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The multiscale boiling project, also known as RUBI, is an experimental project supported by the European Space Agency (ESA) focusing on the nucleate boiling within the framework of the utilization of the International Space Station (ISS). In order to investigate the operational behavior of the experimental components and determine a promising parameter range, an experimental setup with the same heater design is constructed and tested within the similar parameter range in the framework of the ESA 70th parabolic flight campaign. The present work introduces the experimental setup as well as the measurement methodologies. It concentrates on the results obtained for the nucleate boiling in the absence of external forces such as electric field or shear flow, which are also part of the multiscale boiling project. A barium fluoride glass sputtered with chromium on the top of a chromium nitride layer served as the heater. The manufacturing process of the heater substrate is presented in detail. In order to generate a vapor bubble in the subcooled liquid pool, a laser beam is used to provide the necessary heat at an artificial nucleation site situated at the center of the glass. The experimental setup allows for time adjustment between switch-on of the heater and shooting the laser which is defined as preheating time. The effect of the preheating time on the nucleation and behavior of the bubbles is investigated. Furthermore, by selecting a long laser pulse duration the influence of the laser thermal energy on the growth of the bubbles is studied. It is observed that the preheating time has a significant effect on the bubble growth. However, no influence of the laser shot is detected on the bubble growth, even for a long pulse duration.

This investigation analyses the use of the scanning electrochemical microscopy (SECM) to study the open porosity of PVD-coatings through electrochemical ion detection. CrN und TiN PVD coatings with artificially created permeable areas as well as without any mechanical damage were investigated. Furthermore, the thickness of the interlayers was also modified to increase the diffusion layer thickness. As a result, coatings with different protective effect were obtained and used for comparison purposes. The ion detection was done by means of a microelectrode located over the sample surface. It was used to oxidize ferrous Fe2+ ions coming from the substrate to ferric Fe3+ ions. The measurement of higher currents indicates higher anodic dissolution and consequently higher open porosity of the coating. The validity of the SECM measurements was supported by topographical analysis and optical evaluation of the samples after the measurements.

The effect of Ti interlayers on the corrosion resistance of TiN PVD coatings is investigated. The coatings were deposited using direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HIPIMS). Ti interlayers with different thicknesses but same composition and deposition parameters were studied. The barrier effect was investigated using potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) together with a chemical porosity test. Remarkable improvement of the corrosion resistance with increased thickness of the Ti interlayers was found. The results showed a good agreement between potentiodynamic polarization tests, EIS, SECM and the microscopic inspection.

Vermiculargusswerkstoffe zählen zu vergleichsweise schwer zerspanbaren Werkstoffen im automobilen Antriebsstrang. Insbesondere kontinuierliche Schnittbedingungen stellen hohe Anforderungen an die eingesetzten Schneidstoffe. Kryogene Kühlverfahren können einen entscheidenden Beitrag zur Verlängerung der Werkzeugstandzeit von Hartmetall- und diamantbasierten Schneidstoffen leisten. Der Fachbeitrag fasst die Untersuchungen zum Einfluss der Prozesskühlung auf die Werkstoff- und Spanbildungseigenschaften zusammen. Compacted graphite iron (CGI-450) with its excellent mechanical properties has a large and still increasing importance in the field of construction materials, especially in the field of automotive powertrain applications. The choice of tungsten carbide and diamond-based cutting tools with suitable technological constraints and different cooling strategies in view of chip formation, chip shape and cutting energy are to be illustrated in the following tests.

For the traceability of hardness and elasticity measurements with instrumented indenters to SI units, a measuring standard based on a silicon bending spring with a stop limit exists. Besides the bending stiffness of the spring, the bending point of the measured force–displacement curve at the stop limit can be used as an additional calibration point for both the probing force and the displacement. In a round-robin test with six participants and seven devices the bending stiffness, the bending force and the bending deflection were measured and compared. The result of the bending stiffness, the bending force and the bending deflection agree within ±2.8 %, ±4.2 % and ±3.2 %, respectively.

