ranges. Microstructure, morphology and residual stress of the deposited films, as well as the DCMS and HiPIMS plasma composition, are analysed with different characterization techniques. The DCMS samples, where the species are mostly atoms, exhibit the Ti α-phase only and show a tensile residual stress decreasing with thickness. As far as HiPIMS samples are concerned, films deposited in low energy ion conditions (Us=0 V) show the presence of the Ti fcc phase up to a maximum thickness of about 370 nm. Differently, films deposited under high energy conditions (Us= -300 V and -500 V) show the nucleation of the Ti ω-phase for thicknesses greater than 260 and 330 nm, respectively. A compressive-tensile-compressive (CTC) behavior is observed for residual stresses as thickness increases. The formation of these unusual Ti phases is discussed considering the different deposition conditions.

Multi-objective optimization of Pulsed direct current magnetron sputtered titanium nitride thin film using Grey relational analysis

Titanium nitride coatings are extensively adopted as an intermediate adhesion layer in the cutting tools because of its superior mechanical properties. The interdependence of each process parameter during the deposition of such a coating process is nonlinear, and hence, it becomes a challenge to determine the output responses without carrying out a wide range of experiments. So to minimize the experiments, Taguchi-based L9 design of experiments were employed in this study with three factors and three levels such as Argon (Ar): Nitrogen (N2) gas mixture, Pulsed direct current power, and deposition time for depositing titanium nitride thin films on silicon (100) and tungsten carbide substrates using Pulsed direct current magnetron sputtering technique, where conventional direct current magnetron sputtering cannot be deployed using titanium nitride target. Multiple output responses such as average thickness, surface roughness, nano-hardness, Young’s modulus, wear track deformation, and coefficient of friction were measured by carrying out the systematic investigations, and a single optimum solution was obtained using Grey relational analysis. From the Grey relational analysis, the optimum Ar:N2 gas flow mixture, Pulsed direct current power, and deposition time for improved titanium nitride adhesion layer are 300 W, 10:5 sccm, and 5 min, respectively. Further, grazing incidence x-ray diffractometer profiles of deposited films exhibits (111) and (200) reflections corresponding to the titanium nitride phase, and the morphological analysis also revealed the existence of strongly faceted nano-grains with a triangular-shaped morphology.

Rational construction of porous amorphous WO3 nanostructures with high electrochromic energy storage performance: Effect of temperature

Compared to conventional direct current (DC) and radio frequency (RF) magnetron sputtering, the pulsed radio frequency (PRF) magnetron sputtering circumvents the obstacle of a self-annealing temperature effect during the deposition, which may induce irregular crystallization or uneven chemical composition. The porous homogeneous amorphous WO3 film prepared by the PRF magnetron sputtering shows large dual-band optical modulation in the visible and near infrared regions(93.6% in 633 nm and 90.6% in 1500 nm), short response time(3.2s for coloring and 5.6s for bleaching), decent coloration efficiency(56.8 cm2C−1) and superior cycling stability(the optical modulation is dropped by 4.3% after 2000 cycles). In addition, the PRF WO3 film also presents good energy-storage properties (44.0 mF/cm2 areal capacitance), good capacitive cyclic stability without apparent capacitance loss after 2000 cycles and superior rate capability. The obtained bi-functional porous amorphous WO3 film may find great potential in constructing high efficiency electrochromic energy storage and other intelligent nanodevices.

Obtaining SiGe nanocrystallites between crystalline TiO2 layers by HiPIMS without annealing

Formation of SiGe nanocrystals in an oxide matrix via deposition and subsequent annealing is a widely applied approach as it gives good control over optical properties by varying the Ge atomic fraction, the size, shape and crystallinity of the nanocrystals. A common drawback of annealing is a strain relaxation in the structure creating dislocations, point defects, dangling bonds, Ge clustering and altered interface morphology. All these phenomena are well-known to degrade the optoelectronic and electrical properties of the structure. As a proof of concept, in this study we have utilized a modern technique of high impulse power magnetron sputtering (HiPIMS) to obtain a crystalline TiO2/SiGe/TiO2 structure without any pre-/post-annealing. It is furthermore demonstrated how a control of the nano-crystallite size is obtained by altering the HiPIMS discharge power alone. Grazing incidence X-ray diffraction analysis was carried out for the structural characterization, while photocurrent measurements were utilized to access the role of TiO2 structural morphology over interface integrity in determining spectral feature and sensitivity. An increase of 1 – 2 orders magnitude in spectral intensity was achieved for as-grown structures fabricated via HiPIMS in comparison to annealed structure, sputtered with conventional direct current magnetron sputtering.

