The quality and operation performance of layer composites manufactured by thermal spraying is influenced by two different processes, the activation process of the surface prior to coating deposition and the coating process itself. The activation of the substrate surface is mainly performed by grit blasting operations. Surface activation by grit blasting is used in order to improve the bonding between substrate and coating, which is strongly related to the size and nature of the surface topography and roughness generated by the blasting process. Besides the roughening effect, grit blasting induces compressive residual stresses into the substrate surface which can be critical especially for thin walled components, e.g. piston rings, where the component shape is an important factor for the operation behavior and functionality. Another effect is an increase of hardness in the surface region related to the induced compressive stresses. A variety of blasting parameters can influence the surface characteristics, like nozzle diameter, grit medium and size, blasting pressure, distance and time. The influence of these parameters on the surface roughness, hardness, component deformation and residual stresses was investigated by tactile surface metrology, universal hardness and Almen tests as well as experimental residual stress analysis with the incremental hole drilling and milling method. All investigations were performed on rectangular steel strips. The results are discussed concerning quality control features for grit blasting processes in serial production.

Mechanical and tribological properties of layer composites like hardness, bonding strength, friction and wear coefficients as well as operation performance, component reliability and finally the system lifetime are mainly influenced by residual stresses after the thermal spraying and machining process. The residual stress situation in thermally spray coated composites is superimposed by different stress mechanisms occurring during the manufacturing process based on heat and mass transfer during the coating deposition. Using the microhole milling and drilling method, residual stress fields can be measured in a quasi non destructive way over the drilling depth with appropriate resolution. In several drilling and micromilling operations a circular, cylindrically shaped microhole is brought step by step into the component surface. The residual stresses are locally relieved due to material removal, deform the surface around the drilled microhole and are measured by high resolution measurement tools, e.g. strain gauges (DMS), for every drilling step in form of relaxed surface strains. Using calibration curves and material data (E, μ) the measured surface strains are converted into nominal strains at the bottom of the drilled hole for every drilling step. Out of the differentiated strains, in-plane stress fields can be incrementally determined by Hooke's law. This study describes residual stress measurement features, the FEM-calculation and idealization of calibration curves as well as results of exemplary stress measurements.

This paper aims to evaluate various measurement methods for characterizing the elastic behavior of thermally sprayed composites. The behavior of layered composite materials is determined by the interplay of residual stresses, load stresses, and bonding strength. Measuring Young's modulus in such coatings can be difficult, however, due to brittleness and inhomogeneities in microstructure. In this work, the authors determine both the influence of the indentation load on Young's modulus and that of the analysis method. Paper includes a German-language abstract.

The increasing use of magnesium alloys in many engineering applications is mainly limited by their unsatisfying surface properties, especially the poor tribological properties and the poor corrosion resistance. Therefore an effective and well designed coating technology has to be adapted to allow a successful implementation of magnesium alloys under tribological load and in an corrosive environment. This presentation gives an overview of the performance of different functional metallurgical and ceramic coatings on magnesium diecastings which are applied by atmospheric plasma spraying (APS) and high velocity oxygen fuel spraying (HVOF).

Light weight design offers a lot of interesting manufacturing and operation aspects in mechanical engineering, e.g. concerning production and material cost or energy consumption. By means of protective coatings, light metal components can also be used under extreme wear and corrosion conditions. Of tribological interest are coating systems with low friction and wear coefficients. If traditional liquid lubricants cannot be used, the tribological functions must be taken over by material surfaces with solid lubricant capability. Very promising tribological results under dry and mixed friction are obtained by thermally sprayed TiO 2 coatings. The paper presents a general overview about the tribological and mechanical properties of APS and HVOF sprayed TiO 2 coatings on different light metal materials.

Mechanical coating properties like hardness, bond strength and tribological features as well as the layer composite lifetime under thermal and mechanical operation stress conditions are mainly influenced by the residual stress situation in the composite. The final residual stress state in thermally spray coated composites is superimposed by different stress mechanisms occurring during the manufacturing process. By means of the micro milling method, residual stresses are measured in a quasi-nondestructive way over the drilling depth. This paper describes the measurement features as well as experimental and numerical results. Measurements are performed on coated plane composite specimens as well as on inside coated bushing guides of aluminum crankcases for different coating materials. The correlation between residual stresses and coating properties is investigated.

This paper evaluates a wide range of thermal spray coatings for potential use lining cylinder bores in aluminum engines. Coatings were applied by atmospheric plasma spraying (APS) and high-velocity oxyfuel (HVOF) techniques. More than a dozen coating materials were screened, including ceramics, cermets, and metals. The paper describes the equipment and procedures used in the investigation and assesses the resulting coatings based on their microstructure, hardness, friction coefficient, wear resistance, bonding strength, and residual stress.

Turbine blades in hydropower plants have to withstand the most severe seasonal loading conditions when the river water is heavily loaded with sediments. Welded blade surfaces are considered state of the art, but they cannot withstand the aggressive, eroding and abrasive loading conditions in the major rivers in China. Once a year there is flooding with a maximum amount of sediment in the river water. This is why coating systems with maximum wear resistance must be developed, examined, produced and tested over a maximum period of time. In this article, the wear results of various coating systems examined in a special test facility are described in order to obtain comparable results from several proposed coating systems together with material classification tests. Paper includes a German-language abstract.

Thermal spraying offers the possibility of applying functional metal, ceramic or cermet coatings to components with different geometries and materials and significantly improving their thermal, mechanical, and chemical properties. The performance in operation as well as failure due to deformation, cracks, and delamination are mostly determined by the internal stress state within the coated components. This paper reviews coating developments on light metal and glass substrates, sprayed with different atmospheric plasma spray process spray parameters are reviewed. The results show that from the numerical and experimental residual stress analysis, the injection parameters can be influenced individually. This leads to optimized residual stress states in the coated components with regard to the expected operating loads. Paper includes a German-language abstract.