PVD‐Schutzschichten für Werkzeuge des Präzisionsblankpressens

PVD protective coatings for precision molding tools Precision 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.     

IMPROVEMENT OF CUTTING TOOLS BY TiN PVD HARD COATING

A review of recent results obtained in the field of cutting tools improved with a TiN physical vapor deposition (PVD) ion-plated hard coating is presented. Optimization of the tool material, tool surface morphology and interface problems between the TiN coating and the tool surface are discussed in view of their importance in optimum performance tests and the resulting workplace surface quality. The high effectiveness of the TiN PVD coating is demonstrated by selected data from our own data bank and from other sources on six groups of cutting tools, made of high-speed steels (HSS), powder metallurgical high-speed steels (PM-HSS) and of WC based hard metals. We also describe recently introduced, novel hard coatings (TiCN and TiAIN) for cutting tools, and new applications of cutting tools, improved by PVD hard coatings.     

Nanocomposite‐Beschichtungen auf CBN‐Werkzeugen

Nanocomposite coatings on CBN‐tools CBN (cubic boron nitride) cutting materials are often used to improve the properties of cutting tools. This allows new applications and processes, which are not possible with common cutting materials (e.g. hard metals). Today CBN cutting materials are mostly coated to estimate the wear by an optical evaluation. Coatings on CBN cutting materials for enhancement of the tribological properties are normally not used. For improvement of the properties of used CBN tools during the cutting process a coating technology was developed. This technology combines the advantages of CBN cutting materials with the excellent properties (e.g. hardness, temperature stability) of nanostructured materials. Investigations with different coating systems and pre‐treatment processes were done to test the CBN cutting tools. These investigations have been shown, that nanocomposite coatings can be used to enhance the tool life of CBN cutting tools. Important for an increase in the tool life is a very good coating adhesion, which can be reached by special adhesion layers and an optimized coating structure.     

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.     

Performance evaluation of reactive direct current unbalanced magnetron sputter deposited nanostructured TiN coated high-speed steel drill bits

The stainless steels, in general, are considered to be difficult-to-machine materials. In order to machine these materials the surface of the tool is generally coated with physical vapour deposition (PVD) hard coatings such as titanium nitride (TiN), titanium aluminum nitride (TiAlN), etc. The adhesion is of vital importance for the performance of tools coated with PVD coatings. Proper surface treatments (in situ and ex situ) are required to achieve highly adherent PVD coatings on tools. We have deposited nanostructured TiN coatings on high-speed steel (HSS) drill bits and mild steel substrates using an indigenously built semi-industrial four-cathode reactive direct current (d.c.) unbalanced magnetron sputtering system. Various treatments have been given to the substrates for improved adhesion of the TiN coatings. The process parameters have been optimized to achieve highly adherent thick good quality TiN coatings. These coatings have been characterized using X-ray diffraction, nanoindentation and atomic force microscopy techniques. The performance of the coated HSS drill bits is evaluated by drilling a 13 mm thick 304 stainless steel plate under wet conditions. The results show significant improvement in the performance of the TiN coated HSS drill bits.     

Deposition of PVD Coatings on different geometries and local characterization for reliable properties

Although the characteristics of PVD coatings in research and development papers are very promising, in the field of tribology the industrial application of these coating types is restricted to special market segments up to now: the deposition of hard coatings is state of the art on tools, whereas PVD coated machine components are quite rare. This is caused by the coatings profile of properties, the various surroundings and the demands for application reliability. The last aspect is the main topic of this contribution. Reliability is especially important for machine components, because tools may fail after relative short life time compared to machine parts. Besides this tools and the corresponding production equipment are designed for fast tool replacement in contrast to other machines, which should work without standstill and with a minimum of maintenance. Characteristics of coated systems must be guaranteed in practice theory and laboratory experiments have to show what is possible. On the one hand reproduction of the deposition process must be guaranteed to enter application fields with high demands for reliability, on the other hand characterization of coated systems must be standardized with admissible deviations for communication between coaters and users. These aspects are important for decisions concerning the use of coating substrate systems in tribology besides the topics of technical function. The present investigation shows main reasons for deviations in results of PVD coatings.     

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.     

Verschleiß- und Korrosionsschutz durch Chrom und Chromnitrid (PVD-Abscheidung auf Al und Mg)

Wear and corrosion protection using Cr and CrN (PVD coating on Al and Mg) Investigations of the wear behaviour of uncoated Magnesium and Aluminium alloys (AZ 91hp, AlSi 7Mg) are showing very high wear rates of these materials. To improve the wear behaviour both materials were coated with 9 μm CrN using PVD (Physical Vapour Deposition) technology. The tribological behaviour of the coated light metals was tested afterwards by using a plate on cylinder tribometer. Looking at the results, wear is reduced enormously. The great number of defects in the coating of the magnesium alloy is showing almost no influence to the wear behaviour. The corrosion behaviour of chromium and chromium nitride coatings was tested on the magnesium alloy. Because of the defects in the coating, caused by defects like pores in the magnesium, only a short term protection of the alloy can be achieved. The corrosion behaviour of multilayer coatings is better than the behaviour of single layer coatings.     

