Thin Physical Vapor Deposition Research Articles

Mechanical and High-Temperature Tribological Properties of Cr3C2-NiCr/TiN Duplex Coating

Preparation of duplex coating is an innovative way to improve components surface in terms of mechanical and tribological properties by the combination of high velocity oxy-fuel (HVOF) and physical vapor deposition (PVD) technologies. The present work focused on the construction, mechanical properties and high temperature tribological behaviors of the duplex coating consisting of a thick HVOF Cr3C2-NiCr interlayer and a thin PVD TiN top layer, as well as compared it with the Cr3C2-NiCr coating and the single TiN film. The results showed that the Cr3C2-NiCr/TiN duplex coating exhibited higher hardness, elastic modulus, H/E and H3/E2 ratios and superior load-bearing capacity than the single TiN film. The introduction of Cr3C2-NiCr intermediate layer did not affect the microstructure of TiN film but significantly improved the adhesion strength between TiN film and substrate, as well as the wear resistance sliding against WC ball at different temperatures. In addition, the friction and wear mechanism of the Cr3C2-NiCr coating, TiN film and Cr3C2-NiCr/TiN duplex coating was revealed by investigating the friction-induced morphological and structural evolutions of the sliding surface at elevated temperature.

Dünne PVD‐Hartstoffschichten zur Online‐Temperaturmessung

SummaryThin PVD hard coatings for the online temperature measurementIn the processing industry, process control and the improvement of manufacturing processes become increasingly important. Therefore the acquisition of important process data during production becomes the focus of attention. Physical Vapor Deposition (PVD) allows the deposition of only a few micrometers thin coatings, which follow the shape of the coated surface. They have functionalities and can also increase the wear and corrosion resistance of the coated production tool or components. The aim of this article was the development of thin PVD coatings which can measure temperatures ranging from room temperature up to several hundred centigrades. Therefore, two different coating systems are presented and analyzed with regard to their suitability for temperature measurement. The overall aim is intended to measure the temperature in the interface between the tool surface and the processed workpiece in cutting process or between the tool surface and the melt by primary forming. The sensor coating provides the possibility of an online temperature measurement and the forwarding of this process data. The operating principle is based on the thermoelectric effect, which is also known as the Seebeck effect.

On the plastic deformation of chromium-based nitride hard coatings deposited by hybrid dcMS/HPPMS: A fundamental study using nanoscratch test

Tribological behavior and elastic-plastic deformation of hard coatings deposited by physical vapor deposition (PVD) under normal and lateral loads can be investigated using innovative nanoscratch tests. However, a comprehensive study of thin PVD coatings requires a precise insight into mechanisms of the observed plastic deformation. Nanoscratch analyses on nanostructured PVD hard coatings and investigations of the mechanisms of resulted plastic deformation are the subjects of current research. In the presented work, two coatings CrN and (Cr,Al)N deposited on quenched and tempered AISI 420 steel substrate were investigated. The coatings were synthesized using a hybrid technology, consisting of direct current and high power pulse magnetron sputtering dcMS/HPPMS. Nanoscratch tests were performed with constant normal loads applying Berkovich and conical indenters. Despite significant hardness, these coatings deformed plastically under applied forces. Plastic deformation of the coatings was investigated by means of confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) were applied to explore the mechanism of plastic deformation of the investigated coatings. Based on the results of CLSM and SEM, (Cr,Al)N exhibited a higher resistance against plastic deformation compared to CrN. The TEM investigations furthermore revealed that neither micro-crack formation nor dislocation motion inside the individual grains led to the observed plastic deformation. The dominating mechanism of the plastic deformation of investigated coatings is explained by sliding of grain boundaries (GBS) as the main reason.

Plasma thermal performance of a dual-process PVD/PS tungsten coating on carbon-based panels for nuclear fusion application

Various tungsten (W) coating techniques have been used for the application of plasma facing material in nuclear fusion devices, which resulted in limited success. In this study, a dual-process W coating structure was developed on a graphite substrate to improve the thermal performance of the coating structure. The dual-process coating structure consisted of a thin (∼7μm) multilayer W/Mo physical vapor deposition (PVD) coating layer deposited on top of the relatively thick (∼160μm) plasma spray (PS) W coating on a graphite substrate panel. Then the coated sample was exposed to plasma heat flux of 1–3MW/m2 for 300s. With addition of a thin surface PVD coating layer, the microstructure change in underlying PS W coating was substantially reduced compared to the simple PS W coating structure. The thickness of overall coating structure was maintained for the dual-process PVD/PS coated samples after the thermal loading tests, while a significant reduction in thickness due to surface erosion was observed for the simple PS W coated samples. The improvement in surface erosion resistance in the dual-process coating structure was discussed in view of the characteristics of PVD and PS coating layers.

