@misc{WangOehringLorenzetal., author = {Wang, Li and Oehring, Michael and Lorenz, Uwe and Stark, Andreas and Pyczak, Florian}, title = {New insights into perovskite-Ti3AlC precipitate splitting in a Ti-45Al-5Nb-0.75C alloy by transmission electron microscopy}, series = {Intermetallics}, volume = {100}, journal = {Intermetallics}, issn = {0966-9795}, doi = {10.1016/j.intermet.2018.06.006}, pages = {70 -- 76}, language = {en} } @misc{LiPyczakPauletal., author = {Li, Yuzhi and Pyczak, Florian and Paul, Jonathan and Yao, Zekun}, title = {Oxidation behaviors of Co-Al-W-0.1B superalloys in a long-term isothermal exposure at 900 °C}, series = {Journal of Materials Science and Technology}, volume = {34}, journal = {Journal of Materials Science and Technology}, number = {11}, issn = {1005-0302}, doi = {10.1016/j.jmst.2018.03.013}, pages = {2212 -- 2217}, language = {en} } @misc{WangOehringLorenzetal., author = {Wang, Li and Oehring, Michael and Lorenz, Uwe and Yang, Junjie and Pyczak, Florian}, title = {Influence of alloying additions on L1₂ decomposition in γ-γʹ Co-9Al-9W-2X quaternary alloys}, series = {Scripta Materialia}, volume = {154}, journal = {Scripta Materialia}, issn = {1359-6462}, pages = {176 -- 181}, language = {en} } @misc{LazurenkoStarkEsikovetal., author = {Lazurenko, Daria V. and Stark, Andreas and Esikov, Maksim A. and Paul, Jonathan and Bataev, Ivan A. and Kashimbetova, Adelya A. and Mali, Vyacheslav I. and Lorenz, Uwe and Pyczak, Florian}, title = {Ceramic-Reinforced γ-TiAl-Based Composites: Synthesis, Structure, and Properties}, series = {Materials}, volume = {12}, journal = {Materials}, number = {4}, issn = {1996-1944}, doi = {10.3390/ma12040629}, pages = {20}, language = {en} } @misc{SongWangOehringetal., author = {Song, Lin and Wang, Li and Oehring, Michael and Hu, Xingguo and Appel, Fritz and Pyczak, Florian and Zhang, Tiebang}, title = {Evidence for deformation twinning of the D019-α2 phase in a high Nb containing TiAl alloy}, series = {Intermetallics}, volume = {109}, journal = {Intermetallics}, issn = {0966-9795}, doi = {10.1016/j.intermet.2019.03.014}, pages = {91 -- 96}, language = {en} } @misc{WangSongStarketal., author = {Wang, Li and Song, Lin and Stark, Andreas and Liu, Yong and Oehring, Michael and Lorenz, Uwe and Pyczak, Florian}, title = {Identification of Laves phases in a Zr or Hf containing γ-γ′ Co-base superalloy}, series = {Journal of Alloys and Compounds}, volume = {805}, journal = {Journal of Alloys and Compounds}, issn = {0925-8388}, pages = {880 -- 886}, language = {en} } @misc{SongHuWangetal., author = {Song, Lin and Hu, Xingguo and Wang, Li and Stark, Andreas and Lazurenko, Daria V. and Lorenz, Uwe and Lin, Junpin and Pyczak, Florian and Zhang, Tiebang}, title = {Microstructure evolution and enhanced creep property of a high Nb containing TiAl alloy with carbon addition}, series = {Journal of Alloys and Compounds}, volume = {807}, journal = {Journal of Alloys and Compounds}, issn = {0925-8388}, doi = {10.1016/j.jallcom.2019.151649}, pages = {11}, language = {en} } @misc{HanXuWangetal., author = {Han, Liuliu and Xu, Xiandong and Wang, Li and Pyczak, Florian and Zhou, Rui and Liu, Yong}, title = {A eutectic high-entropy alloy with good high-temperature strength-plasticity balance}, series = {Materials Research Letters}, volume = {7}, journal = {Materials Research Letters}, number = {11}, issn = {2166-3831}, pages = {460 -- 466}, language = {en} } @misc{LemosFredelPyczaketal., author = {Lemos, Georges and Fredel, M{\´a}rcio C. and Pyczak, Florian and Tetzlaff, Ulrich}, title = {Influence of distinct manufacturing processes on the microstructure of ni-based metal matrix composites submitted to long thermal exposure}, series = {Key Engineering Materials}, volume = {809}, journal = {Key Engineering Materials}, issn = {1662-9795}, doi = {10.4028/www.scientific.net/KEM.809.79}, pages = {79 -- 86}, language = {en} } @misc{WangOehringLiuetal., author = {Wang, Li and Oehring, Michael and Liu, Yuzhi and Lorenz, Uwe and Pyczak, Florian}, title = {Site occupancy of alloying elements in the L12 structure determined by channeling enhanced microanalysis in γ/γ' Co-9Al-9W-2X alloys}, series = {Acta Materialia}, volume = {162}, journal = {Acta Materialia}, isbn = {1359-6454}, pages = {176 -- 188}, language = {en} } @misc{BreslerNeumeierZieneretal., author = {Bresler, Johannes and Neumeier, Steffen and Ziener, Marco and Pyczak, Florian and G{\"o}ken, Mathias}, title = {The influence of niobium, tantalum and zirconium on the microstructure and creep strength of fully lamellar γ/α2 titanium aluminides}, series = {Materials Science and Engineering}, volume = {744}, journal = {Materials Science and Engineering}, issn = {0921-5093}, doi = {10.1016/j.msea.2018.11.152}, pages = {46 -- 53}, language = {en} } @misc{HauschildtStarkSchelletal., author = {Hauschildt, Katja and Stark, Andreas and Schell, Norbert and M{\"u}ller, Martin and Pyczak, Florian}, title = {The transient liquid phase bonding process of a γ-TiAl alloy with brazing solders containing Fe or Ni}, series = {Intermetallics}, volume = {106}, journal = {Intermetallics}, issn = {0966-9795}, pages = {48 -- 58}, language = {en} } @misc{SchnabelBargmannPauletal., author = {Schnabel, Jan Eike and Bargmann, Swantje and Paul, Jonathan David Heaton and Oehring, Michael and Pyczak, Florian}, title = {Work hardening and recovery in fully lamellar TiAl: relative activity of deformation systems}, series = {Philosophical Magazine}, volume = {99}, journal = {Philosophical Magazine}, number = {2}, issn = {1478-6435}, pages = {148 -- 180}, language = {en} } @misc{WangOehringLietal., author = {Wang, Li and Oehring, Michael and Li, Yuzhi and Song, Lin and Liu, Yon and Stark, Andreas and Lorenz, Uwe and Pyczak, Florian}, title = {Microstructure, phase stability and element partitioning of γ/γʹ Co-9Al-9W-2X alloys in different annealing conditions}, series = {Journal of Alloys and Compounds}, volume = {787}, journal = {Journal of Alloys and Compounds}, issn = {0925-8388}, pages = {594 -- 605}, language = {en} } @misc{LiPyczakStarketal., author = {Li, Yuzhi and Pyczak, Florian and Stark, Andreas and Wang, Li and Oehring, Michael and Paul, Jonathan and Lorenz, Uwe}, title = {Temperature dependence of misfit in different Co-Al-W ternary alloys