Various components need protection against superimposed corrosion and wear (abrasion, erosion) loading, e.g. in off-shore applications. The goal of the research has been to develop a PVD multilayer coating by systematically altering the layer architecture in order to protect components against corrosive environments and erosive loadings. Our approach regarding the coating architecture has been to apply a diamond-like carbon (DLC) layer on top of a multilayer coating system, to ensure an excellent erosion resistance while providing a good corrosion protection. Our investigation is focused on the influence of the application technology (PVD or PECVD) and the resulting coating properties of the DLC top-layer. The investigated PECVD-top-layer was produced by a mixture of acetylene and hydrogen gas, whereas the PVD-top-layers were deposited from a graphite-target and different mixtures of acetylene and argon gas. The applicated DLC top-layers are characterized by hardness values between 11 and 23 GPa and similar adhesion properties. Note that hardness has been determined by nano-indentation and adhesion characterized by scratch testing. Residual stresses of the DLC-top-layers were determined by means of focused ion beam milling and tracking of the resulting relaxation strains by digital image correlation. Residual compressive stresses up to 2 GPa have been determined. Under loading in an erosive environment (combination of abrasive and fatigue loading) the abrasive degradation of the investigated coatings has been found to depend mainly on coating hardness. As expected, the hardest DLC top-layer (PECVD) shows least abrasive degradation. However, when tested under cyclic loading, the coating exhibiting the highest hardness values (PECVD) show the most severe fatigue damage of all DLC coatings investigated.

The present study reports on nucleate boiling tests performed with specifically textured chromium nitride (CrN) coatings exhibiting either predominant (1 1 1), (2 0 0) or (2 2 0) crystal lattice orientations. Those tests reveal promising results concerning thin film applications in the field of heat transfer enhancement during nucleate boiling. High power impulse magnetron sputtering (HiPIMS) in combination with direct current magnetron sputtering (DCMS) was applied to deposit CrN coatings of 4.5 μm thickness on average. A thin coating of pure chromium (Cr) was used as adhesive interlayer between substrate and CrN coating. The crystallographic phases and orientations of the coatings were determined by X-ray diffraction (XRD) in θ/2θ mode and texture coefficients T c (h k l) were calculated. High resolution scanning electron microscope (SEM) visualizes the shapes, sizes and orientations of the grains. Different Cr|CrN coating systems were deposited on pure copper heater samples and boiling curves were measured in nucleate boiling experiments in order to determine heat transfer coefficients (HTC) and critical heat flux (CHF) at dry out of the heater surface. Final comparison among the coatings' heat transfer properties reveals differences in CHF and HTC of a factor of 1.8, respectively 1.6, according to the applied microstructure.

Imperfection on substrate surfaces commonly causes growth defects in hard coatings prepared by magnetron sputtering, leading to local loss of adhesion, higher friction, voids and corrosion at coating defects. CrN coatings are known for their high hardness and good wear resistance. The structure and the mechanical properties of those coatings can be influenced varying bias voltage and gas flow during film growth. Due to variation of those parameters CrN coatings were deposited with preferred crystallized lattice orientations (111) and (200). The main objective of investigation is the potential to cover imperfections to increase robustness, especially under superimposed corrosive loads. With the intent to generate comparable surface defects, Vickers indentations were applied as artificial imperfections. With X-ray diffraction analysis and cross-sectional SEM micrographs film orientation and texture around those artificial imperfections was studied, aiming to examine coating microstructure and grain growths. In this context the potential of specified crystallized lattice orientation to cover imperfections is of particular interest.

Storstellen in Bauteiloberflachen wirken sich haufig ungunstig auf die Schichtnukleation bei PVD-Beschichtungen aus. Sie konnen beim Schichtwachstum zu defekten in der Schichtstruktur fuhren. Die Konsequenz ist eine Minderung der lokalen Haftfestigkeit, hohere Reibwerte und Fehlstellen in der Schicht. Diese begunstigen in korrosiven Medien die Entstehung von lokalen Korrosionselementen an Defekten. CrN-Schichten sind fur ihre hohe Harte und ihre guten Verschleiseigenschaften bekannt. Zudem weisen sie eine bessere Korrosionsbestandigkeit als Ti basierte Nitride auf. Die strukturellen und mechanischen Eigenschaften dieser Schichtsysteme konnen unter anderem durch die Veranderung der Biasspannung und des Stickstoffgehalts wahrend des Schichtwachstums beeinflusst werden. Durch gezielte Variation dieser Parameter beim reaktiven Magnetronsputtern wurden CrN-Schichten mit den bevorzugten Kristallgitterstrukturen (111) und (200) abgeschieden, mit dem Ziel, deren Fahigkeit zur Abdeckung von Storstellen zu untersuchen. 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.

