Citation: Jó´ zwiak, S.; Kozakiewicz, A.; Kachel, S.; Zasada, D. Operational and Material Causes of High-Pressure Turbine Disc Damage in the RD-33 Engine. Materials 2023, 16, 5939. https://doi.org/10.3390/ ma16175939 Academic Editor: In-Chul Choi Received: 11 July 2023 Revised: 23 August 2023 Accepted: 24 August 2023 Published: 30 August 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Article Operational and Material Causes of High-Pressure Turbine Disc Damage in the RD-33 Engine Stanislaw Jó ´ zwiak 1 , Adam Kozakiewicz 2 , Stanislaw Kachel 2, * and Dariusz Zasada 1 1 Faculty of Advanced Technology and Chemistry, Institute of Materials Science and Engineering, Military University of Technology, 00-908 Warszawa, Poland; stanislaw.jozwiak@wat.edu.pl (S.J.); dariusz.zasada@wat.edu.pl (D.Z.) 2 Faculty of Mechatronics, Armament and Aerospace, Institute of Aviation Technology, Military University of Technology, 00-908 Warszawa, Poland; adam.kozakiewicz@wat.edu.pl * Correspondence: stanislaw.kachel@wat.edu.pl; Tel.: +48-261839170 Abstract: This paper presents an analysis of the causes of damage and fragmentation to the high- pressure turbine (HTP) disc of the RD-33 engine mounted in the MIG-29 aircraft. The authors have carried out an analysis of the changes to the structure of the disc material, both in the areas containing cracks and in the undamaged areas. The impact of structural changes on the alterations in the analysed strength properties along the disc radius was assessed. Material tests were correlated with the analysis of the recorded engine parameters, indicating potential causes of the HPT disc fragmentation. Keywords: turbine jet engine; material tests; ember-resistant alloys 1. Introduction An analysis of the causes of aviation accidents related to the MiG-29 aircraft operated in Poland has indicated that 9% of these failures resulted from damage to the RD-33 engine [1]. A vast majority of these events were caused by foreign object damage (FOD), leading to the destruction of both the low- and high-pressure compressor blades. Another significant problem, constituting 13% of RD-33 engine failure cases, is damage to the high- pressure turbine (HPT) blades. The existing literature analyses [2–7] indicate that the main cause of damage to these engine components are thermomechanical loads facilitated by the erosive and corrosive effect of exhaust gases. In addition, there have been two cases of stage IV fatigue cracks of the fan disc, the indirect cause of which was the extension of the service life of the engines from the original 1200 h to 1600 h of operation, leading to mechanical damage and resulting in the initiation and propagation of fatigue cracks [1]. Extending the service life of engines entails an increase in the number of their start- ups, take-offs, and landings, as well as an extension of their operating time in the ranges characterised by the maximum temperature of exhaust gases, which increases the number of engine work cycles. These factors have a huge impact on the structural changes in the materials of the engine components exposed to high temperatures and may lead to a reduction in the general strength properties, even causing the destruction of individual components. The engine components that are most exposed to thermomechanical loads undoubtedly include the HPT turbine blades and disc. In the case of the RD-33 engine, to a certain, limited extent, diagnostics related to the turbine disc blades are possible in operating conditions, although the analysis of its condition can only occur only after engine disassembly during an overhaul. Therefore, turbine discs must be designed in such a way as to exclude the possibility of their failure, which, in extreme cases, leads to defragmentation due to the possibility of aircraft damage caused by the huge kinetic energy found in the fragments torn from the disc. The modern disc design process is focused on rotating elements exposed to maximum stress, such as the turbine blades root and the turbine disc rim. This means that damage may be expected in these areas. The impact of changes in Materials 2023, 16, 5939. https://doi.org/10.3390/ma16175939 https://www.mdpi.com/journal/materials