Correlation between PVD coating strength properties and impact resistance at ambient and elevated temperatures

The performance of PVD films depends on the operational mechanical and thermal loads of coated tools or components. To withstand these loads, sufficient film strength properties, at ambient and elevated temperatures are required. The present paper deals with the mechanical properties and the impact resistance of a TiAlN coating at temperatures up to 400 °C. Nanoindentations were conducted by a nanoindentation device, enabling measurements at room and elevated temperatures in an inert gas atmosphere. The obtained results were evaluated using appropriate FEM algorithms for determining the film's stress-strain curves, at the temperatures of the conducted nanoindentations. Moreover, perpendicular impact tests on the coated specimens were carried out up to 400 °C, for investigating the film's impact behaviour. The developed impressions were recorded by scanning electron microscopy and white light confocal measurements. The attained results demonstrate a non-linear dependence of the film fatigue properties versus the temperature, whereas a significant impact resistance improvement at approximately 150 °C develops. Finally, a convergence between the yield and the fatigue endurance stress versus the temperature was revealed.     

Micro-scale Abrasion and Medium Load Multiple Scratch Tests of PVD Coatings

THIN film coatings such as titanium nitride(TiN)orDiamond Like Carbon(DLC)are commonly used toprovide wear resistance to tools and mechanicalcomponents.Many tests have been developed to assesstheir characteristics;these tests can determine thehardness,the adhesion and the wear resistance of thecoatings;they can be performed as part of a QualityControl(QC)procedure or as a way of investigating thecoatings properties.As wear by abrasion is an important cause of wearproblems in industry and…     

Impact Resistance of PVD Films and Milling Performance of Coated Tools at Various Temperature Levels

Impact tests were conducted on coated cutting inserts, revealing that a temperature increase at first enhances the coating impact resistance, and then leads to its non-linear deterioration. On the other hand, milling investigations with coated cemented carbide inserts demonstrated that the cutting speed increase, up to a certain level, causes initially a significant improvement of the cutting performance. FEM calculations of the developed temperature and stress fields during cutting provided additional insights. The joint study and the subsequent correlation of the aforementioned results, renders the impact test as a convenient and efficient methodological tool for the characterization of coated tools' cutting performance.     

Hydrothermal corrosion of TiAlN and CrN PVD films on stainless steel

Hydrothermal corrosion of thin TiAlN and CrN PVD films (of 3μm thickness) in 100 MPa water over a temperature range of 20-950 °C is compared to the behavior of TiN films over the same T-P conditions. Corrosion resistance increases in the sequence TiN → TiAlN → CrN. A FeTiO₃ (ilmenite) layer on the surface of the TiAlN film is almost chromium-free and provides protective properties up to 700 °C, whilst ülvospinel formation leads to spallation of oxide scale due to high level growth stresses. Formation of a very stable spinel scale on the surface of the CrN films provides long-term corrosion protection in 100 MPa water up to 800 °C. Nitride films on low-alloyed steel can substitute for expensive super alloy in wet air oxidation systems, with working temperatures up to 700 °C in the case of TiAlN, or 800 °C in the case of CrN coatings.     

Improvements on the wear resistance of high thermal conductivity Cu alloys using an electroless Ni-P coating prior to PVD deposition

An attempt to improve the load support for hard PVD coatings on soft Cu alloys has been made by using a medium phosphorous content electroless Ni-P coating prior to PVD deposition, envisaging the application of these coating/substrate systems in plastic injection moulding. Several PVD coatings, including TiN, CrN, CrAlN, multilayered CrAlN, WC-C, multilayered CrAlN/WC-C were deposited onto an Ampcoloy 940 Cu alloy in two conditions: ‘standard’ and electroless Ni-P plated. The effect of the electroless Ni-P coating on the coating/substrate performance was evaluated by pin-on-disc wear and impact tests. Ultra-microhardness and surface roughness measurements were also used to characterise the resulting coating/substrate systems. The electroless Ni-P coating reduced the wear rates of the PVD-coated Cu alloys and increased the impact wear resistance. Among the PVD coatings trialled, CrN, CrAlN and multilayered CrAlN coatings on electroless Ni-P provided the lowest wear rates.     