measured by synchrotron X-ray diffraction}, series = {Journal of Alloys and Compounds}, volume = {819}, journal = {Journal of Alloys and Compounds}, issn = {0925-8388}, pages = {9}, language = {en} } @misc{SongWangZhangetal., author = {Song, Lin and Wang, Li and Zhang, Tiebang and Lin, Junpin and Pyczak, Florian}, title = {Microstructure and phase transformations of omega_o-Ti4Al3Nb based alloys after quenching and subsequent aging at intermediate temperatures}, series = {Journal of Alloys and Compounds}, volume = {821}, journal = {Journal of Alloys and Compounds}, issn = {0925-8388}, pages = {11}, language = {en} } @misc{SongAppelWangetal., author = {Song, Lin and Appel, Fritz and Wang, Li and Oehring, Michael and Hu, Xingguo and Stark, Andreas and He, Junyang and Lorenz, Uwe and Zhang, Tiebang and Lin, Junpin and Pyczak, Florian}, title = {New insights into high-temperature deformation and phase transformation mechanisms of lamellar structures in high Nb-containing TiAl alloys}, series = {Acta Materialia}, volume = {186}, journal = {Acta Materialia}, issn = {1873-2453}, doi = {10.1016/j.actamat.2020.01.021}, pages = {575 -- 586}, language = {en} } @misc{LazurenkoLaptevGolkovskyetal., author = {Lazurenko, Daria V. and Laptev, Ilia S. and Golkovsky, Mikhail G. and Stark, Andreas and Paul, Jonathan and Bataev, Ivan A. and Ruktuev, Alexey A. and Song, Lin and Gollwitzer, Christian and Pyczak, Florian}, title = {Influence of the Ti/Al/Nb ratio on the structure and properties on intermetallic layers obtained on titanium by non-vacuum electron beam cladding}, series = {Materials Characterization}, volume = {163}, journal = {Materials Characterization}, issn = {1044-5803}, pages = {13}, language = {en} } @misc{XuPyczakYanetal., author = {Xu, Peng and Pyczak, Florian and Yan, Ma and Limberg, Wolfgang and Willumeit-R{\"o}mer, Regine and Ebel, Thomas}, title = {Tensile toughening of powder-injection-molded β Ti-Nb-Zr biomaterials by adjusting TiC particle distribution from aligned to dispersed pattern}, series = {Applied Materials Today}, volume = {19}, journal = {Applied Materials Today}, issn = {2352-9407}, doi = {10.1016/j.apmt.2020.100630}, pages = {14}, language = {en} } @misc{XuPyczakYangetal., author = {Xu, Peng and Pyczak, Florian and Yang, Ma and Kong, Fantao and Ebel, Thomas}, title = {Impacts of yttrium on microstructure and tensile properties of biomedical β Ti-Nb-Zr fabricated by metal injection molding}, series = {Materials Science and Engineering: A}, volume = {792}, journal = {Materials Science and Engineering: A}, issn = {0921-5093}, pages = {9}, language = {en} } @misc{NeumeierPyczakGoeken, author = {Neumeier, Steffen and Pyczak, Florian and G{\"o}ken, Mathias}, title = {The temperature dependent lattice misfit of rhenium and ruthenium containing nickel-base superalloys-experiment and modelling}, series = {Materials and Design}, volume = {198}, journal = {Materials and Design}, issn = {0264-1275}, pages = {14}, language = {en} } @misc{SoyamaLimbergEbeletal., author = {Soyama, Juliano and Limberg, Wolfgang and Ebel, Thomas and Pyczak, Florian}, title = {Sintering and Creep Resistance of Powder-Metallurgy-Processed Ti-(43-47)Al-5Nb-0.2B-0.2C}, series = {Advanced Engineering Materials}, volume = {22}, journal = {Advanced Engineering Materials}, number = {8}, issn = {1527-2648}, pages = {7}, language = {en} } @misc{IvanovLazurenkoStarketal., author = {Ivanov, Ivan V. and Lazurenko, Daria V. and Stark, Andreas and Pyczak, Florian and Th{\"o}mmes, Alexander and Bataev, Ivan A.}, title = {Application of Different Diffraction Peak Profile Analysis Methods to Study the Structure Evolution of Cold-Rolled Hexagonal α-Titanium}, series = {Metals and Materials International}, volume = {26}, journal = {Metals and Materials International}, number = {1}, issn = {2005-4149}, doi = {10.1007/s12540-019-00309-z}, pages = {83 -- 93}, language = {en} } @misc{JinHejaziPyczaketal., author = {Jin, Bowen and Hejazi, Seyedsina and Pyczak, Florian and Oehring, Michael and Mohajernia, Shiva and Kment, Stepan and Tomanec, Ondrej and Zboril, Radek and Nguyen, Nhat Truong and Yang, Min and Schmuki, Patrik}, title = {Amorphous Mo-Ta Oxide Nanotubes for Long-Term Stable Mo Oxide-Based Supercapacitors}, series = {ACS Applied Materials and Interfaces}, volume = {11}, journal = {ACS Applied Materials and Interfaces}, number = {49}, issn = {1944-8244}, pages = {45665 -- 45673}, language = {en} } @misc{LiuSongStarketal., author = {Liu, Xu and Song, Lin and Stark, Andreas and Lorenz, Uwe and He, Zhanbing and Lin, Junpin and Pyczak, Florian and Zhang, Tiebang}, title = {Deformation and phase transformation behaviors of a high Nb-containing TiAl alloy compressed at intermediate temperatures}, series = {Journal of Materials Science and Technology}, volume = {102}, journal = {Journal of Materials Science and Technology}, issn = {0861-9786}, doi = {10.1016/j.jmst.2021.06.041}, pages = {89 -- 96}, abstract = {In modern β-solidified TiAl alloys, the decomposition of α2 phase is frequently observed during heat treatment or high-temperature deformation of the alloys. In this study, high-temperature deformation and decomposition mechanisms of α2 phase in a Ti-45Al-8.5Nb-0.2B-0.2W-0.02Y alloy are investigated. In a sample deformed at 800 °C, the precipitation of βo(ωo) phase is observed within the equiaxed α2 phase. The nucleation of ωo particles within the βo matrix indicates the α2→βo→ωo transformation. In addition, numerous γ phase precipitates form within the βo(ω) areas. The α2 lamellae decompose into ultrafine (α2+γ) lamellae and coarsened γ lamellae via α2→α2+γ and α2→γ transformation, respectively. Moreover, the ωo phase nucleates within the ultrafine lamellae via α2→ωo transformation. However, in a sample deformed at 1000 °C, the nucleation of βo particles is sluggish, which is caused by the efficient release of the internal stress via dynamic recrystallization (DRX). These results indicate that complex phase transformations can be introduced by the decomposition of α2 phase in TiAl alloys with a high amount of β-stabilizing elements.