Harald Leiste

Bio: Harald Leiste is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: Thin film & Sputter deposition. The author has an hindex of 22, co-authored 118 publications receiving 1814 citations.

Microstructure and properties of low friction TiCC nanocomposite coatings deposited by magnetron sputtering

Abstract: The objective of nanocomposite coatings combining hard and lubricant phases is the development of advanced multi-functional protective thin films showing abrasion resistance, and simultaneously, low friction. Up to now, no clear relation between constitution, microstructural properties and performance of such nanocomposite coatings based on dry lubricants like carbon or MoS2 has been evaluated. Deposition techniques, constitution, properties and performance of magnetron-sputtered nanocomposite coatings in the TiCC system are presented. The Vickers hardness could be optimized to values of polycrystalline TiC thin films, and at the same time, low friction coefficients against steel, similar to diamond-like amorphous carbon, could be realized. The mechanical properties and the tribological behavior of these thin films are related to the chemical composition and the microstructure of these advanced materials, characterized by electron microprobe analysis, Auger electron spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy.

Investigation and characterisation of silicon nitride and silicon carbide thin films

Abstract: Thin films of silicon nitride (Si3N4) and silicon carbide (SiC) have been deposited by radio frequency (r.f.) magnetron sputtering of stoichiometric targets in non-reactive argon and in the case of Si3N4 additionally in reactive nitrogen–argon atmospheres. The influence of the sputtering atmosphere, the substrate temperature and the substrate bias on the composition and on the mechanical and microstructural properties of the thin films was investigated. FTIR and Raman spectroscopy was used to identify the chemical bonding configuration and to control the chemical composition. Raman investigation showed a change in the bonding configuration from amorphous silicon carbide to a crystalline structure and the incorporation of nitrogen in silicon nitride thin films with increasing substrate bias.

Graded layer design for stress-reduced and strongly adherent superhard amorphous carbon films

Abstract: Diamond-like carbon thin films for tribological applications were deposited by d.c.-magnetron sputtering of a graphite target in a pure argon atmosphere or in a reactive hydrogen or methane atmosphere at pressures between 0.1 and 1 Pa in a graded constitution to improve adhesion and reduce residual stress. The temperature of the metallic, carbon- and ceramic-like substrates was below 100°C. The mechanical, thermal, electronic and optical properties of the carbon thin films show a significant dependence on the ion energy. Below 220 eV, strongly adherent black conductive films with hardness values up to 2000 HV0.05 were obtained. Hard and superhard diamond-like carbon thin films were deposited in an energy range between 220 and 370 eV with hardness values up to 4000 HV0.05. They are insulating, optically transparent and show a high degree of hardness combined with high compressive stress in the order of 4 GPa as well as a low adhesion, which means that the critical loads of failure are below 10 N. Above 370 eV, weak black conductive films with a poor adhesion were deposited. A new concept has been realized, which allows the conservation of the positive properties of superhard films, such as high hardness, sp3 content as well as a low friction coefficient (0.08–0.17 against 100Cr6 and Al2O3) with a simultaneously decreasing stress and increasing adhesion. First, a thin TiC interface layer was deposited, and then, the ion energy was gradually increased during the deposition of the carbon layer. Critical loads of failure in a scratch test of up to 50 N were reached when applying this concept. These amorphous carbon films have shown excellent tribological properties, especially low friction coefficients and low wear under dry sliding wear conditions against 100Cr6 and Al2O3. X-ray diffraction and TEM examinations confirmed a fully amorphous structure of hard carbon films. Substrate temperatures above 200°C result in the deposition of nanocrystalline graphite-like carbon films shown by Raman spectroscopy.

High-entropy alloys

Abstract: Alloying has long been used to confer desirable properties to materials. Typically, it involves the addition of relatively small amounts of secondary elements to a primary element. For the past decade and a half, however, a new alloying strategy that involves the combination of multiple principal elements in high concentrations to create new materials called high-entropy alloys has been in vogue. The multi-dimensional compositional space that can be tackled with this approach is practically limitless, and only tiny regions have been investigated so far. Nevertheless, a few high-entropy alloys have already been shown to possess exceptional properties, exceeding those of conventional alloys, and other outstanding high-entropy alloys are likely to be discovered in the future. Here, we review recent progress in understanding the salient features of high-entropy alloys. Model alloys whose behaviour has been carefully investigated are highlighted and their fundamental properties and underlying elementary mechanisms discussed. We also address the vast compositional space that remains to be explored and outline fruitful ways to identify regions within this space where high-entropy alloys with potentially interesting properties may be lurking. High-entropy alloys have greatly expanded the compositional space for alloy design. In this Review, the authors discuss model high-entropy alloys with interesting properties, the physical mechanisms responsible for their behaviour and fruitful ways to probe and discover new materials in the vast compositional space that remains to be explored.