Effects of sputtering power on mechanical properties of Cr films deposited by magnetron sputtering

Abstract

Chromium (Cr) films were deposited on plain carbon steel sheets by dc and rf magnetron sputtering as well as by electroplating. Effects of dc or rf sputtering power on the deposition rate and properties such as, hardness, adhesion strength, surface roughness and corrosion resistance of the Cr films were investigated. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microcopy (SEM) analyses were performed to investigate the crystal structure, surface roughness, thickness of the Cr films. Salt fog tests were used to evaluate the corrosion resistance of the samples. The deposition rate, hardness and surface roughness of the Cr film deposited by either dc or rf sputtering increase with the increase in sputtering power but the adhesion strength is nearly independent of the sputtering power. The deposition rate, hardness and adhesion strength of the Cr film deposited by dc sputtering are higher than those of the Cr film deposited by rf sputtering, but rf sputtering offers smoother surface and higher corrosion resistance. The sputter deposited Cr film is harder and has a smoother surface than the electroplated one. The sputter deposited Cr film also has higher corrosion resistance than the electroplated one, which may be attributed to the smoother surface of the sputter deposited film.     

Microstructures and corrosion behaviors of Zr modified CrN coatings deposited by DC magnetron sputtering

Zirconium modified chromium nitride coatings with various Zr contents have been prepared by a DC reactive magnetron sputtering technique. The detailed investigations in terms of composition, phase structure, morphology and corrosion properties have been performed by GDOES, XRD, SEM and electrochemical measurements, respectively. The as-deposited coatings with Zr contents ranging from 0 to 3.2 at. % form nanocrystalline solid solutions, where Zr substitute Cr in the CrN lattice. With increasing Zr contents, the lattice parameters increase but the grain sizes show little effects. All the coatings exhibit dense compact columnar structures in SEM cross-sectional observations. Electrochemical measurements in 3.5% NaCl solutions revealed that the additions of Zr into CrN coatings improved their chemical inertness. The coated samples with much low corrosion current densities in nA/cm² range show their excellent protective characteristics to the stainless steel substrates. The corrosion mechanism, however, was due to the slight pitting corrosions, which were mainly localized in the growth defects.     

Topography and microstructure of Cu-Sn coatings deposited by magnetron sputtering

The topographical and microstructural features of Cu-Sn coatings deposited by magnetron sputtering using alloy target of Cu-7.8%Sn and Cu-74%Sn onto ferritic stainless steel substrates with a temperature gradient were investigated by means of optical and scanning electron microscopy.Depending on the substrate temperature the alloy film forms by a vapour → solid process or a vapour → liquid process with solidification after substrate cooling. In between a mixed mechanism of vapour → liquid → solid occurs during condensation in the temperature ranges 990–1170 K and 460–790 K for coatings deposited by sputtering of Cu-7.8%Sn and Cu-74%Sn targets respectively.The copper-rich condensate formed in the temperature range 370–1220 K consists of a single-phase α solid solution of tin in copper. Its lattice parameter decreases with increasing temperature mainly because of the decreasing tin content.The film obtained by sputtering a Cu-74%Sn target has a two-phase η′-Cu₆Sn₅ plus tin structure independently of the deposition temperature.     

Oxidation behavior of Ti-B-C-N coatings deposited by reactive magnetron sputtering

Quaternary Ti-B-C-N coatings with different carbon concentrations are deposited on high-speed steel substrates by reactive magnetron sputtering. The oxidation behavior between 300 and 800 °C under ambient conditions is studied by scanning electron microscopy, high-resolution transmission electron microscopy, Vickers micro-hardness, and X-ray diffraction. The Ti-B-C-N coatings with smaller carbon contents have better oxidation resistance and the oxidation process can be divided into two stages: low-speed oxidation below 700 °C and high-speed oxidation above 700 °C. An oxidation mechanism is proposed to explain the relationship between the reaction with oxygen and observed oxidation behavior.     