Storstellen in Bauteiloberflachen wirken sich negativ auf die Schichtnukleation bei PVD-Schichtsystemen aus. Sie konnen im anschliesenden Schichtwachstum zu Defekten in der Schichtstruktur fuhren. Die Konsequenz ist eine Minderung der lokalen Haftfestigkeit, hohere Reibwerte und Fehlstellen in der Schicht. Diese begunstigen in korrosiven Medien die Entstehung von Korrosion. CrN-Schichten sind fur ihre hohe Harte und ihre guten Verschleiseigenschaften bekannt. Zudem weisen sie eine bessere Korrosionsbestandigkeit als Titan basierte Nitride auf. Die strukturellen und mechanischen Eigenschaften dieser Schichtsysteme konnen unter anderem durch die Veranderung der Biasspannung und des Stickstoffgehalts wahrend des Schichtwachstums beeinflusst werden. Durch gezielte Variation dieser Beschichtungsparameter wurden CrN-Schichten mit den bevorzugten Kristallgitterstrukturen (111) und (200) abgeschieden, mit dem Ziel deren Abdeckungsfahigkeit von Storstellen zu untersuchen. Fur die gezielte Untersuchung und Vergleichbarkeit der Ergebnisse wurden Vickerseindrucke HV 0,5 als bewusst gestaltete Storstellen auf der Grundwerkstoffoberflache aufgebracht. Als Grundwerkstoff diente niedriglegierter Stahl (100Cr6). Die Kristallgitterorientierungen der abgeschiedenen Schichten wurden zunachst anhand von rontgenographischen Messungen (XRD) identifiziert. Anhand weiterer rasterelektronenmikroskopischer Aufnahmen (REM) wurden die bewusst erzeugten Storstellen in Form von Vickerseindrucken und Ritzspuren sichtbar gemacht, mit dem Ziel die Schichtqualitat und die Mikrostruktur um Fehlstellen zu beschreiben. Imperfections on substrate surfaces can cause growth defects in hard coatings prepared by magnetron sputtering, leading to local loss of adhesion, higher friction, voids and corrosion at coating defects. CrN-coatings are known for their high hardness and good wear resistance. In addition CrN-coatings are better corrosion resistant than Ti based nitrides. 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 CrN-coatings were deposited with preferred crystallized lattice orientations (111) and (200). The main objective of investigation is the potential to cover imperfections. Vickers indentations (HV 0.5) were applied as designed imperfections. As base material low alloyed steel was used (100Cr6). At first crystallized lattice orientations were identified by X-ray diffraction (XRD). Further scanning electron microscope analysis (SEM) was applied to identify and study crystallized lattice orientations near those imperfections.

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. (Cr,Al,Y)N-coatings designed at the Institute of Materials Technology 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 (Cr,Al,Y)N coatings is not yet as optimised as that of the TiAlN, which leaves plenty of room for improvement, the (Cr,Al,Y)N shows comparable and partly superior properties to the TiAlN coating. An increasing yttrium content of the (Cr,Al,Y)N leads to a more amorphous microstructure and to finer and denser morphology with a smoother surface. The TiAlN, in contrast, exhibits a porous, columnar structure. This results in advantages in the wear behaviour 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.

In der spanenden Fertigung wird aus vielfaltigen Grunden zunehmend auf den Einsatz von Kuhl- und Schmieremulsion zugunsten der Trockenbearbeitung verzichtet. Die sich dadurch ergebenden hoheren Belastungen der Werkzeugschneiden erfordern eine stete Weiterentwicklung der Beschichtungen. Am Institut fur Werkstoffkunde (IfW) in Darmstadt entwickelte CrAlYN-Beschichtungen zeigen besonders unter hoher Last und hoher Temperatur gunstige tribologische Eigenschaften. Es wurden Proben unterschiedlichen Yttriumgehaltes eingehend charakterisiert und einer industriellen TiAlN-Beschichtung gegenubergestellt. Obwohl die CrAlYN-Schichten in ihrer Zusammensetzung noch nicht ausgereift sind und somit ein hohes Optimierungspotential bieten, zeigen sie vielfach vergleichbare und sogar bessere Eigenschaften als die bereits hochgradig optimierten TiAlN-Schichten. Das mit zunehmendem Yttriumgehalt amorphere Gefuge der CrAlYN-Schichten fuhrt zu einer feinen und dichten Schichtmorphologie mit ebener und glatter Oberflache, die gegenuber der porosen Stengelstruktur des TiAlN Vorteile sowohl beim Verschleis durch Werkstoffzerruttung als auch beim Oxidationswiderstand bietet. Auserdem ist eine deutlich verbesserte Adhasion der Schicht auf dem Tragermaterial festzustellen, die sich in hoheren ertragbaren Lasten beim Ritztest ausert.

