Surface density of growth defects in different PVD hard coatings prepared by sputtering

Growth defects are present in all PVD hard coatings. They have detrimental influence on their tribological properties (higher sticking of workpiece material, higher friction coefficient, worse corrosion resistance, higher gas permeation). In order to improve the tribological properties of PVD hard coatings it is important to minimize the concentration of growth defects. Conventional TiAlN single layer as well as AlTiN/TiN and TiAlN/CrN nanolayer coatings were deposited on cemented carbide, powder metallurgical high speed steel (ASP30) and cold work tool steel (D2) by magnetron sputtering in the CC800/7 and CC800/9 sinOx ML (CemeCon) deposition systems, respectively. The surface morphology of the coated substrates was examined by scanning electron microscope (FE-SEM) in combination with focused ion beam (FIB), and 3D stylus profilometer. By means of 3D-profilometry we performed several measurements and detailed analysis on a series of samples from the several hundred production batches. The influence of growth defects on GDOES (glow-discharge optical emission spectrometry) depth resolution and pitting corrosion was also studied.     

Hierarchical adaptive nanostructured PVD coatings for extreme tribological applications: the quest for nonequilibrium states and emergent behavior

Adaptive wear-resistant coatings produced by physical vapor deposition (PVD) are a relatively new generation of coatings which are attracting attention in the development of nanostructured materials for extreme tribological applications. An excellent example of such extreme operating conditions is high performance machining of hard-to-cut materials. The adaptive characteristics of such coatings develop fully during interaction with the severe environment. Modern adaptive coatings could be regarded as hierarchical surface-engineered nanostructural materials. They exhibit dynamic hierarchy on two major structural scales: (a) nanoscale surface layers of protective tribofilms generated during friction and (b) an underlying nano/microscaled layer. The tribofilms are responsible for some critical nanoscale effects that strongly impact the wear resistance of adaptive coatings. A new direction in nanomaterial research is discussed: compositional and microstructural optimization of the dynamically regenerating nanoscaled tribofilms on the surface of the adaptive coatings during friction. In this review we demonstrate the correlation between the microstructure, physical, chemical and micromechanical properties of hard coatings in their dynamic interaction (adaptation) with environment and the involvement of complex natural processes associated with self-organization during friction. Major physical, chemical and mechanical characteristics of the adaptive coating, which play a significant role in its operating properties, such as enhanced mass transfer, and the ability of the layer to provide dissipation and accumulation of frictional energy during operation are presented as well. Strategies for adaptive nanostructural coating design that enhance beneficial natural processes are outlined. The coatings exhibit emergent behavior during operation when their improved features work as a whole. In this way, as higher-ordered systems, they achieve multifunctionality and high wear resistance under extreme tribological conditions.     

Hierarchical adaptive nanostructured PVD coatings for extreme tribological applications: the quest for nonequilibrium states and emergent behavior

Abstract

Adaptive wear-resistant coatings produced by physical vapor deposition (PVD) are a relatively new generation of coatings which are attracting attention in the development of nanostructured materials for extreme tribological applications. An excellent example of such extreme operating conditions is high performance machining of hard-to-cut materials. The adaptive characteristics of such coatings develop fully during interaction with the severe environment. Modern adaptive coatings could be regarded as hierarchical surface-engineered nanostructural materials. They exhibit dynamic hierarchy on two major structural scales: (a) nanoscale surface layers of protective tribofilms generated during friction and (b) an underlying nano/microscaled layer. The tribofilms are responsible for some critical nanoscale effects that strongly impact the wear resistance of adaptive coatings. A new direction in nanomaterial research is discussed: compositional and microstructural optimization of the dynamically regenerating nanoscaled tribofilms on the surface of the adaptive coatings during friction. In this review we demonstrate the correlation between the microstructure, physical, chemical and micromechanical properties of hard coatings in their dynamic interaction (adaptation) with environment and the involvement of complex natural processes associated with self-organization during friction. Major physical, chemical and mechanical characteristics of the adaptive coating, which play a significant role in its operating properties, such as enhanced mass transfer, and the ability of the layer to provide dissipation and accumulation of frictional energy during operation are presented as well. Strategies for adaptive nanostructural coating design that enhance beneficial natural processes are outlined. The coatings exhibit emergent behavior during operation when their improved features work as a whole. In this way, as higher-ordered systems, they achieve multifunctionality and high wear resistance under extreme tribological conditions.     

