Closed Field Unbalanced Magnetron Sputtering Research Articles

Enhancing toughness of CrN coatings by Ni addition for safety-critical applications

CrN is one of the most important transition metal nitrides, used as protective and anti-wear coating in modern engineering applications. However, CrN coatings are typically brittle and susceptible to catastrophic failure. In this paper, CrNiN coatings with differing Ni contents were deposited on tool steel substrates using a closed field unbalanced magnetron sputtering system. The effects of Ni addition on the microstructure and mechanical characteristics of CrN thin films were studied by combining nanoindentation tests with cross-sectional transmission electron microscopy. A columnar structure was observed in the CrN coating. With an increase in Ni content, the resultant columnar grains exhibited a high aspect ratio. Ni additions to CrN were found to enhance its damage resistance. Notably, the CrN thin film deformed mainly by intercolumnar shear sliding, whereas plastic deformation was favored in the CrNiN thin films exhibiting high aspect ratio columnar grains. More significantly, this change of microstructure with enhanced Ni content led to improved damage tolerance, manifested by a higher load required for crack formation upon a sharp contact (expressed as 1/HE2), and the plastic energy absorbed during nanoindentation.

Flexibility and frictional behaviour of DLC and Si-DLC films deposited on nitrile rubber

The flexibility and frictional behaviour of DLC and Si-DLC films with and without Si–C interlayers were studied in this paper. The films were deposited onto nitrile rubber using a combination of a closed field unbalanced magnetron sputtering ion plating system and plasma enhanced chemical vapour deposition in Ar/C4H10 plasma. Flex tests were used to determine the film flexibility. The frictional and wear characteristics of these films were investigated using a pin-on-disc tribometer for applied loads of 1N and 5N under conditions of dry and wet sliding with a stainless steel counterpart. The induced temperature rise during tribo-testing was used to determine the effect of frictional heating on the frictional behaviour of these films. Lateral cracking was observed for DLC film and Si-DLC film with and without Si–C interlayer after flex tests. More de-bonding was observed for Si-DLC film. The films generally showed excellent frictional results for dry sliding under a normal load of 1N and for wet sliding under normal loads of 1N and 5N. The improved film flexibility was related to enhanced adhesion as a result of the Si–C interlayer. Frictional heating was significant for tribo-testing performed under a normal load of 5N under dry sliding conditions. The induced surface temperature suggests that the influence of frictional heating of the structural transformation taking place within the wear track is minimal compared to the formation of wear debris.

Mechanical Properties and Oxidation Resistance of CrN Coatings Deposited by Closed Field Unbalanced Magnetron Sputter Ion Plating

CrN coatings were prepared by Closed Filed Unbalanced Magnetron Sputter Ion Plating (CFUMSIP). The microstructure and morphologies of CrN coatings before and after oxidation were analyzed by XRD and SEM. At the same time, the mechanical properties and oxidation resistance of CrN coating were also studied. The results indicate that the phase in the dense CrN coatings with a hardness of 1979 HV and a adhension of 54 N was the coexistence of Cr, Cr2N and CrN. Besides, The CrN coatings showed good high-temperature oxidation resistance at 700°C while the coating failed at 800°C.

Effect of N<sub>2</sub> Flow Rate on Structure and Mechanical Properties of CrN Coatings Prepared by Closed Field Unbalanced Magnetron Sputtering

CrN coatings were deposited by Closed Filed Unbalanced Magnetron Sputtering (CFUMS). The effect of N2 flow rate on composition, phase components, morphologies and mechanical properties of CrN coatings were studied. The results show that the deposition rate of CrN coatings declined with the increase of nitrogen flow percentage in a Ar/N2 mixture atmosphere. When the nitrogen flow percentage reached 50% or more, the Cr and N atomic ratio of CrN coatings is close to 1:1. The phase in coatings was the coexistence of Cr, Cr2N and CrN, but the crystal preferred orientation changed significantly with the different N2 flow rates. The columnar crystal CrN coating with low N2 flow rate was denser. The hardness and adhension of CrN coatings have no direct relationship with N2 flow rate.

