Co-Re alloys for ultra-high temperature applications. Investigated by in-situ neutron scattering and complementary methods

Co-Re alloys are a future candidate for high-temperature applications. The alloys are hardened by a dispersion of nano-scaled TaC precipitates. In-situ small-angle neutron scattering (SANS) was used to comprehensively study the precipitate nucleation and coarsening kinetics at high temperatures. Thereby, the activation energies for nucleation, growth and coarsening of the TaC precipitates could be determined. It is shown that they can be used to effectively strengthen the Co-Re alloys up to 1473 K. Neutron diffraction experiments reveal that the Co-Re matrix undergoes an allotropic phase transformation from ε-Co (hcp) → γ-Co (fcc) at T ∼ 1500 K that results in an instability of the nano-scaled TaC precipitates. Cr and B are important for the alloy performance at high temperatures and their influence on this Co-Re phase transformation and the precipitate stability was studied. It is shown that Cr stabilizes the ε-Co phase, while B lowers the matrix transformation temperature. In addition, the creep behavior of the Co-Re alloy was investigated during an in-situ diffraction experiment with synchrotron radiation at 1373 K. X-ray diffraction and microscopy yielded complementary results on the high-temperature behavior of the Co-Re microstructure.