QT600材料表面离子镀AlCrN涂层的耐磨性能研究

采用多弧离子镀膜的方法在空压机转子QT600表面制备AlCrN涂层,详细研究干滑动摩擦条件下,不同载荷对涂层和基体的滑动摩擦学特性。研究结果表明:转子基体的磨损形式主要为黏着与磨粒磨损,载荷越高,磨粒磨损越严重;AlCrN涂层在2N载荷下的磨损形式主要为黏着磨损,在8N载荷下主要为黏着与磨粒磨损。     

Einsatz von Hartstoffbeschichtungen bei Spindellagern

Application of hard surface coatings for spindle bearings The demands on modern Machine Tools ascends continuously with the requirements of the production for high quality and short‐time processings. Particularly the increase of the processing‐ and removal times of the last years dues to higher loads of the main spindle bearing. The bearing as a central machine component characterises the performance of the Machine Tool for the cutting process and defines the reliability of the main spindle. The majority of the applicated spindle bearings are ball bearings. A large amount of the spindle fall‐outs is caused by a non adequate or defecitive lubrication and is effected by the tribological properties of the bearing elements. For the reduction of friction and wear nowadays several materials, coatings and lubrication additives are applied. Actual researches focus on the development of hard surface coatings (a‐C:H:W) with a nano structure for the rolling contact of ball bearings to increase their reliability. In this article the test of nano structured hard surface coating systems for the reduction of friction, warming and wear are presented. Thus the coating systems are verificated for the application in spindle bearings by pretesting. According to the evaluation the inner and outer raceway of standard‐hybrid bearings are coated and the adhesion in reference to rotational speed, resistance and wear performance at high acceleration is analysed. Concluding the emergency running properties at dry‐running condition is evaluated to identify the field of application for the coatings.     

Verschleißmechanismen von CrAlYN PVD Schichten bei erhöhten Temperaturen

Wear mechanisms of CrAlYN PVD coatings at elevated temperatures Over the past years there have been developments in machining operations to replace the use of liquid cooling by dry cutting operations. This results in higher loads for the tools and therefore demands the continuous development of surface coatings. CrAlYN‐coatings designed at the Institute for Materials Technology (IfW) in Darmstadt, Germany, show beneficial tribological properties especially at high loads and high temperatures. Samples of different yttrium content have been distinguished and compared to an industrial TiAlN coating. Even though the configuration of the CrAlYN coatings is not yet as optimized as that of the TiAlN, which leaves plenty of room for improvement, the CrAlYN shows comparable and partly superior properties to the TiAlN coating. An increasing yttrium‐content of the CrAlYN leads to a more amorphous microstructure and to finer and denser morphology with a smoother surface. The TiAlN on the other hand exhibits a porous, columnar structure. This results in advantages in the wear behavior as well as in the oxidation resistance. Furthermore, a distinct improvement of the adhesion of the layer to the carrier is determinable, which results in higher sustainable loads at the scratch test.     

Einfluss der HiPIMS‐Parameter beim PVD‐Verfahren

Effect of PVD process parameters on structural properties of CrN layers Commonly, imperfections on substrate surfaces influence layer nucleation unfavorably. They cause growth defects in the coating structures prepared by physical vapor deposition. In consequence this leads to local loss of adhesion, higher friction, voids and thus favoring pitting corrosion. CrN‐coatings are known for their high hardness and good wear resistance. Further they have a better resistance to corrosion than Ti‐based nitrides. Among other parameters, the structure and the mechanical properties of those coatings can be influenced by varying bias voltage and gas flow during film growth. Due to variation of those parameters during reactive magnetron sputtering CrN‐coatings were deposited with preferred crystallized lattice orientation (111) and (200). The main objective of investigation is the potential to cover imperfections.     

