TY - GEN A1 - Liang, Zhida A1 - Paul, Jonathan A1 - Stark, Andreas A1 - Bezold, Andreas A1 - Neumeier, Steffen A1 - Göken, Mathias A1 - Pyczak, Florian T1 - High-Temperature CoNi-Based Superalloys Strengthened by γ′-(Ni,Co)3(Cr,Al,Ti,X): The Effect of Refractory Elements T2 - Metallurgical and materials transactions. A, Physical metallurgy and materials science N2 - Recent research on Co-based and CoNi-based alloys revealed that the Co–Al–W-system provides interesting properties, however, the high content of W addition triggers high mass density of alloys which limits its industrial application. Therefore, new high temperature superalloys based on the Co–Ni–Al–Ti-system with high content Cr and strengthened by γ′-(Ni,Co)3(Cr,Al,Ti) precipitates, have been developed, and the effect of different refractory element additions was investigated. STEM-EDS and HEXRD were employed to determine the elemental partitioning behavior and the lattice misfit between the γ and γ′ phases. Ta and Nb strongly concentrate within the γ′ phase, whereas Mo weakly partitions to the γ phase. W distributes equally between the γ and γ′ phases. These new superalloys have an unexpectedly high positive misfit compared with some conventional Ni-based superalloys and Co-based superalloys. Nb and Ta additions increase the lattice misfit further, while Mo and W decrease the lattice misfit. The effect of refractory elements alloying on the yield stress at room temperature was evaluated by analyzing the contributions of different strengthening mechanisms. Alloying with Nb or Ta significantly improves precipitation strengthening by increasing the antiphase boundary energy. Mo has the highest solid solution strengthening effect in the γ phase, followed by W. Compared with some conventional Ni-based superalloys, the investigated new CoNi-based superalloys exhibited better mechanical properties at high temperature, which indicates that these compositionally complex alloys are possible candidates for high temperature applications. Y1 - 2022 U6 - https://doi.org/10.1007/s11661-022-06795-y SN - 1543-1940 VL - 54 (2023) IS - 5 SP - 1620 EP - 1634 ER - TY - GEN A1 - Li, Longjun A1 - Wang, Li A1 - Liang, Zhida A1 - He, Junyang A1 - Qiu, Jingwen A1 - Pyczak, Florian A1 - Song, Min T1 - Effects of Ni and Cr on the high-temperature oxidation behavior and mechanisms of Co- and CoNi-base superalloys T2 - Materials and Design N2 - The high-temperature oxidation behaviors of Co- and CoNi-base alloys with different Ni and Cr additions were investigated by isothermal oxidation in air at 900 and 1000 °C. The structure, composition, and element distribution in the three layers within the oxide scales in different alloys have been explored in detail by electron microscopy, especially with regard to the fine oxide particles in the intermediate layer. Based on the microstructure and phase constitution of the oxide scales, the synergetic effects of alloying elements on the oxidation mechanisms and resistance have been elucidated in detail with the aid of CALPHAD calculation. Y1 - 2022 U6 - https://doi.org/10.1016/j.matdes.2022.111291 SN - 1873-4197 VL - 224 ER - TY - GEN A1 - Liang, Zhida A1 - Neumeier, Steffen A1 - Rao, Ziyuan A1 - Göken, Mathias A1 - Pyczak, Florian T1 - CALPHAD informed design of multicomponent CoNiCr-based superalloys exhibiting large lattice misfit and high yield stress T2 - Materials Science and Engineering: A, Structural materials N2 - Usually, Co-based superalloys contain a high fraction of W and/or Mo. The refractory elements stabilize the precipitate phase, but cause a high density. In this work, new L12-phase hardened, low-density CoNiCr-based superalloys were developed with the assistance of CALPHAD calculations. Several alloys were studied experimentally and their microstructures, elemental distributions, lattice parameters and the lattice misfit between the γ and γ′ phases were evaluated using scanning electron microscopy, transmission electron microscopy, atom probe tomography and high energy X-ray diffraction. The alloys exhibit a very high misfit, good phase stability and excellent mechanical strength. It was found by hardness tests that a two-step heat treatment improves the strength of the new alloys even further. In comparison with conventional Co-based superalloys, Co–Al–W based superalloys and Co–Ti based superalloys, as well as Ni-based superalloys, i.e. Udimet 720Li, they have a low mass density and high yield stress. They also overcome the problem of a generally low lattice misfit of previous L12-phase hardened CoNiCr-based superalloys with high Ni and Cr contents. As a result, they show cuboidal-shaped precipitates similar to Co–Al–W and Co–Al–Mo based superalloys. Y1 - 2022 U6 - https://doi.org/10.1016/j.msea.2022.143798 SN - 1873-4936 SN - 0921-5093 VL - 854 ER - TY - GEN A1 - Shang, Yuanyuan A1 - Liu, Shaofei A1 - Liang, Zhida A1 - Pyczak, Florian A1 - Lei, Zhifeng A1 - Heidenreich, Tim A1 - Schöckel, Alexander A1 - Kai, Ji-jung A1 - Gizer, Gökhan A1 - Dornheim, Martin A1 - Klassen, Thomas T1 - Developing sustainable FeTi alloys for hydrogen storage by recycling T2 - Communications Materials N2 - Intermetallic alloys such as FeTi have attracted ever-growing attention as a safe and efficient hydrogen storage medium. However, the utilization of high-purity metals for the synthesis of such materials poses considerable concerns over the environmental sustainability of their large-scale production. Here, we report an approach for synthesizing FeTi from industrial scraps of iron (steels C45 and 316 L) and titanium (Ti alloy Grade 2) to reduce the carbon footprint associated with FeTi alloy synthesis, without compromising their hydrogen storage properties. At 50 °C and a pressure of 0 to 100 bar, the alloys obtained by using C45-Ti Grade 2 and 316L-Ti Grade 2 can absorb a maximum amount of hydrogen of 1.61 wt.% and 1.50 wt.%, respectively. Moreover, depending on the type of steel utilized, the thermodynamic properties can be modified. Our findings pave a pathway for developing high-performance, environmentally-sustainable FeTi alloys for hydrogen storage purposes using industrial metal wastes. Y1 - 2022 U6 - https://doi.org/10.1038/s43246-022-00324-5 SN - 2662-4443 VL - 3 IS - 1 ER - TY - GEN A1 - Liang, Zhida A1 - Lilleodden, Erica A1 - Ovri, Henry A1 - Pyczak, Florian T1 - Surface Recrystallization in a Co-Based Superalloy During High Temperature Exposure T2 - Metallurgical and materials transactions. A, Physical metallurgy and materials science N2 - The effect of grinding on static recrystallization and oxidation of a novel Co-based superalloy has been studied. The evolution of surface recrystallization after heat treating at 850 °C in air was revealed by comparing ground specimens with electropolished ones. The loss of Al and Ti from the bulk material leads to the formation of a γ′-free region and further promotes recrystallization at the surface. Y1 - 2022 U6 - https://doi.org/10.1007/s11661-022-06852-6 SN - 1543-1940 VL - 53 IS - 12 SP - 4156 EP - 4160 ER - TY - GEN A1 - Pyczak, Florian A1 - Liang, Zhida A1 - Neumeier, Steffen A1 - Rao, Ziyuan T1 - Stability and Physical Properties of the L12-γ′ Phase in the CoNiAlTi-System T2 - Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Y1 - 2023 U6 - https://doi.org/10.1007/s11661-022-06949-y SN - 1073-5623 VL - 54 IS - 5 SP - 1661 EP - 1670 ER -