8 INŻYNIERIA MATERIAŁOWA MATERIALS ENGINEERING ROK XXXVIII The application of tumble finishing in surface preparation process for deposition of TBC coatings Sławomir Kotowski 1* , Andrzej Nowotnik 1 , Jan Sieniawski 1 , Andrzej Butkiewicz 1 1 Department of Material Science, Rzeszow University of Technology, Rzeszow, Poland, * skot@prz.edu.pl Thermal barrier coatings (TBC) are widely used for protection of turbine blades against aggressive thermomechanical and chemical degradation during operation in hot section of aircraft engine. Quality and properties of TBC coating is strictly related to preparation of substrate material (grinding, and round- ing off edges, polishing and cleaning). In the article, tumble finishing as method for surface preparation before deposition of thermal barrier coatings has been described. The process was performed for different types of ceramic feedstock and base material in order to obtain homogeneous roughness. Tumbling was carried out using centrifugal polishing machine. The research was divided into three stages. The first one consisted in investigation of the influence of rotational velocity and water flow, on the course of tumbling process. Afterwards, proper type of ceramic feedstock has been selected. During the last stage, ready-to-use recipes for polishing of samples made of for CMSX–4, Inconel® 718 and stainless steel 1.4016 were developed. Key words: tumbling, tumble finishing, TBC, thermal barrier coatings, surface preparation. Inżynieria Materiałowa 1 (215) (2017) 8÷14 DOI 10.15199/28.2017.1.2 © Copyright SIGMA-NOT MATERIALS ENGINEERING 1. INTRODUCTION Taking into account the actual trends in aircraft engine design, in- cluding constant shifting conditions in the hottest section of aircraft engines towards higher temperature and more aggressive thermo- mechanical and chemical conditions, it is imperative to apply mate- rials characterized by highest mechanical properties and protective coatings providing thermal insulation and chemical barrier for base material. Increasing the operating temperature allows to improve the engine efficiently and reduce fuel consumption and the emission of carbon dioxide [1, 2]. This canalizes the research on modifica- tion of engine design in order to improve the resistance to influence of high temperature, oxidizing gases environment and mechanical loads which are present in operating conditions. In the article, the comprehensive procedure of manufacturing thermal barrier coatings (TBC) is presented on the example of tur- bine blade which is a component of hot section of aircraft engine. The casting process of CMSX–4 blade, surface preparation process, heat treatment, also the deposition processes of duplex-structure thermal barrier coatings (TBC) with metallic interlayer (bond coat) and external ceramic layer (top coat), were described. The bonding and external layers were formed during, corre- spondingly, chemical vapour deposition (CVD) and electron beam physical vapour deposition processes (EB-PVD). Proper surface characteristics is important in terms of coatings performance at high temperature also in the presence of highly oxidizing gases. 2. MANUFACTURING OF SUBSTRATE MATERIAL In order to obtain high temperature creep-strength, fatigue and oxidation resistance, coating performance and retention of perfor- mance in thin-walled configurations, CMSX–4 elements are manu- factured using controlled alloy crystallization in vacuum which provides single crystal structure [3]. In this form, CMSX–4 alloy is widely used for elements of hot section of aircraft engines, e.g. tur- bine blades. There are numerous methods applied to manufacturing of single crystal castings. In Research and Development Labora- tory for Aerospace Materials (Rzeszow University of Technology) turbine blades are created using one of most popular casting tech- niques — Bridgeman method (Fig. 1). During the process, ceramic shell mould with liquid alloy is shifted from the heating to cooling zone of the furnace. The chamber assembly provides directional heat flow in the mould and thus di- rectional solidification of casting. Application of spiral shaped grain selector allows single grain to grow along direction close to [001] axis. Vacuum furnace VIMIC 2 E – DS/SC, located in the Research and Development Laboratory for Aerospace Materials, makes pos- sible to establish precisely the values of process parameters, espe- cially critical speed of mould withdrawal. At this stage, simulation software is applied in order to predict casting microstructure and optimize the casting process parameters (Fig. 2). Fig. 1. Vacuum furnace VIMIC 2 E – DS/SC (ALD Vacuum Technolo- gies GmbH) used for conducting casting processes by Bridgeman meth- od. Research and Development Laboratory for Aerospace Materials [4] Rys. 1. Piec próżniowy VIMIC 2 E – DS/SC (ALD Vacuum Technologies GmbH) do prowadzenia procesu odlewania metodą Bridgemana. Uczel- niane Laboratorium Badań Materiałów dla Przemysłu Lotniczego [4]