Gas-atomized Cu-10Sn powders as a potential substitute for sintered bronze layers are usually employed in plain-bearing shells produced by cold spray (CS) processes on steel substrates (AISI 1010). In this study, the effective thickness, i.e., approx. 450 µm, of the bronze overlay required for the bearing shell was successfully and cost-effectively deposited in a short time. A ball-on-disc test setup was used to explore the tribological behavior of cold-sprayed bronze coatings under dry sliding conditions, and the electrochemical corrosion behaviors of sprayed coatings at room temperature were also evaluated by using the potentiodynamic scanning (PDS) technique in acidic (0.01 M Na2SO4) and alkaline (3.5% NaCl) environments. The characterization of the sprayed bronze coatings revealed no formation of oxidation or new phases during cold spraying and that the coatings were well-adhered to the substrates, implying good bonding. The wear results demonstrated that, as the load and sliding distance increased, the friction coefficients and wear rates of the sprayed coatings decreased. The PDS results showed that the corrosion resistance of the Cu-10Sn coating layer in an acidic environment is higher than that in an alkaline environment. In addition, the coated layer presented no passivation or pitting onset due to the heavy corrosion reaction in an alkaline solution.
Abstract The present work builds on investigations of cold gas-sprayed Al coatings on Al2O3, which strongly indicated that heteroepitaxial growth is a possible mechanism supporting the adhesion between metal and ceramic at their interface. The present study was focused on the deposition of Al on further ceramic substrates (AlN, Si3N4 and SiC). In particular, it should be clarified whether the different ionicity of the chemical bonding in these substrate materials influences the interface formation or not. Aluminum coatings were deposited alternatively by using cold-gas spraying (CGS) and magnetron sputtering. In CGS coatings, the effect of substrate roughness, substrate temperature and powder fraction on the adhesion of the coating was investigated. The magnetron-deposited coatings were used to evaluate the role of the heteroepitaxy in the interface formation and to identify microstructure defects in the metal/ceramic interface, which are caused solely by the lattice misfit between the counterparts and not by the impact-induced deformation that is typical for cold gas-sprayed coatings. Interface characterization was conducted by scanning electron and high resolution transmission electron microscopies combined with XRD.
Verletzungen des vorderen Kreuzbands (vKB) ohne aktive Einwirkung eines Gegenspielers sind ein groses Problem im Fusball. Als moglicher Risikofaktor wird in diesem Zusammenhang oft das Stollendesign der Fusballschuhe genannt. Ziel der Arbeit war daher die Untersuchung der Frage, ob es einen Zusammenhang zwischen dem Stollendesign der Fusballschuhe und den Belastungen im vorderen Kreuzband gibt, oder nicht.
Da Messungen wahrend Fusballspielen nicht moglich sind und Probanden aus ethischen Grunden nicht akuter Verletzungsgefahr ausgesetzt werden durfen, ist die einzige Moglichkeit zur Untersuchung der Problemstellung die Verwendung mechanischer Tests. Um hiermit aussagekraftige Daten ermitteln zu konnen ist eine moglichst realistische Belastung der Fusballschuhe wahrend der experimentellen Tests von elementarer Bedeutung.
Hierfur wurde in der vorliegenden Arbeit die Kinematik und die Bodenreaktionskraft realer Verletzungssituationen mittels der Poser-Methode bestimmt und uber eine anschliesende invers-dynamische Computersimulation die resultierenden Gelenkmomente berechnet. Diese Daten definierten die Randbedingungen fur den experimentellen Vergleich von vier unterschiedlichen Stollendesigns mit dem neu entwickelten mechanischen Testgerat TrakTester.
Bei den durchgefuhrten Vergleichsmessungen zeigten sich aussagekraftige Unterschiede bei den gemessenen Kraften und Momenten zwischen den Stollendesigns. Zur Abschatzung des Einflusses des Stollendesigns auf die Belastungen des vKB wurden aus den Messwerten, unter Berucksichtigung biomechanischer und medizinischer Erkenntnisse, Gefahrdungspotentiale fur jedes Stollendesign bei jedem untersuchten Lastfall bestimmt. Diese Gefahrdungspotentiale lassen den Schluss zu, dass das Stollendesign die Krafte im vKB beeinflusst, allerdings erheblich von den exakten Randbedingungen abhangt.
Grundsatzlich bestatigt die vorliegende Arbeit die Annahme, dass von lamellenformigen Stollen pauschal eine grosere Gefahr fur das vKB ausgeht, nicht.
