ICMCTF2004 Session G1: Innovations in Surface Coatings and Treatments

Innovative PVD coatings led to a significant reduction of wear and friction and to a tremendous increase in performance of modern cutting tools. Hereupon numerous coating and substrate parameters should match and have to be adapted best to a particular application in order to meet the elevated demands of modern manufacturing procedures. Such parameters are the tool macro and micro geometry, the substrate data and especially the superficial mechanical properties and topomorphy, the coating system, the deposition process technology etc.

In the present paper the effect of some of the previously mentioned parameters, on the coated tool wear behaviour will be demonstrated and explained with the aid of finite elements method (FEM) based simulations of the cutting process. In these FEM calculations the coating elasto-plastic and fatigue properties are required. These data are extracted through nanoindentations and impact tests respectively, as it will be described. Coating and substrates internal stress alterations, during tool micro-blasting or annealing procedures occurring, have to be considered and can be detected effectively by means of nanoindentations and an algorithm developed, to evaluate the corresponding measurements results.

ZnO, TiO₂ and ZrO₂ thin films have been deposited by chemical spray pyrolysis onto differently galvanized steel strips (ThyssenKrupp Steel) for its potential use as protective layer against degradation due to ambient impact during long term outdoor exposure. The steel strips shall be used as base material for unglazed solar collectors and must thus comply including all its overcoats (oxide barrier-, selective-, antireflection layer) with manufacturing requirements for collectors as moulding, forming, cutting, etc. (EU project: SOLABS)¹. In order to improve the so-called weatherability of the galvanized steel strip by overcoating it with an oxide barrier layer, conditions as total substrate coverage, high compactness and an optical transparency better than 90% of the oxide barrier layer have to be fullfilled. These oxide barrier layers have been produced by spraying adequate aqueous precursor solutions, using air as driving gas, onto the heated steel substrate (T<300ºC) where pyrolysis takes place and the corresponding oxide layer grows. In this communication we present a comparative study of the morphological, structural, chemical and optical properties of these oxide layers (ZnO, TiO₂, ZrO₂) deposited by spray pyrolysis on three types of galvanized steel substrates. Results from complementary analytic techniques as SEM, XRD, XPS and UV/VIS/IR spectroscopy demonstrate that highly compact and thin oxide layers can be produced by spray pyrolysis protecting the steel. We would like to stress that after a preselection of the most adequate oxide barrier material, upscaling to large surfaces and high speed deposition is intended as required in a conventional coil coating technique. Furthermore we would like to mention that chemical spray pyrolysis, using air as driving gas and aqueous precursor solutions, is an environmentally friendly and, since working under ambient atmosphere, inexpensive deposition technique.

¹ http://www.solabs.net/.

Plasma surface engineering has become a key technology in Germany during the past two decades. Today plasma based processes are widespread in various industrial branches. They are used by 50% of German companies being active in the field of machine construction. A further growth is limited by high costs and a qualification deficiency. Nevertheless, a lot of companies, in particular small and medium sized enterprises plan to introduce new processes or modernize existing ones within the next two years.

New developments focus on tribological coatings like diamond-like carbon (DLC) and cubic boron nitride (c-BN). Pulse magnetron sputtering has opened the door to new applications of optical coatings on large areas. Solar cell manufacturers ask for low cost deposition of semi-conducting thin films and transparent conductive oxides. Concerning the field of information technology, high performance mirrors for EUV lithography and ultra thin carbon overcoats for magnetic disks are in the centre of interest.