Design of wear and corrosion resistant PVD‐coatings for magnesium alloys

Although magnesium alloys became popular in the first half of the 20^th century, the bad corrosion properties prevented their breakthrough in industrial mass production. Since the technology for the production of high purity alloys was introduced in the 1970s, magnesium alloys became more and more in the focus of industrial attention. Today magnesium alloys are state of the art in structural parts in automotive industry. Despite its outstanding properties like good castability, low density and nearly unlimited availability the negative aspects like weak corrosion and wear behaviour still limit the application of magnesium in industry [1]. So, the only economic solution is the deposition of a coating or a suitable surface treatment which provides both, wear and corrosion resistance. Today, plasma electrolytic anodisations are state of the art [2–5]. They provide acceptable corrosion resistance and protect the magnesium from mechanical damage due to their high hardness. On the other hand, their high porosity limits their use in combination with electrochemically noble materials, leading to galvanic corrosion [6]. In addition, the high surface roughness of the plasma electrolytic anodisations restricts their use in tribological applications, particularly under dry sliding conditions [7]. On the other hand, due to the high life time recommendations the application of magnesium in the automotive industries motion component field is a long term process. Nevertheless, there is a quite high industrial interest to apply magnesium in the motion component field in consumer applications like do‐it‐yourself or gardenig. Some examples are motor components of lawnmovers, motor saws or drills. Especially for these fields of application there are quite high demands on the corrosion properties due to undefined storage and the conditions during usage. In order to achieve smooth surfaces with high quality, the PVD technology moves into the centre of interest. Since the 1980s PVD coatings are well established and widely used for different industrial applications, mainly for steel and tool coatings. The authors were the first who carried out serious studies on the development of PVD coatings for magnesium alloys since 1999 [6, 7]. The extensive research activities lead to the recent development of a coating system, which provides both, good wear properties as well as good corrosion behaviour.     

Recent Advances in Disordered and Nanostructured Carbon Coatings for Superl Ubricity and Wearless Sliding

Increasingly more demanding and very stringent operating conditions envisioned for future mechanical and tribological systems will certainly require new materials and coatings that are superhard and at the same time self-lubricating.For example, dry machining is a much desired practice in manufacturing sector, but it is currently very difficult to realize mainly because of high friction and severe wear losses. However, recent advances in surface engineering and coating technologies may enable design and production of novel coatings architectures that can combine superhardness with self-lubricating properties in both the disordered or nanostructured forms. Recently developed nearly frictionless carbon films, ultrananocrystalline diamond and carbide derived carbon films can dramatically lower friction and at the same time reduce wear under very harsh sliding conditions. These coatings can be formulated in such a way that they can substantially increase the load-bearing capacity of sliding surfaces and hence improve their resistance to scuffing. It is also possible to design nano-composite coatings that can form self-replenishing and-lubricating tribofilms on their sliding surfaces and thus help increase the overall lubricity of these surfaces. In this paper, an overview of recent advances in disordered and nanostructured carbon films will be presented. Specific examples will be given to demonstrate the superior performance and durability of such novel coatings under a very wide range of tribological conditions. The major emphasis is placed on super low friction carbon films. The fundamental tribological mechanisms that control their exceptional friction and wear behaviors are also discussed.     

Potentiale moderner PVD‐Beschichtungen

Potentials of Innovative PVD Coatings Hard PVD‐Coatings for wear protection of tools are commonly used in many production purposes for about 20 years. Based on the experiences made with PVD‐processes for deposition of hard coatings “tribological coatings” with optimized friction properties have been developed. These friction optimized coatings can take over some of the lubricants functions in unlubricated processes. Today in many operations the use of additional lubricants can be avoided or at least minimized using innovative tool coatings. As a consequence expensive cleaning processes of the parts can be omitted and environmental pollution is reduced.     

