AbstractZum Schutz vor mechanischen und korrosiven Einflüssen werden Radsatzwellen heute üblicherweise lackiert. Beschädigungen im Betrieb erfordern jedoch enge Inspektionsintervalle zur Überprüfung zulässiger mechanischer und korrosiver Schädigungstiefen.Die Untersuchung einer möglichen Steigerung der Korrosionsschwingfestigkeit durch induktive Randschichtbehandlung für den Radsatzwellenwerkstoff EA4T (25CrMo4+vergütet und angelassen) stehen im Fokus dieser Forschung. Hierzu wurden Verfahrensparameter der induktiven Randschichthärtung identifiziert und optimiert, um sowohl an leicht gekerbten Proben eine ausreichend hohe Einhärtetiefe und Härte der Randschicht einzustellen. Nachfolgend wurden an Luft und in 5 % NaCl‐Lösung Schwingfestigkeitsuntersuchungen für den Ausgangszustand und den gehärteten Zustand durchgeführt. Durch Gegenüberstellung der ermittelten Schwingfestigkeitsergebnisse wurde das erwartete Potenzial der Steigerung von Schwingfestigkeit und Korrosionsschwingfestigkeit bestätigt. Zur Darstellung von Steinschlag‐ und Korrosionsbeanspruchung wurden weitere Versuche mit gezielt in der Randschicht eingebrachten mechanischen und korrosiven Beschädigungen ergänzt. Die erzielten Erkenntnisse zeigen das Potenzial der Randschichthärtung für zukünftig deutlich wartungsärmere Radsatzwellen im Güterverkehr auf.

Wheelset shafts are usually coated to protect them from mechanical and corrosive influences. However, damage during operation requires close inspection intervals to check permissible damage depths. The focus of this research is to investigate a possible increase in corrosion fatigue strength through inductive surface layer treatment for the wheelset shaft material EA4T (25CrMo4+quenched and tempered). For this purpose, process parameters for inductive surface hardening were identified and optimized in order to achieve a sufficiently high hardening depth and hardness of the surface layer on lightly notched test specimens. Subsequently, fatigue strength tests were carried out in air and in 5 % NaCl solution for the initial state and the hardened state. By comparing the fatigue strength results determined, the expected potential for increasing fatigue strength and corrosion fatigue strength was confirmed. In order to demonstrate stone chipping and corrosion stress, further tests were repeated with damage specifically introduced into the surface layer. The findings indicate the potential of surface layer hardening for significantly lower-maintenance wheelset shafts in freight transport in the future.

This study discusses the development of various thermally sprayed coatings for the use in the valve industry. Based on established coating systems for wear protection, different solid lubricants were integrated into these coatings in order to optimize the wear and friction behavior at application oriented loads. Wear protection coatings based on WC/CoCr and Cr3C2/NiCr were applied. As solid lubricants, nickel-encapsulated graphite and hexagonal boron nitride were investigated. The thermal spraying processes high velocity oxygen fuel flame spraying (HVOF) and the novel ultra high velocity flame spraying (UHVOF) were investigated. The results show that through an appropriate coating composition a wear reduction of 53 % and a friction reduction of 31 % are possible.

High-velocity oxyfuel (HVOF) sprayed coatings of Cr3C2-NiCr containing solid lubricants such as nickel cladded graphite and hexagonal boron nitride were successfully developed and characterised with the aim of optimizing their friction and wear behaviour. HVOF technology was used for the integration of solid lubricants to achieve strong cohesion between particles while minimizing thermal decomposition. Coating microstructure and composition were measured and correlated to the results of tribological and corrosion tests. The integration of the solid lubricant greatly reduced friction and wear volume at room temperature, but the lubricating effect was highly dependent on atmosphere and temperature. Cr3C2-NiCr with hBN, however, tends to exhibit more stable wear resistance over a wider temperature range and can be used at temperatures beyond 450 °C.