}, language = {en} } @misc{HaussmannNeumeierBresleretal., author = {Haußmann, Lukas and Neumeier, Steffen and Bresler, Johannes and Keim, Simon and Pyczak, Florian and G{\"o}ken, Mathias}, title = {Influence of Nb, Ta and Zr on the Interdiffusion Coefficients and Solid Solution Strengthening of γ-TiAl Single Phase Alloys}, series = {Metals}, volume = {12}, journal = {Metals}, number = {5}, issn = {2075-4701}, doi = {10.3390/met12050752}, abstract = {The alloying elements Nb, Ta and Zr improve the creep properties of fully lamellar γ/α2 titanium aluminides significantly. Since high temperature deformation mainly occurs in the γ-phase of γ/α2 titanium aluminides, the diffusivity and the solid solution hardening effect of these three elements in the γ-phase is studied by analyzing the concentration gradients of the alloying elements and the resulting hardness across the interdiffusion zone of diffusion couples by energy dispersive X-ray diffraction and nanoindentation. The results reveal that Zr has the highest interdiffusion coefficient but also the largest solid solution hardening coefficient. The mechanical properties of single γ-phase Ti-54Al-5X alloys were investigated by strain rate jump tests. The addition of 5 at.\% Nb or Ta lead to an increased strength compared to a binary γ-Ti-54Al alloy. The Zr-containing γ-TiAl alloy reveals the highest strength at 750°C and 900°C, which is discussed to be due to the strong solid solution hardening effect of Zr. However, in comparison to the other alloys, Ti-54Al-5Zr shows quite brittle behavior up to 900°C. The lower diffusivity of Ta compared to Nb leads to a higher strength of the Ta-modified alloy at 900◦C.}, language = {en} } @misc{DistlHauschildtRashkovaetal., author = {Distl, Benedikt and Hauschildt, Katja and Rashkova, Boryana and Pyczak, Florian and Stein, Frank}, title = {Phase Equilibria in the Ti-Rich Part of the Ti-Al-Nb System—Part I: Low-Temperature Phase Equilibria Between 700 and 900 °C}, series = {Journal of Phase Equilibria and Diffusion}, volume = {43}, journal = {Journal of Phase Equilibria and Diffusion}, number = {3}, issn = {1863-7345}, doi = {10.1007/s11669-022-00963-8}, pages = {355 -- 381}, abstract = {Precise knowledge of the phase equilibria in the Ti-Al-Nb system between 700 and 900 °C is of crucial importance for the urgently needed improvement of TiAl-based turbine materials already in industrial use to achieve further energy savings. As a result of the occurrence of the two ternary intermetallic phases ωo ("Ti4NbAl3") and O ("Ti2NbAl"), which form in the solid state just in the range of the application-relevant temperatures, the phase relations are very complex and not well studied. In the present investigation, isothermal sections of the Ti-rich part of the Ti-Al-Nb system at 700, 800, and 900 °C were determined by a systematic study of 15 ternary alloys, one solid-solid diffusion couple, and three liquid-solid diffusion couples. Using scanning electron microscopy, electron probe microanalysis (EPMA), x-ray diffraction (XRD), high-energy XRD (HEXRD), differential thermal analysis (DTA), and transmission electron microscopy (TEM) investigations, type and composition of phases as well as phase transitions were determined. With these results, the phase equilibria were established. A focus of the investigations is on the homogeneity ranges of the two ternary phases ωo and O, which both are stable up to temperatures above 900 °C. Based on the compositions measured for the ωo phase and its crystal structure type, a new formula (Ti,Nb)2Al is suggested. The results also indicate that the phase field of the ωo phase is split into two parts at 900 °C because of the growing phase field of the ordered (βTi,Nb)o phase.}, language = {en} } @misc{WangKongOehringetal., author = {Wang, Li and Kong, Yi and Oehring, Michael and Song, Min and Pyczak, Florian}, title = {Atomic site occupancy of alloying elements and Laves phase stability in γ-γ′ Co-base superalloys}, series = {Journal of Alloys and Compounds}, volume = {906}, journal = {Journal of Alloys and Compounds}, issn = {1873-4669}, doi = {10.1016/j.jallcom.2022.164261}, abstract = {The atomic site occupancy of alloying elements in the ZrCo2 and HfCo2 based Laves phases formed in the Co-9Al-9W-2Zr and Co-9Al-9W-2Hf alloys was experimentally determined by the combined techniques of energy-dispersive X-ray spectroscopy mapping with atomic resolution and the atom location by channeling enhanced microanalysis (ALCHEMI) method. The results show that both Al and W occupy the Zr site in the C15 and the Hf site in the C36 crystal structure. The atomic locations of Al and W were further confirmed by comparing calculated inelastic cross-sections with experimental ALCHEMI results. Using the determined atomic site occupancies of alloying elements, special quasirandom structure solid solution models with 192 atoms were constructed and employed in first-principles calculations. It is found theoretically that the energy of formation of the C15 structure is always lower than that of the C36 structure at 0 K in both ZrCo2 and HfCo2 phases, no matter whether Al and W are incorporated or not. However, further ab initio molecular dynamics simulations suggest that lattice vibration at finite temperature contributes significantly to the phase stability, stabilizing the C36 structure compared to the C15 type for the (Hf, Al, W)Co2 phase at finite temperature, which fits well with the experimental findings.}, language = {en} } @misc{LazurenkoPetrovMalietal., author = {Lazurenko, Daria V. and Petrov, Ivan Yu and Mali, Vyacheslav I. and Esikov, Maksim A. and Kuzmin, R. I. and Lozanov, V. V. and Pyczak, Florian and Stark, Andreas and Dovzhenko, G. D. and Bataev, Ivan A. and Terentiev, D. S. and Ruktuev, Alexey A.