Combined Surface Treatment of Electron Beam Alloying and PVD Hard Coating for Al Alloys

Due to their typically high hardness, excellent resistance against wear, and their low coefficient of friction, Physical Vapor Deposition (PVD) hard coatings are used on steels for a wide range of tools and components. Currently, however, the potential for wear protection of Al alloy components cannot be exploited. The thin PVD layers tend to collapse and disintegrate due to plastic deformation of the soft base material. Present research is focused on electron beam (EB) surface alloying, using Co-based additives to increase the surface hardness of the Al base material, producing an improved supporting effect for PVD coatings. The influence of different beam deflection techniques and EB parameters on the microstructure and hardness of alloyed layers was investigated. The properties of the duplex composite layers produced are strongly dependent on the thermal stability of the EB alloyed layers (type and amount of intermetallic compounds, coarsening effects) which are affected by the temperature-time cycle of the PVD process. This will be discussed by means of SEM and EDX investigations in correlation with XRD analysis. Measurements using scratch test with increasing load result in critical load values for the combined treatment that are 3 to 5 times higher when compared to only PVD-coated base material.

Nanomechanical study of thin film nanocomposite and PVD thin films on polymer substrates for optical applications

The mechanical properties of ultrathin (<120 nm) films differ substantially from the bulk properties of the material and are also strongly substrate dependent. We compare the properties of two differing film systems; a high particle loading nanocomposite of silica and a multiple layer physical vapour deposition (PVD) coating by nanoindentation, nano-scratch and nano-impact followed by structural analysis. The work is undertaken on hardcoated polymer substrates and uses two types of anti-reflection coatings as test systems. The nanocomposite film comprises of a high (>50%) loading of silica nanoparticles in an inorganic binder, which demonstrates significant flex and elastic recovery whereas PVD films are subject to brittle failure even at low applied loads. Failure of the nanocomposite film, with the exception of minor plastic deformation, does not occur until the underlying substrate fails. Although the PVD film has a greater hardness than the nanocomposite, failure occurs at lower loads due to a number of toughness reducing factors including reduced modulus, modulus mismatch with the substrate and film thickness. The resistance of ultrathin films to external mechanical stresses is therefore related to a number of factors and not simply to film hardness, the most important of which are film structure and film mechanical matching to the substrate.

The Effectiveness of Surface Coatings on Preventing Interfacial Reaction During Ultrasonic Welding of Aluminum to Magnesium

Abstract High power ultrasonic spot welding (USW) is a solid-state joining process that is advantageous for welding difficult dissimilar material couples, like magnesium to aluminum. USW is also a useful technique for testing methods of controlling interfacial reaction in welding as the interface is not greatly displaced by the process. However, the high strain rate deformation in USW has been found to accelerate intermetallic compound (IMC) formation and a thick Al12Mg17 and Al3Mg2 reaction layer forms after relatively short welding times. In this work, we have investigated the potential of two approaches for reducing the IMC reaction rate in dissimilar Al-Mg ultrasonic welds, both involving coatings on the Mg sheet surface to (i) separate the join line from the weld interface, using a 100-μm-thick Al cold spray coating, and (ii) provide a diffusion barrier layer, using a thin manganese physical vapor deposition (PVD) coating. Both methods were found to reduce the level of reaction and increase the failure energy of the welds, but their effectiveness was limited due to issues with coating attachment and survivability during the welding cycle. The effect of the coatings on the joint’s interface microstructure, and the fracture behavior have been investigated in detail. Kinetic modeling has been used to show that the benefit of the cold spray coating can be attributed to the reaction rate reverting to that expected under static conditions. This reduces the IMC growth rate by over 50 pct because at the weld line, the high strain rate dynamic deformation in USW normally enhances diffusion through the IMC layer. In comparison, the thin PVD barrier coating was found to rapidly break up early in USW and become dispersed throughout the deformation layer reducing its effectiveness.