Effect of Temperature on Structure and Mechanical Properties of CrN Coatings Deposited by Closed Field Unbalanced Magnetron Sputtering

CrN coatings were fabricated by Closed Filed Unbalanced Magnetron Sputtering (CFUMS). The effect of substrate temperature (TS) on phase components, morphologies and mechanical properties of CrN coatings were studied. The results show that the phase in coatings, which has little to do with TS, was the coexistence of Cr, Cr2N and CrN. The grain shape of the columnar crystal CrN coating was the coexistence of pyramidal and plane topography. The hardness and adhension of CrN coating first increased with the rise of temperature, then decreased when the values of both them were constant ones. It has the highest hardness and bonding strength simultaneously at 300°C.

The deposition of crystallized TiO2 coatings by closed field unbalanced magnetron sputter ion plating

Metallic oxide coatings, for example TiO2, are of increasing technological importance in a wide range of industrially relevant functional surfaces on components for renewable energy sector, self-cleaning, antimicrobial surfaces etc.Reactive closed field unbalanced magnetron sputter ion plating (CFUBMSIP) provides an effective, industrially-compatible processing route for the deposition of metallic oxides, with controlled composition, structure, mechanical, electronic and optical properties. The production of crystallized as-deposited TiO2 thin coatings by reactive CFUBMSIP process is described. The arrangement of the deposition system; deposition parameters, including: working gases, deposition pressure, the sputtering power; and the influence of interlayer on the nucleation and the crystalline structure of TiO2 coatings are investigated.

Research on Microstructure and Tribological Properties of Cr-Based Hard Coatings

In this paper, three kinds of Cr-based hard coatings have been studied for its structural, mechanical and tribological properties at room temperature. By the technology of closed field unbalanced magnetron sputter ion plating (CFUMSIP), CrN CrAlN and CrTiAlN hard coatings were deposited onto DC53 cold die steel and silicon (100) substrate. The coatings were characterized by means of field emission scanning electron microscopy (FESEM), X-ray diffractometer (XRD), microhardness tester, optical microscope and ball-on-disc tribometer, in order to check their structural, as well as to determine the mechanical and tribological properties. The experimental results showed that the CrTiAlN coating performed better than the CrN coating and the CrAlN coating in terms of mechanical and tribological properties. The wear resistances of CrN, CrAlN and CrTiAlN coatings have been significantly improved compared with DC53 steel substrate.

Performance of Multilayered PVD Coated Cemented Carbide Inserts during Dry Turning of AISI 304 Austenitic Stainless Steel

AISI 304 austenitic stainless steel is generally “difficult-to-cut” material than other types of steel on account of their high strength, high work hardening tendency and poor thermal conductivity. The focus of the paper is on the dry, high speed machining which is ecologically desirable and cost effective. It is also the future of machining and called as green machining. PVD multilayered TiN/TiAlN and TiAlN/TiSiN coated inserts were used for dry, high speed turning of AISI 304 austenitic stainless steels material. TiN/TiAlN coating was deposited using “Cathodic Arc Evaporation” (CAE) technique where as TiAlN/TiSiN coating was deposited using “Closed-Field Unbalanced Magnetron Sputtering” (CFUBMS) technique. Coatings are deposited on K-grade (K-20) cemented carbide insert. Scanning Electron Microscopy (SEM), microhardness tester and scratch tester were used to examine microstructure, microhardness and adhesion of coating. The thickness of the both coating was found to be 3.8 ±2 µm. TiN/TiAlN coating demonstrated micro-hardness value 34 GPa where as TiAlN/TiSiN coating shows 37 GPa. The adhesion strength of the TiAlN/TiSiN coating is 86 N and that of TiN/TiAlN coating is 83 N.The turning tests were conducted in dry machining environment at cutting speeds in the range of 100 to 340 m/min, feed in the range of 0.08 to 0.20 mm/rev keeping depth of cut constant at 1 mm. The influences of cutting speed, feed and tool coating were investigated on the machined surface roughness, flank wear and cutting force. TiAlN/TiSiN coated tool showed better performance and exhibited lower cutting forces than TiN/TiAlN coated tool. Built-up edge was not observed during using coated tool due to better thermal stability of the coating. The research work findings will also provide useful economic machining solution in case of dry, high speed turning of AISI 304 stainless steel, which is otherwise usually, machined by costly PCD or CBN tools. The present approach and results will be helpful for understanding the machinability of AISI 304 stainless steel during dry, high speed turning for the manufacturing engineers.