Multi-functional nano-multilayered AlTiN/Cu PVD coating for machining of Inconel 718 superalloy

Machining of Ni-based aerospace alloys is one of the major challenges of modern manufacturing. Application of cemented carbide tooling with nano-multilayered AlTiN/Cu PVD coating results in a significant tool life improvement under conditions of turning the hard-to-machine aerospace Ni-based Inconel 718 superalloy. Studies of the structure, properties, tribological and wear performance of the nano-multilayered AlTiN/Cu PVD coating have been performed. The structure of the coating has been investigated using High Resolution Transmission Electron Microscopy. Various properties of the coating including microhardness, thermal conductivity and coefficient of friction vs. temperature were measured.Investigations of the coated tool life, wear behavior and chip formation for cutting tools with nano-multilayered AlTiN/Cu PVD coating were performed. Morphology of the worn tools has been studied using SEM/EDX. AlTiN/Cu coatings present multi-functionality because they combine self-lubricating behavior with reduced thermal conductivity. This beneficial combination of properties results in significant improvement of the coated tool life.     

PVD TBC experience on GE aircraft engines

The higher performance levels of modern gas turbine engines present significant challenges in the reli-ability of materials in the turbine. The increased engine temperatures required to achieve the higher per-formance levels reduce the strength of the materials used in the turbine sections of the engine. Various forms of thermal barrier coatings have been used for many years to increase the reliability of gas turbine engine components. Recent experience with the physical vapor deposition process using ceramic material has demonstrated success in extending the service life of turbine blades and nozzles. Engine test results of turbine components with a 125 μm (0.005 in.) PVD TBC have demonstrated component operating tem-peratures of 56 to 83 °C (100 to 150 °F) lower than non-PVD TBC components. Engine testing has also revealed that TBCs are susceptible to high angle particle impact damage. Sand particles and other engine debris impact the TBC surface at the leading edge of airfoils and fracture the PVD columns. As the impacting continues, the TBC erodes in local areas. Analysis of the eroded areas has shown a slight increase in temperature over a fully coated area ; however, a significant temperature reduc-tion was realized over an airfoil without TBC.     

Adhesive interlayers' effect on the entire structure strength of glass molding tools' Pt–Ir coatings by nano-tests determined

Precision glass molding is a technology for the medium to large scale production of complex optical components with high surface quality and form accuracy. However, the process is only economically viable if a long lifetime of the molding tools can be guaranteed. This can be achieved by using protective coatings on the optical surfaces of the molding tools. The most commonly used coatings for this application are based on noble metals, as they show reduced interaction with the glass during molding. The coatings must have excellent mechanical and chemical properties at high temperatures to withstand the stresses during molding and simultaneously extreme low surface roughness and defect density. The form accuracy of the molding tools is in the sub-μm range and must be maintained even after the coating deposition. Therefore, very thin films of approximately 300 nm thickness are used. High film adhesion and strength properties are necessary for preventing surface defects and coating delamination.In the described investigations, platinum (Pt)–iridium (Ir) coatings were deposited directly on cemented carbide samples by Physical Vapour Deposition (PVD) process. Moreover, for improving the adhesion, different materials such as of Ni and Cr were employed as adhesive interlayers at various thicknesses. These interlayers were deposited on the substrate before the Pt–Ir film, during the same PVD process. Appropriate experimental procedures were conducted for characterizing the coatings' mechanical and adhesion properties such as nanoindentations, nano-impact and nano-scratch tests. FEM calculations simulating the films' loadings during nano-impact test explain the effect of the adhesive interlayer on the entire coating substrate structure strength.     