Elektronenstrahlbehandlung von PVD‐Hartstoffschichten

Electron beam treatment of PVD – hard coatings Coatings of the type CrN_x, (Ti, Cr)N, (Ti, Al)N, Ti(C, N) and Ti(B,N) were deposited on the quenched and tempered steel C45 to investigate the effect of electron beam treatment on the structure and the properties of hard coated steels. A controlled energy input by electron beams was used to investigate the thermal behaviour of hard coatings with fixing the transformation levels by self‐quenching. Simultaneously a different case hardening of the substrate was caused providing a different effect of supporting the hard layer. There are big differences in the thermal stability of the investigated coatings. The surface hardness, adhesion and wear resistance of the composit hard coating/steel was improved in dependence on the energy input. The use of electron beam technologies enables the generation of support layers which locally increase the working behaviour of hard coated steel.     

Corrosion behaviour of steel with PVD CrxN coatings

The application of PVD coatings for wear protection of tools is well known. Since many years, TiN coated cutting and forming tools are state of the art. In contrast, the application of PVD coatings on machine parts is not standard today. This is caused by the problems of coating deposition on components as well as the fact that wear protection and corrosion protection is demanded for many parts with longer lifetime. TiN produced by means of PVD technique is good for wear protection, but with respect to corrosion there are problems. On the other hand electropolated chromium is a reliable coating to resist corrosion, but wear resistance is limited. PVD Cr_xN coatings promise to combine the advantages of hard coatings and electropolated chromium. The present study focuses on the corrosion properties of magnetron sputtered Cr_xN coatings. Different types of coatings on steel substrates with various amounts of nitrogen were investigated in order to take into account aspects of coating deposition resp. coating material, coating structure and coating morphology. Additionally several graded and multilayer coatings were studied to show influences of coating system design. Electroplated hard chromium was used as reference material for corrosion resistance. To explain the corrosion behaviour, crystallographic phases and structure of coatings were analysed by X‐ray diffraction and morphology by SEM. It could be shown that the corrosion behaviour depends on all these parameters and that 8 μm chromium nitride provides the same corrosion protection as 48 μm electroplated chromium.     

The effect of PVD coatings on the corrosion behaviour of AZ91 magnesium alloy

In this study, multilayered AlN (AlN + AlN + AlN) and AlN + TiN were coated on AZ91 magnesium alloy using physical vapour deposition (PVD) technique of DC magnetron sputtering, and the influence of the coatings on the corrosion behaviour of the AZ91 alloy was examined. A PVD system for coating processes, a potentiostat for electrochemical corrosion tests, X-ray difractometer for compositional analysis of the coatings, and scanning electron microscopy for surface examinations were used. It was determined that PVD coatings deposited on AZ91 magnesium alloy increased the corrosion resistance of the alloy, and AlN + AlN + AlN coating increased the corrosion resistance much more than AlN + TiN coating. However, it was observed that, in the coating layers, small structural defects e.g., pores, pinholes, cracks that could arise from the coating process or substrate and get the ability of protection from corrosion worsened were present.     

Schichtentwicklung für die schmiermittelfreie Umformung von hochfesten Aluminiumwerkstoffen

Development and evaluation of coatings for lubricant free forming of high strength aluminium Many applications in light weight construction require massive formed high strength aluminium parts. For economical and ecological reasons the use of lubricants for massive forming has to be avoided. Both, lubricant free forming and processing of high strength materials are big challenges that can be realized by using coated tools with functional surfaces that show high wear resistance, low friction and low adhesion to aluminium [1–7]. For goal‐oriented surface engineering different coating technologies, such as Physical Vapour Deposition (PVD) and Chemical Vapour Deposition (CVD) have been used for the preparation of specimens. The coating properties are evaluated by mechanical tests and numeric simulation to investigate the massive forming processes and the coating‐substrate‐behaviour. On the base of TiCN‐, TiC‐TiN‐ and DLC‐coatings on steel it is shown how relevant coating properties like Young’s Modulus, crack behaviour and hardness can be analyzed with regard to small coating thicknesses. In order to scale up the results to industrial conditions, finally the simulation is correlated to real deforming.     

