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Methods for inspecting coating mechanical properties and adhesion on final products, considering quantitative criteria are of high importance. In this paper, relevant characteristic examples for determining the adhesion of a MoN and a TiC PVD coating deposited on steel substrate are introduced. The mechanical properties of the coatings and their steel substrates were determined via nano-indentations and a FEM supported evaluation of the obtained results. The coatings' adhesion and fatigue were quantified by inclined and perpendicular impact tests respectively, coupled with appropriate finite elements method (FEM) calculations. The inclined impact tests were conducted under lubricated conditions for avoiding abrasion caused by sliding friction on the coated surfaces. In this way, the coating fatigue failure during this test was mainly affected by the impact load, the film adhesion and the material's properties. Based on these results, the coating adhesion was estimated considering the impact loads and the determined material properties. [ABSTRACT FROM AUTHOR]

The below investigations aim at quantifying the effect of the residual stresses, developed in the Nano-Crystalline Diamond (NCD) coating structure on the fatigue strength of NCD coating-substrate inter-phase boundary layer (IB layer) at operational temperatures up to 400°C. A dynamic 3D-FEM thermo-mechanical model simulating the inclined impact test is employed in order to achieve this target. This FEM model takes into consideration the temperature-dependent residual stresses in the NCD coating. By means of this 3D-FEM model, the fatigue strength of the coating-substrate IB layer is quantified in terms of a shear failure stress (SFLS ) for IB layer damage after 106 impacts. This metric also depends on the treatments conducted prior to the deposition of the NCD coating for enhancing the adhesion of the coating to its cemented carbide substrate. The results of the inclined impact test using NCD coated cemented carbide inserts with improved or insufficient adhesion, were employed as input data to these FEM calculations. The effectiveness of the conducted pre-treatments prior to NCD coating deposition can be assessed and quantified by decoupling the effect of residual stress in the NCD film structure on the interfacial fatigue strength. [ABSTRACT FROM AUTHOR]

The determination of the temperature dependent interface fatigue strength of Nano-Crystalline Diamond (NCD) coatings facilitates a thorough understanding of the NCD coated cutting tools wear mechanisms. In the present paper, the fatigue strength of the interface region between a NCD film and its hardmetal substrate was investigated by inclined impact tests at various temperatures. Depending upon the impact load and the applied temperature, after a certain number of impacts, damages in the film-substrate interface develop, resulting in coating detachment and lifting. These effects were attributed among others to the release of highly compressive residual stresses in the NCD coating structure. The attained inclined impact test's results contributed to the explanation of the wear-evolution of NCD-coated tools with diverse film-substrate adhesion qualities. The related milling experiments using as work material AA 7075 T6 verified the dominant effect of the film adhesion on the NCD coated tool life. [ABSTRACT FROM AUTHOR]

This study aims to provide insights into biofilm resistance associated with their structural properties acquired during formation and development. On this account, the wetting and imbibition behavior of dehydrated Pseudomonas fluorescens biofilms grown on stainless steel electropolished substrates is thoroughly examined at different biofilm ages. A polar liquid (water) and a non-polar liquid (diiodomethane) are employed as wetting agents in the form of sessile droplets. A mathematical model is applied to appraise the wetting and imbibition performance of biofilms incorporating the evaporation of sessile droplets. The present results show that the examined biofilms are hydrophilic. The progressive growth of biofilms leads to a gradual increase of substrate surface coverage─up to full coverage─accompanied by a gradual decrease of biofilm surface roughness. It is noteworthy that just after 24 h of biofilm growth, the surface roughness increases about 6.7 times the roughness of the clean stainless steel surface. It is further found that the imbibition of liquid in the biofilm matrix is restricted only to the biofilm region under the sessile droplet. The lack of further capillary imbibition into the biofilm structure, beyond the droplet deposition region, implies that the biofilm matrix is not in the form of an extended network of interconnected micro/nanopores. All in all, the present results indicate a resilient biofilm structure to biocide penetration despite its hydrophilic nature.