Electrochemical behaviour of chromium nitride coatings with various preferred orientations deposited on steel by unbalanced magnetron sputtering

Abstract

Chromium nitride coatings Cr₂N(111) and preferred orientations of CrN(111) and CrN(200) were successfully deposited on AISI 304 stainless steel by an unbalanced magnetron sputtering method. The electrochemical corrosion properties of the deposited films were studied in a 0·5M H₂SO₄ + 1M NaCl aqueous solution at ambient temperature by electrochemical measurements, including the corrosion potential E _corr, linear polarisation, potentiodynamic polarisation and electrochemical impedance spectroscopy. The structural characterisation and surface morphology were investigated using X-ray diffraction, scanning electron microscopy and atomic force microscopy. The experimental results indicated that the CrN(200) coating possesses the best corrosion resistance property, followed by the CrN(111) coating, while the Cr₂N coating has the least resistance among the three types of CrN(111), CrN(200) and Cr₂N(111) coatings. The porosity, corresponding to the ratio of the polarisation resistance of the uncoated and the coated substrates, was higher in the Cr₂N(111) coating than in the other CrN coatings. The CrN(200) coating had a dense microstructure almost without porosity. The void defects of CrN(111) and Cr₂N(111) coatings are responsible for the decrease in corrosion protection.     

Comparison of chromium nitride coatings deposited by DC and RF magnetron sputtering

Chromium nitride coatings were deposited by DC and RF reactive magnetron sputtering on AISI 304 stainless steels without substrate heating. A Cr₂N phase was formed in the RF sputtered coatings with a low N₂ flow content ranging within 30-50%. A NaCl type CrN_x phase was obtained by DC magnetron sputtering with different N₂ flow contents. The coating hardness increased with the increase of the N₂ flow content. When the coatings deposited with the same N₂ flow content were compared, the hardness of the RF sputtered CrN_x was higher than that of the DC sputtered CrN_x, which was mainly due to the distinct difference between the dense structure (RF process) and the porous structure (DC process). The RF sputtered CrN_x coatings showed an excellent adhesion strength as compared to the DC sputtered coatings. By selecting the deposition method and optimizing the N₂ flow content, CrN_x coatings with a preferred microstructure could be obtained, which would be a candidate material for research and applications in nano-science.     

The effects of pulse frequency and substrate bias to the mechanical properties of CrN coatings deposited by pulsed DC magnetron sputtering

The chromium nitride coatings have been prepared by the bipolar symmetric pulsed DC magnetron reactive sputtering process at 2 kHz and 20 kHz pulse frequencies, respectively. Different substrate bias was applied with a pulsed DC bias unit with 50 kHz pulse frequency. Oscilloscope traces of the I–V waveforms indicate high power and high current density outputs during the symmetric bipolar pulsed mode. It is concluded that the (200) orientation of CrN films is observed. The grain size decreases with increasing pulse frequency and substrate bias. The substrate bias has a strong influence on the mechanical properties of CrN films. The scratch tests of the CrN coatings show that almost only tiny chipping failure is occurred. Sufficient adhesion strength quality of the coating is also observed. The substrate bias for the deposition of CrN films with sufficient hardness and adhesion properties combination is − 290 V at 20 kHz and − 408 V at 2 kHz pulse frequency, respectively.     

Microstructure and mechanical properties of austempered AISI 9255 high-silicon steel

The present investigation is focused on evaluating the microstructure and mechanical properties of American Iron and Steel Institute 9255 high-silicon steel austempered at different temperatures and durations. Material characterisation was done using a scanning electron microscope and an X-ray diffractometer. Results show the bainite microstructure over a temperature range of 280–400°C. Bainite structure gains coarseness at higher temperatures at 360 and 400°C. A significant improvement in the tensile properties was observed for all austempered specimens; with a maximum tensile strength of 1852?MPa and elongation up to 35%. An excellent strain hardening response was observed from the samples austempered at temperatures of 360 and 400°C. Tensile properties were found to be superior at 15?min of austempering duration for all austempering temperatures.     

Corrosion behaviour of decorative and wear resistant coatings on steel deposited by reactive magnetron sputtering - Tests and improvements

Depositions of decorative and wear resistant single layer coatings like TiN, Ti(B,N), CrN, NbN, NbON, (Ti,Mg)N and multilayer coatings like Cr/CrN, Nb/NbN, CrN/NbN and NbN/Nb-C:H were performed using reactive magnetron sputtering. The corrosion behaviour of the coated high speed steel substrates was studied in sodium chloride containing media by open-circuit-potential measurements, potentiodynamic corrosion tests and salt spray tests. Up to now, the best improvements with respect to the corrosion resistance in salt spray tests could be obtained for the system (Ti,Mg)N/high speed steel.     