Although magnesium alloys became popular in the first half of the 20th 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. Entwicklung von verschleis- und korrosionsbestandigen PVD-Schichten fur Magnesiumlegierungen Mit der industriellen Beherrschung der Herstellung hochreiner Magnesium-Legierungen ruckt der Konstruktionswerkstoff Magnesium seit etwa 30 Jahren mit steigender Tendenz ins Blickfeld der Fertigungs- und Leichtbauindustrie und ist heute im Bereich statischer Bauteile in der Automobilindustrie nicht mehr wegzudenken. Trotz positiver Eigenschaften wie geringe Dichte, einfache Giessbarkeit und praktisch unbegrenzte Verfugbarkeit stehen der Ausschopfung wirtschaftlich relevanter Anwendungsfelder bis heute negative Eigenschaften wie mangelnde Verschleis- und Korrosionsbestandigkeit – insbesondere im Verbund mit anderen Metallen – und zu teure bzw. umweltfeindliche Verfahren zur Oberflachenvergutung im Wege [1]. Zur Losung dieser Probleme sind Oberflachenbehandlungen von Magnesium unerlasslich, bei denen gegenwartig vorwiegend Verfahren zur anodischen Oxidationen unter Funkenentladung zum Einsatz kommen [2–5]. Diese Oberflachenbehandlungen weisen eine gute Korrosionsbestandigkeit auf und schutzen den Grundwerkstoff durch ihre hohe Harte vor mechanischen Beschadigungen. Die ausgepragte Porositat der Oxidschichten schrankt die Anwendung unter Kontaktkorrosionsbedingungen allerdings stark ein bzw. macht diese unmoglich [6]. Daruber hinaus wirkt sich die hohe Rauheit der Oberflachen auf tribologische Anwendungen unter Gleitbeanspruchung negativ aus [7]. Obwohl das Potenzial von Magnesiumlegierungen aufgrund des gunstigen Massentragheitsmoments gerade im bewegten Bauteilbereich ideal ausgeschopft werden kann, ist ein Einsatz in der Automobilindustrie aufgrund der hohen Lebensdaueranforderungen ein langfristiger Prozess. Dennoch besteht ein hohes Interesse der Industrie, Magnesium-Legierungen im bewegten Bauteilbereich einzusetzen. Als Beispiele sind Heimwerker- oder Gartengerate zu nennen, zum Beispiel Rasenmaher, Motorsagen oder Bohrer. Gerade im Heimwerker- und Gartenbereich sind die Anforderungen an die Korrosionsbestandigkeit auf Grund undefinierter Lager- und Betriebsbedingungen jedoch sehr hoch. Zur Erzielung sehr glatter, qualitativ hochwertiger Oberflachen fur Magnesium-Legierungen ruckte in jungster Vergangenheit die PVD-Technologie immer mehr in den Vordergrund. Bereits seit den achtziger Jahren des 20. Jahrhunderts kommen PVD-Schichten zum Einsatz und finden heute breite Anwendung in zahlreichen Industriezweigen. Seit Ende der neunziger Jahre des 20. Jahrhunderts befassen sich die Autoren mit der Entwicklung von PVD Schichten fur Magnesiumlegierungen [6, 7]. Umfassende Forschungsaktivitaten fuhrten in jungster Zeit zu der Entwicklung eines Schichtsystems, dass sowohl gute Verschleis- als auch gute Korrosionseigenschaften aufweist und im Folgenden beschrieben wird.

The current study discusses the influence of yttrium content of magnetron sputtered chromium-based coatings on the wear behavior in dry machining of steel and aluminum alloy. Both tribological tests and practical wear experiments in dry turning and drilling were performed. The characterization of the coatings includes the measurement of thickness and hardness, as well as a detailed analysis of the coating composition. Dry turning and drilling operations were performed in order to evaluate the wear resistance of CrxAlyN and CrxAlyYzN during practical applications.