Triode plasma diffusion treatment of titanium alloys

In this paper the structure, properties and tribological behaviour of the binary β titanium alloy Ti–15Mo have been investigated. Low-pressure triode plasma diffusion processes were used to improve the wear resistance of this material and the results were compared with equivalent work carried out on the more popular and better known α+β alloy, Ti–6Al–4V. In order to study these materials, X-ray diffraction, micro- and nano-indentation hardness, surface profilometry, optical microscopy, electron backscatter diffraction and ball-on-plate reciprocating wear testing were employed. These techniques show stark differences between the two titanium alloys, not only in their structure and properties, but also in their response to the surface engineering treatments investigated. It was found that the relatively coarse-grained Ti–15Mo experiences a larger increase in surface roughness when plasma diffusion-treated, particularly where nitrogen is used to provide the active ionised gas species. However, physical vapour deposition (PVD) of a thin pure α-Ti layer can effectively reduce this roughening effect to acceptable levels without compromising the diffusion treatment efficacy in terms of the case hardness and depth achieved. Once a thin PVD layer of α-Ti has been deposited onto the untreated Ti–15Mo, significant improvements in the wear resistance of this alloy can be achieved by either nitrogen plasma-diffusion treatment or by a duplex process routine which includes the final deposition of a hard PVD TiN ceramic coating. Furthermore, the results presented here show that triode plasma oxidation is also a simple (yet very effective) method that can be used to drastically improve the tribological performance of this alloy, where the careful control of (oxide) compound layer formation can produce a hard and wear-resistant surface without the need for duplex PVD coating.

Strain rate effect on the fatigue failure of thin PVD coatings: An investigation by a novel impact tester with adjustable repetitive force

Physical vapor deposition (PVD) coated surfaces are often subjected to repetitive impact loads. In such cases, the strain rate’s effect on the coating fatigue failure is pivotal. This effect was investigated via a novel impact tester which facilitates the modulation of the applied impact force versus the time through an adjustable piezoelectric actuator. Using the developed test arrangement, impact loads of various patterns, frequencies and durations were generated and the coated specimens’ surface response and film fatigue fracture were captured. Based on these results, it was possible to correspond impact forces of various data to equivalent quasi static ones which induce approximately the same coating and substrate deformation. At the latter loads, the coated specimen deformation was determined by Finite Element Method (FEM) calculations taking into account elastic–plastic film and substrate properties attained by an analytical evaluation of nanoindentation results. Moreover, strain, strain rate combinations insuring film fatigue endurance after one million impacts were estimated.

Effect of Thin Y-O and Si-O Films on In-situ Formed CaO Coatings on V-4%Cr-4%Ti in Liquid 2.8 at.% Ca-Li

ABSTRACTWe are developing electrically insulated coatings for the liquid-metal/structural-material interface of the breeder blanket for magnetic fusion reactors. Our earlier experimental studies indicated that sintered Y2O3 is compatible with liquid Li. In continuing studies, we have deposited thin (0.2 and 0.8 μm) yttrium films on V-4Cr-4Ti structural material by physical vapor deposition (PVD). Annealing the thin Y-metallic PVD film on O-charged V-4Cr-4Ti at 750°C for 17 h formed an oxide film by the solid-state reaction between O and Y. Both energy dispersive spectroscopy (EDS) and X-ray diffraction indicated that the Y-metallic films converted to either YVO3 or Y8V2O17 after annealing. When these samples were exposed in 2.8 at.% Ca-Li at temperatures of 700°C for 99 h, a uniformly microstructured CaO layer was formed on the top of the Y-V oxides, but localized Y was not detected by cross-sectional EDS analysis. The addition of Si was found to minimize the V incorporation in the in-situ forming film.

CVD and PVD copper integration for dual damascene metallization in a 0.18 μm process

Various methods of copper filling are studied as interconnect metallizations in advanced ultra large scale integration (ULSI) devices. The filling mode comprising organometallic chemical vapor deposition (OMCVD) Cu followed by physical vapor deposition (PVD) Cu reflow for 0.3 μm diameter trench and via filling has been investigated. This paper presents an evaluation of both the long-throw PVD copper, and CVD copper fundamental process steps. The excellent step coverage of CVD Cu as a seed layer is presented. The corresponding initial PVD Cu deposition step requires a low DC power to facilitate Cu reflow before creating the characteristic overhang of the PVD process, which in turn facilitates subsequent void formation. So the PVD DC power was optimised at 1.6 kW. Furthermore, the full sequential integration of the CVD and PVD process was investigated as a function of liner thickness, deposition temperature and DC power. The filling process has been optimised with a relatively thick liner, to avoid dewetting on the TaN barrier, and with a high deposition temperature to obtain sufficient reflow. However, a thin PVD Cu ‘flash’ layer was necessary to resolve interface stability issues between CVD Cu and TaN. Electrical results are compared to those from a standard copper process flow and these first results are 15% higher than with a standard copper metallization.

