Papers by Author: Emmanouil Bouzakis

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Authors: Konstantinos D. Bouzakis, G. Skordaris, Emmanouil Bouzakis, Eleftheria Lili
Abstract: If the film of a coated component deforms plastically because of operational loads, residual stresses are developed in the coating material after the load removal. In this way, material mechanical properties changes occur due to endogenous reasons i.e. induced by the coating crystalline structure plastic deformation. In this case, the determination of the effective film mechanical properties has been introduced in a recent publication [1]. Moreover, if the loading conditions lead only to a substrate plastic deformation, the coating remains elastically deformed during the relaxation, due to the substrate residual stresses. Thus, the associated material mechanical properties changes are caused by exogenous parameters related to the permanent substrate deformation. In the present paper, a novel experimental-analytical method based on FEM calculations is introduced to determine the effective film mechanical properties when the coating is stressed elastically due to a plastic substrate deformation. The perpendicular impact test is a convenient experimental procedure to investigate such an effect because under appropriate loading conditions, the substrate deforms plastically and the coating elastically. The pristine constitutive law of the applied PVD film was determined by nanoindentation and FEM supported results evaluation. Impact tests were conducted at various loads and loading cycles. The impact test was simulated by a two dimensional FEM model. Additionally, the developed elastic residual stress fields in the coating and the plastic ones of the substrate in the imprint were determined. In these calculations, a rate-independent anisotropic plasticity with kinematic hardening material law was considered and the film as an anisotropic material with variable mechanical properties in three main directions. Finally, by a FEM supported simulation of the nanoindention, the coating’s load-displacement behaviour in various areas of the impact imprint were predicted and the effective coating mechanical properties as well.
Authors: Konstantinos D. Bouzakis, M. Batsiolas, G. Malliaris, Maria Pappa, Emmanouil Bouzakis, G. Skordaris
Abstract: In the paper, innovative methods for characterizing coatings’ properties at ambient and elevated temperatures are introduced based on various experimental procedures. Nanoindentation results, which were obtained at elevated temperatures, are evaluated by FEM algorithms, rendering possible the determination of temperature dependent coating mechanical properties. Impact tests conducted on coated specimens revealed a non-linear film impact resistance versus the temperature. The latter results were evaluated by appropriate FEM supported procedures, to predict the coating fatigue endurance stress versus the temperature. In these investigations, the impact load was induced electromagnetically for a duration of ca. 1ms, depending on the force amplitude. To change the impact load characteristics, such as frequency, impact duration etc., a new test device has been developed, employing a piezoelectric actuator. This device enables the investigation of the impact time effect on the dynamic response of coated surfaces and on the coating fatigue endurance stress. Finally, diffusion phenomena in coatings were examined by a developed convenient experimental setup. A specimen is pressed onto a coated surface at adjustable high temperature and pressure in an inert atmosphere. After this test, the diffusion of characteristic elements into the coating and vice versa is detected by EDX-microanalyses. These results contribute, among others, to the description of diffusion phenomena between coatings and various materials.
Authors: Fritz Klocke, Christof Gorgels, Arne Stuckenberg, Emmanouil Bouzakis
Abstract: In today’s production engineering nearly every cutting tool is coated. In the field of coating technology and tool treatment blasting is a common way to increase tool life or hold it on a constant level for several reconditioning steps. The latest innovation referring blasting are micro blasted coatings. For this technology a parameter variation was examined and the consequential tool life was compared with common testing method for tool systems in order to qualify the coating treatment. The investigations were carried out using an aluminum and zirconium oxide as blasting abrasive and by varying the blasting parameters pressure and duration. Finally, the treatment led to an optimized tool wear behavior due to micro blasting of the coating and the wear behavior could be referenced against the testing methods.
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