Quantification of silver ion release,in vitro cytotoxicity and antibacterial properties of nanostuctured Ag doped TiO2 coatings on stainless steel deposited by RF magnetron sputtering

Surface treatments on biomaterials using several methods have greatly reduced the in vivo bacterial attachment, surface colonization and formation of biofilm. In this study, the effect of silver (Ag) ion release against in vitro antibacterial activity and cytotoxicity of 1–4wt% Ag doped titania (TiO₂) thin film coatings were evaluated. These coatings were deposited for 1–6 h onto stainless steel substrate (SS) using (radio frequency) RF magnetron sputtering technique. The coatings predominantly in the crystalline anatase phase were configured using X-ray Diffraction (XRD). Scanning electron microscopy (SEM) observation showed the presence of Ag–TiO₂ nanoparticles of less than 100 nm in all the coated surfaces confirming the formation of nanostructured coatings. An initial rapid release, followed by a sustained lower release of Ag ion concentration was measured between 0.45 and 122 ppb when all the coated substrates immersed in Phosphate Buffered Saline (PBS) for 1–10 days. The obtained concentration was less than the maximum toxic concentration for human cells; yet achieved antibacterial concentration, sufficient to kill or inhibit the growth of bacteria. In vitro cytotoxicity results have indicated that 1–4 wt% of Ag doped TiO₂ coatings had no adverse effect on mouse fibroblast proliferation, confirming its cytocompatibility. The antibacterial assessment was performed on 1 and 2 wt% Ag–TiO₂ coatings using Staphylococcus aureus (S. aureus) whereby significant antibacterial activity was observed in 2 wt% Ag–TiO₂ coatings.     

磁控溅射WS2薄膜的制备工艺及其性能

采用孪生中频磁控溅射的方法在低温条件下制备了WS2薄膜,利用X-射线衍射仪(XRD)、扫描电子显微镜(SEM)、能谱仪(EDX)、显微硬度仪、划痕仪和球盘式摩擦磨损试验机对薄膜的物相结构、微观形貌以及摩擦学性能进行了研究。结果表明:所制备的WS2薄膜呈现出明显的(002)晶面择优生长,S/W原子比1.52,在大气环境中摩擦系数可低于0.01,载荷与转速对薄膜的摩擦系数影响显著,在一定范围内加大载荷和提高转速都会增大其摩擦系数。     

MoSx-Ta composite coatings on steel by d.c magnetron sputtering

Sputter-deposited MoS₂ films have been often used as dry lubricant in various industrial fields, such as space application and much attention has been paid to reduction of friction coefficient and improvement of mechanical properties in recent decades. One way to achieve this is to deposit a MoS₂ film doped with another metal. The MoS_x-metal films were found to be denser, more adhesive and more oxidation-resistant than pure MoS₂. In this study, MoS_x-Ta composite films were synthesized by Electron Cyclotron Resonance microwave source enhanced DC sputtering with different target powers. The effects of doping Ta on mechanical properties of MoS_x-Ta films were investigated. The morphology and structure of films were investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). The microhardness was evaluated using microhardness test instrument, and the adhesion strengths were obtained using a scratch tester. The results showed that the S/Mo ratio was influenced by the dc sputtering target power. Typical MoS₂ (100) (103) (002) orientations were present in pure MoS_x films, but disappeared with the increase in doped Ta, with the S/Mo content ratios decreasing from 1.52 to 0.84, and the hardness increasing from 3.55 to 15.23 GPa. The roughness and surface topography, friction coefficient and adhesion were significantly affected by the Ta, Mo and S content. The content of doped Ta plays a dominant role on the change in the Mo/S ratio, thereby influencing the mechanical and tribological properties of the MoS_x-Ta composite films.     

Electrical properties and structures of tantalum thin films deposited by bias ion beam sputtering

A spatial resolution down to 500 Å is one of the excellent features of the Auger scanning electron microscope. In this paper we describe various factors which determine the spatial resolution and two analytical techniques, beam brightness modulation and a computer control system, which contribute to improving the resolution and reducing the electron-induced specimen damage during analysis.     

