Physical Vapor Deposition Coatings Research Articles

A strategy to improve tool life by controlling cohesive failure in thick TiAlN coating during turning of CGI

Beside machining condition and parameters, coating properties is one of the main factors affecting tool performance and wear pattern. These properties include coating hardness and elastic modulus, adhesion to substrate, roughness, defects, and most importantly residual stress. In general, the properties of a physical vapor deposition (PVD) coating can be controlled by adjusting deposition parameters such as substrate bias voltage and nitrogen pressure. Therefore, a coating can be tailored to withstand a specific wear mode which is dominant in machining the workpiece material. In this work a strategy is suggested to decrease adhesion wear and formation of built-up edge during machining of compacted graphite iron (CGI). This strategy involves deposition of thick TiAlN coating with low residual stress in order to promote cohesive failure within the coating. For this purpose, monolayer Ti40Al60N PVD coatings with high thickness (5–10 μm) were deposited under various deposition parameters. A comprehensive coating characterization was done using scanning electron microscope (SEM), X-ray diffraction (XRD), nanoindentation, and scratch test. Tool life of selected coatings were then tested under dry finishing of compacted graphite iron, and wear pattern was investigated with optical and scanning electron microscope. The results showed that coating under low compressive residual stress is successful in reducing sticking and built-up edge formation. This phenomenon happens with gradual cohesive failure of the coating under adhesion wear, resulting in a higher tool life under adhesive wear.

Development and application of physical vapor deposited coatings for medical devices: A review

Abstract Physical vapor deposition (PVD) technology can modify the surface properties of equipment without changing the biomechanical properties of the substrate, and has been increasingly used in medical devices. Medical devices can be divided into surgical instruments, implantable medical devices and interventional medical devices according to the object and the way of application. For the defects of different medical devices during use, this paper reviews the development and application of PVD coatings to improve the performance and extend the life of medical devices. Finally, the development of PVD coatings for medical devices is expected.

Self‐Lubricating Physical Vapor Deposition Coatings for Dry Cold Massive Forming

Cold massive forming, particularly forward extrusion of steel, is characterized by high material utilization, product quality, and resource efficiency. Currently, enormous quantities of mostly ecologically harmful lubricants are required, leading to the demand for lubricant‐free cold forming. Furthermore, cost savings are achievable due to shorter lead times. However, the requirements for the tools cannot be met without the application of wear‐resistant and friction‐reducing hard coatings. The self‐lubricating hard coatings (Cr,Al)N + Mo:S and (Cr,Al)N + W:S with attuned material design deposited by physical vapor deposition (PVD) offer high potential for the realization of dry cold forming of steel. The process chain for the comprehensive characterization of the developed coating systems comprises analyses of coating and compound properties as well as two different model tests to determine the tribological behavior. One of the used tribometers represents an open tribological system, which is particularly suitable for simulating the loads occurring during cold massive forming of steel. The analyses reveal that with Mo and S modified coatings exhibit higher potential for ecologically sustainable cold forming due to their better mechanical properties and compound properties between the coatings and the cold work steel substrate compared with W and S modified coatings.

Self‐Lubricating Physical Vapor Deposition Coatings for Dry Cold Massive Forming

Self‐Lubricating Physical Vapor Deposition Coatings for Dry Cold Massive Forming

Effect of Interlayer Thickness on Nano-Multilayer Coating Performance during High Speed Dry Milling of H13 Tool Steel

The TiAlCrSiYN-based family of physical vapor deposition (PVD) coatings were systematically designed through the incorporation of TiAlCrN interlayer to increase coating adhesion and consequently the tool life for extreme conditions that arise during dry high-speed milling of hardened tool steels. The investigation in the present paper intends to explain the effect of TiAlCrN interlayer thickness on the overall coating properties and cutting performance. A comprehensive characterization of the structure and properties of the coatings has been performed using focused ion beam (FIB), scanning electron microscope (SEM), X-ray powder diffraction (XRD), nanoindentation, ramped load scratch test, repetitive load wear test, and nano-impact test. The wear test at a subcritical load of 1.5 N showed that there was a gradual improvement in coating adhesion to the substrate as the interlayer thickness increased from 100 to 500 nm. However, the wear performance, being related to the ability of the coating layer to exhibit minimal surface damage under operation, was found to be associated with micro-mechanical characteristics (such as hardness, elastic modulus). Around a 40% increase in the cutting performance with 300 nm interlayer exhibited that a substantial increase in tool life can be achieved through interlayer thickness variation, by obtaining a balance between mechanical and tribological properties of the studied coatings.

