Investigation of the particle strengthening mechanism under creep loading of TaC-reinforced Co-Re base alloys
Final Report Abstract
The intention of the research project was to investigate the strengthening mechanism of tantalum carbide (TaC) precipitates during creep loading of Co-Re-based alloys, a new class of metallic high-temperature materials, and to explore the potential of other carbides (TiC, HfC) for precipitation hardening. A central result was that the carbide particles, due to their elongated shape, are remarkably strong obstacles for dislocation climb in the investigated temperature range (800°C, 900°C) and that climb over the particles rather than detachment of the dislocation from the particle backside is rate-limiting. This obstacle effect is so strong that strengthening at 800°C is still equivalent to that at room temperature. It was also shown that titanium carbide is another attractive particle type with comparable strengthening effect as the TaC precipitates and that the addition of approx. 1.8at.% Ta plus C or Ti plus C is optimal. Furthermore, a preferred orientation relationship between TaC/TiC and matrix was identified with the aid of transmission electron microscopy, which deviates significantly from that expected on the basis of theoretical considerations. Due to the fact that dislocation detachment proved to be irrelevant in the investigated temperature range, it was naturally not possible to gain insights into this mechanism from the experimental investigations. However, this was possible by molecular dynamics (MD) simulation of the particle-dislocation-interaction. For this purpose, atomistic simulations were first carried out for the TaC precipitate phase and, based on this, an interaction potential between the two types of atoms in this phase was parametrized, which served as input information for the MD simulations. On this basis, dislocation line energies were calculated adjacent to the TaC particles and in the matrix. The key result is that an attractive interaction between dislocation and particle was found, with its strength enormously depending on the orientation relationship between particle and matrix. A remarkably strong attraction with a relaxation factor k=0.75 was determined for the experimentally observed orientation relationship. This is of particular relevance because it is to be expected that the detachment mechanism becomes rate-limiting at very high temperatures instead of the climb mechanism. Thus, experiment in conjunction with simulation revealed that TaC (and presumably also TiC) allows for highly efficient particle strengthening for high-temperature applications.
Publications
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“Investigation of different MC-carbides for particle strengthening of Co-Re-based alloys”, Beyond Nickel-Based Superalloys IV International Conference, June 26 - 30, 2023, Potsdam, Germany
Seif, E.; Rösler, J., Werner, J. Weirich, T.E. & Mayer, J. M.
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Ab initio investigation of Co/TaC interfaces. Journal of Alloys and Compounds 2021, 853, 156944
I. Hocker, S.; Lipp, H.; Schmauder, S.; Bakulin, A.V. & Kulkova, S.E.
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Investigation of TaC and TiC for Particle Strengthening of Co-Re-Based Alloys. Materials, 16(23), 7297.
Seif, Eugen; Rösler, Joachim; Werner, Jonas; Weirich, Thomas E. & Mayer, Joachim
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Reassessment of the Matrix Composition of Co-Re-Cr-Based Alloys for Particle Strengthening in High-Temperature Applications and Investigation of Suitable MC-Carbides. Materials, 16(12), 4443.
Seif, Eugen & Rösler, Joachim
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Temperature-Dependent Young’s Modulus of TaC- and TiC-Strengthened Co-Re-Based Alloys. Metals, 14(3), 324.
Fiedler, Torben; Seif, Eugen; Sinning, Hans-Rainer & Rösler, Joachim