}, title = {Ti-Al3Ti metal-intermetallic laminate (MIL) composite with a cubic titanium trialuminide stabilized with silver: Selection of fabrication regimes, structure, and properties}, series = {Journal of Alloys and Compounds}, volume = {916}, journal = {Journal of Alloys and Compounds}, issn = {1873-4669}, doi = {10.1016/j.jallcom.2022.165480}, abstract = {Ti-Al3Ti metal-intermetallic laminate (MIL) composites are known as promising structural materials due to the unique combination of their specific properties. However, their application is still limited due to the extremely high brittleness of the Al3Ti phase. In this study, we attempt to address this issue by changing the D022 crystal structure of Al3Ti to the more ductile L12 structure by alloying it with silver. To select the best fabrication regimes of Ti-Ti(Al1-xAgx)3 composites, in situ synchrotron X-ray diffraction analysis was performed to reveal the chemical reactions occurring upon heating the Ti-Al-Ag sample. The analysis showed that the highest amount of Ti(Al1-xAgx)3 phase with the L12 structure appears at 930 °C. This temperature was chosen for subsequent spark plasma sintering experiments. Scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction analysis revealed that the sintered sample consisted mainly of Ti, Ti(Al1-xAgx)3, and a minor fraction of the Ag-Al compound distributed in the central parts of the intermetallic layers and at the grain boundaries. Modification of the titanium trialuminide crystal structure positively affected the properties of the composite, providing a 60\% increase in fracture toughness. The Ag-Al phase also contributed to toughening, causing an additional crack deflection effect.}, language = {en} } @misc{LemosFredelPyczaketal., author = {Lemos, Georges and Fredel, M{\´a}rcio C. and Pyczak, Florian and Tetzlaff, Ulrich}, title = {Creep resistance improvement of a polycrystalline Ni-based superalloy via TiC particles reinforcement}, series = {Materials Science and Engineering: A, Structural materials}, volume = {854}, journal = {Materials Science and Engineering: A, Structural materials}, issn = {1873-4936}, doi = {10.1016/j.msea.2022.143821}, abstract = {In order to develop highly efficient aircraft engines, the use of alloys for turbine blades that combine high creep resistance and lower density brings substantial benefits. That may be achieved by the introduction of a reinforcing phase, such as a discontinuous reinforcement. So far, most researched particle-reinforced Ni-based superalloys made use of sub-micrometer particles, such as oxides and borides, often produced by in-situ reactions. These are proposed solely as dislocation immobilizers, in a role comparable to that carried out by γ' precipitates, while metal matrix composites (MMCs) containing micro-scale particles offer a load-transfer potential. To combine both approaches, a recently designed polycrystalline Ni-based γ'-strengthened superalloy reinforced with TiC particles was produced by low energy mixing of powders, followed by pressure sintering. The composite, along with a non-reinforced reference, was submitted to compression creep tests at 973 K (700 °C), with stresses varying from 280 to 500 MPa. Selected specimens had their microstructure evaluated with techniques such as EBSD and XRD. When simulating a working turbine, the material density influences directly the centripetal forces acting on a section of a turbine blade, and consequently the creep rates. In the proposed composite, not only an increase in the threshold stress by a load-transfer component was obtained, but also the density reduction affected remarkably the creep rates. Moreover, the presented MMC not only presented a superior creep resistance in relation to the non-reinforced alloy, but also exhibited higher stability of primary and secondary γ' volumes after 500 h in creep tests.}, language = {en} } @misc{LiangNeumeierRaoetal., author = {Liang, Zhida and Neumeier, Steffen and Rao, Ziyuan and G{\"o}ken, Mathias and Pyczak, Florian}, title = {CALPHAD informed design of multicomponent CoNiCr-based superalloys exhibiting large lattice misfit and high yield stress}, series = {Materials Science and Engineering: A, Structural materials}, volume = {854}, journal = {Materials Science and Engineering: A, Structural materials}, issn = {1873-4936}, doi = {10.1016/j.msea.2022.143798}, abstract = {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.}, language = {en} } @misc{SongAppelPyczaketal., author = {Song, Lin and Appel, Fritz and Pyczak, Florian and Zhanbing, He and Junpin, Lin and Tiebang, Zhang}, title = {Characterization of primary, secondary and tertiary {202¯1}<1¯014> successive internal twins in the D019 ordered hexagonal α2-Ti3Al phase}, series = {Acta Materialia}, journal = {Acta Materialia}, number = {222}, issn = {1873-2453}, doi = {10.1016/j.actamat.2021.117391}, abstract = {Due to the lack of independent slip systems and the difficulty in mechanical twinning, D019 ordered α2-Ti3Al phase is known to be of substantial mechanical anisotropy, which partly accounts for the low ductility of two-phase (α2+γ) TiAl alloys. However, recent studies have shown that in Al-rich α2 phase compression deformation twins can be activated, which could be beneficial for the ductility of the alloys. In the present study, for the first time, we have revealed a novel internal twinning mechanism of α2 phase in a TiAl alloy deformed at high temperature. Three twin generations of a common type {202¯1}[removed] were revealed: Secondary twins formed within the primary twin, and tertiary twins formed in the secondary twin. It is important to note that this internal twin structure can only be observed in the [removed] direction but not the commonly used [removed] direction. The shear plane P of all twin variants is of type {12¯10}. Due to the variation of the twinning elements between the twin variants, the twinning shear is blunted. The interfaces between the twin variants are characterized by high-resolution electron microscopy. Special attention was paid to the structure of the coherent and incoherent twin boundaries. The effect of chemical ordering is discussed. Our results also shed light on the complex twinning mechanisms in hexagonal structures.