Although magnesium alloys were popular in the first half of the 20th 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 construction 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 magnesiums in industry, due to the need of sufficient surface protection (E. Aghion, B. Bronfin, Mater. Sci. Forum2000, 350–351, 19). Today, plasma electrolytic anodisations are state-of-the-art (H. Haferkamp, “Magnesiumkorrosion—Prozesse, Schutz von Anode und Kathode”, in: Moderne Beschichtungsverfahren, F.-W. Bach, T. Duda, Eds., Wiley-VCH, Weinheim 2000, ISBN 3-527-30117-8, 242; M. Thoma, Metalloberflache1984, 38, 393; T. W. Jelinek, Galvanotechnik2003, 94, 46; A. Kuhn, Galvanotechnik2003, 94, 1114). 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 (J. Senf, “Untersuchung und Beschreibung von Magnesiumdruckgusslegierungen unter tribologischer, korrosiver und mechanisch-korrosiver Beanspruchung, Berichte aus der Werkstofftechnik”, Shaker Verlag, Germany 2001, ISBN 3-8265-8428-7). In addition, the high surface roughness of the plasma electrolytic anodisations restricts their use in tribological applications, particularly under sliding conditions (H. Hoche, “Grundlegende Untersuchungen zur Entwicklung von PVD-Beschichtungen auf Magnesiumlegierungen im Hinblick auf die Erhohung der Verschleisbestandigkeit und unter Berucksichtigung des Korrosionsverhaltens”, Dissertation, TU-Darmstadt D17, Shaker Verlag, Germany 2004). 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 in 1999 (J. Senf, “Untersuchung und Beschreibung von Magnesiumdruckgusslegierungen unter tribologischer, korrosiver und mechanisch-korrosiver Beanspruchung, Berichte aus der Werkstofftechnik”, Shaker Verlag, Germany 2001, ISBN 3-8265-8428-7; H. Hoche, “Grundlegende Untersuchungen zur Entwicklung von PVD-Beschichtungen auf Magnesiumlegierungen im Hinblick auf die Erhohung der Verschleisbestandigkeit und unter Berucksichtigung des Korrosionsverhaltens”, Dissertation, TU-Darmstadt D17, Shaker Verlag, Germany 2004). 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.

Bei der Trockenbearbeitung wirkt an der Werkzeugschneide ein Belastungskollektiv aus mechanischen, thermischen und chemischen Einflussgrosen. Im Vergleich zur konventionellen Bearbeitung unter Verwendung von Vollstrahl-Emulsionskuhlung erhoht die Trockenbearbeitung die auf den Schneidkeil wirkenden Belastungen. Eine sehr gute Moglichkeit die Schneide vor thermischen, abrasiven und tribo-oxidativem Verschleisangriff zu schutzen stellt die Verwendung von PVD Beschichtungen dar. Neu entwickelte PVD Beschichtungen aus CrxAlyYzN, CrxAlyBzN und CrxAlySizN- wurden sowohl im tribologischen Modelltest als auch im realen Zerspanungstest auf ihre Eignung zur Trockenbearbeitung untersucht. In diesem Paper wird neben der verwendeten Beschichtungstechnologie detailliert auf die Schichteigenschaften eingegangen. Im Zusammenhang mit dem im Zerspanungstest gemessenen Verschleisverhalten und der Prozesskrafte werden anschliesend Ruckschlusse auf das weitere Optimierungspotential dieser Schichtsysteme gezogen. Tool coatings for dry machining During dry machining a strain collective consisting of mechanical, thermal, and chemical loads is imposed upon the cutting edge. Compared to conventional machining using cooling lubrication fluids, the loads are increased in dry cutting. A feasible solution to protect the cutting edge from thermal wear, abrasion, and tribo-oxidation is the application of hard coatings. Newly developed CrxAlyYzN, CrxAlyBzN and CrxAlySizN PVD coatings were both evaluated in tribological model tests and machining tests concerning their suitability for dry cutting applications. Herein, the used coating technology and the coating properties are described in detail. The measured tool wear and the process forces give further hints for the optimization of the coating system.

Induktiv randschichtgehartete Komponenten werden zur Verbesserung der Bauteilzahigkeit, der Bearbeitbarkeit und zur Vermeidung von Verzug unter Betriebsbedingungen in den meisten Fallen zusatzlich im Ofen angelassen. In der Regel wird angelassen, wenn noch geschliffen werden soll. Entsprechend den Anlassbedingungen andern sich der nach dem Harten vorliegende Gefugezustand und damit auch die Werkstofffestigkeit. Die hier durchgefuhrten Untersuchungen sollen zeigen, ob und bei welchen Temperaturen das bisherige Ofenanlassen durch induktives Kurzzeitanlassen ersetzt werden kann und wie sich diese Warmebehandlung auf die Walzermudungseigenschaften auswirkt. Es konnte gezeigt werden, dass bei optimierten Kurzzeitanlassparametern Werkstoffzustande erreicht werden, welche sich bei Walzbeanspruchung gunstiger verhielten als Proben, welche im Ofen oder gar nicht angelassen wurden. Damit offnet sich fur zahlreiche Anwendungen die Moglichkeit, das bisherige Anlassen im Ofen durch das schnellere und kostengunstigere induktive Kurzzeitanlassen nach induktivem Randschichtharten zu ersetzen. Ball bearing fatigue after inductive short time tempering To improve toughness, machiniability and to avoid distortion under operating conditions inductive hardened components often were additional tempered in an oven. As a general rule tempering is applied when grinding is required. According to tempering conditions the present hardness, toughness and the microstructure will change. In the present studies it is shown, that with optimized inductive short term tempering conditions it was possible to achieve even better mechanical properties in comparison with oven tempered components. Ball bearing fatigue testings showed an improvement of wear resistance. The achieved findings opens the possibility for numerous applications to exchange the previous oven tempering through the more rapid and more low-cost inductive short-term inductive surface layer hardening.