In dieser Studie wird die Entwicklung verschiedener thermisch gespritzter Beschichtungen für den Einsatz im Armaturenbau diskutiert. Basierend auf etablierten Verschleißschutzschichten der Armaturenindustrie wurden verschiedene Festschmierstoffe in diese Beschichtungen integriert, um das Verschleiß‐ und Reibungsverhalten bei anwendungsnahen Belastungen für Armaturen zu verbessern. Für die Anwendungen wurden Verschleißschutzschichten auf Basis von WC/CoCr und Cr 3 C 2 /NiCr entwickelt. Als Festschmierstoffe wurden nickelumhülltes Graphit und hexagonales Bornitrid untersucht. Die Verfahrensvarianten Hochgeschwindigkeitsflammspritzen mit Sauerstoff (HVOF) und das neuartige Ultrahochgeschwindigkeitsflammspritzen (UHVOF) wurden untersucht. Die Ergebnisse zeigen, dass durch eine passende Beschichtungszusammensetzung eine Reduktion des Verschleißes von 53 % und der Reibung von 31 % unter anwendungsnahen Belastungen möglich ist.

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 70 th 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.

Silicon carbide (SiC) can be tribo-chemically smoothened during a self-mated sliding procedure in the aqueous environment. As well reported in the point-contact tests, this smoothening process works well due to the abundant water as oxidant. After this smoothening process, the tribo-surface is well polished, a closely mated tribo-gap naturally forms, and an ultra-low friction state is built. However, water in the tribo-gap could be insufficient in industrial applications, e.g., the seal gap in mechanical seals. In this study, the tribo-chemical smoothening behavior in such environment was researched. A surface-contact reciprocating test was used to simulate the aqueous environment where water was insufficient. After tests, compared to the published results from the point-contact tests, the same ultra-low friction state was achieved. A part of the tribo-surface was tribo-chemically smoothened. The obtained smoothened surface microstructure was consistent with the published information. Meanwhile, severe abrasive wear occurred. A porous oxygen-rich layer was found existing beneath the abrasion-induced grooves, in which numerous smashed wear debris adhered on the worn surfaces. We concluded that the shortage of water initiated the severe abrasion, meanwhile the generated wear debris aggravated the wear condition. This understanding is instructive for developing new methods to avoid the severe abrasion in the same water insufficient environment.

This investigation presents the use of the electrochemical ion detection to evaluate the permeability of TiN coatings deposited using physical vapor deposition (PVD). The ferrous iron ions Fe(II) produced due to the anodic dissolution of the substrate were used as indicators of the permeability of the coating. A Pt-mesh located on the sample surface was used as ion detector. It was polarized at the oxidation potential of Fe(II) into Fe(III). The measurements were carried out on ten different Ti-TiN coatings, deposited on steel DIN EN ISO X153CrMoV12. The samples had different degrees of permeability and they were used to evaluate the capabilities of the proposed test setup. The coatings were prepared with different interlayers and top layers thickness. Furthermore, two different structures of the TiN layer were deposited and evaluated. The measurements were done both with and without polarization of the samples. The electrochemical ion detection showed excellent capabilities to investigate the permeability of the coatings.

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.

Translation abstract Adjusting the topography of implant surfaces on a micro-scale allows improvement of osseointegration. Titanium surface modification like sand blasting is one of the known methods to alter the topography of the surface. Polyetheretherketone as a biomaterial is a suitable alternative to titanium but exhibits an inert surface character. The aim of this study was to combine the positive bulk properties of polyetheretherketone with the positive surface properties of sand blasted titanium. For the creation of particle free structured polyetheretherketone surface, four different sand blasted die were pressed on counter die polyetheretherketone to transfer the structure. Furthermore, a titanium layer was applied on the surface using physical vapor deposition. The transfer process of the four different topographies was investigated with roughness measurements and scanning electron microscope. One topography, created with aluminum oxide particles on copper, was found with the required R-a value of 1m and R-z value of 9.2m for improved osseointegration. Ein Schwerpunkt derzeitiger Implantatforschung liegt bei der gezielten Modifikation von Implantatoberflachen zur Unterstutzung der Osseointegration. Raue Oberflachen gelten generell als vorteilhaft. Bei Implantaten aus Titan bietet Sandstrahlen eine gute Moglichkeit, raue Implantatoberflachen zu erstellen. Wird Titan jedoch als Implantatwerkstoff durch ein titanbeschichtetes (6m Titan mittels physikalischer Gasphasenabscheidung) Polyetheretherketon substituiert, mussen Risiken wie Schichtabtrag oder Partikeleinbau in die Oberflache ausgeschlossen werden. Als vielversprechende Alternative wurde ein Verfahren zur Strukturubertragung mittels eines Prageverfahrens entwickelt und patentiert. Hierzu werden gezielt strukturierte Stempel auf Polyetheretherketon gepresst und anschlie ss end beschichtet. Die ubertragene Struktur nach der Strukturierung und nach der Beschichtung wurde mit Hilfe eines Konfokalmikroskops charakterisiert. Au ss erdem wurde das Schichtwachsverhalten rauheitsabhangig mittels Rasterelektronenmikroskop dokumentiert. Es konnte ein R-a Wert von 1m und R-z Wert von 9,2m fur eine der erzeugten Oberflachen zur Verbesserung der Osseointegration erreicht werden.