}, language = {en} } @misc{PengEbelPyczaketal., author = {Peng, Xu and Ebel, Thomas and Pyczak, Florian and Willumeit-R{\"o}mer, Regine and Sen, Yu}, title = {Influence of defects on damage tolerance of Metal-Injection-Molded β titanium alloys under static and dynamic loading}, series = {Powder Metallurgy}, volume = {65}, journal = {Powder Metallurgy}, number = {5}, issn = {1743-2901}, doi = {10.1080/00325899.2022.2069077}, pages = {354 -- 364}, abstract = {The β titanium alloys are key materials in lightweight and biomedical applications, due to the combination of excellent biocompatibility and mechanical properties. However, the Binder-based Powder Technologies such as Metal-Injection-Molding (MIM), Binder-Jetting and Fused-Filament-Fabrication, normally introduce three major processing-related defects in the as-sintered Ti-parts: (i) residual porosity, (ii) high impurity level and (iii) coarse-grained structure. The previous studies revealed that these processing defects invariably tend to be even more severe in β titanium alloys than in α/β Ti-6Al-4V alloy, all fabricated by powder metallurgical route. In this work, these processing defects and their likely origins in MIM β titanium alloys are analysed. Furthermore, the influence of these defects on damage tolerance and fracture mechanisms of MIM β titanium alloys under either static or dynamic loading is investigated. Based on the studies, strategic technical improvements in the processing to improve the reliability of MIM β titanium alloys products are proposed.}, language = {en} } @misc{LiangPaulStarketal., author = {Liang, Zhida and Paul, Jonathan and Stark, Andreas and Bezold, Andreas and Neumeier, Steffen and G{\"o}ken, Mathias and Pyczak, Florian}, title = {High-Temperature CoNi-Based Superalloys Strengthened by γ′-(Ni,Co)3(Cr,Al,Ti,X): The Effect of Refractory Elements}, series = {Metallurgical and materials transactions. A, Physical metallurgy and materials science}, volume = {54 (2023)}, journal = {Metallurgical and materials transactions. A, Physical metallurgy and materials science}, number = {5}, issn = {1543-1940}, doi = {10.1007/s11661-022-06795-y}, pages = {1620 -- 1634}, abstract = {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.}, language = {en} } @misc{TangLiLietal., author = {Tang, Yingchun and Li, Wei and Li, Changle and Lu, Song and Vitos, Levente and Pyczak, Florian}, title = {First-Principles Calculations of Elastic and Thermodynamic Properties for Multi-component Co-based Superalloys}, series = {Metallurgical and materials transactions. A, Physical metallurgy and materials science}, volume = {54 (2023)}, journal = {Metallurgical and materials transactions. A, Physical metallurgy and materials science}, number = {5}, issn = {1543-1940}, doi = {10.1007/s11661-022-06891-z}, pages = {1635 -- 1648}, abstract = {First-principles calculations were performed to investigate the elastic and thermodynamic properties for multi-component Co-based superalloy systems and explored the effect of alloying on stabilizing the γ′ phase. First, the comparisons were carried out for the γ′ phase in Co3(Al,TM) (TM being transition metals) and Ni3Al systems between the present computational results using the EMTO-CPA method and other available DFT calculations as well as experimental data. The lattice parameters, elastic constants, and Debye temperatures are consistent with experimental results and other calculations. The predicted thermodynamic properties, e.g., the Gibbs free energy, excess entropy, and linear thermal expansion coefficient, agree well with CALPHAD results, experimental results, and other available first-principles calculations. A combination of EMTO-CPA method and Debye-Gr{\"u}neisen model is utilized in this work to ensure that the alloying effect on the stability of the γ′ phase in a multi-component Co-based system is captured efficiently. This could open the path for designing novel multi-component Co-based alloys based on first-principles calculation. To demonstrate this, predictions for the properties of multicomponent systems were undertaken. Our results show that Ni aids in the stabilization of the (CoNi)3(Al, Mo, Nb) phase.}, language = {en} } @misc{DistlHauschildtPyczaketal., author = {Distl, Benedikt and Hauschildt, Katja and Pyczak, Florian and Stein, Frank}, title = {Phase Equilibria in the Ti-Rich Part of the Ti-Al-Nb System—Part II: High-Temperature Phase Equilibria Between 1000 and 1300 °C}, series = {Journal of Phase Equilibria and Diffusion}, volume = {43}, journal = {Journal of Phase Equilibria and Diffusion}, number = {5}, issn = {1863-7345}, doi = {10.1007/s11669-022-00999-w}, pages = {554 -- 575}, abstract = {The knowledge of phase equilibria in the Ti-Al-Nb system above 1000 °C is of importance for the manufacturing of TiAl-based parts for high-temperature structural applications. Especially the extended homogeneity range of the cubic (βTi,Nb) phase, which is determined by its Al solubility, and the position and extension of the high-temperature (αTi) phase is of crucial importance for the hot-workability and microstructure control of these alloys. However, the phase diagrams reported in the literature are very contradicting especially regarding these aspects. For this reason, a systematic reinvestigation of the phase equilibria in this part of the system was carried out. A total of 17 ternary alloys were synthesized, heat-treated at 1000-1300 °C, and analyzed by electron probe microanalysis (EPMA), x-ray diffraction (XRD), high-energy XRD (HEXRD), and differential thermal analysis (DTA) to determine composition and type of equilibrium phases as well as transition temperatures. With this information, isothermal sections of the Ti-rich part of the Ti-Al-Nb system at 1000, 1100, 1200, and 1300 °C were established. An isolated (βTi,Nb)o phase field is found to be stable at 1000 and 1100 °C. Furthermore, the formation and homogeneity range of (αTi) at high temperatures as well as the presence of Ti3Al at 1200 °C is experimentally investigated and discussed. Based on the observed phase equilibria and transition temperatures, an improved reaction scheme for the entire Ti-Al-Nb system is proposed.}, language = {en} } @misc{LiuSongLiuetal., author = {Liu, Xu and Song, Lin and Liu, Tong and Stark, Andreas and Pyczak, Florian and He, Zhanbing and Lin, Junpin and Zhang, Tiebang}, title = {In- and ex-situ study of the deformation behavior of the βo(ωo) phase in a Ti4Al3Nb alloy during high-temperature compression}, series = {Journal of Alloys and Compounds}, volume = {918}, journal = {Journal of Alloys and Compounds}, issn = {0925-8388}, doi = {10.1016/j.jallcom.2022.165626}, abstract = {In-situ synchrotron-based high energy X-ray diffraction (HEXRD) and ex-situ Gleeble tests were conducted to investigate the deformation behavior of the βo(ωo) phase in a Ti4Al3Nb alloy. In samples compressed at 600 and 800 °C, the brittle ωo phase deforms mostly elastically, resulting in the failure of the Ti4Al3Nb alloy by premature fracture. In a sample deformed at 900 °C, the ωo phase mostly transforms into the βo phase under uniaxial loading. Moreover, the ductility of a Ti4Al3Nb alloy is largely enhanced at this temperature. In a sample deformed at 1000 °C, dynamic recrystallization (DRX) of the βo phase extensively takes place. Direction 1 (D1) and Direction 2 (D2) deviating from the loading direction with an angle of 65° ± 5° and 15° ± 5° are selected to analyze the lattice strain evolution of (110)βo lattice planes. At the late stage of macro strain hardening, deformed[removed]βo//D1 oriented grains bear a higher load due to the occurrence of DRX in[removed]βo//D2 oriented grains. Subsequently, DRX continues in[removed]βo//D1 oriented βo grains. The coordinated deformation of βo grains ensures the good deformability of a Ti4Al3Nb alloy at 1000 °C.