Corrosion resistance of PVD hard coatings for tribological engineering applications

The present paper focuses on corrosion resistance of hard coatings deposited on tool steel via Physical Vapour Deposition (PVD) process. Three coating types were investigated – TiN, TiCN and DLC/TiAlN. An immersion corrosion test was performed on the PVD coated tool steels in accordance to ASTM G31 standard. With immersion corrosion test in aggressive media of 3.5% NaCl solution at ambient temperature of 33°C and exposure duration of up to 72 hours, the presence of the PVD coatings on the tool steel surface have improved the corrosion resistance of the tool steel surfaces. The results showed that the DLC/TiAlN coated tool steel has the highest corrosion resistance with corrosion rate of 36.58 mm/year, followed by TiCN and TiN coatings with corrosion rate of 42.10mm/year and 96.86 mm/year, respectively. The uncoated tool steel exhibits the lowest corrosion resistance of 140.61 mm/year. The present study suggests that the DLC coating deposited on SKD11 tool steel substrate has better stability than that of TiCN- and TiN-coated surfaces because the DLC can prevent the corrosion more efficiently than TiCN and TiN.

Effect of Cr/Al Atomic Ratio on the Oxidation Resistance in 1200°C Steam for the CrAlSiN Coatings Deposited on Zr Alloy Substrates

Cr-based physical vapor deposition coatings have been considered as having the potential to enhance the accident tolerance of Zr alloy fuel claddings. Comparative studies on the high-temperature oxidation behavior were conducted on the Zr alloy coupons that were coated with magnetron-sputtered CrAlSiN quaternary coatings with various Cr/Al atomic ratios. It has been found that the oxidation resistance and the external scale are closely associated with the Cr/Al atomic ratio. A Cr/Al ~ 3.1 coating provided effective protection for its Zr alloy substrate in 1200°C steam for 6 h, where a dense and homogeneous Cr2O3/α-Al2O3 bilayer scale was evidenced in the whole process. However, for Cr/Al ~ 1.3 and the Cr/Al ~ 0.6 coatings, their oxidation resistance was greatly degenerated, because of the forming of brittle α-Al2O3-rich scales. The results demonstrate that the Cr/Al atomic ratio is crucial to the protective capability of CrAlSiN coatings for Zr alloy coupons in high-temperature steam.

Arc PVD (Cr,Al,Mo)N and (Cr,Al,Cu)N coatings for mobility applications

Efficiency during operation is besides reliability and cost effective production one of the most important demands on machines and components. Especially within the automotive sector, components need to fulfill these requirements. Since the demands for high efficiency and reliability cannot be met solely by typical base materials such as case hardened steels, physical vapor deposition (PVD) coatings for the application on highly loaded components gain increasing importance. A possible approach to reduce friction and wear in tribological systems are triboactive and tribocatalytic coatings which contain triboactive elements such as Mo and Cu which can interact with lubricants and lead to the formation of friction and wear reducing tribochemical reaction layers. Besides coating development, also the design of lubricants is in the focus of research activities to reach friction reductions. Therefore, increasing interest gains towards low viscosity lubricants e.g. for e-mobility applications, since reduced friction would lead to extended range.Within the current work, triboactive (Cr,Al,Mo)N and (Cr,Al,Cu)N, (Cr,Al,Mo,Cu)N coatings were deposited by means of cathodic arc evaporation (Arc PVD) in an industrial scale coating unit. The contents of Mo and Cu were varied. As substrate material the case hardened gear steel AISI 5115 (16MnCr5E) was used. The effects of Mo and Cu on the phase formation were investigated by means of X-ray diffraction (XRD). Analysis of the mechanical properties was conducted by nanoindentation (NI) measurements. Tribological behavior of the coatings was analyzed under continuous sliding conditions in pin on disc (PoD) tribometer under minimum quantity lubrication with lubricant amounts of V = 0.05 ml at a temperature T = 80 °C. As lubricants, a low viscosity lubrication oil and a conventional mineral oil were used. Both lubricants contained sulphur and phosphor (S-P) or sulphur (S) additives. In order to investigate the influence of the counter part material on the tribological behavior, inert Si3N4 balls and 100Cr6 steel balls were used. Initial Hertzian contact pressures were set to pH ≈ 1400 MPa and pH ≈ 1600 MPa, respectively. Wear was analyzed by confocal laserscanning microscopy (CLSM). Tribochemical interactions between the coatings and lubricants were studied by Raman spectroscopy. It was found that tribochemical interactions between Mo of the coatings and S of the lubricants can lead to the in situ formation of MoS2 in tribological contact.

