Sebastian Haas

University of Bayreuth · Department of Metallic Materials

Trace elements play an important role in the fine-tuning of complex material properties. This study focuses on the correlation of microstructure, lattice misfit and creep properties. The compositionally complex alloy Al 10 Co 25 Cr 8 Fe 15 Ni 36 Ti 6 (in at. %) was tuned with high melting trace elements Hf and W. The microstructure consists of a γ...

Since the high entropy concept was proposed at the beginning of the millennium, the research focus of this alloy family has been wide ranging. The initial search for single-phase alloys has expanded with the aim of improving mechanical properties. This can be achieved by several strengthening mechanisms such as solid-solution hardening, hot and col...

Due to its matrix/γ′ structure, the compositionally complex alloy (CCA) Al10Co25Cr8Fe15Ni36Ti6 has excellent properties that fulfill the requirements for a high-temperature material. This base alloy is alloyed with small amounts of high melting elements to a further improvement of its properties, which results in different shapes, fractions and siz...

Three novel precipitation strengthened bcc alloys which exhibit a smooth microstructural gradient with composition have been fabricated in bulk form by induction casting. All three alloys are comprised of a mixture of disordered A2-(Fe, Cr) and L21-ordered (Ni, Fe)2AlTi type phases both as-cast and after long-term annealing at 900 ∘C. The ratio of...

Three novel precipitation strengthened bcc alloys which exhibit a smooth microstructural gradient with composition have been fabricated in bulk form by induction casting. All three alloys are comprised of a mixture of disordered A2-(Fe, Cr) and L2$_1$-ordered (Ni, Fe)$_{2}$AlTi type phases both as-cast and after long-term annealing at 900 $^{\circ}...

Superalloy inspired Al10Co25Cr8Fe15Ni36Ti6 compositionally complex alloy is known for its gamma-gamma' microstructure and the third Heusler phase. Variations of this alloy, gained by replacing 0.5 or 1 at. pct Al by the equivalent amount of Mo, W, Zr, Hf or B, can show more phases in addition to this three-phase morphology. When the homogenization...

Misfits of γ-γ' based Al10Co25Cr8Fe15Ni36Ti6 and its Mo- and Hf-variations are studied up to a temperature of 980 °C and compared with Ni- and Co-based superalloys. The trace elements decrease (Hf) or increase (Mo) the edge radii of the γ' cuboids without changing their sizes. Atom probe measurements revealed that the Hf alloy prefers the γ' phase...

The main difference between high entropy alloys and conventional alloys is the solid solution strengthening effect, which shifts from a single element to a multi-element matrix. Little is known about the effectiveness of this effect at high temperatures. Face-centered cubic, equiatomic, and single crystalline high entropy alloy CrMnFeCoNi was pre-a...

Misfits of γ- γ’ based Al10Co25Cr8Fe15Ni36Ti6 and its Mo- and Hf-variations are studied up to a temperature of 980 °C and compared with Ni- and Co-based superalloys. The trace elements decrease (Hf) or increase (Mo) the edge radii of the γ’ cuboids without changing their sizes. Atom probe measurements revealed that the Hf alloy prefers the γ’ phase...

Improving the properties of durable high-temperature alloys is based on the fundamental understanding of the link between microstructure and three-dimensional (3D) nanochemistry. Here we utilize a complementary approach of transmission electron microscopy and atom probe tomography to link microstructure and 3D nanochemistry of a ternary single crys...

Recently introduced Al10Co25Cr8Fe15Ni36Ti6 compositionally complex alloy has been investigated in the as-cast state and after heat treatment in a thorough characterization. The combination of optical, scanning and transmission electron microscopy, three dimensional atom probe and x-ray diffraction, both at lab and synchrotron level provides precise...

The Ni-Mo-Cr system is critical for the design of nickel-based superalloys. This system stabilizes different topologically close packed (TCP) phases which precipitate in many of the commercially used superalloys. A diffusion multiple approach was applied to map the phase diagram of the ternary system in a highly efficient manner. Two isothermal sec...

High entropy or compositionally complex alloys provide opportunities for optimization towards new high-temperature materials. Improvements in the equiatomic alloy Al17Co17Cr17Cu17Fe17Ni17 (at.%) led to the base alloy for this work with the chemical composition Al10Co25Cr8Fe15Ni36Ti6 (at.%). Characterization of the beneficial particle-strengthened m...

We determined the entropy of high entropy alloys by investigating single-crystalline nickel and five high entropy alloys: two fcc-alloys, two bcc-alloys and one hcp-alloy. Since the configurational entropy of these single-phase alloys differs from alloys using a base element, it is important to quantify the entropy. Using differential scanning calo...

Compositionally complex alloys, or high entropy alloys, are good candidates for applications at higher temperatures in gas turbines. After their introduction, the equiatomic Al17Co17Cr17Cu17Fe17Ni17 (at.%) served as a starting material and a long optimization road finally led to the recently optimized Al10Co25Cr8Fe15Ni36Ti6 (at.%) alloy, which show...

This contribution presents a comprehensive analysis of the low temperature deformation behavior of CoCrFeMnNi on the basis of quasistatic tensile tests at temperatures ranging from room temperature down to 4.2 K. Different deformation phenomena occur in the high-entropy alloy in this temperature range. These include (i) serrated plastic flow at cer...