Development of advanced duplex surface systems by combining CrAlN multilayer coatings with plasma nitrided steel substrates

Both modelling analyses and experimental work have recently confirmed that the failure of thin coatings on steel, especially under high loads for some demanding applications, is related to the lack of mechanical support from the substrate, which means that the exceptional hardness, toughness and wear resistance of state of the art PVD coatings cannot be fully exploited. To this end, two types of new duplex surface systems have been developed from this research: i) PVD (specifically Closed Field UnBalanced Magnetron Sputter Ion Plating, CFUBMSIP) CrAlN multilayer coating deposited on ex-situ, 20-h active-screen plasma nitrided (ASPN) steel samples, and ii) in-situ 3-h, high power medium frequency pulsed plasma nitriding (HPMFPPN) treatment, followed by a similar CrAlN coating, but performed in a serial, single batch process in an otherwise conventional CFUBMSIP equipment. The microstructures of these two duplex surface engineered systems were characterised using XRD and SEM, while their hardness, adhesion, load bearing capacity and tribological properties were compared by micro-hardness tests, scratch adhesion tests and pin-on-disc sliding wear measurements. Post-test examinations were conducted and the results confirmed that a hard coating on a nitrided substrate can fully exploit the advantages of both the nitrided sub-surfaces for increased load bearing capacity and of the PVD coating for increased hardness, high temperature stability and extreme wear resistance. Finally, the advantages and disadvantages of these two new duplex surface systems were compared and their potential applications were discussed.

Hybrid HIPIMS and DC magnetron sputtering deposition of TiN coatings: Deposition rate, structure and tribological properties

High power impulse magnetron sputtering (HIPIMS) has the advantage of ultra-dense plasma deposition environment although the resultant deposition rate is significantly low. By using a closed field unbalanced magnetron sputtering system, a hybrid process consisting of one HIPIMS powered magnetron and three DC magnetrons has been introduced in the reactive sputtering deposition of a TiN hard coating on a hardened steel substrate, to investigate the effect of HIPIMS incorporation on the deposition rate and on the microstructure and mechanical and tribological properties of the deposited coating. Various characterizations and tests have been applied in the study, including XRD, FEG-SEM, cross-sectional TEM, Knoop hardness, adhesion tests and un-lubricated ball-on-disc tribo-tests. The results revealed that, both the DC magnetron and hybrid-sputtered TiN coatings exhibited dense columnar morphology, a single NaCl-type cubic crystalline phase with strong (220) texture, and good adhesion property. The two coatings showed similar dry sliding friction coefficient of 0.8–0.9 and comparable wear coefficient in the range of 1–2×10−15m3N−1m−1. The overall deposition rate of the hybrid sputtering, being 0.047μm/min as measured in this study, was governed predominantly by the three DC magnetrons whereas the HIPIMS only made a marginal contribution. However, the incorporated HIPIMS has been found to lead to remarkable reduction of the compressive residual stress from −6.0 to −3.5GPa and a slight increase in the coating hardness from 34.8 to 38.0GPa.

Research on Microstructure and Tribological Properties of the Cp/AlSn Coatings Deposited by Magnetron Sputtering

The influences of microstructure and tribological properties of Cp/AlSn (Cp: carbon particule) composite films were applied to AlZn4.5Mg bearing alloy substrates using the closed-field unbalanced magnetron sputtering ion plating technique. The microstructure, phases and bond states of the coatings were separately characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The friction coefficients were measured using a pin-on-disc set-up. Results showed that the grain size and roughness of the films both decreased with increasing of carbon target current (IC) from 0.2 A to 0.8 A. Phases in the films were Al, Sn and C, although the films transformed from a crystalline state to amorphous when the carbon target current was applied. Al and Sn existed as pure metals. Carbon, composed of sp2and sp3bonds, mainly as sp2bonds, provided transfer films to reduce the friction coefficient of the films from 0.35 to 0.15. The specific wear ratio was a minimum, when the carbon target current was 0.4 A.