Influence of bias voltage on structure and mechanical properties of TiCrN-Mo2N-Ni coatings

In this work, the influence of bias voltage on the structure, composition and physical properties of TiCrN-Mo2N-Ni arc Physical Vapor Deposition (arc-PVD) coatings were studied. Multilayer structure formed at all applied bias voltage due to planetary rotation of substrates. Thickness of sublayers range from 1 to 32 nm and defined by the plasma flow intensity from evaporators. Monte-Carlo calculation was used to study structure of prepared coatings. According to calculation and analysis of TEM images, sublayers composed by nitrides mixture. All coating characterized by high hardness, which correlated with residual stress of coatings.

Corrosion mechanism investigation of TiN/Ti coating and TC4 alloy for aircraft compressor application

It is imperative to develop multifunctional erosion and corrosion resistant coatings for compressor blades of aircraft engines in harsh environment. PVD (Physical Vapor Deposition) technology has the advances in processing erosion-resistant coatings; however, the performance of PVD coatings to combat corrosion depends on various coating defects. Determining and comparing the corrosion performances of PVD TiN/Ti coating and uncoated TC4 alloy was the main objective of present work. The 960 h salt spray corrosion and 116 h hot corrosion tests were conducted to simulate the grounding and working environments of the aircraft compressors. The corrosion mechanisms due to the coating defects such as pinhole, columnar boundary and large grain were analyzed based on the OM, Confocal microscope, electrochemical measurements, SEM, XRD and EDS results. Owing to the disordered state associated with the columnar boundary and the coating defect, nitrogen could be easily replaced by oxygen in the hot corrosion process, these structures were channels for fast diffusion of oxygen. Moreover, the Gibbs energy changes of Ti oxidation and TiN oxidation were thermodynamically calculated according to the working condition of aircraft compressors, and considerable research effort was focused on mapping out the phase diagram of Ti, TiN and high pressure gases. The findings of this research can provide insights into developing multifunctional coatings for future aircraft engines.

Tribological behavior of differently deposited Al-Si layer in the improvement of Inconel 718 machinability

Inconel 718 suffers from very poor machinability which limits its application and causes very high machining costs. Therefore, maximizing the tool performance is of prime importance for improving its machinability and reducing the high costs. Physical vapor deposition (PVD), of coatings on the tool material, is the common method, suggested by many studies, to improve the tool performance during cutting of difficult-to-cut materials. Previously, authors have introduced an easy and cost-effective process for depositing the target material on the tool as an alternative for PVD coatings. In the novel proposed process, referred to by the authors as the “pre-machining” method, the material is deposited on the tool surface during a few seconds of machining of the target workpiece. In the current study, the performance of the new proposed technique is compared with the conventional PVD method. The target material used for deposition is a very soft material (Al-Si) which itself has not been used before for coatings used for difficult-to-cut materials. Thus, for this study, a single layer of soft Al-Si material is deposited on the tool through two different techniques; a typical PVD technique under a high vacuum environment in a coater chamfer and the “pre-machining” technique. The comprehensive machinability analysis performed on the tools showed that application of Al-Si as the target materials through both techniques is very beneficial for the cutting tools used for cutting Inconel 718. Moreover, results showed that the performance of the new, easy to perform, and cost-effective deposition technique is very similar to the performance of conventional PVD coatings and even outperforms a PVD coating in some respects. The results showed that the tool life of the Al-Si-coated tool with 1- and 0.7-μm thicknesses and Al-Si pre-machined tool are significantly higher than that of the uncoated tool by 321%, 231%, and 205% respectively. They also outperform the conventional TiAlN hard coating used for machining of this class of material. The study also demonstrated that the cutting force decreased significantly by using Al-Si-coated and pre-machined tools. Furthermore, chipping, abrasion wear, adhesion, BUE formation, and machining-induced work hardening of the workpiece material reduced significantly by using the Al-Si pre-machined/coated tools. Investigation of the chips produced during the machining process and coefficient of friction measurements also confirmed the friction reduction and better flow of the material at the tool-chip interface as a result of Al-Si deposition with both techniques.