PVD – Eine Erfolgsgeschichte mit Zukunft

PVD – A success story with a future PVD coatings in the range of a few nanometers up to some microns have become state of the art in engineering technology. PVD coatings can be found anywhere in our everday lives. They are used in data storage mediums such as CDs or DVDs. Car or architectural glasses are improved by thermal insulation coatings. A diffusion barrier is achieved via PVD coatings at food packaging. For decorative aspects sham jewelery and accessoires are coated as well as fittings. In the last three decades PVD coatings have been established in a variety of technical applications acquiring wear protection and/or friction reduction. First, coatings for tools have been developed, later on for components as well. So, in the past lots of experiences have been made not only in coating development, but likewise in methodical product design. By contrast, the surface has not yet been regarded as construction element. Here the knowledge is just at the beginning. The achieved performance of coated components can be improved drastically if the tribological system consisting of coating, substrate and intermediate material is designed for one single application with regard to the macro‐ and micro geometry. An exemplary application derived from the collaborative research center (SFB 442) “Environmentally friendly tribosystems” at the RWTH Aachen university is discussed. Results of fundamental research and their way into industrial applications are presented. The research development is reflected with regard to the development of the industrial PVD market. Regarding a process chain for the exemplary application the development method of surface technology is explained beginning with the production up to field testing of a new product.     

Funktionale Oberflächen auf Duplex‐Stahl durch Laserfeinbeschichten

Functional surfaces on duplex stainless steel by lasercladding The product‐lubricated axial and radial bearings installed in multistage high‐pressure pumps inevitably encounter severe mixed friction conditions as the pumps start and stop. This leads to extremely high tribological loads on the bearing components, compounded by the effects of a highly corrosive pumped fluid. The present paper describes a laser cladding process which produces near‐net‐shape coatings of new, highly corrosion and wear resistant functional layers which can be deposited directly on high‐alloy stainless steels without requiring additional buffer layers and without affecting the mechanical properties and corrosion resistance of the substrate. The results cover the solidification behaviour of the coatings as well as the microstructure resulting from various heat treatment conditions. In addition, the technological properties of the coatings and the resulting composites are discussed. The coating systems are tested as to their corrosion resistance and tribological characterization in a pump‐specific tribological system.     

Impact of post-curing duration on mechanical,thermal and tribological behavior of an organic friction material

This paper aimed to study the influence of post curing duration on mechanical, thermal and tribological behavior of friction materials elaborated with simplified formulation. Surface mechanical properties and thermal conductivity were analyzed and tribological behavior was studied for various thermal severities of sliding conditions. Results indicated that post curing for long duration allowed to reduce thermal conductivity and to homogenize the surface mechanical properties of the friction material. Concerning tribological behavior, it was shown that a longer post curing duration permitted to reduce the level of friction and to increase wear resistance. Worn surface morphology investigation using SEM revealed that wear and friction mechanisms involved in the contact were sensitive to post curing duration.     

Tribological characterization of microarc oxidized alumina coatings for biological applications

Coatings with high wear and corrosion resistance are desirable in tribological and biological applications. In an attempt to develop such coatings, we used microarc oxidation (MAO) method to generate noble coatings of alumina on aluminum alloys. This paper reports our tribological investigations on these coatings with a pin-on-disk tribometer in synthetic biofluid. The frictional behavior and wear mechanisms were studied through surface characterization using a scanning electron microscope and a surface profilometer. It was found that the MAO coatings were highly wear resistant in the biofluid environment. The frictional behavior depends on the relative hardness of the ball-on-disk materials. The increased α-Al₂O₃ and γ-Al₂O₃ phases with an increase in the current intensity were found to reduce the friction.     