Plain and fretting fatigue behavior of Ti6Al4V alloy coated with TiAlN thin film

In this study, plain and fretting fatigue behaviors of Ti6Al4V alloy coated with TiAlN thin film by using closed field unbalanced magnetron sputtering system (CFUBMS) were investigated. Coating process was carried out in two different power parameters as dc bias and pulse. It was observed that both plain and fretting fatigue resistance of Ti6Al4V alloy improved after TiAlN coating process. Pulsed films were more effective than biased films in terms of fatigue resistance. Also, fretting fatigue behavior of uncoated and coated specimens was examined with finite element analysis. The finite element analysis results were analogous with experimental test results.

Near-edge X-ray absorption fine structure studies of Cr1−xMxN coatings

• Al or Si is doped on CrN and AlN coatings using magnetron sputtering system. • NEXAFS analysis is conducted to measure the Al and Si K-edges, and chromium L-edge. • Structural evolution of CrN matrix with addition of Al or Si element is investigated. Cr 1− x M x N coatings, with doping concentrations (Si or Al) varying from 14.3 to 28.5 at.%, were prepared on AISI M2 tool steel substrates using a TEER UDP 650/4 closed field unbalanced magnetron sputtering system. Near-edge X-ray absorption fine structure (NEXAFS) characterization was carried out to measure the aluminum and silicon K-edges, as well as chromium L-edge, in the coatings. Two soft X-ray techniques, Auger electron yield (AEY) and total fluorescence yield (TFY), were employed to investigate the surface and inner structural properties of the materials in order to understand the structural evolution of CrN matrix with addition of Al (or Si) elements. Investigations on the local bonding states and grain boundaries of the coatings, using NEXAFS technique, provide significant information which facilitates understanding of the local electronic structure of the atoms and shed light on the origins of the high mechanical strength and oxidation resistance of these technologically important coatings.

Raman analysis of DLC and Si-DLC films deposited on nitrile rubber

In this study a hybrid diamond-like carbon (DLC) and silicon doped diamond-like carbon (Si-DLC), with and without Si–C interlayers, were deposited onto nitrile rubber substrates. The deposition was done in a closed field unbalanced magnetron sputtering ion plating (CFUBMSIP) rig in Ar/C4H10 plasma. A combination of visible (488nm) and ultra-violet (UV; 325nm) Raman analysis was used to determine the G-peak dispersion of the films. Raman analysis was also used to estimate the hydrogen concentration and residual stress in the films. Calculated hydrogen values for all of the films were between 26 and 31%. The residual stress estimates of the films indicated that the inclusion of Si dopant and Si–C interlayers reduced compressive stress in these films. Raman analysis of the wear tracks indicated an increase in the G-peak position which could indicate that graphitization occurred during pin-on-disc experiments.

Microstructure, mechanical and tribological properties of a-C/a-C:Ti nanomultilayer film

An a-C/a-C: Ti multilayer film with a bilayer period of 40 nm was deposited on medical Ti6Al4V alloy using a closed field unbalanced magnetron sputtering. The microstructure and chemical composition of the multilayer film were investigated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The mechanical and tribological properties were evaluated from nanoindentation, Rockwell and scratch tests, and ball-on-disk tribometer. Nanoindentation tests showed that the hardness of the multilayer film reached 25 GPa with good toughness. Due to the interface effect, the adhesion strength of the nanomultilayer was significantly improved. In humid air without lubrication, the a-C/a-C: Ti nanomultilayer film had a low friction coefficient of 0.080 and wear rate of 1.95×10−16 m3 N−1 m−1 at a load of 10 N. While in Hanks' solution, the film exhibited lower friction coefficient of 0.074 and wear rate of 4.25×10−17 m3 N−1 m−1.