Characterization and properties of GaN films deposited by middle-frequency magnetron sputtering with anode-layer ion source assistance

GaN films were deposited on Si (111) substrates at a high growth rate of 94 nm/min using middle-frequency (MF) magnetron sputtering method with anode-layer ion source assistance. XRD, TEM and PL experiments were used to investigate the structure and optical properties of the resulting films. GaN films produced under optimal conditions have an almost 1:1 N: Ga ratio. The O concentration decreased while the deposition rate increased with the increasing of bias voltages. Hexagonal polycrystal nature of the films was detected by the TEM and XRD measurements. Peaks located at 3.36 eV labeled as free-exciton were detected in the temperature dependence photoluminescence spectra. The binding energies of N 1s and Ga 3d were centered at 397.5 and 19.8 eV, respectively. The results show that the ion beam-assisted MF reactive magnetron sputtering method can be an encouraging method for deposition of polycrystalline GaN films at low temperatures.     

Characterization and properties of GaN films deposited by middle-frequency magnetron sputtering with anode-layer ion source assistance

GaN films were deposited on Si (111) substrates at a high growth rate of 94 nm/min using middle-frequency (MF) magnetron sputtering method with anode-layer ion source assistance. XRD, TEM and PL experiments were used to investigate the structure and optical properties of the resulting films. GaN films produced under optimal conditions have an almost 1:1 N: Ga ratio. The O concentration decreased while the deposition rate increased with the increasing of bias voltages. Hexagonal polycrystal nature of the films was detected by the TEM and XRD measurements. Peaks located at 3.36 eV labeled as free-exciton were detected in the temperature dependence photoluminescence spectra. The binding energies of N 1s and Ga 3d were centered at 397.5 and 19.8 eV, respectively. The results show that the ion beam-assisted MF reactive magnetron sputtering method can be an encouraging method for deposition of polycrystalline GaN films at low temperatures.     

Comparison of microstructure and mechanical properties of chromium nitride-based coatings deposited by high power impulse magnetron sputtering and by the combined steered cathodic arc/unbalanced magnetron technique

Sliding, abrasive, and impact wear tests were performed on chromium nitride (CrN)-based coatings deposited on mirror-polished M2 high speed steel substrates by the novel high power impulse magnetron sputtering (HIPIMS) utilising high peak cathode powers densities of 3000 W cm⁻². The coatings were compared to single layer CrN and multilayer superlattice CrN/NbN coatings deposited by the arc bond sputtering (ABS) technique designed to improve the coating substrate adhesion by a combined steered cathodic arc/unbalanced magnetron (UBM) sputtering process. The substrates were metal ion etched using non-reactive HIPIMS or steered cathodic arc at a substrate bias voltage of −1200 V. Subsequently a 2- to 3-μm thick CrN or CrN/NbN coating was deposited by reactive HIPIMS or UBM. No bias was used during the HIPIMS deposition, while the bias during UBM growth was in the range 75-100 V. The ion saturation current measured by a flat electrostatic probe reached values of 50 mA cm⁻² peak for HIPIMS and 1 mA cm⁻² continuous during UBM deposition. The microstructure of the HIPIMS coatings observed by transmission electron microscopy was fully dense in contrast to the voided columnar structure observed in conventional UBM sputtered CrN and CrN/NbN. The sliding wear coefficients of the HIPIMS CrN films of 2.3×10⁻¹⁶ m³ N⁻¹ m⁻¹ were lower by a factor of 4 and the roughness of the wear track was significantly reduced compared to the UBM-deposited CrN. The abrasive wear coefficient of the HIPIMS coating was 2.2×10⁻¹³ m³ N⁻¹ m⁻¹ representing an improvement by a factor of 3 over UBM deposited CrN and a wear resistance comparable to that of the superlattice CrN/NbN. The adhesion of the HIPIMS deposited CrN was comparable to state-of-the-art ABS technology.     

溅射电流对磁控溅射CrN_x薄膜结构与性能的影响

采用非平衡磁控溅射技术在不锈钢以及单晶硅基体上制备了CrNx薄膜,并利用X射线衍射仪(XRD)、场发射扫描电镜(FESEM)、能量色散X射线能谱仪(EDS)和纳米压痕仪对薄膜的结构和性能进行了表征。结果表明,随着溅射电流的增大,薄膜中N/Cr比值减小,相组成由CrN(200)向Cr2N(111)转变;晶粒尺寸减小,柱状结构消失,结构变得致密;由于在大溅射电流下,易于形成Cr2N高硬度相,而且形成的薄膜晶粒细小、结构致密,所以硬度值随溅射电流单调升高,在21A时达到最高,为21GPa。