Beschichtungen lassen Werkzeuge kalt

Temperature of cutting tools by thin films During the cutting process, cutting tools are exposed to complex mechanical, thermal, dynamic and tribological loads. Especially in the case of dry machining the demands on cutting tools are very high. Dry machining becomes more and more interesting because of tightened up ecolaws and increased costs for the handling of coolants. Due to a renunciation on coolants the cutting tools need to be modified to the process of dry machining. Thereby modern plasma and ion based surface technologies can be used to deposit a thin film adopting the functions of coolants, e.g. cooling and lubricating. In this research project several coating types, e.g. titanium and chromium based coatings, where developed and characterized regarding their mechanical, tribological and thermal properties. For the research, four partners collaborated permuting all steps of surface and coatings design. Materials Science Institute (WW), Aachen University of Technology, performed the development of PVD coatings and the thermophysical characterization by thermal wave analysis. Surface modifications of uncoated and coated tools by ion beam assisted deposition were carried out at Stiftung Institut für Werkstofftechnik (IWT), Bremen. To determine the cutting properties of coated tools, practical tests were performed at Laboratory for Machine Tools and Production Engineering (WZL), Aachen University of Technology.     

Failure of tools for metallic powder compaction

Surfacing with single- or multilayer hard coatings represents a modern trend in the prolongation of tool lifetime. The tools for metal powder compaction were vacuum heat treated, pulsed plasma ion nitrided and coated with TiN or CrN by PVD. Industrial tests of tools, during normal production, showed that, after the same hard coating process, the lifetime of some tools was prolonged by at least twice, but some tools failed very quickly. Research showed that the main reason for early tool wear or failure was improper diameter of the tools after coating.     

Optimization of Surface Morphology and tool material for tin (PVD) efficiency in a given tribo-system

Introduction of hard coatings in an already optimized tribo-system in industrial conditions represent an interdisciplinary problem. For high efficiency, tribosystem must include as many as possible well controlled parameters. Today process technology and performance experiences offers indication that for the properly chosen hard coating, one can derive for a given tribo-system some general rules. Our own development of hard coatings and experience with TiN coatings in more than 200 factories of various production is a basis of this work in which we analyse those parameters of each tribo-system studied, that gave us sufficient statistics to derive first general rules in this field. For our analysis we use SEM, thin film X-ray technique, AES depth profiling, Talysurf profiler, optical microscopy, STEM with EDAX and metallography. As tool materials we studied HSS, HSS-Co, ASP and hard metals, while coating was only TiN. The following items were investigated: stoichiometry on various tool materials; topography of tool surface and coating on it; defects on original surfaces; microhardness on tools; quality of produced surfaces and optimization of tool life; productivity and reliability of TiN coated tools in industrial conditions. All these data were compiled to other references and used as basis to derive general rules.     

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.     

Dünne PVD-Hartstoffschichten zur Online-Temperaturmessung

Thin PVD hard coatings for the online temperature measurement In 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.     

Fatigue resistance of PECVD coated steel alloy

The thin hard coating deposition techniques CVD and PVD have been used for a long time in industry. Such coatings prove very effective in improving the tribological and corrosive resistant properties of the substrate. It was shown that the compressive residual stresses are introduced on the surface layer from the PVD deposition process that helps to increase the fatigue limit of coated structural components. The aim of this work is to evaluate the effect of a SiO_x coating, deposited by means of PECVD technique, on the fatigue resistance of a quenched and tempered alloy steel (39NiCrMo3). Rotating bending fatigue tests were carried out to assess its fatigue limit and characterize any possible variation between the coated and the uncoated material. Fracture surface observations were made using SEM on fracture surfaces, and scratch tests were performed on samples to assess the coating-substrate interface delamination.     

PVD‐CrN Beschichtungen auf Magnesium AZ91hp und Stahl 100Cr6 – Untersuchung des Substrateinflusses auf die Schichteigenschaften

PVD‐CrN coated magnesium alloy AZ91hp and steel 100Cr6 – Investigation on the influence of the substrate material on coating properties PVD‐chromium‐nitride coated samples of substrates of the magnesium alloy AZ91hp and the roller and ball bearing steel 100Cr6 were investigated regarding structure, mechanical characteristics, adhesion and internal stresses. For the coatings the parameters layer thickness and substrate BIAS voltage were varied. Both substrate materials were coated in one lad. Results of the x‐ray analysis of the internal stresses show significant differences between the coated magnesium and the coated steel substrates. In the case of the variation of the substrate BIAS voltage, for the coated steel a dependency of the internal stresses to coating parameters could be obtained. For the coated magnesium no dependency was recognizable. The coating structure was examined with scanning electron microscopy. Element depth profiles of the coated samples were performed with SIMS.     

物理气相沉积技术制备的硬质涂层耐腐蚀的研究进展

根据物理气相沉积技术制备的硬质涂层的腐蚀机制，指出提高硬质涂层的抗腐蚀性能的关键在于提高涂层的致密性和涂层/基材界面的性能，对提高硬质涂层耐蚀性的各种措施分别予以评述，提出了今后的研究方向。