Zugl.: Stuttgart, Universiẗat, Diss., 2002.

Heidelberg, Universiẗat, Diss., 2003. / Dateien im PDF-Format.

Zugl.: Stuttgart, University, Diss., 2002.

In the current work, two different coatings, nitrocarburised (CN) and titanium carbonitride (TiCN) on M2 grade high speed tool steel, were prepared by commercial diffusion and physical vapour deposition (PVD) techniques, respectively. Properties of the coating were characterised using a variety of techniques such as Glow-Discharge Optical Emission Spectrometry (GD-OES) and Scanning Electron Microscopy (SEM). Three non-commercial, oil-based lubricants with simplified formulations were used for this study. A tribological test was developed in which two nominally geometrically-identical crossed cylinders slide over each other under selected test conditions. This test was used to evaluate the effectiveness of a pre-applied lubricant film and a surface coating for various conditions of sliding wear. Engineered surface coatings can significantly improve wear resistance of the tool surface but their sliding wear performances strongly depend on the type of coating and lubricant combination used. These coating-lubricant interactions can also have a very strong effect on the useful life of the lubricant in a tribological system. Better performance of lubricants during the sliding wear testing was achieved hen used with the nitrocarburised (CN) coating. To understand the nature of the interactions and their possible effects on the coating-lubricant system, several surface analysis techniques were used. The molecular level investigation of Fourier Transform Infrared Spectroscopy (FTIR) revealed that oxidative degradation occurred in all used oil-based lubricants during the sliding wear test but the degradation behaviour of oil-based lubricants varied with the coating-lubricant system and the wear conditions. The main differences in the carbonyl oxidation region of the FTIR spectra (1900-1600 cm-1) between different coating-lubricant systems may relate to the effective lifetime of the lubricant during the sliding wear test. Secondary Ion Mass Spectrometry (SIMS) depth profiling shows that the CN coating has the highest lubricant absorbability among the tested tool surfaces. Diffusion of chlorine (C1), hydrogen (H) and oxygen (O) into the surface of subsurface of the tool suggested that strong interactions occurred between lubricant and tool surface during the sliding wear test. The possible effects of the interactions on the performance of whole tribological system are also discussed. The study of Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) indicated that the envelope of hydrocarbons (CmHn) of oil lubricant in the positive TOF-SIMS spectra shifted to lower mass fragment after the sliding wear testing due to the breakage of long-chain hydrocarbons to short-chain ones during the degradation of lubricant. The shift of the mass fragment range of the hydrocarbon (CmHn) envelope caries with the type of both tool surface and lubricant, again confirming that variation in the performance of the tool-lubricant system relates to the changes in surface chemistry due to tribochemical interactions at the tool-lubricant interface under sliding wear conditions. The sliding wear conditions resulted in changes not only in topography of the tool surface due to mechanical interactions, as outlined in Chapter 5, but also in surface chemistry due to tribochemical interactions, as discussed in Chapters 6 and 7.

Three samples of Ti(C,N) were fabricated with 40 vol.% Ni3Al: Ti(C0.3N07), Ti(C0.5N0.5) and Ti(C0.7N0.3), as well as TiC with 10, 20, 30 and 40 vol.% Ni3Al binder addition by means of melt infiltration and sintering. Each sample was evaluated for density and microstructure before being placed in a flat cell for electrochemical testing. Open circuit potential was evaluated, followed by the application of a cathodic potential, whereby the response was tracked using Corrware corrosion software throughout the duration of potentiodynamic testing. Following corrosion testing, each sample was reevaluated for changes in microstructure and chemical composition. Ti(C,N) samples were found to have adequate resistance to corrosion, with increased resistance with increasing carbon content, however these samples demonstrated a greater frequency of breakdown and repassivation, suggesting a greater susceptibility to corrosion, despite the initial improved resistance. SEM imaging demonstrated significant crevice corrosion throughout. TiC-cermets demonstrated similar results in terms of SEM evaluation of microstructure. TiC-cermets with the lowest binder content (10 vol.% Ni3Al) demonstrated greater initial resistance to corrosion but also had the greatest potential for breakdown.

Zugl.: Darmstadt, Techn. Univ., Diss., 2007

Zugl.: Darmstadt, Techn. Univ., Diss., 2008

Lower k and low-leakage silicon carbonitride (SiCxNy ) films were fabricated using single precursor by using radio-frequency (RF) plasma-enhanced chemical vapor deposition (PECVD). We explored precursors with (1) cyclic-carbon-containing structures, (2) higher C/Si ratio, (3) multiple vinyl groups, as well as (4) the incorporation of porogen for developing low-k SiCxNy films as etch-stop/diffusion barrier (ES/DB) layer for copper interconnects in this study. SiCxNy films with k values between 3.0 and 3.5 were fabricated at T≦ 200 o C, and k~4.0-4.5 at 300-400 °C. Precursors with vinyl groups yielded SiCxNy films with low leakage, excellent optical transmittance and high mechanical strength due to the formation of cross-linked Si-(CH2)n-Si linkages.

Es werden die physikalischen Grundlagen zur inelastischen Streuung mittelschneller Elektronen im Hinblick auf die Untersuchung des Energieverlustes beschrieben. Die instrumentellen Grundlagen der Energieverlust-Spektroskopie unter besonderer Berücksichtigung des Einsatzes in Transmissionselektronenmikroskopen werden erläutert. Der Einfluß des erfaßsten Streuwinkelbereichs wird diskutiert. Es werden Möglichkeiten zur Auswertung von Energieverlustmessungen im Bereich der Interbandübergangs- und Plasmonanregungen sowie im Bereich der Anregung von tieferliegenden (Rumpf-)Zuständen angegeben. Zur Anwendung der Elektronen-Energieverlust-Spektroskopie werden einige Beispiele angeführt. Von Messungen an ionengestützt abgeschiedenen Kohlenstoff- und Kohlenstoff-Stickstoff-Schichten werden Aussagen zur elektronischen und atomaren Struktur abgeleitet. Diese Ergebnisse werden unter Berücksichtigung relevanter Strukturmodelle und Abscheideparameter diskutiert. Aus Untersuchungen von Bornitridschichten wird eine vertikale Schichtung von kubischem Bornitrid über hexagonal koordiniertem verifiziert. Die Streuphase des bei der Ionisation des Al-1s-Zustandes entstehenden Sekundärelektrons bei der Rückstreuung an den nächsten Nachbarn wird durch Untersuchung der kantenfernen Feinstruktur bestimmt. Weitere Untersuchungen kantennaher Feinstrukturen an einer amorphen SiCrAl-Schicht sowie an Kohlenstoffschichten werden vorgestellt. Mögliche Einflüsse kovalenter Bindungen auf die Ergebnisse werden dabei diskutiert. Schließlich werden räumlich hochauflösende Energieverlustmessungen vorgestellt, die zum Nachweis etwa 2 nm dicker Vanadiumoxidschichten auf Rutilkristalliten führten.

Chemnitz, Techn. Univ., Diss., 1998.