The newly designed abradable coatings are usually validated by rig tests, where samples are rubbed by the contact of a dummy blade with given running speed and incursion rate, simulating actual working conditions in an aircraft engine. The aim of this work was to develop a model of abradable coating rig tests, allowing extensive studies on the influence of coating properties and test conditions on the thermal behaviour of the system. The proposed model includes several steps implementing different numerical tools. Firstly, a relevant structural description of an abradable coating is obtained from micrographs, using an original image analysis route. FE (Finite Element) calculations based on this description allow then to estimate the coefficients of an anisotropic elastic law of mechanical behaviour. Furthermore, a plasticity law is deduced from a FE simulation of the material HR15Y hardness. These parameters are used as input of a FE simulation of a single blade-to-coating rubbing hit, resulting in calculated stresses and temperatures. Finally a global approach of the complete abradability test, based on the results obtained from the simulation of a single hit and on various assumptions, provides predictions of the blade and coating temperature variations versus time during a complete abradability test.

Abradable coatings are widely used in aerospace turbine engines to improve seal performance between rotating and stationary parts and thus the engine efficiency. As they are elaborated by thermal spraying of composite powders, these materials are highly heterogeneous. Their behaviour in working conditions is quite complex and not fully understood. This study contributes to a better knowledge of the mechanical behaviour of a range of abradable coatings. Finite Element calculations were derived from the analysis of micrographs and allowed to estimate the coefficients of an anisotropic elastic law of behaviour. Several models were investigated in the case of an AlSi-PE (Polyester) coating. As the PE % appeared to be a determinant factor, its influence was quantified ranging from 0% to 100%, using virtual micrographs deduced from the original ones. The computed Young's moduli Ex (in coating longitudinal direction) were quite consistent, considering the hypotheses made. An empirical relationship giving the variation law of Ex versus the PE % was suggested and applied to predict the modulus Ex of a real coating, which was close to the measured value.

The aim of this study is to develop for thermal barrier applications a new process in which coatings exhibit properties between those of APS and EBPVD. This process includes two conventional D.C. plasma torches working in a chamber whose pressure can vary between 30 and 100 kPa. Micro-sized yttria stabilized zirconia powders are injected in both plasma jets to vaporize them, at least partially, and produce finely-structured coatings from vapor and micro-droplets deposition. The torch arrangement allows separating the vapor and the very small particles (less than 1 µm) from the partially vaporized bigger ones. The diagnostics are based on optical emission spectroscopy, pyrometry, imaging of particles trajectories and coating microstructural characterization.

Nanostructured YSZ is expected to exhibit a high strain tolerability due to its low Young’s modulus and consequently high durability. In this study, a porous YSZ as the thermal barrier coating was deposited by plasma spraying using an agglomerated nanostructured YSZ powder on a Ni-based superalloy Inconel 738 substrate with a cold-sprayed nanostructured NiCrAlY as the bond coat. The heat treatment in Ar atmosphere was applied to the cold-sprayed bond coat before deposition of YSZ. The isothermal oxidation and thermal cycling tests were applied to examine failure modes of plasma-sprayed nanostructured YSZ. The results showed that YSZ coating was deposited by partially melted YSZ particles. The nonmelted fraction of spray particles retains the porous nanostructure of the starting powder into the deposit. YSZ coating exhibits a bimodal microstructure consisting of nanosized particles retained from the powder and micro-columnar grains formed through the solidification of the melted fraction in spray particles. The oxidation of the bond coat occurs during the heat treatment in Ar atmosphere. The uniform oxide at the interface between the bond coat and YSZ can be formed during isothermal test. The cracks were observed at the interface between TGO/BC or TGO/YSZ after thermal cyclic test. However, the failure of TBCs mainly occurred through spalling of YSZ within YSZ coating. The failure characteristics of plasma-sprayed nanostructured YSZ are discussed based on the coating microstructure and formation of TGO on the bond coat surface.

In the present study, yttria-partially-stabilized zirconia (YSZ)/Al 2 O 3 coatings, which are used for jet engines, gas turbines and diesel engines were coated with thermal barrier coatings (TBCs) to provide high thermal resistance, reduce the metal surface temperatures, and increase component durability. The effect of alumina addition from 0 to 80 wt% on the properties of plasma sprayed YSZ coatings was investigated. The coatings were produced using a METCO 3MB plasma spray gun on stainless steel and graphite substrates. Scanning electron microscopy (SEM) was used to analyze the microstructures of the coated samples. The microhardness was investigated depending on the alumina contents. Vickers hardness on cross section of coatings was observed to increase with the increase in alumina mixing ratio. The presence of alumina phase commonly improves the mechanical properties of YSZ.

One major shortcoming of thermal barrier coatings applied to gas turbine components is the spallation of the ceramic coating under mechanical stress developing during thermal cycling environments. In order to study the evolution of failure and the expectancy of lifetime under realistic conditions cycling burner rig tests are a well established matter of choice. In the same way the techniques of acoustic emission (AE) testing and infrared (IR) thermography have been widely proofed to provide insight to microscopic crack formation and localization of hidden delaminations, respectively. Both techniques can be utilized to record the evolution of microscopic and macroscopic defects in advance to the apparent failure. Indirectly, this knowledge allows to verify and to improve lifetime models. The aim of this study is to expand the use of AE and IR testing as a rugged in-situ monitoring tools for combustion driven cycling rigs and to provide spatial resolved information on thermal load and failure evolution of the TBC in those tests. For a successful application to an experiment using a gas fired and air cooled burner rig some it is necessary to overcome some limitations which are mainly due to the high level of interfering signals under those experimental conditions.

Abradable seals are used in aerospace applications to control the overtip leakages between the blades of an engine rotor and its static parts. To achieve the combination of properties required, these seals have been developed with thermally sprayed coatings and are generally elaborated from a range of two or three phase powder mixtures. In the present study, the thermal conductivity of thermally sprayed AlSi/Polyester abradable coatings produced with Metco 601 NS and Durabrade 1605 powders was measured and investigated using finite element and finite difference methods based on two-dimensional structures obtained from micrographs. The computed values were compared to the experimental results.

Cr 3 C 2 -NiCr thermal spray coatings have been extensively applied to mitigate erosion in high temperature applications such as aircraft and power generation turbines. Much laboratory based erosion research has been conducted under ambient temperature and mild erosion conditions. However, little has been presented about the coating response under the high temperature, high velocity erosion conditions typically experienced in industrial applications. This work presents the mechanisms of high velocity erosion based on experiments conducted under realistic service conditions. Single impact studies were carried out on a range of Cr 3 C 2 -NiCr coatings to assess the variation in erosion mechanism with phase degradation and starting powder morphology. Comparisons were made between the coating response in the as-sprayed state and after long-term heat treatment to determine how the erosion response changes as a function of exposure time in-service. Erosion of the as-sprayed coatings was heavily influenced by splat boundary related mass loss mechanisms. This was accentuated by in-flight carbide dissolution in the coatings based on agglomerated/sintered powders. Heat treatment led to splat sintering and a transition in the erosion response towards more microstructural based erosion mechanisms. The variation in erosion response as a function of microstructural development with heat treatment and starting powder type is presented.