Effect of interfacial interdiffusion on magnetism in epitaxial Fe4N films on LaAlO3 substrates

Epitaxial Fe4N thin films grown on lattice-matched LaAlO3 (LAO) substrate using sputtering and molecular beam epitaxy techniques have been studied in this work. Within the sputtering process, films were grown with conventional direct current magnetron sputtering (dcMS) and for the first time, using a high power impulse magnetron sputtering (HiPIMS) process. Surface morphology and depth profile reveal that HiPIMS deposited film has the lowest roughness, the highest packing density and the sharpest interface. La from the LAO substrate and Fe from the film interdiffuse and forms an undesired interface spreading to an extent of about 10-20 nm. In the HiPIMS process, layer by layer type growth leads to a globular microstructure which restricts the extent of the interdiffused interface. Such substrate-film interactions and microstructure play a vital role in affecting the electronic hybridization and magnetic properties of Fe4N films. The magnetic moment (Ms) was compared using bulk, element-specific and magnetic depth profiling techniques. We found that Ms was the highest when the thickness of the interdiffused layer was lowest and only be achieved in the HiPIMS grown samples. Presence of small moment at the N site was also evidenced by element-specific x-ray circular dichroism measurement in HiPIMS grown sample. A large variation in the Ms values of Fe4N found in the experimental works carried out so far could be due to such interdiffused layer which is generally not expected to form in otherwise stable oxide substrate. In addition, a consequence of substrate-film interdiffusion and microstructure results in different kinds of different kind of magnetic anisotropies in films grown using different techniques.

Differences in surface reactivity in two synthetic routes between HiPIMS and DC magnetron sputtered carbon

Diamond-like carbon (DLC) is an amorphous form of carbon with a significant fraction of sp3 bonds. In general, it enjoys high hardness, chemical inertness, and optical transparency. It can be deposited by various chemical (CVD) and physical (PVD) vapor deposition methods, including sputtering, which is an industrially important PVD method. Here we investigate the reactivity of carbon deposited by conventional direct current magnetron sputtering (DCMS) and by the newer high power impulse magnetron sputtering (HiPIMS). Scanning electron microscopy (SEM) showed that HiPIMS produced more compact films. Both types of carbon films were very smooth by atomic force microscopy (AFM): for HiPIMS: 1.20 ± 0.55 nm and for DCMS: 1.55 ± 0.27 nm. X-ray photoelectron spectroscopy (XPS) revealed chemical differences between the two types of carbon surfaces. Two functionalization schemes were investigated. The first consisted of amidation of the surfaces by activation with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy sulfosuccinamide (sulfo-NHS) followed by reaction with a range of water-soluble and insoluble amines, and the second consisted of activation via halogenation with PCl5 or PBr5 followed by subsequent amination. The resulting surfaces were characterized by XPS and wetting. HiPIMS-deposited carbon showed higher levels of amidation. On the other hand, the DCMS surface showed greater functionalization in the halogenation/amination route. These results are consistent with the higher level of oxidized carbon initially found on the HiPIMS surface.

Evaluation of DC-MS and HiPIMS TiB2 and TaN coatings as diffusion barriers against molten aluminum: An insight into the wetting mechanism

TaN and TiB2 ceramic coatings on steel were tested as barriers to protect steel against molten aluminum by sessile drop experiments. Coatings tested were deposited by PVD using conventional DC-MS (Direct Current Magnetron Sputtering) and HiPIMS (High-Power Impulse Magnetron Sputtering) techniques. The evolution of contact angle and contact radius of the molten aluminum drop was recorded at 800 °C for H13 tool steel bare and coated samples. The influence of the thickness and microstructure of the coatings was investigated by XRD, SEM/EDS to elucidate the mechanism of the wetting process. Spreading rate of aluminum on coated samples was between 10 and 50 times slower than on bare steel samples. Coated samples showed reactive wettability with a reaction-controlled spreading stage observed as a constant spreading rate after an initial transient stage. The spreading mechanism of the molten metal on coated samples is a two-step mechanism: (i) molten metal infiltration through the coatings and (ii) fracture of the coating after the formation of Fe-Al intermetallic compounds that leads to an increased volume of the metallic substrate. The quantification of both steps proves that the coating's thickness plays a key role in the reactive wettability kinetics. Results show that HiPIMS deposited TaN coatings could be a promising candidate to protect steels against molten aluminum attack.