Josua Kottke, MSc

Curriculum Vitae (CV)

Research Focus

• Radiotracer diffusion of fcc high-entropy alloys
  High-entropy alloys, i.e. multicomponent alloys with a large number of constituting elements in equiatomic or nearly equiatomic composition, attract an increased attention as a potential structural material due to attractive mechanical and physical properties. It is anticipated that when the number of elements is equal or larger than 5 and the concentration of each of the alloying elements is between 5 and 35 atomic percent (at.%), the high mixing entropy can significantly reduce the Gibbs free energy and stabilize solid-solution-like phases with relatively simple crystal structures, compared to intermetallic phases, especially at high temperatures . Hereby, we are investigating radiotracer diffusion of the constituting elements in AlxCoCrFeNi and (CoCrFeMn)100-xNix alloys and thus contributing to a debate about the hypothetical sluggish diffusion phenomenon in HEAs . On the one hand, the impact of the high-entropy effect in pure FCC matrix, i.e. the (CoCrFeMn)100-xNix alloys, is investigated. On the other hand, diffusion is measured in AlxCoCrFeNi which correspond to a mixture of FCC, BCC and B2 phases depending on the Al content x. As the Al content x in the AlxCoCrFeNi alloys is increased, a two-phase FCC+BCC microstructure replaces the single phase FCC one at x > 0.3 and the material becomes single phased BCC at x = 2 . A careful microstructure examination using XRD, SEM and EBSD analyses allows quantifying the measured diffusion profiles in terms of two separate contributions to long-range diffusion in FCC and BCC phases.

Publications