Project Details
Projekt
Polycrystalline High Entropy Superalloys (PHESA) – Combining novel strengthening mechanisms in compositionally complex CoNiCr-based superalloys with a large fraction of multicomponent intermetallic precipitates
Applicant
Dr.-Ing. Steffen Neumeier
Subject Area
Mechanical Properties of Metallic Materials and their Microstructural Origins
Term
since 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 450901523
One recent focus in the research on High-Entropy Alloys (HEAs) is on a microstructure- and mechanism-based design approach. This aims at developing HEAs that combine, for example, the massive solid solution strengthening effect and a low stacking fault energy known from single-phase HEAs with specific mechanisms such as twinning induced plasticity or precipitation strengthening known from conventional materials such as TWIP-steels or Ni-base superalloys to generate advanced materials with superior properties.In this project, "Polycrystalline High Entropy Superalloys (PHESA)" will be studied that are developed by such a mechanistic design approach. Our PHESA combine the beneficial effects of a CoNiCr high-entropy fcc gamma-matrix alloyed with the refractory elements Mo and W and a very high fraction of multicomponent L12 (Ni,Co)3(Al,W/Mo,Cr) precipitates for precipitation strengthening. The PHESA are compositionally complex alloys derived from recently developed CoNiCr-based superalloys that have a high potential for application due to their attractive property profile of very good oxidation resistance, workability and exceptional creep strength. Alloys with W or Mo are compared to study the effect of both elements particularly with respect to their segregation behavior to defects and their different tendency to form intermetallic phases for phase transformation strengthening. Additionally, different contents of minor elements such as Ti and Ta are alloyed for varying planar fault energies, twin thicknesses and twin densities and to trigger a potential deformation induced phase transformation.The key point is that different deformation mechanisms, such as twinning, will occur in these PHESA during high temperature deformation in comparison to traditional polycrystalline Ni-base superalloys due to the low stacking fault energy of the high entropy matrix and the multicomponent precipitate phase.The objective of this project is to further improve our understanding of the underlying deformation behavior in order to utilize and combine novel strengthening mechanism in High-Entropy Superalloys (HES) that are not established in existing high temperature materials and pave the way for a new generation of polycrystalline creep resistant high temperature materials.The magnitude of these strengthening mechanisms such as secondary hardening by the Suzuki mechanism and the interaction of nanotwins is currently unknown in HES. Thus, their potential will be evaluated in this project. Segregation of alloying elements does not only play a significant role in these strengthening mechanisms but also in the propagation of dislocations during high temperature deformation. Thus, the segregation behavior to planar faults and along dislocations needs to be investigated. The potential of these advanced high temperature alloys is further evaluated by more application-oriented testing methods such as tensile testing and tensile creep testing.
DFG Programme
Priority Programmes