High Temperature Friction and Wear Performance of PVD Coatings under Press Hardening Contact Conditions

Press hardening is widely employed to produce automotive structural and safety components from advanced high-strength steels. This process depends on friction between the forming tools and the work piece. Wear of the forming tools affects the dimensional accuracy of produced components and reduces their service life. It is therefore desirable to reduce wear of forming tools for press hardening applications. One way to achieve this is by applying hard physical vapour deposited (PVD) coatings on the tool. In this work, the tribological behaviour of PVD coated tool-work piece material pairs has been studied at elevated temperatures in an experimental set-up simulating the tribological conditions in press hardening. Four different PVD coatings deposited on tool steel and uncoated tools as reference were studied during sliding against uncoated and Al-Si coated 22MnB5 steel. Results show that uncoated tools exhibited the lowest coefficient of friction when sliding against uncoated 22MnB5 steel. A CrWN coating initially showed low coefficient of friction but it increased with increasing sliding distance. A TiAlN coating and one of two AlCrN coatings showed similar frictional behaviour when sliding against uncoated 22MnB5 steel. During sliding against uncoated 22MnB5 steel, adhesive wear has been found to be the dominant wear mechanism. Adhesive wear was considerably reduced in the case of hard PVD coated tools in comparison to that of uncoated tools. During sliding against Al-Si coated 22MnB5 steel, no clear advantage in terms of friction behaviour of uncoated or PVD coated tools was observed. However, the transfer of Al-Si coating material from the work piece to the tools was significantly reduced for PVD coated tools. Frictional instabilities in all cases involving Al-Si coated work piece material further confirmed the occurrence of adhesive material transfer.

On the fatigue strength of uncoated and DLC coated 7075-T6 aluminum alloy

7075-T6 aluminum alloy is widespread in aerospace and automotive applications thanks to its favorable strength-to-mass ratio. However, the mechanical properties of the alloy decrease when it is exposed to aggressive media and cyclic loading. The deposition of low temperature hard coatings such as Diamond-Like Carbon (DLC) Physical Vapor Deposition (PVD) coatings guarantees good tribological behavior and corrosion resistance without compromising the mechanical properties of the substrate. The influence of DLC PVD coating deposition on the fatigue strength of the alloy in air environment is here described.

Broadband High-Reflection Dielectric PVD Coating with Low Stress and High Adhesion on PMMA

Polymethyl methacrylate (PMMA) is an attractive optical plastic that is widely used in augmented reality, virtual reality devices, display, wearable devices, portable optical equipment, and lightweight optics. Thin film prepared by physical vapor deposition (PVD) is the primary choice of coating on PMMA. However, it faces problems with coating adhesion and stress. In this paper, we analyze the problems existing in the current PMMA high-reflection (HR) coating in detail and propose a way to effectively solve issues with bonding force and stress. Based on the current research background, the bonding force was enhanced by introducing a special hard coating as the connection layer between the dielectric film and the substrate. After comparing the stresses of different coating materials and material combinations, the optimal combination of Nb2O5 and SiO2 was determined, and the requirements were successfully prepared. An HR coating that satisfies requirements, with low stress and excellent environmental adaptability, was successfully prepared. Based on this, a broadband HR coating from 750 to 1550 nm was formed on the surface of PMMA by adjusting the partial pressure of oxygen.