Growth defects in PVD hard coatings

In PVD coatings, various growth defects typically appear during the deposition. Such defects are drawbacks in coating application. In order to improve the tribological properties of PVD hard coatings it is important to minimize the defect density. Various PVD hard coatings were prepared by evaporation using a thermionic arc and by sputtering using unbalanced magnetron sources. Coating topography was analyzed using a 3D stylus profilometer and other analytical techniques (SEM, FIB). We studied the influence of different types of substrate materials, the substrate position in the vacuum chamber, pre-treatment and deposition parameters on defect density.     

The effect of PVD coatings on the tensile strength and low‐cycle fatigue resistance of stainless steel and titanium alloys

PVD coatings applied to components form hard, stronger layers and generate high residual compressive stresses that limit the plastic deformation in surface layers of the base metal thus increasing its tensile strength and resistance to fatigue loading. The purpose of this paper is to experimentally determine the influence of the deposition of 2 to 16.5‐μm‐thick PVD coatings of TiN, Cr, (Cr+TiN), (TiC)N, (TiAl)N onto specimens of stainless steel 321 and titanium alloys of types MILT‐81556A and (10‐2‐3; 4966) on their tensile strength and low‐cycle fatigue resistance when the development of large elastic–plastic strains takes place. The tensile and low‐cycle fatigue tests were conducted under conditions of axial zero‐to‐tension cycle of the stress‐controlled loading on flat 1‐ to 1.5‐mm‐thick specimens in the initial state (uncoated specimens) and after application of a PVD coating, including those after pretensioning or after cyclic prestraining in the low‐cycle fatigue range. The deposition of PVD coatings is found to enhance the characteristics of tensile strength and low‐cycle fatigue resistance in the quasi‐static fracture range. The deposition of PVD coatings on specimens cyclically prestrained to the values of 53–86% of the number of cycles to fracture, changes the cyclic properties of the material and predetermines the fatigue fracture mode only.     

Einfluss der Mikrostruktur auf das Verschleiß‐ verhalten der hartanodisierten Aluminium‐legierungen EN AW‐6082 und EN AW‐7075

Microstructural effect on the wear behaviour of the hard‐anodised aluminium alloys EN AW‐6082 and EN AW‐7075 The suitability of hard‐anodising of high‐strength Al alloys (EN AW‐7075‐T651) for the fabrication of protective coatings which are also applicable on screws was investigated. A medium‐strength AlSi1MgMn alloy (AA60682‐T6), generally rated as applicable for anodising, was used as reference material. After possible setting phenomena of a screw joint, the load‐bearing surface of the screw can be subjected to an oscillating relative movement. The damaging tribological load was simulated in an oscillation wear test. The resulting wear appearances have revealed that the untreated oxide coatings on the EN AW‐6082 substrate are not capable of providing protection against tribological load. Since hot‐water sealing increases the hardness of the coating but also contains the technology‐induced risk of softening the substrate material, other tribological protection methods have been looked for. The analysis of the tribological tests (characterisation of the structure and the resulting properties of the material, measurement of the wear amount and analysis of the wear appearance) have shown that the films sealed with wax emulsion on both substrate materials are the most promising candidates for the application of devices under oscillation wear. The obtained roughness, friction coefficients and hardness values confirm the positive behaviour of the anodically oxidised EN AW‐7075‐T651 alloy under the chosen tribological load.     

An investigation into the tribological performance of Physical Vapour Deposition (PVD) coatings on high thermal conductivity Cu-alloy substrates and the effect of an intermediate electroless Ni-P layer prior to PVD treatment