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.

Additional silica (silicon dioxide) nanoparticles were added in the tribo-gap to prevent the severe abrasive wear. The method was a flat surface-contact reciprocating sliding test between the sintered silicon carbide surfaces with water lubrication. Before testing, the silica nanoparticles were added in the tribo-gap. These silica nanoparticles acted as a buffer layer during the initial running-in, thus the abrasion risk was decreased. After running-in, the silicon carbide surface was tribo-chemically smoothened without severe abrasion. Comparing to the same tests without silica nanoparticles, the same ultra-low friction state (friction coefficient was approx. 0.01) was built, and the running-in period was shortened by 80 %. As has been well reported, the tribo-chemical smoothening process for silicon carbide needs abundant water, e. g., in the point-contact tests. However, in the surface-contact case, water is locally insufficient, which induces severe wear. The preset silica nanoparticles can solve this wear problem. Therefore, it is not necessary to polish the silicon carbide surfaces as the seal faces in mechanical seals. Instead, a pair of rough silicon carbide surfaces can be pressed onto each other and then proceed to a running-in with preset silica nanoparticles. After running-in, a pair of precisely mated tribo-chemically smoothened surfaces can be naturally obtained.

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.

This paper presents an experimental work on general tribological behaviour with water lubrication at elevated temperatures. A surface contact friction type with reciprocating movement is chosen to simulate the start-stop and accident working condition of mechanical seals in water pumps. From the results, when the heating temperature is above a critical value that is higher than saturation point, vaporization in friction gap firstly occurs near atmosphere side, and then expands into water side. Vaporization causes unstable friction behaviour and severe wear of the tribo-couple. Finally, potential applications of this friction test fore valuating the wear behaviour of seals at elevated temperatures are discussed.

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. (C) 2013 Elsevier B.V. All rights reserved.

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 4.5μm 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 Tc (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.

From the technological and economic point of view it is desirable to reduce the influence of defects on substrate material surface on coating and hence component performance. Defects in technical component surfaces influence the proceeding film nucleation significantly and hence determine the development of the coatings microstructure. As a consequence the subsequent functional properties of the coatings are affected. The aim of this work is to quantitatively determine the covering ability of PVD thin coatings in regard to the process parameter depending microstructure. It is known that the microstructure of PVD coatings for example depend on the process parameters such as the process gas composition and the bias voltage. Within this work CrN thin coatings with different specific microstructures due to PVD process parameter variations and additional usage of HiPIMS were deposited on various substrate materials and thoroughly characterized. Specific geometric profiles are placed in the samples surface and the profiles are measured before and after deposition processes using a μ-surf 3D surface profilometer. Based on this data a grading coefficient is calculated and the covering abilities of different thin coatings are compared. Before the deposition the substrate surfaces were prepared with Vickers indentations. Those indentations have a defined geometry and thus serve as a model for surface defects. Based on the achieved profile image data, both the depth profile of the coated Vickers indents and the two diagonals of this specific Vickers geometry can be quantified. The resolved data allows determining the residual volume of the coated Vickers indentations. The difference between the Vickers volume before and after deposition is used as a quantitative degree of coverage. The developed method allows differentiating the ability of different coatings microstructures to cover surface imperfections.