Cylinder linings of lightweight combustion engine blocks made from aluminium cast alloys are typically coated with thermally sprayed layers to enhance the chemical resistance.Finish machining of the cylinder linings is currently done by honing.A substitution of this process by machining with geometrically defined cutting edges would have significant advantages, especially concerning ecological aspects.For the investigations Fe17Cr2Ni0.2C iron based coatings applicated by atmospheric plasma spraying on substrates, prepared with a dovetail microstructure are machined by turning.In the experiments the feed is varied in the range of 0.025 mm to 0.15 mm.The tools used comprise CBN tips involving a rake angle of 0°.Tool wear and machining forces are determined.The geometrical properties of the machined surfaces are detected by tactile measurements, 3D laser scanning microscopy and SEM.The residual stresses are characterised by XRD.An increase of the feed results in increasing components of the resultant machining force and higher values for Ra, Rz, Rpk, Rk and Rvk.Additionally, the amount of opened pores and pulled out coating material is reduced for high feeds.By increasing the feed the absolute values of the compressive principle stresses decrease.The increase of the knowledge in machining of thermally sprayed coatings by tools with defined cutting edges contributes to a substitution of the honing process and hence enables a more material and energy efficient production.
Abstract Mittels HVOF‐Spritzverfahren hergestellte Cermet‐Schichten für den Verschleißschutz, wie die Systeme WC‐Co(Cr) und Cr 3 C 2 ‐NiCr, haben in der Vergangenheit eine breite industrielle Anwendung gefunden. Durch den Einsatz chromhaltiger Matrizes weisen sie neben der hervorragenden Verschleißbeständigkeit auch eine gute Korrosionsbeständigkeit auf. In der gegenwärtigen Forschung im Bereich der Pulvermetallurgie und des Plasma‐Pulver‐Auftragschweißens wurden Eisenbasislegierungen mit hohem Chrom‐ und Vanadiumgehalt entwickelt, welche über ähnliche Eigenschaften verfügen und sich damit als kostengünstige Alternative zu den etablierten Cermet‐Schichten anbieten. HVOF‐gespritzte Schichten dieser Eisenbasislegierungen werden hinsichtlich ihrer wirtschaftlichen Verarbeitbarkeit und ihrer Korrosions‐ und Verschleißeigenschaften untersucht.
Reinforced PTFE materials can be designed to show high mechanical stability against harder materials under sliding wear conditions. Especially bearing metal-reinforced PTFE is of high practical interest. In this class of materials, bronze-filled PTFE was reported to obtain high wear resistance, a low coefficient of friction (COF), and excellent self-lubrication properties in sliding conditions. In the statistical approach of this work, PTFE composites reinforced with 25 vol%, 40 vol%, and 60 vol% bronze particles were evaluated against pure PTFE regarding wear behavior under varied wear test parameters, i.e., material, normal load, and sliding speed. Wear tests were planned to use a standard orthogonal array based on the Taguchi design method. An analysis of variance test was utilized to quantify the effects of test parameters on the wear behavior of the bronze/PTFE composites and pure PTFE. According to the variance analysis, the material type has the largest influence on the COF and the specific wear rate (SWR) under test conditions of this work. Both COF and SWR were found to be influenced by the material type (29.83% and 96.16%), the normal load (33.34% and 0.95%), and sliding speed (9.14% and 1.28%). The lowest SWR and COF values were achieved at the optimum wear test conditions where the wear test parameters were 1 m/s sliding speed (A4B2C2) at PTFE + 60 vol.% bronze reinforced composite 50 N application load and 0.32 m/s sliding speed (A4B3C1) at PTFE + 60 vol.% bronze reinforced composite 100 N application load, respectively.
This paper demonstrates the concept of wafer-level fabrication and integration of robust bulk SMA microactuators based on selective adhesive bonding of cold-rolled SMA sheets to silicon wafers. Contact printing of an adhesive polymer ensures a selective bonding when transferring full SMA sheets to silicon structures on a patterned wafer. The induced stress of a thin dielectric film deposited on top of the SMA sheet ensures a stable and built-in reset mechanism of the actuators. The trimorph microactuators can be actuated by indirect resistive heating using electrical current through a thin metal film. We report on the successful wafer-scale fabrication of actuator cantilevers and their characteristics. First test cantilevers show a cold-state deflection of 300 mu m which, however, is limited by the silicon substrate. Upon heating, the cantilever shows a stroke of approx. 80 mu m.
Thermal spraying is one of the most variable and diverse surface coating techniques concerning materials to be processed as well as possible geometries to be coated. The group of thermal spray processes covers a large parameter field to combine nearly each coating with each base material. Thermally sprayed coatings can be applied very evenly and therefore allow to be applied on final-shaped components. Otherwise, if further treatment or finishing is necessary, thermal spray coatings can be processed by grinding or even milling. Masking during the coating process permits the selective coating of specific surface parts or the application of required geometrically structures, e. q. conductor structures. The main application field of thermal spray coatings is the (combined) wear and corrosion protection of selected component parts.
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