}, language = {en} } @misc{LiWangLiangetal., author = {Li, Longjun and Wang, Li and Liang, Zhida and He, Junyang and Qiu, Jingwen and Pyczak, Florian and Song, Min}, title = {Effects of Ni and Cr on the high-temperature oxidation behavior and mechanisms of Co- and CoNi-base superalloys}, series = {Materials and Design}, volume = {224}, journal = {Materials and Design}, issn = {1873-4197}, doi = {10.1016/j.matdes.2022.111291}, abstract = {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.}, language = {en} } @misc{LiangLilleoddenOvrietal., author = {Liang, Zhida and Lilleodden, Erica and Ovri, Henry and Pyczak, Florian}, title = {Surface Recrystallization in a Co-Based Superalloy During High Temperature Exposure}, series = {Metallurgical and materials transactions. A, Physical metallurgy and materials science}, volume = {53}, journal = {Metallurgical and materials transactions. A, Physical metallurgy and materials science}, number = {12}, issn = {1543-1940}, doi = {10.1007/s11661-022-06852-6}, pages = {4156 -- 4160}, abstract = {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.}, language = {en} } @misc{ShangLiuLiangetal., author = {Shang, Yuanyuan and Liu, Shaofei and Liang, Zhida and Pyczak, Florian and Lei, Zhifeng and Heidenreich, Tim and Sch{\"o}ckel, Alexander and Kai, Ji-jung and Gizer, G{\"o}khan and Dornheim, Martin and Klassen, Thomas}, title = {Developing sustainable FeTi alloys for hydrogen storage by recycling}, series = {Communications Materials}, volume = {3}, journal = {Communications Materials}, number = {1}, issn = {2662-4443}, doi = {10.1038/s43246-022-00324-5}, abstract = {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.}, language = {en} } @misc{AmherdHidalgoEbelFrykholmetal., author = {Amherd Hidalgo, Alexandra and Ebel, Thomas and Frykholm, Robert and Carre{\~n}o-Morelli, Efra{\´i}n and Pyczak, Florian}, title = {High-oxygen MIM Ti-6Al-7Nb: Microstructure, tensile and fatigue properties}, series = {Materials Today Communication}, volume = {Vol. 34}, journal = {Materials Today Communication}, issn = {2352-4928}, doi = {10.1016/j.mtcomm.2022.104982}, language = {en} } @misc{GabrischJanovskaRackeletal., author = {Gabrisch, Heike and Janovsk{\´a}, Michaela and Rackel, Marcus W. and Pyczak, Florian and Stark, Andreas}, title = {Impact of microstructure on elastic properties in the alloy Ti-42Al-8.5 Nb}, series = {Journal of Alloys and Compounds}, volume = {Vol. 932}, journal = {Journal of Alloys and Compounds}, issn = {1873-4669}, doi = {10.1016/j.jallcom.2022.167578}, language = {en} } @misc{WangLiangLiuetal., author = {Wang, Li and Liang, Xiaopeng and Liu, Bin and Oehring, Michael and Paul, Jonathan David Heaton and Liu, Jie and Song, Min and Pyczak, Florian and Liu, Yong}, title = {Stacking fault formation in perovskite Ti3AlC carbides in a TiAl based alloy during creep at 800°C}, series = {Scripta Materialia}, volume = {Vol. 222}, journal = {Scripta Materialia}, issn = {1872-8456}, doi = {10.1016/j.scriptamat.2022.115034}, language = {en} } @misc{LiuStarkPyczaketal., author = {Liu, Xu and Stark, Andreas and Pyczak, Florian and Zhang, Tiebang}, title = {In-situ synchrotron high energy X-ray diffraction study on the internal strain evolution of D019-α2 phase during high-temperature compression and subsequent annealing in a TiAl alloy}, series = {Journal of Materials Science and Technology}, volume = {Vol. 163}, journal = {Journal of Materials Science and Technology}, issn = {1941-1162}, doi = {10.1016/j.jmst.2023.04.027}, pages = {212 -- 222}, language = {en} } @misc{SongAppelLiuetal., author = {Song, Lin and Appel, Fritz and Liu, Wenhao and Pyczak, Florian and Zhang, Tiebang}, title = {{11¯01} tension twins and {11¯01}-{22¯01}/{22¯01}-{11¯01} double twins in the D019 ordered hexagonal α2-Ti3Al phase}, series = {Acta Materialia}, volume = {260}, journal = {Acta Materialia}, number = {3}, doi = {10.1016/j.actamat.2023.119335}, language = {en} } @misc{FroebelStarkPauletal., author = {Fr{\"o}bel, Ulrich and Stark, Andreas and Paul, Jonathan and Pyczak, Florian}, title = {Assessment of the capability of Zr, Y, La, Gd, Dy, C, and Si to enhance the creep strength of gamma titanium aluminide alloys based on their effect on flow stress and thermal activation parameters}, series = {Intermetallics}, volume = {Vol. 162}, journal = {Intermetallics}, issn = {1879-0216}, doi = {10.1016/j.intermet.2023.108018}, language = {en} } @misc{GussoneRackelTumminelloetal., author = {Gussone, Joachim and Rackel, Marcus W. and Tumminello, Silvana and Barriobero-Vila, Pere and Kreps, Frederic and Kelm, Klemens and Stark, Andreas and Schell, Norbert and Pyczak, Florian and Haubrich, Jan and Requena, Guillermo}, title = {Microstructure formation during laser powder bed fusion of Ti-22Al-25Nb with low and high pre-heating temperatures}, series = {Materials and Design}, volume = {Vol. 232}, journal = {Materials and Design}, issn = {0264-1275}, doi = {10.1016/j.matdes.2023.112154}, language = {en} } @misc{LauhoffAroldBolenderetal., author = {Lauhoff, Christian and Arold, Tizian and Bolender, Artjom and Rackel, Marcus W. and Pyczak, Florian and Weinmann, Markus and Xu, Wenzheng and Molotnikov, Andrey and Niendorf, Thomas}, title = {Microstructure of an additively manufactured Ti-Ta-Al alloy using novel pre-alloyed powder feedstock material}, series = {Additive Manufacturing Letters}, volume = {Vol. 6}, journal = {Additive Manufacturing Letters}, issn = {2772-3690}, doi = {10.1016/j.addlet.2023.100144}, language = {en} } @misc{GuoSongLiuetal., author = {Guo, Xiang and Song, Lin and Liu, Xu and Stark, Andreas and Pyczak, Florian and Zhang, Tiebang}, title = {In-situ synchrotron HEXRD study on the phase transformation mechanisms of the ω-related phases in a Ti4Al3Nb alloy}, series = {Materials Characterization}, volume = {Vol. 200}, journal = {Materials Characterization}, issn = {1873-4189}, doi = {10.1016/j.matchar.2023.112901}, language = {en} } @misc{PyczakLiangNeumeieretal., author = {Pyczak, Florian and Liang, Zhida and Neumeier, Steffen and Rao, Ziyuan}, title = {Stability and Physical Properties of the L12-γ′ Phase in the CoNiAlTi-System}, series = {Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science}, volume = {54}, journal = {Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science}, number = {5}, issn = {1073-5623}, doi = {10.1007/s11661-022-06949-y}, pages = {1661 -- 1670}, language = {en} } @misc{VolpatoPereiraLemosetal., author = {Volpato, G. M. and Pereira, A. S. P. and Lemos, G. and Schmitt, M. and Pyczak, Florian and Tetzlaff, Ulrich and Fredel, M{\´a}rcio C.}, title = {Out-of-Equilibrium Formation of Ni3Ti η-Phase in Inconel X-750 Produced via Laser Powder Bed Fusion and Spark Plasma Sintering}, series = {Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science}, volume = {54}, journal = {Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science}, number = {5}, issn = {1073-5623}, doi = {10.1007/s11661-022-06946-1}, pages = {1924 -- 1936}, language = {en} } @misc{ZhangWangPyczaketal., author = {Zhang, Haoyin and Wang, C. P. and Pyczak, Florian and Ebel, Thomas and Liu, X. J.}, title = {A New Kind of Biomedical Ti-Mn-Nb Alloy}, series = {Physica Status Solidi. A, Applications and Materials Science}, volume = {220}, journal = {Physica Status Solidi. A, Applications and Materials Science}, number = {7}, issn = {1862-6300}, doi = {10.1002/pssa.202200348}, language = {en} } @misc{LiuSongStarketal., author = {Liu, Xu and Song, Lin and Stark, Andreas and Pyczak, Florian and Zhang, Tiebang}, title = {In-situ synchrotron high energy X-ray diffraction study on the deformation mechanisms of D019-α2 phase during high-temperature compression in a TiAl alloy}, series = {Journal of Materials Research and Technology}, volume = {33}, journal = {Journal of Materials Research and Technology}, publisher = {Elsevier BV}, issn = {2238-7854}, doi = {10.1016/j.jmrt.2024.10.231}, pages = {5850 -- 5862}, language = {en} } @misc{CaoWangTaoetal., author = {Cao, Xianli and Wang, Li and Tao, Hui and He, Weiwei and Liang, Xiaopeng and Liu, Bin and Oehring, Michael and Paul, Jonathan and Pyczak, Florian and Liu, Yong}, title = {Morphology evolution of P-Ti3AlC carbides and their influence on creep properties in a crept Ti-45Al-5Nb-0.75C alloy}, series = {Journal of Materials Research and Technology}, volume = {29}, journal = {Journal of Materials Research and Technology}, publisher = {Elsevier BV}, issn = {2238-7854}, doi = {10.1016/j.jmrt.2024.02.146}, pages = {4181 -- 4190}, language = {en} } @misc{WangWangPyczaketal., author = {Wang, Li and Wang, Yihao and Pyczak, Florian and Oehring, Michael and Song, Min and Liu, Yong}, title = {Revealing complex planar defects and their interactions at atomic resolution in a Laves phase containing Co-base superalloy}, series = {Acta Materialia}, volume = {264}, journal = {Acta Materialia}, publisher = {Elsevier BV}, issn = {1359-6454}, doi = {10.1016/j.actamat.2023.119568}, pages = {1 -- 20}, language = {en} } @misc{TangLiLuetal., author = {Tang, Yingchun and Li, Changle and Lu, Song and Li, Wei and Vitos, Levente and Pyczak, Florian}, title = {Magneto-chemical effects in the elastic properties of Co3Al-based compounds}, series = {Materials Today Communications}, volume = {41}, journal = {Materials Today Communications}, publisher = {Elsevier BV}, issn = {2352-4928}, doi = {10.1016/j.mtcomm.2024.110507}, pages = {1 -- 11}, language = {en} } @misc{HeidariPebdaniJanischPyczak, author = {Heidari Pebdani, Zeinab and Janisch, Rebecca and Pyczak, Florian}, title = {Effect of V-VIB group ternary elements on the properties of Ti2AlM-type O-phases: A first-principles study}, series = {Computational Condensed Matter}, volume = {40}, journal = {Computational Condensed Matter}, publisher = {Elsevier BV}, issn = {2352-2143}, doi = {10.1016/j.cocom.2024.e00945}, pages = {10}, language = {en} } @misc{GuptaPaulSchmittetal., author = {Gupta, Vipul and Paul, Jonathan David Heaton and Schmitt, Ingo and Pyczak, Florian}, title = {SciLitMiner : an intelligent system for scientific literature mining and knowledge discovery}, series = {Advanced intelligent systems}, journal = {Advanced intelligent systems}, publisher = {Wiley}, address = {Weinheim}, issn = {2640-4567}, doi = {10.1002/aisy.202501235}, pages = {1 -- 20}, abstract = {Recent advances in data mining have enabled automation in literature-based discovery (LBD), allowing synergistic evaluation of experimental findings reported in scientific publications. However, existing tools and digital libraries fall short in generating relevant literature collections and evaluating them for highly specific questions. This article presents SciLitMiner, an intelligent system to address this gap. SciLitMiner enables federated ingestion of literature from digital libraries; applies advanced retrieval techniques, including dataset-aware retrieval from visual elements, to identify relevant studies; and leverages retrieval-augmented generation (RAG) tailored to domain-specific knowledge reasoning. The system is applied in materials science to study the creep behavior of γ-TiAl alloys, revealing the intricate interplay between material, process, microstructure, and creep rate, represented through knowledge graphs. Two domain experts rate responses from the knowledge reasoning workflow with OpenAI large language models (LLMs) as the backbone above "good" (3 on a 5-point Likert scale) in over 90\% across qualitative criteria, indicating strong performance. In a case study, the workflow also outperforms gpt-4.5-turbo with web search and other leading tools in reliability. A second case study benchmarks open-source LLMs as drop-in replacements for proprietary models, demonstrating comparable-to-superior performance. The system's flexibility enables its use in automated LBD across diverse research domains.