RESEARCH OBJECTIVES IN THE SECOND FUNDING PHASE (2016-2019)
Single crystal Ni-base superalloys represent key materials for turbine blades in modern gas turbines for aero engines and power plants. International mobility and global energy supply rely on this fascinating class of high temperature materials. Improvements in efficiency and emissions demand new concepts in single crystal technology, which require progress in four areas of expertise:
- A basic understanding of all aspects of alloy design and performance. This comprises the role of heterogeneities, both on a large scale (dendritic and interdendritic regions) and small scale (gamma / gamma prime microstructure). It includes the exact role of alloying elements (especially: d-shell elements). It is important to understand how microstructural and atomistic parameters affect thermodynamic equilibria, the evolution of microstructure during processing and high temperature deformation. Focus is on creep and fatigue deformation and damage mechanisms, microstructural stability (nucleation and growth of new phases, coarsening of the gamma / gamma prime microstructure), castability (porosity, parameters of the dendritic structructure), heat treatments and HIP, surface integrity (oxidation and coatings) and rejuvination. We are consider new alloy compositions with better performance which also reflect the need to make most efficient use of global ressources. Target alloy compositions must also reflect the availability a possible scarcity of strategic elements (e.g. less Re, more Ru, W, Mo and others). In addition to Ni-base superalloys, Co-based single crystal super alloys with gamma / gamma prime microstructures will also be considered.
- The continuous improvement and innovation of processing technologies for establishing specific nano and micro structures with a better homogeneity and with improved properties (single crystalline solidification in a fluidized bed, additive processing using selective electron beam melting, heat treatments under hydrostatic pressure, coating technologies, rejuvenation procedures).
- More detailed knowledge of materials properties and microstructure through use of new test procedures, either mechanical measurements (like miniaturized creep and fatigue testing, shear and circular notched specimen testing, nano metrology) or characterization methods (high resolution, aberration corrected transmission electron microscopy, 3D atom probe, dark field diffraction contrast TEM in scanning mode). These new techniques will help to identify elementary processes which govern the formation of new phases, the microstructural coarsening of the gamma / gamma prime microstructure and the interaction of deformation and damage mechanisms.
- Materials modeling bridging all scales, from atomistic (ab-initio-methods, molecular dynamics) to mesoscopic (discrete dislocation modeling and themodynamic/kinetic modeling of microstructural evolution) and macroscopic (physically sound constitutive equations).