Dental Resin-Zirconia Bonding Promotion Using High-Silica PVD Coating with High Ionization Sputtering Processing

Purpose: To evaluate the effect of high-silica coating deposited by high-silica physical vapor deposition (PVD) as a chemical bonding method on resin-zirconia bond strength under different aging conditions. Methods: Twelve Y-TZP blocks were used as the substrates. Four resin cement stubs were bonded on each Y-TZP block, with a total number of 48 resin cement stubs. Two test groups (n = 24) were evaluated: conventional Tribochemical silica-coating (TSC) and high-silica PVD with high ionization sputtering processing. Experimental silane primer (MPS) was brushed over the surface treated Y-TZP blocks, then a polyethylene mold was placed over the coated Y-TZP blocks and filled with the adhesive resin cement, then light-cured for 40 s. The shear bond strength (SBS) was then evaluated in dry condition and after thermo-cycling for 6000 cycles. Surface roughness, mode of failure, surface topography and elemental analysis were also evaluated. Results: In dry condition, PVD-coated zirconia specimens showed significantly higher mean SBS values (11.7 ± 1.3 MPa) compared to TSC (10.2 ± 1.1 MPa) (p = 0.027). The SBS values of TSC and PVD-coated samples after thermo-cycling were higher than in dry condition, but with no statistical significant difference (p > 0.05). Tetragonal-to-monoclinic phase transformation was detected in TSC, but not in PVD-coated zirconia. Significant decrease in surface roughness of PVD samples compared to TSC samples (p < 0.001). The silica content in PVD coating was 51% as detected by EDX. Conclusions: High-silica PVD coating on zirconia can give a reliable resin-zirconia chemical bond without any phase transformation and surface destruction by conventional grit-blasting.

PVD‐Schutzschichten für Werkzeuge des Präzisionsblankpressens

SummaryPVD protective coatings for precision molding toolsPrecision glass molding (PGM) is a replicative hot forming process for the production of complex optical components, such as aspherical lenses for digital and mobile phone cameras or optical elements for laser systems. The efficiency and thus also the profitability of the PGM depend on the unit price per pressed component, which correlates primarily with the service lifetime of the pressing tools. To increase tool lifetime, the tool surfaces are coated with protective coatings based on precious metals or carbon using physical vapour deposition (PVD). The PVD coating technology enables the deposition of thin coatings, which also follow more complex surface geometries and achieve a high surface quality. PVD coatings are also commonly used to protect tools from wear and corrosion. This paper presents two chromium‐based nitride hard coatings produced by an industrial PVD unit and investigated for their applicability for PGM. Two different coating architectures were implemented, on the one hand a single coating chromium aluminium nitride (Cr,Al)N coating and on the other hand a nanolaminar CrN/AlN coating with alternating layers of chromium nitride and aluminium nitride. The latter is a coating consisting of hundreds of nano‐layers, only a few nanometers thick. Both coatings, (Cr,Al)N and CrN/AlN, each have a thickness of s ∼ 300 nm in order to follow the tool contour as closely as possible. The properties of the coating systems, which are of particular relevance for PGM, are considered. These include on the one hand the adhesion of glass, the roughness and topography of the surface and the adhesion between the coating and the tool material. In addition, the barrier effect of the coatings against diffusion of oxygen was investigated. In order to reproduce the thermal boundary conditions of the PGM, thermocyclic aging tests are performed and their influence on the different properties is described.

Studying the Influence of Mg Content on the Microstructure and Associated Localized Corrosion Behavior of Zn-Mg PVD Coatings Using SVET-TLI

Physical vapour deposited (PVD) zinc and zinc-magnesium coatings are compared to commercial galvanized zinc and zinc-magnesium-aluminum coatings in terms of bare metal corrosion when immersed in chloride-containing solution. A scanning vibrating electrode technique has been augmented to capture photographic images, in-situ, which complement the spatially and temporally resolved electrochemical data by providing visual evidence of corrosion events and their subsequent stabilization or propagation over the surface. Hot dip galvanized zinc coatings demonstrate heterogeneous localized corrosion behavior, contrary to the general corrosion of the PVD pure zinc layer. The PVD coating containing 4 wt% magnesium has a discrete microstructure much finer than the structure of hot dip zinc-magnesium-aluminum coatings, which results in smaller and more abundant anodic features. Increasing the magnesium content in PVD zinc-magnesium to 10 wt% coatings increases the relative size of the anodic events and reduces the number observed accordingly. A further increase in magnesium content to 20 wt% sees a reduction in anode size and evidence of de-activation during the experiment. A clear correlation between magnesium content and the intensity of characteristic staining on the PVD coatings is also observed.

