Kurzbeschreibung
(Englisch)
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A) Investigation of the changes in the microstructure and the mechanical properties, in different orientation, due to long-term lcreep loading of single crystal Nickel based superalloy CMSX-4. Additionally, the effectiveness of the rejuvenation treatments will be estimated. B) The consumption and degradation of corrosion resistant coatings and thermal barrier coatings (TBC) will be investiga-ted. Coatings will be evaluated regarding their oxidation and corrosion resistance under service relevant conditions. Coa-tings will be investigated in the virgin condition, after degradation and after repair procedures.The data generated is to be used in predictive models including debit factors for repaired structures.
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Partner und Internationale Organisationen
(Englisch)
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BE, CH, CZ, DE, DK, ES, FI, FR, IT, LT, NL, PL, PT, SE, SK, UK
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Abstract
(Englisch)
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Project A The main objectives of the COST538 activities are the extension of the reliable lifetime of the critical components in the high temperature Power Plants. These components requiredetailed investigations of the degradation processes of the microstructure and the mechanical properties. Additionally, the development of optimum rejuvenation treatment for such components which necessitate a clear understanding of the kinetics and mechanisms of the microstructural changes that take place in the respective alloys. Hence the working group WP3 of the COST538 has been organized to achieve these goals by providing the results on the starting microstructure, the microstructural changes of the investigated alloys and the corresponding degradation in mechanical properties to WP4. The microstructral degaradation had to be modeled. The working group WP4 aims to develop reliable lifetime estimation methods based on the microstructural models and the determined mechanical properties determined in the framework of WP3.The developed models on microstructural changes in addition to the reliable lifetime calculation procedures will constitute the main part of the 'Toolbox'. The application of that 'Toolbox' will result in avoiding pre-mature component removal, hence making full effective use of the components lifetime. The superalloys of interest were CMSX-4, and CCIN738LC. Since Alstom Switzerland (Mohamed Nazmy) was leading WP3, Alstom was in charge of the procurement of test material i.e. negotiation with supplier and the subsequent distribution of the material to the partners involved. This also includes the preliminary mechanical testing of the supplied test materials in advance to distribution. The objectives in the final period of the project were: Establishing a model based on the relationship between the parameters relevant to the application i.e. stress, temperature & time and the yield stress of CMSX-4. A second rafting model in CMSX-4 has been developed in collaboration with the projects DE 2 (BAM) & DE9 (TU Berlin). This model will enable the partners of WP4 to accurately predict the amount of microstructural degradation and hence the corresponding remnant mechanical properties. The precise estimation of the remnant life of the component will result in the full use of its lifetime without unnecessary early removal from service. In addition, one can carry out promptly the rejuvenation treatment. Both factors will result in the life extension of the component. Summary & conclusions Specimens from CMSX-4 test bars were mechanically tested, under different conditions, in the as-received and degraded states. The changes in the mechanical properties were correlated to the microstructural degradation parameters. A model correlating the tensile properties to degradation conditions was developed for CMSX-4. A detailed microstructural model was also developed in joint collaboration with the partners of BAM & TU Berlin. The achieved results on different aspects of mechanical properties have been provided to WP4. These models were applied to a 'Case Study', within WP5, using an ex-service CMSX-4 blade from a Siemens-Westinghouse gas turbine. Project B In this project, the influence of the degradation of TBC-systems on their mechanical behaviour will be investigated. The reference system IN738/Amdry 995/TBC has been degraded by ageing under different conditions of time, temperature and cycling atmosphere. Afterwards, the resulting mechanical behaviour was determined using 4-point bending. Similar investigations were carried out on the single crystal material CMSX-4 using Amdry 995 and TBC. The behaviour of the two alloy systems was different. The given explanation was that the IN738LC superalloy had lower mechanical strength than that of the single crystal CMSX-4. The degradation, due to ageing, in the coated IN738 specimens was attributed to reduction ductility as compared with the virgin condition. The evolution of degradation in the coating system during its exposure to different environments could be monitored by the 4-point bending technic. Additionally, the technic of evaluating the lifetime of coated component using the changes in the microstrucral characterisics and the degradation in the coating has been utilised in a 'case study'. An ex-service Siemens vane of the superalloy IN939 coated with Amdry 995 was used in this 'case study'. The changes in the Gamma` were nicely correlated with the degradation in the coating. Summary & conclusions In this project, the degradation in the coating systems, using 4-point bending method, could be reasonably correlated to the lifetime of the component of interest from different Nickel-base superalloys. The applicability of such approach has been demonstrated on actual ex-service gas turbine component i.e. vane, in the form of 'case study'. Using such approach one can estimate the remnant useful lifetime of coated gas turbine compents. Hence, one can avoid premature removal of noble components before they achieve their full safe operating lifetime.
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