Carlos Ziebert

WEAR STUDIES AND CUTTING TESTS OF Ti–Al–N–C NANOCOMPOSITE COATINGS IN MILLING OPERATIONS – TECHNICAL COMMUNICATION

New carbon-based nanostructured composite coatings of the material system Ti–Al–N–C were deposited on cemented carbide milling tools, and their feasibility for selected dry high-speed machining operations was assessed. For this purpose, wear studies with instrumented cutting machines in dry cutting tests were carried out in milling operations on Uddeholm hardened steels (AISI H13, and, AISI A2, respectively). The tools were coated in an industrial sputtering machine of the Hauzer HTC 625 type. The new nanocomposite coatings showed a good performance in the dry cutting operations and were benchmarked versus industrial state-of-the-art coatings.

Microwave Crystallization of Lithium Aluminum Germanium Phosphate Solid-State Electrolyte

Lithium aluminum germanium phosphate (LAGP) glass-ceramics are considered as promising solid-state electrolytes for Li-ion batteries. LAGP glass was prepared via the regular conventional melt-quenching method. Thermal, chemical analyses and X-ray diffraction (XRD) were performed to characterize the prepared glass. The crystallization of the prepared LAGP glass was done using conventional heating and high frequency microwave (MW) processing. Thirty GHz microwave (MW) processing setup were used to convert the prepared LAGP glass into glass-ceramics and compared with the conventionally crystallized LAGP glass-ceramics that were heat-treated in an electric conventional furnace. The ionic conductivities of the LAGP samples obtained from the two different routes were measured using impedance spectroscopy. These samples were also characterized using XRD and scanning electron microscopy (SEM). Microwave processing was successfully used to crystallize LAGP glass into glass-ceramic without the aid of susceptors. The MW treated sample showed higher total, grains and grain boundary ionic conductivities values, lower activation energy and relatively larger-grained microstructure with less porosity compared to the corresponding conventionally treated sample at the same optimized heat-treatment conditions. The enhanced total, grains and grain boundary ionic conductivities values along with the reduced activation energy that were observed in the MW treated sample was considered as an experimental evidence for the existence of the microwave effect in LAGP crystallization process. MW processing is a promising candidate technology for the production of solid-state electrolytes for Li-ion battery.

Nano-Scale, Multi-Functional, Cubic Boron Nitride Coatings

Protective coatings for tools and components are nowadays required in an increasingly demanding and sophisticated profile with respect to the desired mechanical, tribological, physical or chemical properties. Frequently, the necessary requirements can only be realized by multi-functional coatings through a nano-scale thin film design and the selection of materials with outstanding properties. Cubic boron nitride (c-BN) is superhard, has a chemical stability against ferrous metals at high temperatures, a large thermal conductivity and is a promising protective coating for cutting tools, increasing operation lifetime and cutting speed. It can be produced by physical vapour deposition or by plasma assisted chemical vapour deposition. Up to now, for the formation of the cubic phase ion bombardment is necessary. The nucleation and the subsequent growth of the cubic phase can be described independently of the deposition method by the ion energy, ion current density, angle of incidence of the ions, growth rate, and substrate temperature. The strong ion bombardment generates a high compressive stress, which can be reduced by optimisation of deposition parameters, deposition at high substrate-temperature, post-annealing, post-ion implantation, changing of deposition parameters after nucleation of cBN, addition of a third element, and nano-composite coatings consisting of cBN and diamond-like carbon. Based on these general stress reduction mechanisms, different coating concepts are discussed allowing the production of thick c-BN coatings with reduced compressive stress and good adhesion.