Corrosion Behavior and Surface Properties of PVD Coatings for Mold Technology Applications

Chrome plating is still one of the best solutions to coat martensitic steel used in the molding of plastics and rubbers. However, current stringent regulations on environmental impact call for more sustainable processes. In the present work, some physical vapor deposition (PVD) nitride coatings were produced on X155CrMoV12 steel and characterized in terms of both corrosion behavior and surface properties. Results indicated that titanium-based PVD coatings could be a valuable alternative to chromium-based coatings as they exhibited a good compromise between corrosion and surface properties. AlTiN and TiN PVD coatings exhibited adequate hardness for plastic mold applications, with AlTiN reaching hardness as high as 2000 HV. Moreover, the critical loads and adhesion properties were found to be definitely better than those of chromium-based coatings. From a corrosion point of view, the presence of multilayers in AlTiN did not seem to be beneficial as the breakdown potential for TiN (single layer) was ca. 1.1 V vs. saturated calomel electrode (SCE) compared to 0.85 V vs. SCE for AlTiN in aggressive media (NaCl).

Complex Behavior of Nano-Scale Tribo-Ceramic Films in Adaptive PVD Coatings under Extreme Tribological Conditions.

Experimental investigations of nano-scale spatio-temporal effects that occur on the friction surface under extreme tribological stimuli, in combination with thermodynamic modeling of the self-organization process, are presented in this paper. The study was performed on adaptive PVD (physical vapor deposited) coatings represented by the TiAlCrSiYN/TiAlCrN nano-multilayer PVD coating. A detailed analysis of the worn surface was conducted using scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) methods. It was demonstrated that the coating studied exhibits a very fast adaptive response to the extreme external stimuli through the formation of an increased amount of protective surface tribo-films at the very beginning of the running-in stage of wear. Analysis performed on the friction surface indicates that all of the tribo-film formation processes occur in the nanoscopic scale. The tribo-films form as thermal barrier tribo-ceramics with a complex composition and very low thermal conductivity under high operating temperatures, thus demonstrating reduced friction which results in low cutting forces and wear values. This process presents an opportunity for the surface layer to attain a strong non-equilibrium state. This leads to the stabilization of the exchanging interactions between the tool and environment at a low wear level. This effect is the consequence of the synergistic behavior of complex matter represented by the dynamically formed nano-scale tribo-film layer.

Microstructure and adhesion strength quantification of PVD bi-layered ZnMg-Zn coatings on DP800 steel

In this study, ZnMg-Zn bi-layered coatings with different Mg contents, a single layer ZnMg coating and a pure zinc coating are deposited on steel substrates by physical vapor deposition (PVD) process. A set of experiments and simulations are performed to study the microstructure, mechanical properties and adhesion behavior of the PVD coatings. It is found that Mg2Zn11 and MgZn2 form in the microstructure of the ZnMg top layer with increasing Mg content. MgZn2 fully covers the microstructure at 14.1 wt% Mg. Scratch tests are carried out to quantify the adhesion strength of the coatings. It is observed that ZnMg single layer coating shows poor adhesion to the steel substrate and the addition of a Zn interlayer is essential for enhancing the adhesion strength. It was found that the measured critical load (LC) in scratch test is not a suitable criterion to evaluate the adhesion strength of ZnMg-Zn bi-layer coatings with different combination of thickness and/or mechanical properties. Instead, the Benjamin-Weaver model is modified to quantify the adhesion strength at ZnMg/Zn interface by scratch test revealing consistent results with the BMW crash adhesion test (BMW AA-M223) currently used in industry for adhesion qualification.