Bias-graded deposition and tribological properties of Ti-contained a-C gradient composite film on Ti6Al4V alloy

Ti-contained a-C gradient composite film with a thickness 1.5μm was deposited on medical Ti6Al4V alloy substrate using a closed field unbalanced magnetron sputtering with bias-graded voltage through −20V to −150V. The mechanical and tribological properties were evaluated from nanoindentation, scratch test and ball-on-disk tribometer. Compared with the constant-bias film deposited at −150V, the bias-graded film has the approximate hardness (19GPa) but high toughness and adhesion strength. At a normal load of 10N, the bias-graded composite film shows a low friction coefficient of 0.08 and wear rate of 2.89×10−16m3N−1m−1 in ambient air. While in Hanks’ solution, the film has the same low friction coefficient but low wear rate of 4.63×10−17m3N−1m−1. Excellent wear resistance in Hanks’ solution may bring about a biological application for the Ti-contained a-C gradient composite film.

Effect of Annealing Treatment on the Wear Properties of Ni Rich NiTi Alloy Coatings

In the present study, NiTi alloy coatings were deposited onto AISI 316L stainless steel substrates using the Closed Field Unbalanced Magnetron Sputtering (CFUBMS) system. The as-deposited NiTi alloy coating was Ni rich NiTi alloy with a composition of 44.1 at. % of Ti and 55.9 at. % of Ni and demonstrated an amorphous structure. The post-annealing treatment of the as-deposited Ni rich NiTi alloy coating was successfully produced a crystalline structure. The as-deposited and the annealed Ni rich NiTi alloy coatings were characterized to determine the effect of the annealing process on their wear properties. The Ni rich NiTi phases and structure were determined by XRD. Wear morphology was investigated using the pin-on-disk wear test. The existence of a TiO2 rutile layer with a combination of the Ni3Ti and NiTi B2 parent phases, that formed during the annealing process produced a significant improvement over the wear performance compared to the as-deposited Ni rich NiTi SMA coating. The post-sputtered annealing process at the annealing temperatures of 550°C for a period of 60 minutes and 600°C for a period of 30 minutes succeeded in increasing the adhesion and wear resistance of the Ni rich NiTi coating. The findings show the potential the post-sputtering annealing process in creating an excellent structure of NiTi coating which demonstrates significant wear resistance properties for tribological applications.

Effect of CrTiAlN Coatings on High-Temperature Oxidation Behavior of H13 Steel

CrTiAlN hard coatings have been deposited on H13 steel for improving the oxidation resistance by Closed Field Unbalanced Magnetron Sputter Ion Plating (CFUMSIP). The phase components, surface and section morphology of H13 steel before and after oxidation were analyzed by XRD and SEM. The results showed that the columnar crystal film possesses three major parts, i.e., the internal Cr bonding layer, the intermediate CrN transition layer, the external CrTiAlN gradient coating. The selective oxidation of Cr element was found on the surface of uncoated H13 steel while oxidation, but a continuous protective layer was not formed because of low Cr content, finally a lot of alpha Fe2O3 particles took place on the surface of H13 steel owing to the oxidation of the matrix element. O element can diffuse much more easily through the coating and oxide scales at 800 °C, and spallation and cracks were not found during the oxidation. These results indicated that the CrTiAlN coating have excellent high-temperature oxidation resistance at 800 °C.

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

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

Properties of carbon film deposited on stainless steel by close field unbalanced magnetron sputter ion plating

Carbon films are deposited on 304 stainless steel (SS304) by close field unbalanced magnetron sputter ion plating using different substrate bias voltages and target currents to improve the corrosion resistance and electrical conductivity of bipolar plates made of SS304 in proton exchange membrane fuel cells (PEMFCs). The surface morphology, Raman scattering spectra, corrosion resistance, interfacial contact resistance (ICR), and contact angle with water of the carbon films are determined. A dense carbon film is produced on the SS304 by this technique and the corrosion resistance is improved significantly. The ICR value diminishes drastically and water contact angle increases after deposition. In addition, the passive current density in the simulated PEMFC environment decreases initially, increases as the substrate bias voltage is increased, and drops with decreasing target current. As the substrate bias is increased, the ICR between the carbon film and carbon paper exhibits an initial diminishing trend and then increases, but the effect of the target current on the ICR is not as substantial as that of the bias voltage.