The use of high thermal conductivity copper alloys in plastic injection moulds provides the benefit of rapid moulding cycles through effective heat transfer. However, copper alloys are relatively soft and wear rapidly so manufacturers are now developing copper alloys with increased hardness and wear resistance. Their wear resistance can be further improved by the deposition of hard coatings such as electroplated chromium, electroless nickel and Physical Vapour Deposition (PVD) coatings. In this paper, the tribological performance of three proprietary high-strength Cu alloys (Ampcoloy® 940, Ampcoloy® 944 and Ampcoloy® 83) coated with PVD CrN and CrAlN coatings has been evaluated. A medium phosphorous content electroless Ni-P (ENi-P) plated layer was also deposited as a pre-treatment to PVD CrN and CrAlN coatings to increase the load support. The effect of this intermediate ENi-P layer was also evaluated. Surface roughness and instrumented hardness measurements were used to characterise all coated systems in both plated (i.e. with the intermediate ENi-P coating) and standard (i.e. unplated) conditions. Scratch tests were also performed to evaluate the effect of the ENi-P on PVD coating adhesion to Cu alloy substrates. The tribological behaviour of PVD-coated Cu alloy systems was evaluated by pin-on-disc wear tests and ball-on-plate impact tests. Results demonstrate that the ENi-P layer improves the load support for PVD coatings on Cu alloys, thereby improving their tribological performance. However, for PVD-coated Cu alloys in the standard condition, the Cu alloy substrate type plays an important role in the tribological performance of PVD coatings. For instance, PVD CrN coatings were more suited to a certain Cu alloy type whilst CrAlN to the other two types.     

WC/Co含量对Ni-WC/Co纳米复合镀层摩擦学性能的影响

为了探究Ni-WC/Co纳米复合镀层对材料表面摩擦学性能的影响,采用脉冲电沉积制备出Ni-WC/Co纳米复合镀层,研究镀液中WC/Co含量对复合镀层晶体结构、晶粒尺寸和硬度的影响;室温下,在MM-W1B立式万能摩擦磨损试验机上测试复合镀层的摩擦学性能,分析其磨损机理。结果表明:随着镀液中加入WC/Co颗粒含量的增加,复合镀层平均晶粒尺寸先减小后增大,硬度则是先增大后减小,镀层的摩擦系数和磨损速率都是先降低后升高;当WC/Co含量为30.0 g/L时,复合镀层的平均晶粒尺寸最小,硬度最高,摩擦系数和磨损速率最低,耐磨性能最佳,复合镀层表面只呈现出轻微划痕,是由磨料磨损造成的,没有犁削和黏着磨损的特征。     

Erosions‐Korrosions‐Untersuchungen an gradierten Multilayer‐Chromkarbidschichten

Erosion corrosion of graded chromium carbide coatings in multi layer structure So far PVD‐ and PECVD‐Layers have proved their value as wear protection mainly on cutting tools for machining. Depending on the composition of the layers not only a reduction in wear but also a reduction in friction is possible, e.g. by integration of hydrogen containing carbon. Furthermore such carbon containing layers use to be electrochemically inert. Thus they don’t corrode in aqueous media. Because they do also have a very dense structure, an application as corrosion protection seems to be promising. For the intended investigations under service‐like erosiv‐corrosiv loading a new testing rig was developed and constructed. The erosiv‐corrosiv loading was achieved by exposure of coated specimen to a flowing medium, that contains abrasive corund‐particles. Thus the erosion‐corrosion‐behaviour of new graded Multilayer‐Chromiumcarbide‐Coatings should be investigated. The aim was to identify the mechanisms of deterioration to promote a further developement of these layers. In addition the potential of PVD/PECVD‐coated low‐alloy steel to be in‐service under such conditions should be evaluated. For comparison an up‐to‐date industrial DLC‐coating and a high‐alloy duplex‐steel were also investigated. As a result of the conducted investigations an application of PVD‐/PECVD‐coated low‐alloy steel under erosive‐corrosive conditions with impingement wear could not yet be recommended. However the graded Multilayer‐Chromiumcarbide‐Coatings have the potential for a good erosion‐corrosion‐protection, if erosion promoting flaws are avoided. Because hard PVD‐ and PECVD‐coatings are relative brittle, a loading with hard particles, which hit the surface under a high angle, is very tough. Hence the question is, if the investigated layers possibly have a better wear behaviour under more abrasive loading in a more tangential flowing medium, which is also typical for in‐service‐conditions. This is intended to be investigated in future tests.