Scope of work
To maintain reliable energy supply at reasonable costs while resources are limited and protection of climate and environment are an issue of increasing concern, renewable energy such as wind and solar power will become more important. However, to get stable electricity supply, electricity generation by conventional, coal or gas fired power plants will stay essential and their efficiency needs to be further improved. For conventional coal fired steam power plants, gas turbines and internal combustion engines as well as for combined cycle power plants using the exhaust heat of a gas turbine in a subsequent steam power plant, a further increase of thermal efficiency can only be reached if the process temperatures and -pressures are risen beyond the actual state-of-the-art. Therefore, the potential of high performance materials currently used for compressors, combustors and turbines must be fully exploited, materials need to be further improved and new materials for components undergoing extreme thermal and mechanical loadings have to be developed and tested under service-relevant conditions. Metallic oxidation protection layers and ceramic thermal barrier coatings will, together with improved cooling strategies, strongly contribute to a further increase of process temperatures.
Especially in development and testing of new materials not only the technical possibilities of realization but also economic issues have to be considered and it has to be assured that the resulting components are reliable during long term service. A further option to reduce CO2 emission is the combination of coal or gas fired power plants with CO2 capture and storage. To realize this approach with reasonable efficiency, the oxyfuel-process is a promising option, where oxygen has to be separated from the air before combustion. This approach can be realized using ceramic mixed ion-electron conducting membranes. To achieve sufficient throughput, such membranes are used at temperatures of approx. 800°C and high pressure gradients. Therefore, besides the necessary functionality and chemical stability, the mechanical properties at high temperature must be characterized to get a reliable database for process development and component design. Furthermore, solid oxide fuel cells (SOFCs) are a promising approach for electricity supply in highly flexible small- and medium-size units. The thermo-mechanical loadings of the metal-ceramic compounds of which these systems consist are a major challenge in material development and component design for SOFCs.
A major prerequisite for systematic materials development is sound understanding of the correlations between chemical composition, processing, microstructure and physical, chemical and mechanical properties, including their stability during long-term service. To realize best technical and economical usage of expensive high performance materials, design data must be determined under service relevant loadings (e.g. long-term creep, creep in combustion atmosphere, fatigue, thermo-mechanical fatigue). At the same time, reliable methods for lifetime prediction under the complex loadings occurring in power plants and engines have to be established.
On this background, the research work of the materials mechanics section currently covers the following issues:
Dieses breite fachliche Portfolio wird durch folgende drei Arbeitsgruppen der Abteilung abgedeckt:
- Investigation of mechanical strength, failure probability and long-term stability of ceramic oxygen separation membranes
- Mechanical characterization and damage analysis of SOFC-materials and components
- Investigation of chemical degradation and thermal shock relevant properties of refractory ceramics without carbon or with reduced carbon content
- Experimental investigation and modeling of damage and lifetime of metallic oxidation protection layers and of ceramic thermal barrier coatings under isothermal exposure, thermal cycling and thermo-mechanical fatigue loading
- Mechanical characterization and investigation of adhesion mechanisms of metal-ceramic compounds produced by reactive brazing
- Determination of mechanical properties (creep, isothermal and thermo-mechanical fatigue) and alloy development of ferritic steels for solid oxide fuel cells, exhaust gas systems and steam power plant components
- Fatigue of ferritic steels for steam turbines at extremely high cycle numbers