Advanced Homogenization Strategies in Material Modeling of Thermally Sprayed TBCs

Abstract

Partially yttria stabilized zirconia (PYSZ) thermal barrier coatings (TBCs) are applied in aircraft engines and gas turbines. Especially PYSZ coatings on turbine blades fulfill a heat and corrosion functionality during the operational use of the gas turbines. The PYSZ-layers lead to an increase of the life time of the turbine blades due to a decrease of the thermal and mechanical loading of the Ni-alloy components during gas turbine operation. For this reason, PYSZ-TBCs can also limit the costs of the turbine engine's maintenance.There are different technological methods to produce PYSZ thermal barrier coatings. The most applied methods in practice are the thermal spraying technologies, especially atmospheric plasma spraying (APS), and electron beam physical vapour deposition (EB-PVD).The chosen process technology and the set of process parameters directly affect the microstructure of the PYSZ-TBC. The coatings show a specific physical behavior in combination with the Ni-base alloy blade due to this specific microstructure. It is known, that APS PYSZ-TBCs have a lower thermal conductivity than EB-PVD-PYSZ-TBCs. Therefore, the thermal insulation of the first coatings is better than of the second ones. But the lateral strain tolerance of EB-PVD coatings is higher due to the columnar structure. This makes the EB-PVD-coatings more resistant against thermal cycling loading.But if a specific process is looked at, then the microstructure of the PYSZ-TBCs can be influenced highly by the process control, the adjustable process parameters. This can be investigated by experimental studies. Process simulations have been becoming an alternative technique since years and the quality of simulation results increases with the quality of the developed simulation models and the hardware capacities. The PYSZ-TBC microstructure influences the physical behaviour of the coating/component compound in the mesoand macroscale consideration. Modelling and simulation methods can also be applied here as a complement or an alternative to experimental measurements to determine the correlation between the microstructure and the meso-and macroscale physical coating behaviour.This article focuses on the application of advanced homogenization strategies in the material properties and laws estimation for thermally sprayed (APS) PYSZ-TBCs.Thermally sprayed thermal barrier coatings made of partially yttria stabilized zirconia show a characteristic microstructure. SEM-images of polished samples illustrate the porous, lamellar and micro-cracked structure ( Fig. 1(a)). These SEM-images are used as basis for the application of homogenization methods. This is an example for the combination of experimental and simulation methods. Alternatively, the microstructure can be obtained by a full APS process simulation. This can be realized in future, if the gaps in the coating formation simulation modeling (e.g. contact phenomena, crack formation and progression) are closed.Investigation of microstructure by spectral analysis: The SEMimages of polished APS-PYSZ-TB...

Simulation of PYSZ particle impact and solidification in atmospheric plasma spraying coating process

“…This model has shown the influence of substrate surface on deformation and solidification of the particle and it was found that the substrate surface can also significantly influence on the deposition efficiency. This model will be further developed for a successive particle impact and overlaying to simulate the evolution of microstructure built during atmospheric plasma spray processes which will be used to calculate effective mechanical and thermal properties by homogenisation methods [16].…”

Structural Evolution and Mechanical Properties Modification of MELTPRO (in Situ Remelted) Processed Thermal Barrier Coatings during Thermal Shocks

“…This result arises because the columnar structure and the pore-crack architecture of in situ remelted coatings improve the compliance and decrease the permeability of TBCs; hence reducing the TGO formation. [20] Moreover, as-sprayed and in situ remelted coatings present the same resistance of about 75±80 cycles to thermal shock tests. It could be that this test is too severe as a means to differentiate these coatings.…”

Modeling of Coating Process, Phase Changes, and Damage of Plasma Sprayed Thermal Barrier Coatings on Ni‐Base Superalloys

“…Descriptions of the methods as well as consideration of the peculiarities of their application to coating structures can be found in Refs. [33][34][35][36][37][38][39][40][41][42] Here, temperature dependency of effective Young's modulus was investigated with use of the homogenization for periodic structures. This method, described firstly in Ref., [41,42] needs properties of the microstructure components (ceramics and ''voids'' in our case) together with the representative volume element (RVE) of the microstructure as input.…”