Abstract This paper presents novel results of a series of experiments intended to study the role of the size of the feedstock powder on the microstructure of the deposits. For this purpose, Metco and the feedstock powder, yttria-stabilized (8% wt) zirconia, with number-weighted mean particle sizes of 32, 47, 56, and, 88 micrometer, are used. Small-angle neutron scattering and multiple small-angle neutron scattering (MSANS) methods are applied to determine the microstructure of the four deposits. Companion indentation measurements are performed to determine the elastic moduli of the deposits. The paper also discusses the MSANS 3-void model in relation to the anisotropic elastic properties. Paper includes a German-language abstract.

Abstract The melting of plasma-sprayed thermal barrier coatings (TBC) using highly concentrated energy sources is one of the methods associated with increasing the density of the sprayed material and modifying the phase composition in order to improve the properties of these coatings. This paper presents the results of the investigations into TBC melting using pulse and continuous carbon dioxide lasers. Paper includes a German-language abstract.

Abstract In this paper, plasma sprayed thermal barrier coatings (TBCs) with and without bond coat are stressed to various stress levels under four point bending with in situ acoustic emission (AE) to monitor any cracking activities. Micro- and macro-cracks occurring during the tests are investigated to better understand the failure mechanisms of TBCs. The results show that limited AE activities were detected in the first four stress-relief cycles, while plastic deformation and the greatest AE activity were observed when the applied load exceeded the yield point. In addition, they show that a TBC system that contained an adhesive layer had less AE activity (cracking events) than the TBC without an adhesive layer. In addition, the samples tested at a main speed of 5 micrometer/s resulted in a higher AE activity than the samples tested at 10 micrometer/s. With increasing plastic deformation, macro cracks and surface cracks also occurred. Paper includes a German-language abstract.

Abstract In this paper, the mechanical properties and cracking features of yttria stabilized zirconia with and without bond coat on steel substrates is investigated. Four point bending tests have been used to evaluate the mechanical properties, while acoustic emission (AE) has been used to in situ monitor the cracking behavior during the bend tests. In the sprayed state, the samples were characterized by four-point bending tests with local noise emission. In comparison with the substrate, the coated samples showed an increased flow pressure. It is also shown that the processing parameters, the cooling, and the adhesive layer have a significant influence on the flow pressure. It is proven that the cooling affects the behavior of the load-displacement curves. The AE analysis shows the different deformation behavior of the coating-substrate system for the different processing conditions. This is supported by the surface crack analysis. Paper includes a German-language abstract.

Abstract The formation of the microstructure is influenced by a number of parameters. The spray angle is considered to be one of the most important and difficult to control parameters, especially for substrates with complex shapes. In this paper, the influence of the spray angle on the microstructure of gray aluminum oxide and yttrium oxide stabilized (8% by weight) zirconium oxide applications is investigated. Plots are made from each material at four spray angles (90 degree, 70 degree, 55 degree, and 45 degree). Their microstructure is characterized by means of intrusion porosimetry and SEM. The results show clear differences between the two materials. The aluminum oxide microstructure is significantly influenced by the spray angle, while the YSZ microstructure is almost independent of the spray angle. Paper includes a German-language abstract.

Abstract This paper evaluates different techniques for measuring bond coat surface roughness, explores the influence of different thermal spray processes on the surface roughness of bond coats, and correlates bond coat surface roughness with spray parameters. The results of an evaluation of various techniques for measuring the surface roughness of the adhesive layer including the influence of the thermal spraying process, the powder size, the travel speed, and the coating thickness on the roughness of the thermal barrier coatings (TBCs) adhesive layers are presented. Light microscopy, a needle-tracking profile stylus, and non-contact interferometry with white light are used to characterize the adhesive layer surfaces. The results show that the measurement technique used had significant effects on some of the measured surface roughness values. Paper includes a German-language abstract.

Abstract Yttrium oxide-stabilized zirconium dioxide is mainly used in thermal barrier coatings. However, the desired higher gas inlet temperatures have initiated the search for novel materials. Low thermal conductivity and high melting points are important criteria for the selection of these materials. This paper investigates a zirconate material with a pyrochlore structure and a high melting point. In addition, it investigates the sintering behavior of the coatings at elevated temperatures. Dilatometer tests are carried out at 1200 deg C for at least 70 hours. For samples which had been annealed for 24 hours at 1250 deg C, the change in the porosity distribution is determined by means of mercury porosimetry. The paper presents the first results of thermal cycling tests on a plasma-sprayed coating. These first results are very promising. Paper includes a German-language abstract.

Abstract Thermal barrier coatings systems are composed of a zirconium dioxide-(6 to 8 wt.%) yttrium oxide ceramic top coat about 300-500 micrometer in thickness, deposited either by air plasma spraying or electron beam assisted physical vapour deposition, over an MCrAlY (M = Ni, Co or NiCo) bond coat, about 100 micrometer thick, deposited by vacuum plasma spraying. In this paper, the stiffness of as-sprayed zirconia is measured using three different techniques, namely cantilever beam bending, ultrasonic resonance and nanoindentation. The paper explores the effect of post-deposition heat treatment on the value obtained. The results show that the cantilever bend technique, employed with a high precision scanning laser method of displacement measurement, was found to be the most reliable procedure. Paper includes a German-language abstract.