The present study investigates the potentials of newly developed (Cr,Al)N coatings compared to uncoated tools. The aim of using chromium-based coatings is to create a thermal barrier and thus redirecting the heat from work piece and tool into the chip. Due to their high resistance for oxidation, CrxAlyN coatings with different chromium to aluminum contents were deposited onto indexed carbide inserts. In order to find improved coatings for dry machining operations both tribological and wear tests were performed. These tests include fundamental properties such as thickness, hardness, and critical load. With Glow Discharge Optical Emission Spectroscopy (GDOES) depth profile analyses were conducted. In reciprocating sliding tests, using an SRV III apparatus from Optimol, friction and wear has been studied in a ball-on-disc arrangement. Longitudinal turning tests were performed to characterize the dry machining characteristics. As described above, the coatings' characteristics such as hardness and critical load as well as the results from the reciprocating sliding test correlate with the dry turning tests. The best coatings in the tests have similar chromium and aluminum contents in the region of 15 at.%, the nitrogen content was about 60 at.%, respectively. An increase of the Cr content in the coating deteriorates the performance of the coated carbide beneath the level of the uncoated tool. An adhesion phenomenon that leads to a formation of an adherent layer on the cutting edge is attributed to the completely unlimited mutual solid solubility of Cr and Fe at a temperature beyond 800 °C.

Amorphous Si/C/N:H where synthesized by plasma enhanced chemical vapor deposition (PE-CVD) using the single-source precursors hexamethyldisilazane (HMDS) and bis(trimethylsilyl)carbodiimide (BTSC). The films produced using the HMDS precursor were rich in carbon, while the films synthesized from the BTSC precursor were high in nitrogen content. All films were amorphous and exhibited a similar hardness to SiC or Si 3 N 4 . Fundamental properties of the films were determined in tests such as ultra micro-hardness, elastic modulus, thickness and adhesion. To investigate the composition of the films, composition depth profiles were determined by GDOES. The wear behaviour was studied in sliding tests under oscillating motion. To investigate the wear mechanisms, the wear tracks were examined with topographical analysis, REM as well as EDX.

Tools for cutting operation are subject to very high abrasive, adhesive, and thermal loads. Process security and preparation quality as well as a sufficiently high tool life demand for the development of hard coatings with reduced seizure tendency, high hot hardness, and increased wear resistance especially under dry machining conditions. TiAlN coatings are the state-of-the-art coatings for machining operations. Hard materials on chromium basis like CrN or CrAlN are preferably used for bending and stamping tools. Thus, these coatings could have a high potential in machining operations. The aim of using chromium-based coatings is to redirect the heat from the workpiece and tool into the chip, thus acting as a thermal barrier. Due to their high oxidation resistance, CrN and Cr x Al y N coatings were deposited on WC/Co inserts. In order to find improved coatings for dry machining operations, mechanical characterizations and turning tests were performed. The characterization of the coatings includes fundamental properties such as thickness, hardness, and critical load. With Glow Discharge Optical Emission Spectroscopy (GDOES), depth profile analyses were executed. SEM analyses supplemented the picture of the scratch tests. Turning operations were performed in model tests to characterize the dry machining characteristics. The wear properties of CrN and Cr x Al y N coatings were compared with industrially coated (Ti,Al)N carbide inserts. Calculations of the friction coefficient supplemented the tests.