Design and evaluation of tribological coatings

The use of coatings to improve the tribological properties of components such as tools for metal cutting and forming, and machine elements e.g. sliding bearings, seals and valves is constantly increasing. This paper presents tribological design considerations of coating composites and recommends methods and techniques for their evaluation. It is aimed both for those involved in scientific development of coatings and for the practising tribology engineer. Current design concepts of coatings for tools and machine elements are exemplified together with successfully coated components. Techniques for evaluation of some of the more important fundamental and tribological properties will be presented and several examples are given mainly with thin physical vapour deposition (PVD) coatings. The evaluation techniques can be utilised both in coatings selection and in development of new coatings. Some recent trends and speculations about the future end the paper.

Integration of Chemical Vapor Deposition Aluminum and Physical Vapor Deposition Aluminum for Aluminum Plug Process of Sub-Quarter Micron Devices

A chemical vapor deposition (CVD)-physical vapor deposition (PVD) Al plug process was successfully integrated to fabricate device wafers with sub-quarter micron technology. Metalorganic CVD (MOCVD) TiN stacked on ion metal plasma (IMP) Ti was used as the underlayer of CVD Al from dimethylaluminum hydride (DMAH). Thin, conformal CVD Al film deposited at a low temperature functioned as an effective wetting layer for PVD Al reflow. If the CVD Al film is too thick, a complete via fill is not achieved. After PVD Al reflow, Al bumps were observed atop the via, which originated from the abnormal growth of the Al grain with a non-<111> direction. A two-step PVD Al process was applied for bump removal, because a thin PVD Al layer deposited at low temperature with high power acted as a seed layer for grain growth. The CVD-PVD Al plug process exhibited via resistance and electromigration resistance superior to those of the conventional W plug process.

High-Heat-Flux Loading of Tungsten Coatings on Graphite Deposited by Plasma Spray and Physical Vapor Deposition

Tiles of fine-grain graphite coated with tungsten layers by different plasma spray techniques (thickness 100 to 550 µm) and by physical vapor deposition (PVD) (thickness 20 to 100 µm) were subjected to heat fluxes, as expected for the divert or of the Axially Symmetric Divertor Experiment (ASDEX)-Upgrade tokamak. By a stepwise increase of the applied heat flux up to 16 MW/m2 and different pulse durations (1 to 5 s), the maximum load for disabling damage of the coating was determined. The fatigue behavior of the coatings was investigated by cyclic loading. The results show that plasma spray coatings are able to withstand heat loads up to 15 MW/m2 for a 2-s pulse without structural changes and cyclic loading with 1000 cycles at 10 MW/m2 and a 2-s pulse. The PVD coatings show damage by crack formation and melting at slightly lower heat loads than most of the plasma spray coatings. Under cyclic loading, the thin PVD coatings fail by extensive crack formation. The results of the tests indicate that the good performance of the plasma spray coatings is related to their higher porosity, which provides a crack-arresting mechanism, and to their mechanical strength.

X-ray photoelectron spectroscopy and transmission electron microscopy studies of the NiAl/Al2O3 interfacial chemical compatibility

β-NiAl thin films were prepared by physical vapor deposition (PVD) either on thin PVD Al2O3 films on Si substrates or on sapphire single crystals. These samples were characterized by x-ray diffraction and electron spectroscopies [Auger electron spectroscopy and x-ray photoelectron spectroscopy (XPS)]. Crystalline films were obtained after deposition at room temperature. XPS depth profiles and transmission electron microscopy cross sections show that the NiAl–Al2O3 interface is sharp (1 nm) and that NiAl oxidation occurs. Ni remains chemically unaffected by the presence of oxygen while the formation of Al3+ compounds is discussed. Within the film Al and Ni appear in a single chemical environment characterized by binding energies close to those of pure intermetallic compounds. Annealing of these wafers at 600 °C induces surface oxidation and, particularly, the formation of an Al2O3 protective layer.