Chair for Materials Science and Engineering

Within the framework of his doctoral thesis, Maik Rajkowski is working on the subproject B8 of the collaborative research center SFB/TR 103 (single-crystalline Ni and Co-base superalloys) and a project of the priority program 2006 (high-entropy alloys and compositionally complex alloys, HEAs/CCAs) which are funded by the German Research Foundation (DFG). Project B8 deals with Co-base superalloys discovered in 2006, which represent a relatively new class of structural materials for applications in gas turbines. These alloys exhibit a microstructure consisting of ~75 vol.% of an ordered L12 phase (γ' phase) forming cuboidal precipitates separated by thin channels of a disordered and face-centered cubic solid solution (γ phase). The focus here is on the γ phase and the influence of small compositional variations on phase stability, atomic mobilities, and creep behavior. In his work, Maik Rajkowski prepares his alloys by vacuum induction melting, followed by homogenization and rotary swaging. He then performs heat treatments to study their stability using several experimental techniques such as X-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive X-ray spectroscopy. He also investigates the diffusion kinetics in his alloys by performing diffusion multiple experiments and he studies their creep properties.

As part of the priority program SPP 2006, a high-entropy alloy (TiZrNbHfTa) is being investigated. This so-called Senkov alloy is single-phase body-centered cubic in the as received state and decomposes into multiple phases during long-term aging below 900°C. Using similar experimental methods as those described above, Maik Rajkowski investigates the precipitation kinetics of secondary phases in this alloy to establish a temperature-time transformation diagram. As the Senkov alloy shows a large solubility for oxygen, Maik Rajkowki also investigates how this element affects its phase stability and decomposition kinetics.