Wear and Adhesion Optimization of Thin TiAlN Films by Structure Design
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Wear and adhesion optimization of thin TiAlN films by structure design Lugscheider E., Knotek O., Bobzin K., Beckers M., Colmenares C.1 Leyendecker A., Erkens G.2 1 2
Materials Science Institute, University of technology, Germany CemeCon GmbH, Germany
ABSTRACT The structure of TiAlN and other thin films depends on the coating method, parameter variation and an eventual treatment of the coating after deposition. Concerning the coating process, reactive sputter and evaporation parameters influence structure formation as well as plasma driven chemical reaction on the substrate surface. Besides, crystal formation and agglomeration depends on energetic level and flow rates in the coating system, the kind and number of reactive partners, temperature and specific parameters of the coating plant. Post-deposition treatments on the other hand may influence the formation of residual stresses but not the crystallization of different phases within the complete coating. Besides, mechanical treatment may change the coating’s morphology which may be important depending on the application since sometimes a columnar structure is to be optimized in size, amount and location. Thus a homogeneous coating is not always the optimum solution. In the experiments presented here we investigated the wear properties of thin TiAlN films. They were post-treated by sandblasting and heating in order to reduce frictional forces between the contacting bodies or analyze the effects of elevated temperatures respectively. These wear properties were evaluated by turning of 42CrMo4V at low cutting speed. INTRODUCTION Chemical Vapour Deposition (CVD) TiN coatings were the first to be industrially assigned by manufacturing branches. However, very soon these coatings could not fulfil the growing demands of machine cutting industry. Thus in the consequence these binary CVD TiN coatings just functioned as a starting point for different coatings being developed in the early 80’s, like Physical Vapour Deposited (PVD) TiAlN. Sputtered TiAlN films show a significant hardness increase in comparison to ordinary TiN and even beyond a remarkable oxidation resistance due to the formation of passivating oxide layers [1], which has been investigated by a number of authors [2-4]. Therefore these coatings can also be used for turning at higher cutting speeds and difficult to machine materials [5]. New concepts of coating development tend to multilayered or so-called nano-structured materials. According to a Hall-Petch relation these multilayer structures possess higher hardnesses at lower values of Young’s modulus. Such properties lead to an improvement of the coating’s performance especially at higher loads like for example in cold forming processes [6]. Especially in the field of environmentally compatible tribological systems enusing biodegradable lubricants Ti-Hf-Cr-N multilayer coatings have shown very good performance both in turning and cold forming as has been described elsewhere [7]. Nevertheless, the development of new coating concepts takes both time and money,
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