J. Bøttiger

Nanoindentation of amorphous aluminum oxide films I. The influence of the substrate on the plastic properties

Using nanoindentation, the elastic moduli of composite film/substrate systems of amorphous Al2O3 thin films, with the thickness ranging from approximately 3 nm (native oxide) to 300 nm on aluminum and sapphire substrates, were studied. When indenting deeper into the samples, the transition from the elastic modulus of the film to that of the substrate is found to scale with the ratio of depth of indentation to film thickness (h/t) and is described by a transitional function. The measured elastic modulus and the corresponding compliance are compared with the Doerner and Nix expression, with the parameterization of King, and with the predictions of the model of Gao et al. It is found that the measured transitional function is not a unique function applicable both to rigid/soft and soft/rigid film/substrate systems, but is sensitive to the relative mechanical properties of the film and the substrate, in contrast to the predictions of the theoretical treatments mentioned above. The comparison of the experimental results with a model based on a hydrostatic core, where the dependence of the transitional function on the relative elastic moduli of the film and the substrate is taken into account, shows a reasonable agreement.

Accelerated bone ingrowth by local delivery of strontium from surface functionalized titanium implants

Studies have indicated systemic treatment with strontium (Sr) as a potential route to increase bone quality and formation around osseointegrating implants. However, adverse effects are linked to such treatment. In this study we present a surface modification method designed for sustained local release of Sr from implants. The four groups used were prepared by a magnetron co-sputtering process and selected on the basis of Sr release data. The composition, morphology and mechanical stability of the coatings were analyzed and the Sr release profiles were investigated in vitro by washout experiments. Mesenchymal stem cells were cultured on the different coatings to evaluate potential cytotoxic effects and the effect on cellular proliferation. No indication of toxicity was found. A rodent study demonstrated a significant increase in direct bone-to-implant contact and peri-implant bone volume, for several of the groups, four weeks after implantation when compared to a Grade 4 titanium reference group. Median values of bone-to-implant contact and new bone formation was found to be 19% and 53%, respectively, for the best group compared to 0% for both parameters with respect to the Grade 4 titanium reference. The results indicate that this method may have applications within the orthopedic and dental industry.

On plasma nitriding of steels

Abstract With the aim of optimizing the nitriding process, experimental studies of the plasma nitriding of four selected steels were carried out, using a d.c. glow discharge. The process parameters were varied systematically. By means of transmission and scanning electron microscopy and X-ray diffraction, the microstructures, including the thicknesses of the compound zones and the diffusion zones of the nitrided steels, were obtained. Using cross-sectional samples and a micro-Vickers indenter, hardness depth profiles were also obtained. From the time and temperature dependences of the hardness profiles, effective diffusion constants and corresponding activation enthalpies were obtained. Furthermore, in an attempt to shed some light on the atomistic nitriding mechanisms, the glow discharges were studied by measuring energy spectra of the energetic ions hitting the cathode (the steel test specimens). It was shown that an increase of the mean energy of the ions bombarding the steel significantly increases the number of N atoms taken up by the steel.

Deposition, microstructure and mechanical and tribological properties of magnetron sputtered TiN/TiAlN multilayers

By using unbalanced magnetron sputtering, TiN/TiAlN multilayers with bilayer lengths from 10 nm to 30 nm and thickness of 3 μm were deposited on steel substrates. The multilayer microstructure was characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy; and the chemical composition by Rutherford backscattering and elastic recoil detection analysis. The mechanical properties were investigated by nanoindentation and stress measurements, where the radius of curvature of the substrate was measured. Tribological properties were obtained by pin-on-disc measurements. Similar hardness values were observed for the multilayers and the single-layer coatings, while large improvements of the wear properties were observed for the multilayers compared to the single-layer coatings. This was connected to a change in wear mechanism, the adhesive wear being significantly reduced in the multilayers.

Diffusional aspects of the solid state amorphization reaction

Abstract Diffusional aspects of the solid state amorphization reaction (SSAR), specifically in early transition metal-late transition metal (ETM-LTM) systems, are considered. Self- and tracer diffusivities of ETM and LTM components in crystalline and amorphous phases are reviewed. The alloy characteristics leading to fast diffusion of LTM species and to good glass-forming ability are described. The nucleation of the amorphous phase in the SSAR is analysed, drawing parallels with interstitial-substitutional diffusion in semiconductors. Interdiffusion in amorphous ETM-LTM phases is considered in detail, taking into account stress effects, structural relaxation and the mixing thermodynamics of the amorphous phase.

Development of texture in TiN films by use of in situ synchrotron x-ray scattering

During growth, the microstructural development of TiN films was studied—especially the change in texture with film thickness. The films were deposited by use of a magnetron sputtering source in a vacuum chamber equipped with two magnetron sources and mounted on a goniometer located at a synchrotron radiation beam line. X-ray diffraction and reflectivity measurements were carried out in situ to follow the microstructure as a function of film thickness. With the deposition parameters that were chosen, a crossover was observed: grains with a (002) plane parallel to the film surface dominated at small thicknesses, while, at larger thicknesses, (111) grains dominated. Recrystallization was identified as a mechanism that controls this texture development. The driving force for change of orientation of the individual grains arose from minimalization of the sum of the surface energy and the strain energy of the individual grains.

Low‐Cost High‐Performance Zinc Antimonide Thin Films for Thermoelectric Applications

Zinc antimonide thin films with high thermoelectric performance are produced by a simple sputtering method. The phase-pure Zn(4)Sb(3) and ZnSb thin films fulfill the key requirements for commercial TE power generation: cheap elements, cheap fabrication method, high performance and thermal stability. In addition, two completely new meta-stable crystalline phases of zinc antimonide have been discovered.

Nanoindentation of amorphous aluminum oxide films. II: Critical parameters for the breakthrough and a membrane effect in thin hard films on soft substrates

Abstract By means of nanoindentation, the sudden advances of the tip (“pop-ins”) were systematically studied in thin hard films on soft substrates (amorphous aluminum oxide films on aluminum). The critical load and critical indentation depth at the breakthrough of the film were measured as a function of the film thickness. A model, based on the load-induced expansion of the plastic zone in the film, is developed to describe the critical parameters. The model predictions are in good agreement with the measured values for large film thicknesses, while deviations are observed for the thinnest films. These deviations are attributed to a membrane effect in the hard film/soft substrate system. The contribution of this effect is analyzed in comparison with estimates based on a model of a yielding substrate under film deflection and on another model of a “plate on elastic foundation”.

A parametric study of the microstructural, mechanical and tribological properties of PACVD TiN coatings

Abstract In order to design coatings with optimal wear and corrosion performance, knowledge of the structures and properties of the coatings and their dependence on the process parameters is required. Coatings of TiN deposited onto tool steels using an industrial, pulsed DC plasma-assisted chemical vapour deposition chamber were investigated. The process parameters, i.e. voltage, pressure, and flows of H 2 ,, Ar, N 2 and TiCl 4 ,, were varied. The microstructural, mechanical and tribological properties of the coatings were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nanoindentation, pin-on-disc measurements and Rutherford backscattering spectrometry. The residual stress level and hardness varied significantly with changes in the process parameters, whereas the tribological properties displayed only minor variations.

Ionic conductivity and thermal stability of magnetron-sputtered nanocrystalline yttria-stabilized zirconia

Thermally stable, stoichiometric, cubic yttria-stabilized zirconia (YSZ) thin-film electrolytes have been synthesized by reactive pulsed dc magnetron sputtering from a Zr-Y (80/20 at. %) alloy targ ...