Sufficient corrosion resistance of technical magnesium alloys is generally ensured by anodising the components in aqueous electrolytes. In the majority of cases, these processes bear environmental risks due to the highly toxically electrolytes and are subjected to substantial legal regulations. Considering these facts, the plasma anodisation seems to be a prospective method to obtain comparable corrosion resistance without using toxic substances. The main goal of the method of the plasma anodisation is the substitution of the aqueous electrolyte by an oxygen plasma. The plasma anodised surfaces were well characterized and the corrosion resistance was proved in the salt spray test according to DIN 50021 SS. For the tests the magnesium die cast alloy AZ91hp was used. The tests included plasma anodised, plasma anodised and PVD coated and only PVD coated specimens.

Extensive investigations of the authors showed the possibility of producing reliable plasma vapour deposition (PVD) hard coatings on magnesium alloys with good wear properties comparable to PVD coated steel or titanium based alloys. In presence of corrosive mediums crucial contact and pitting corrosion, induced by process related coating pinholes are the main failure mechanisms of coated magnesium alloys, even without any tribological load applied. The authors developed the new method of plasma anodisation to ensure acceptable corrosion resistance. In contrast to conventional anodisation processes the aqueous electrolyte is substituted by an oxygen plasma. The main advantages are that the process uses no toxic electrolytes, there is no waste and anodising and PVD-coating can be done in one process. The article gives a brief view of our extensive work starting from the first approach in PVD deposition of magnesium alloys up to the present work in establishing the plasma anodisation.

Sufficient corrosion'resistance of technical magnesium alloys is generally ensured by anodising the components in aqueous electrolytes. In the majority of cases these processes bear environmental risks due to the highly toxically electrolytes and are subjected to substantial legal regulations. Considering these facts the plasma anodisation seems to be a prospective method to obtain good corrosion resistance without using toxic substances. The main goal of the plasma anodisation is the substitution of the aqueous electrolyte by an oxygen plasma. The plasma anodised surfaces were well characterized and the corrosion resistance was proved in the salt spray test according to DIN 50021 SS. For the tests the magnesium die cast alloy AZ91 hp was used. The tests included plasma anodised, plasma anodised and PVD coated and only PVD coated specimens. After the salt spray test the surface of plasma anodised specimens showed sporadic filliform corrosion. The plasma anodised specimens showed superior corrosion behaviour in comparison to the only PVD- coated ones. The polished magnesium as well as the as casted samples showed more corrosion attack than the anodised specimens.

Eine gangige Methode, zu beschichtende Oberflachen von Verunreinigungen zu befreien und die Adhasionseigenschaften von PVD-Schichten zu verbessern, ist das sogenannte Sputter-Atzen vor dem eigentlichen PVD-Beschichtungsprozess. Beim Sputter-Atzen wird der Beschichtungsprozess umgekehrt und die Oberflache des Substrates selbst wird gesputtert. Im Rahmen dieser Veroffentlichung wurden vor der Abscheidung von PVD-CrN Schichten die Substrate der Magnesium Druckgusslegierung AZ91 unterschiedlichen Atzzeiten unterzogen und deren jeweiliger Einfluss auf die Grenzflache Schicht-Grundwerkstoff, auf die Schichtoberflache und auf die mechanischen Eigenschaften des beschichteten Systems hin untersucht. Die Grenzflachenuntersuchungen wurden mit tiefenaufgeloster XPS und mit SIMS durchgefuhrt. Die Oberflachen wurden mit hochauflosender Rasterelektronenmikroskopie und AFM untersucht. Die Charakterisierung der mechanischen Eigenschaften beinhaltet Schichtdicke, Schichtharte, Hartetiefenprofile, Schichthaftung, Schichteigenspannungen und die Schichtstruktur. Es wurden zum Teil sehr starke Eigenschaftsanderungen mit zunehmender Atzzeit festgestellt. Dies betrifft vor allem einige mechanische Eigenschaften sowie die Oberflachenrauheit der beschichteten Systeme. Beim Schichtsystem AZ91-Cr/CrN fuhren langere Atzzeiten zu einer Verbesserung der Schichtqualitaten. Investigating the Influence of the Sputter Etching Process on the Properties of PVD-CrN Coatings on Magnesium Die Cast Alloy AZ91hp A common method prior to the PVD deposition is the sputter etching process of the substrate itself to clean the surface from adhesion products and to improve the coating adhesion. This report deals with the sputter etching of magnesium die cast alloy AZ91hp to investigate the influences on the coating-substrate interface, the surface properties and the mechanical properties of PVD-CrN hard coatings. The coating-substrate interface of the Cr-AZ91 coating systems was investigated with XPS and SIMS. Surface studies were carried out by high resolution electron microscopy and AFM. The characterization of the mechanical properties of the CrN-AZ91 compound systems includes thickness, coating hardness and hardness depth profiles, coating adhesion, structure and residual stresses. Some properties show a strong dependency of the etching time, especially the mechanical properties and the coating roughness. Increasing etching times lead to an improvement of the coating quality.