An investigation into the correlation between nano-impact resistance and erosion performance of EB-PVD thermal barrier coatings on thermal ageing

Nanomechanical testing (nano-impact and nanoindentation mapping) has been carried out on the top surfaces of as-received and aged 8 wt.% yttria stabilised zirconia (YSZ) thermal barrier coatings (TBCs) produced by electron-beam physical vapour deposition (EB-PVD). The correlation between the nanomechanical test results and the previously reported erosion resistance of the TBCs has been investigated. The experimental results revealed that aged TBCs on zirconia for 24 h at 1500 °C or on alumina for 100 h at 1100 °C resulted in large increases in their hardness (H), modulus (E), H/E and H³/E² ratios but their erosion resistance was reduced. Nano-impact tests showed a dramatic decrease in impact resistance following the ageing of these TBCs, which is consistent with the erosion results. The strong correlation between the nano-impact and erosion resistances has confirmed the premise that rapid laboratory impact tests must produce deformation with similar contact footprint to that produced in the erosion tests.     

Investigating the correlation between nano-impact fracture resistance and hardness/modulus ratio from nanoindentation at 25-500 °C and the fracture resistance and lifetime of cutting tools with Ti1−xAlxN (x = 0.5 and 0.67) PVD coatings in milling operations

A novel laboratory technique, nano-impact testing, has been used to test Ti_1−xAl_xN (x = 0.5 and 0.67) PVD coated WC-Co inserts at 25-500 °C. Cutting tool life was studied under conditions of face milling of the structural AISI 1040 steel; the end milling of hardened 4340 steel (HRC 40) and TiAl6V4 alloy. A correlation was found between the results of the rapid nano-impact test and milling tests. When x = 0.67 improved resistance to fracture was found during milling operations and also in the nano-impact test of this coating compared to when x = 0.50. The coating protects the cutting tool surface against the chipping that is typical for cutting operations with intensive adhesive interaction with workpiece materials such as machining of Ti-based alloys. The results give encouragement that the elevated temperature nano-impact test can be used to predict the wear and fracture resistance of hard coatings during milling operations. At 500 °C nanoindentation shows there is a lower H/E_r ratio for the PVD coatings compared to room temperature, consistent with reduced fracture observed at this temperature in the nano-impact test.     

Combinative influence of impact and pressing forces on coating failure behaviour

In this work, a ball-on-plate impact fatigue test was proposed as an experimental technique to investigate the failure behaviour of coating-substrate systems under simulated stamping force conditions. Each impact cycle consisted of an impact force and a pressing force which could be adjusted by changing the distance between the impact ball and the plate surface and by regulating air pressure in the air cylinder of the impact tester, respectively. Two PVD (CrN and TiAlN) and one CVD (TiC) coatings on D2 substrates were tested at combinations of different impact/pressing loads (i.e., 200 N/400 N, 400 N/400 N and 600 N/400 N) for 10,000 cycles. It was found that the sizes of the impacted craters were linearly increased with the impact forces and were more dependent on the substrate than the coatings. The possible failures of the tested coatings included not only cohesive and adhesive failure modes but also fatigue cracking. The CrN coating was the best against the failures at all load combinations. While the TiC coating only showed a small degree of chipping after the test at the highest impact/pressing load, all cohesive and adhesive failures and fatigue cracks could be observed on the TiAlN coating even at the lowest impact/pressing load condition.     

PVD技术在镁合金表面防护领域的应用及研究进展

综述了近年来国内外镁合金表面PVD技术制备的膜层对其耐蚀性的影响研究,提出:PVD膜层能够降低镁合金的腐蚀电流,提高其耐蚀性;造成膜层失效的主要原因是由于膜层中存在的微孔等结构缺陷充当了腐蚀通道;通过膜层体系的结构设计、制备工艺参数优化等方法,可降低膜层结构缺陷、提高膜基体系耐蚀性.     

