The wear resistance of thermal spray coatings mainly depends on coating properties such as the microstructure, hardness, and porosity, as well as on the residual stress in the coating. The residual stress is induced by a variety of influences e.g., temperature gradients, difference of the thermal expansion coefficient of the coating/substrate materials, and the geometry of the components. To investigate the residual stress, the impulse excitation technique was employed to measure the Young’s and shear moduli. The residual stress was determined by the hole-drilling method and x-ray diffraction. Pin-on-Disk and Pin-on-Tube tests were used to investigate the wear behavior. After the wear tests, the wear volume was measured by means of a 3D-profilometer. The results show that the value of the residual stress can be modified by varying the coating thickness and the substrate geometry. The compressive stress in the HVOF-sprayed WC-Co coatings has a significant positive influence on the wear resistance whereas the tensile stress has a negative effect. © 2015, ASM International.

WC-W2C iron based cermet coatings are widely used in the field of wear protection. In surface engineering, machine hammer peening (MHP) is a novel surface treatment technology, which enhances the surface properties, especially for surfaces in tribological contact. In this study, the wear behavior of peened WC-W2C FeCrCMnSi arc sprayed coatings is characterized and compared to conventional coatings under as-sprayed conditions. The resulting strain hardening effects were measured by mechanical response using nanoindentation. In addition, residual stresses at the surfaces were determined using X-ray diffraction and the sin2ψ method. © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license.

In this research work HVOF WC-12Co coatings were deposited on C45 steel (1.0503) substrates. Unfavorable residual stresses can lead to delamination and spallation and thus have to be avoided by optimizing the handling parameters. This study investigates the influence of the following handling parameters: substrate temperature, number of overruns, stand-off distance, track pitch, and gun velocity on the residual stress and hardness. Additionally, the effect of post-treating the coating by means of surface grinding was determined. For the HVOF spraying experiments, fine agglomerated and sintered WC-12Co powders (2-10. μm) with WC particles in the submicron range (400. nm) were chosen. It was determined that alterations of these handling parameters had significant effects on the residual stress and the hardness. © 2014 Elsevier B.V.

The objective of this article is to develop and apply a model for the design and evaluation of X-ray diffraction experiments to measure phase-specific residual stress profiles in multilayer systems. Using synchrotron radiation and angle-dispersive diffraction, the stress measurements are performed on the basis of the sin2ψ method. Instead of the traditional Ω or χ mode, the experiments are carried out by a simultaneous variation of the goniometer angles χ, Ω and φG to ensure that the penetration and information depth and the measuring direction φ remain unchanged when the polar angle ψ is varied. The applicability of this measuring and evaluation strategy is demonstrated by the example of a multilayer system consisting of Ti and TiAlN layers, alternately deposited on a steel substrate by means of physical vapour deposition. © 2014 International Union of Crystallography.

Currently, the determination of the mass loss is usually used for a quantitative evaluation of wear tests, while the analysis of wear tracks is utilized for a qualitative evaluation of wear. Both evaluation methods can only be used after the wear testing process and their results only present the final outcome of the wear test. However, the changes during the wear test and the time-dependent wear mechanisms are of great interest as well. A running wear test in a large chamber scanning electron microscope (SEM) offers the first opportunity to observe the wear process in situ. Different wear mechanisms, such as the adhesive, abrasive wear, surface fatigue and tribochemical reaction, can be recorded with high magnification. Within this research, a special pin-on-disk testing device is designed for a vacuum environment. Using this device, arc-sprayed NiCrBSi coatings and high-velocity-oxygen-fuel-sprayed WC-12Co coatings were tested in a large chamber SEM with Al2O3 ceramic balls as wear counterparts. During the wear testing, different wear mechanisms were determined and the processes were recorded in short video streams. © 2014, ASM International.

Residual stresses in the substrate and in the PVD coating have a significant influence on the coating adhesion and lifespan of machining as well as forming tools. Therefore, the understanding and control of the system's residual stresses will lead to a better performance of the coated components. Moreover, although investigations were conducted in the field of stress analysis of PVD coatings, they do not focus on interdependencies of residual stresses in the substrate and in the coating. In this investigation, three different metallographically prepared substrates were used. SiC grinding, diamond grinding, and SiC grinding and plasma nitriding preparations were selected, due to the substantial differences in their final residual stress states. Additionally, a Ti/TiAlN multilayer coating and a reference TiAlN monolayer were deposited on each pre-treated substrate. Their initial and final residual stress states were measured by means of X-ray diffraction. In addition to the residual stress analyses, tribo-mechanical tests, such as nano-indentation, ball-on-disc, and scratch tests were performed in order to correlate the results with these residual stress states. © 2014 Elsevier B.V.

