Laser-Interference-Metallurgy is a rather new surface processing technology, allowing a quick as well as direct structuring of geometrically precise periodic and long range ordered microstructures on macroscopic areas. In this technique, a high power nanosecond laser pulse is split into several coherent sub beams which interfere on the surface of the sample. This technique facilitates various metallurgical processes such as melting, recrystallization, recovery and the formation of intermetallic phases for example on the lateral scale of the microstructure but also topography effects in metals, ceramics or polymers. With regard to topography effects, laser surface texturing is for many years an established method to reduce stiction in magnetic storage devices or to enhance the tribological properties by the production of micro dimples serving as lubricant reservoirs.

In this research work, we will focus on the microstructural tailoring of metallic multilayer thin films i.e. TiAl multilayer films. The idea is to create lateral periodic intermetallic phase composites consisting of hard and soft regions and therefore providing an improved wear resistance. Many classical wear theories only emphasize the importance of hardness as the main factor influencing wear resistance. According to Archard´s equation, the volume loss per sliding distance is linearly proportional to the applied normal load F_N and reciprocal to hardness H. Recent studies revealed the relevance of the ratio of hardness to Young´s modulus (H/E), called the elastic strain to failure. Therefore, thin films being composed of hard hard intermetallic phases laterally arranged in a ductile matrix could exhibit superior properties. By controlling the size and distribution of the corresponding phases, it could be possible to make a balance between hardness and elastic modulus which is decisive with respect to tribological applications.

The tests were made in moist air, dry nitrogen and vacuum. The tests made under vacuum made use of the in-situ SEM capability of the micro-tribometer yielding a near realtime image record of the deformation that had taken place.

The coatings that were examined included TiN, TiAlN, CrN, MOST, and various types of DLC coatings.

The deformation that took place was evaluated with confocal optical microscopy and AFM.

It was found that the friction and wear that was found was dependent on both the contact geometry and the test environment. These results are discussed with respect to observations of the scratches made with a high resolution SEM.

Nanoindentation has become one of the most widely used techniques for measuring mechanical properties of thin films. Conventionally, nanoscratch and nanoindentation tests are performed on the surface of the films to evaluate its mechanical integrity, elastic modulus and hardness. However, in complex systems such as compositionally graded thin films, small spatial variations in mechanical properties are difficult to distinguish using this approach. In this work, polished cross sections of functionally graded CVD mullite coatings on silicon carbide substrates have been evaluated. To assess the intrinsic mechanical properties and their spatial variation, nanoindentation tests have been carried on mullite coatings with constant and graded Al:Si ratios. Additionally, transverse nanosctratch tests to evaluate the adhesive and cohesive resistance of the coatings and the structural integrity of the system were preformed. Different damage morphologies were identified at the interface and inside the coating by using complementary characterization techniques. In the case of functionally graded coatings a gradual increase in the hardness and elastic modulus with increasing distance from the substrate/coating interface was observed. Nanoscratch on the cross sections allowed the determination of the critical loads for adhesive and cohesive damage. Graded coatings exhibited the best combination of properties for structural applications.

Contact resonance force microscopy (CRFM) has been used to evaluate the elastic properties of multilayered films for flexible display: LiF, Alq3 and aluminum. With CRFM, quantitative images of the spatial distribution in nanoscale elastic properties were acquired. The average values of plane strain modulus for each layers were 62.1 ~ 65.4 GPa, 11.5 ~ 13.0 GPa and 74.8 ~ 76.3 GPa for the LiF, Alq3 and aluminum, respectively. Obtained values showed good agreement ( ~ 15 % difference) with values determined by nanoindentation. These results provide insight into using CRFM methods to attain reliable, accurate measurements of elastic properties on the nanoscale.

In the tribology research community, efforts are underway to develop improved lubricants and lubricant additives to improve energy efficiency. With the advent of nanotechnology, research into lubricants and lubricant additives has experienced a paradigm shift. New nanomaterials and nanoparticles are currently under investigation as lubricants or lubricant additives because of their unusual properties as alternatives to traditional materials. Most of these investigations focus on the nanoparticle film friction on one type of surface rather than investigating nanoparticle friction in relation to surface roughness and structure. By contrast, it has been shown that even a 1-2 nm roughness can significantly affect adhesion and friction in the case of dry lubrication. However, to date, there is still no general theory for the interactions of rough and structured surface coatings across either nanoparticle films or any systemic experiments that identify the main trends. Therefore, it is increasingly necessary to correlate adhesion and friction of nanoparticle films to surface roughness morphology and compliance. This presentation will highlight the current state of art on these issues and describe our recent results on effects of surface coating roughness, structure, and mechanical properties on the adhesion and friction interactions across nanoparticle films.