The tribological behaviour of PVD Chromium-Nitride coated magnesium alloy AZ91hp was investigated in wear tests by variation of temperature and load. A combination of different investigation methods revealed information about the failure modes and wear mechanisms. The authors show that failure of the CrN-AZ91 systems is due to the unsatisfactory load-carrying capacity of the magnesium.

In the future dry running machine elements may play a more important role, due to environmental legislation. The economical demand for cost and timesaving causes higher mechanical and thermal stresses for tools in high-speed production processes. Is it possible to improve the wear resistance by the use of thin hard coatings and will they find an area of application especially at elevated temperatures where lubricants fail? Therefore, oscillating sliding motion dry wear experiments at specific temperatures ranging from 30 to 700°C (900°C is possible) were performed on PVD-coated steels and light metal alloys. The characterisation of the coatings includes fundamental properties such as thickness, hardness, structure and residual stresses. The tribological tests were done with an SRV3 apparatus from Optimol, the coatings were tested against 100Cr6 balls using a ball-on-disk arrangement. The friction and wear behaviour was documented. The wear traces were characterised using a Hommel Tester T 8000. Topographical microanalysis was done with SEM and EDX.

An PVD-Chromnitrid beschichteten Proben der Magnesiumlegierung AZ91hp und dem WA¤lzlagerstahl 100Cr6 wurden vergleichende Untersuchungen hinsichtlich Struktur, mechanischen Eigenschaften, Haftfestigkeit und Eigenspannungen durchgefA¼hrt. FA¼r die Beschichtungen wurden die Parameter Schichtdicke und Substrat-BIAS variiert. Beide Substratwerkstoffe wurden in einer Charge zusammen beschichtet. Bei der rA¶ntgenographischen Analyse der Eigenspannungen in den Schichten zeigten sich signifikante Unterschiede zwischen dem beschichteten Magnesium und dem beschichteten Stahl. Beim Stahl war eine AbhA¤ngigkeit der Eigenspannungen vom Substrat-BIAS erkennbar, beim Magnesium war dies nicht der Fall. Die Schichtstruktur wurde im Rasterelektronenmikroskop untersucht. An den beschichteten Substraten wurden mit SIMS Element-Tiefenprofile aufgenommen.

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 CrxN coatings promise to combine the advantages of hard coatings and electropolated chromium. The present study focuses on the corrosion properties of magnetron sputtered CrxN 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. Korrosionsverhalten von CrxN beschichtetem Stahl Anwendungen von PVD-Beschichtungen im Bereich des Verschleisschutzes, z. B. TiN-Schichten auf Zerspanungs- und Umformwerkzeugen sind Stand der Technik. Im Gegensatz dazu sind Anwendungen von PVD-Schichten auf Bauteilen kaum im Einsatz. Grunde hierfur sind unter anderem Probleme bei der Schichtabscheidung, aber auch die fur Bauteile im Gegensatz zu Werkzeugen typischen kombinierten Anforderungen bzgl. Verschleis- und Korrosionsschutz. TiN (PVD) zeichnet sich durch gute Verschleiseigenschaften, nicht aber durch die Verbesserung von Korrosionseigenschaften aus. Bei galvanisch abgeschiedenen Chromschichten kann man hingegen von gutem bzw. verlasslichem Korrosionsschutz bei hinlanglich ausreichendem Verschleiswiderstand sprechen. PVD CrxN Schichtsysteme scheinen die Vorteile von Hartstoffschichten und galvanisch abgeschiedenen Chromschichten zu vereinen. Inhalt dieser Arbeit sind die Korrosionseigenschaften von mittels HF-Magnetronsputtern abgeschiedenen CrxN Schichten. Die dazu untersuchten auf Stahlsubstraten abgeschiedenen Schichtsysteme unterscheiden sich in ihrem Schichtaufbau (Gardientenschicht, Mehrlagenschicht) und in ihrer stofflichen Zusammensetzung (Stickstoffgehalt). Es konnte gezeigt werden, das das Korrosionsverhalten von allen Aufbauparametern abhangt und das 8 μm Chromnitrid denselben Korrosionsschutz liefern kann, wie 48 μm galvanisch abgeschiedenes Chrom.