In this research work, Ti/TiAlN multilayers of various designs were deposited on substrates pretreated by nitriding and etching procedures. The influence of the multilayer design on residual stress depth profiles was systematically analyzed for multilayers with different Titanium interlayer thicknesses. The depth-dependency of stress was measured by a modified sin2ψ method, using various defined gracing incident angles and measuring angles that ensure constant penetration depths. The residual stresses were investigated by synchrotron X-ray diffraction (SXRD) at the HASYLAB at DESY in Hamburg, Germany. SXRD allows a phase specific stress evaluation of the ceramic and metallic layers of the multilayer systems and the adjacent substrate region. This investigation reveals an influence of the Ti layer thickness on the values and the slope of the residual stress profile in ceramic TiAlN layers. © (2014) Trans Tech Publications, Switzerland.

Even though the application of thermal spray coatings on complex geometries gained a greater interest in the last decade, the effect of different geometrical features on the wear behavior is still ill-defined. In this study, the wear resistance of FTC-FeCSiMn coated 3D surfaces was investigated. The wear test was carried out by means of two innovative testing procedures. The first test is a Pin-on-Tubes test where the rotating motion is realized by a lathe chuck. The specimens in the second test were fixed on the table and a robot arm operated the pin. This wear test was applied on specimens with concave or convex surfaces. The residual stresses, which were determined by means of an incremental hole-drilling method, show a dependency on the substrate geometry. The obtained stresses were put in relation to the different radii. After the wear test, a 3D-profilometer determined the wear volume and the sections of the coatings were characterized by a scanning electron microscope. The results indicate that the wear resistance is strongly influenced by the geometry of the substrate. © 2013 ASM International.

Thermally sprayed coatings are usually defined by their hardness, porosity, roughness, and wear resistance. Even though the Young's modulus is an essential property, which describes the mechanical behavior of the coated components during their use, only few efforts have been made in the past to determine this property. The most common measurement methods of the Young's modulus of thermally sprayed coatings are tensile tests, bending tests, and nanoindentations. During the tensile and bending tests a sliding of the splats can occur due to the laminar structure of the thermally sprayed coatings, influencing the measurement value. When using the nanoindentation test, only the elastic behavior of some splats can be determined because of a minimal measuring volume. However, the Young's modulus of thermally sprayed coatings can also be determined by means of a resonant method, called impulse excitation technique. In this paper, the values of the Young's moduli of thermally sprayed coatings, measured by several methods, are compared with each other and correlated to the microstructure of the coatings, investigated by means of scanning electron microscopy. © 2012 ASM International.

In this research work, Ti/TiAlN multilayers of various designs were deposited onto substrates pretreated by different etching procedures. The influence of multilayer design and substrate pretreatment on multilayers adhesion, hardness, wear and friction coefficients was systematically analyzed and correlated with residual stresses of these multilayers as well as with residual stresses on the coating-near substrate region, which were analyzed by synchrotron X-ray diffraction at HZB-BESSYII. These investigations show that the adhesion can be improved by a specific etching procedure, which cause increased compressive stress in the coating-near the substrate region. Additionally, it was found, that the multilayer with the thickest ceramic layers has the highest hardness and the lowest wear coefficients as well as the lowest compressive residual stress within studied multilayers. © 2011 Elsevier B.V. All rights reserved.

Hard and wear resistant thin layers provides significant improvements in tools employed in manufacturing industry and are recently of great interest to increase as well as to enhance the tools? performance and lifetime. Ceramic PVD-layers already feature a high hardness combined with a high abrasive wear resistance. However, such layers possess only a limited lifetime due to their low toughness. To increase the toughness as well as the durability of such layers multilayer systems are steadily developed. This research work presents the first results of the influence of the steel substrate pretreatments, multilayer designs and coating process parameters on the properties of two innovative PVD metal-ceramic multilayers, Ti/TiAIN and Cr/CrAIN. It was obviously that the substrate pretreatment and the multilayer design have a large influence on the layer properties and residual stresses. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.