金属陶瓷及硬质合金表面CVD/PVD涂层的摩擦与切削性能

为研究涂层沉积方式对金属陶瓷和硬质合金性能的影响,采用粉末冶金技术制备了Ti(C,N)基金属陶瓷和YT15硬质合金,在基体表面先后采用CVD和PVD制备涂层。采用SEM、EDS等手段对涂层的微观组织和元素含量进行分析,并对涂层试样进行划痕、摩擦因数、切削性能检测。结果表明,通过复合CVD+PVD工艺,CVD涂层和PVD涂层结合良好。不论是金属陶瓷还是硬质合金,CVD涂层的膜基结合力和摩擦因数均为最大,PVD涂层最小,复合CVD+PVD涂层介于两者之间。对于金属陶瓷和硬质合金而言,复合CVD+PVD涂层的切削性能最好,CVD涂层最差,PVD涂层介于两者之间。切削过程中的磨损机理主要是氧化磨损和磨粒磨损。     

Characterization of fatigue and adhesion properties of a-C:H/CrN coatings on bearing rings by impact tests

The impact test is used for the quantitative assessment of various properties of thin hard coatings, deposited on machine elements, tools etc. This test is mainly applied on coated specimens with simple geometries such as of cutting inserts and coated plates. In the described investigations, perpendicular and inclined impact tests were conducted directly on PVD coated bearing rings. The tests were performed with the aid of appropriate fixtures on the internal cylindrical surface of the outer bearing ring, as well as on the external one of the inner ring. Through a developed FEM simulation of the contact between the indenter ball and the cylindrical ring surfaces during the perpendicular and the inclined impact test, the film fatigue endurance stress was determined and the coating's adhesion was quantified. The mechanical properties of the applied thin films and substrates, used in the FEM calculations, were detected by nanoindentations and appropriate results evaluation. The obtained film fatigue endurance stress of the investigated coating can be considered as adequate however the coating adhesion is assessed as poor.     

Correlation between texture and corrosion properties of magnesium coatings produced by PVD

Physical vapour deposition with energetic ions is an established technology for creating functional surfaces where changing morphologies are observed with increasing energy deposition. In this presentation, magnetron sputtering (MS) is compared with ion beam sputtering (IBS) and vacuum arc deposition (VAD) for corrosion resistant Mg coatings. With increasing average energy flux along the three methods, a transition from a columnar growth regime towards a layer-by-layer growth at increased energies was observed, while a basal texture with the c-axis normal to the surface was found in all cases. However, the full width at half maximum (FWHM) of the corresponding Mg(002) rocking curves showed a pronounced minimum of 3° for IBS deposited films, apparently caused by the reflected high energy primary Ar⁺ ions. For pure Mg films, no larger differences in the corrosion potential and the corrosion rates were measured.     

Crack formation and its prevention in PVD films on epoxy coatings

Severe cracking was found to occur in PVD titanium films on epoxy powder coatings. After all baking treatments, the epoxy coating had smooth, crack-free surfaces and the cracking of both the titanium film and the epoxy only took place as a result of physical vapour deposition. Tensile cracks were observed in the titanium film and not the compressive cracks expected from the conventional two-layered theoretical model. An alternative model has been developed for the prediction of thermal stress in a three-layered film-epoxy-substrate system. The model is consistent with the experimental trials and showed that cracking originated from thermal stresses developed in the titanium-epoxy-aluminum system due to the PVD process. Tensile instability and cracking were initiated where pores intersected the film-coating interface. The results showed that crack formation could be prevented by increasing the baking temperature to 210 °C. This critical temperature activates full crosslinking in the epoxy structure and raises its strength sufficiently to avoid tensile instability due to residual stress. Crack-free and high-gloss sputtered titanium films could therefore be produced on organic coatings. This offers the potential of a combined in-line PVD-powder coating technology as an alternative to electroplating.     

Corrosion study of PVD coatings and conductive polymer deposited on mild steel: Part I: Polypyrrole

Electrochemical deposition of polypyrrole on mild steel substrate was carried out by cyclic voltammetry and galvanostatic technique from neutral aqueous sodium tartrate medium. Homogenous polypyrrole layer for further studies was achieved by galvanostatic technique at constant current density of 5 mA/cm². TiN, CrN and diamond-like carbon (DLC) coatings deposited by physical vapor deposition (PVD) technique on mild steel were used for comparison of corrosion properties with polypyrrole film. Electrochemical synthesis of polypyrrole was also applied as a solution for the PVD coatings porosity problem. Polypyrrole film was successfully deposited on all studied PVD coatings by the galvanostatic technique under special conditions. The protection against corrosion was studied by several methods — measurement of potentiodynamic polarization curves, Tafel plot analysis and electrochemical impedance spectroscopy in 3% NaCl solution.     

