Saxonian Institute of Surface Mechanics

Ummanz, Germany

Saxonian Institute of Surface Mechanics

Ummanz, Germany
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Seibert F.,Balzers Ag | Dobeli M.,ETH Zurich | Fopp-Spori D.M.,Balzers Ag | Glaentz K.,Balzers Ag | And 4 more authors.
Wear | Year: 2013

Cathodic arc evaporation was utilized to synthesize Cr-N, ta-C, Al-Mo-N, Mo-N, Mo-O-N and Mo-Cu-N coatings. The coatings were characterized with respect to their stoichiometry, morphology and mechanical properties. A reciprocating wear test was used to compare the wear behavior for the unpolished coatings under dry conditions and polished coatings under lubricated (Mo-DTC) conditions. The test allows a classification of the coatings with respect to material transfer similar to scuffing or fretting and with respect to wear of the counter-part and may be utilized for a pre-selection of coatings for engine tests. © 2012 Elsevier B.V.


Schwarzer N.,Saxonian Institute of Surface Mechanics | Duong Q.-H.,CSM Instruments SA | Bierwisch N.,Saxonian Institute of Surface Mechanics | Favaro G.,CSM Instruments SA | And 4 more authors.
Surface and Coatings Technology | Year: 2011

The proper design of wear resistant coatings applied to cutting tools comprises the optimization of the mechanical properties (Young's modulus, yield strength, adhesion, intrinsic stresses, fracture, fretting etc.) of the coating-tool system. The goal is to find material and structural solutions which keep the resulting stress-strain field under typical application conditions below the stability limits of the system. Based on nanoindentation measurements obtained from the coating-tool system which should be optimized, a scratch test is dimensioned with respect to load range and indenter geometry. The measured data from this "Physical Scratch Test" are used to simulate spatial stress profiles and to calculate the von Mises stress characteristics and the maximum normal stresses in the scratch direction. In a further step, the simulations are used to suggest scratch parameters for a "Fine Tuned Scratch Test" which increase the sensitivity of the test for specific depth regions in the coating-tool architecture and allow improved and more sensitive investigations of critical interfaces, transition layers and surface-near substrate regions. The tests were performed at PVD coated inserts (nitrides and oxides) and compared with the results obtained from cutting tests. © 2011 Elsevier B.V.


Liskiewicz T.W.,University of Leeds | Beake B.D.,Micro Materials Ltd. | Schwarzer N.,Saxonian Institute of Surface Mechanics | Davies M.I.,Micro Materials Ltd.
Surface and Coatings Technology | Year: 2013

In this work, a new global increment nano-fretting wear model based on the effective indenter concept has been used and the results were compared with experimental data. A series of DLC coatings with varied mechanical properties was deposited using industrial scale PECVD system and characterised on a low-drift nanomechanical test platform (NanoTest Vantage). 4500. cycle nano-scale fretting measurements have been performed in order to examine the tribological properties of the coatings. A physical analysis of the nanoindentation test enabled the true coating Young's Modulus (E) and the coating yield strength (Y) to be determined. In comparison to the hardness (H) this is the basis for a more generic understanding of the mechanical coating behaviour. This allowed a direct examination of the influence of the variation of Y/. E in the coatings on the observed nano-fretting wear, with the coating with highest Y/. E showing significantly improved resistance to nano-fretting wear. A preliminary evaluation of the stress field evolution during the test and the extraction of wear and fretting parameters provides the opportunity to discuss the effects possibly being dominant within the nano-scale tribo-tests. © 2013 Elsevier B.V.


Sebastiani M.,Third University of Rome | Bemporad E.,Third University of Rome | Schwarzer N.,Saxonian Institute of Surface Mechanics | Carassiti F.,Third University of Rome
Solid Mechanics and its Applications | Year: 2014

In this chapter, we present an overview of an optimized method for the determination of surface elastic residual stress in thin ceramic coatings by instrumented sharp indentation. The methodology is based on nanoindentation testing on focused ion beam (FIB) milled micro-pillars. Finite element modeling (FEM) of strain relief after FIB milling of annular trenches demonstrates that full relaxation of pre-existing residual stress state occurs when the depth of the trench approaches the diameter of the remaining pillar. Under this assumption, the average residual stress present in the coating can be calculated by comparing two different sets of load-depth curves: the first one obtained at the center of stressrelieved pillars, the second one on the undisturbed (residually stressed) surface. The influence of substrate's stiffness and pillar's edges on the indentation behavior can be taken into account by means of analytical simulations of the contact stress distributions. Finally, the effect of residual stress on fracture toughness and deformation modes of a TiN PVD coating is analyzed and discussed here. © Springer Science+Business Media Dordrecht 2014.


Sebastiani M.,Third University of Rome | Bemporad E.,Third University of Rome | Carassiti F.,Third University of Rome | Schwarzer N.,Saxonian Institute of Surface Mechanics
Philosophical Magazine | Year: 2011

We present a new procedure for the determination of surface elastic residual stress by instrumented sharp indentation, based on nanoindentation testing on focused ion beam (FIB) milled micro-pillars. Finite element modeling (FEM) of strain relief after FIB milling of annular trenches demonstrates that full relaxation of pre-existing residual stress state occurs when the depth of the trench approaches the diameter of the remaining pillar. Considering this, the average residual stress present in the sample material can be calculated by the comparison of two different sets of load-depth curves, the first one obtained at the center of stress relieved pillars, the second on the undisturbed (residually stressed) surface. Analytical modeling of the contact stress distribution in non-halfspace conditions was adopted to take into consideration the additional boundary conditions given by the edges of pillars and the elastic properties of the substrate (in case of coatings). The results are presented for residual stress evaluation of a 3.8-μm TiN coating on WC-Co substrate obtained by cathodic arc evaporation-physical vapor deposition (CAE-PVD) techniques, showing an average compressive stress state of -5.63 GPa. This result is in close agreement with the estimation obtained by XRD (sin 2 ψ method) analysis of -5.84 GPa of the same sample, adopting the same elastic constants. © 2011 Taylor & Francis.

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