Influence of the nanostructuration of PVD hard TiN-based films on the durability of coated steel

The design of thin hard coatings at a nanometric scale is very promising to improve the surface characteristics of coated parts. Unfortunately, most often only one specific property is really enhanced. Besides, the origin of such a “nanostructure effect” remains still not clearly elucidated, and a wider industrial development requires a better understanding of the relations linking structure and functionality.This paper results from an invited review presented within the framework of the EMRS 2007 spring meeting. Its objective is to present how it is possible to control the films structure to achieve optimized performance in terms of tribological, mechanical, and physico-chemical behaviours. Two types of films architecture are studied, resulting either from a stratification of nanolayers, or from a nanodistribution of a crystallised phase into an amorphous matrix. To illustrate both structures, arc-evaporated nanomultilayered TiN/CrN and TiSiN nanocomposite coatings are more particularly developed, and compared to TiN, CrN and SiN_x references.High wear resistance of TiN/CrN is explained by an original propagation mode of the cracks due to a fluctuating residual stress field, evidenced by TEM and synchrotron measurements. Corrosion behaviour depends mainly on the nature of the outer layer. An external CrN layer, presenting a p-type semiconductive character, affords an enhanced protection. A beneficial role of the nanostratification, susceptible to strongly improve the density of films, was also evidenced. The high oxidation resistance of TiSiN is attributable to the network of refractory SiN_x, which acts as a diffusion barrier for oxygen and insulates the highly reactive TiN nanograins from the aggressive atmosphere.     

含铜PVD硬质涂层的结构及其性能研究现状

表面摩擦和磨损是机械零部件失效和损伤的主要形式,影响和决定着材料的使用寿命。传统降低材料磨损的主要措施是采用液体润滑油,但在高温、真空和海水等环境下,润滑油脂无法充分发挥作用,PVD硬质耐磨减磨涂层成为减磨润滑材料发展的新成果,目前已得到广泛的研究和开发。在海洋工业领域,淤泥、海藻和细菌等海洋生物附着于舰船和海工装备表面,降低了船舶的抗摩擦性能和设备稳定性,影响船舶航行速度,增加船舶的燃料消耗,严重威胁着海洋航行安全。硬质防污涂层可以很好地应用于海洋装备零部件的保护。综述了将软质金属Cu引入物理气相沉积的硬质涂层,来拓展硬质涂层的功能,实现硬质涂层自润滑耐磨及抗菌防污性能的研究现状。重点介绍了Cu的引入对PVD硬质涂层结构、硬度、摩擦学行为和抗菌性能的影响,探讨了硬质涂层中Cu的减摩机理,阐明了Cu的抗菌机制,展望了含Cu物理气相沉积硬质涂层未来的发展方向和应用前景。     

Influence of surface roughness of PVD coatings on tribological performance in sliding contacts

The influence of surface roughness on the tribological performance, i.e. friction, wear and material pick-up tendency, of two different commercial PVD coatings, TiN and WC/C, in sliding contact with ball bearing steel has been evaluated using two different types of sliding wear laboratory tests. Post-test characterisation using SEM/EDS, AES, ToF-SIMS and XPS was used to evaluate the prevailing friction and wear. The results show that the surface roughness of the coating is of importance in order to control the initial material pick-up tendency and thus the friction characteristics in a sliding contact. Once initiated, the material pick-up tendency will increase, generating a tribofilm at the sliding interface. For steel-TiN sliding couples a FeO-based tribofilm is generated on the two surfaces and FeO/FeO becomes the sliding interface (interfilm sliding) resulting in a high friction coefficient. For steel-WC/C sliding couples the WC/C displays a pronounced running-in behaviour which generates a WO₃-based tribofilm on the steel surface while a carbon rich surface layer is formed on the WC/C surface, i.e. WO₃/C becomes the sliding interface (interface sliding) resulting in a low friction coefficient.