}, language = {en} } @misc{LiuSongPyczaketal., author = {Liu, Xu and Song, Lin and Pyczak, Florian and Stark, Andreas and Wang, Li and Guo, Xiang and Zhang, Tiebang}, title = {Stress-induced orthorhombic O phase in TiAl alloys}, series = {Acta materialia}, volume = {286}, journal = {Acta materialia}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {1359-6454}, doi = {10.1016/j.actamat.2025.120751}, pages = {1 -- 13}, abstract = {The orthorhombic O phase precipitation within the D019-α2 phase has attracted increasing attention recently in high Nb containing TiAl (high Nb-TiAl) alloys since the precipitation temperature is close to the expected service temperature of the alloys. In this study, in-situ synchrotron high energy X-ray diffraction (HEXRD) reveals that the O phase precipitates at 550 °C while it dissolves into the α2 phase at 750 °C during heat treatments. However, under external stress the O phase unexpectedly precipitates from α2 phase at 800 °C and even 900 °C. The O phase formation proceeds further in the presence of a critical stress promoted by internal stress accumulation in the α2 phase, whereas the reverse O→α2 phase transformation takes place when the internal stresses are relaxed. Additionally, it has been revealed that the O phase preferentially precipitates from specifically oriented α2 grains with one of their <110> directions aligned perpendicular and their 〈0001〉 directions rotated by an angle of 120° out of the external load axis. This α2 phase orientation facilitates the α2→O crystal transition during uniaxial compression. Transmission electron microscopy (TEM) study shows that stress-induced α2→O transformation is governed by small atomic shifts in the α2 lattice. In addition, the selective growth of certain O variants via shuffling along an [110]α2 direction is found to accommodate the external strain component in this direction.}, language = {en} } @misc{StarkRackelPyczak, author = {Stark, Andreas and Rackel, Marcus W. and Pyczak, Florian}, title = {How rapid heating and quenching cycles affect phase evolution in advanced γ-TiAl alloys : an in situ synchrotron radiation study}, series = {MRS communications}, volume = {15}, journal = {MRS communications}, number = {4}, publisher = {Springer Science and Business Media LLC}, address = {Berlin}, issn = {2159-6867}, doi = {10.1557/s43579-025-00756-3}, pages = {790 -- 795}, abstract = {Additive manufacturing (AM) processes are increasingly considered as an alternative manufacturing route to produce complex aircraft components out of γ-TiAl-based alloys. Due to the process-related high and short-time energy input, extremely fast heating and cooling rates occur which can result in thermodynamic and chemical disequilibrium. We studied the effect of rapid heating and quenching cycles in a Ti-48Al-2Nb-2Cr (in at.\%) alloy by carrying out in situ high-energy X-ray diffraction experiments in which AM-related heating cycles were simulated. These in situ experiments allow to determine the influence of cooling rate and a chosen powder bed temperature on phase evolution.}, language = {en} } @misc{StarkLottPyczak, author = {Stark, Andreas and Lott, Dieter and Pyczak, Florian}, title = {A dilatometer and in situ synchrotron X-ray diffraction study : α-quenching and reheating of a Nb-rich titanium aluminide alloy}, series = {MRS advances}, volume = {10}, journal = {MRS advances}, number = {14}, publisher = {Springer Science and Business Media LLC}, address = {Cham}, issn = {2731-5894}, doi = {10.1557/s43580-025-01382-w}, pages = {1767 -- 1772}, abstract = {Intermetallic γ-TiAl-based alloys are currently used as structural materials for turbine blades in aero engines. Additive manufacturing is increasingly considered as an additional manufacturing route for components consisting of γ titanium aluminides; however, the high heating and cooling rates result in chemical and thermodynamical disequilibrated microstructures. In our study, in situ synchrotron X-ray diffraction was applied to follow the formation of the disequilibrium microstructure during quenching and to study its re-equilibration during a subsequent annealing treatment in a Nb-rich γ-TiAl-based alloy. The quenched sample showed an incomplete massive transformation, with large remaining α2 grains. During reheating, the analysis of the collected data showed that equilibration of the quenched microstructure takes place in several reordering and transformation steps, e.g., orthorhombic distortion of the hexagonal α2 phase (around 550 °C), almost complete transformation of the supersaturated quenched α2 to γ (around 850 °C), and retransformation of γ to new α2 (around 1050 °C).}, language = {en} } @misc{LiuLiuWuetal., author = {Liu, Shen and Liu, Xu and Wu, Qiaohan and Li, Yixuan and Shi, Qiuyi and Song, Lin and Pyczak, Florian and Stark, Andreas and Li, Xiaobing and Zhang, Tiebang}, title = {In-situ synchrotron high energy X-ray diffraction study on the internal strain evolution of an extruded Ti-45Al-8Nb-0.2C alloy during high-temperature compression}, series = {Materials characterization}, volume = {230}, journal = {Materials characterization}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {1044-5803}, doi = {10.1016/j.matchar.2025.115746}, pages = {1 -- 12}, abstract = {Due to their exceptional properties, γ-TiAl based alloys present substantial prospect for aerospace and automotive applications. However, the significant disparity in plasticity between the D019-α2 and L10-γ phases greatly affects TiAl alloys' service behavior. This study investigates the internal strain accumulation in the α2 and γ phases of an extruded Ti-45Al-8Nb-0.2C alloy during compression at 900 °C and the subsequent stress relaxation behavior during annealing at 850 °C, using in situ synchrotron high-energy X-ray diffraction (HEXRD). During compression, the γ phase starts to yield plastically at approximately 410 MPa true stress, progressively shifting the load to the α2 phase and generating high residual stress in the α2 phase after deformation. However, annealing at 850 °C for 30 min only partially relieves the residual stress in the α2 phase, with the relaxation rate decreasing substantially after the first 10 min. Furthermore, when the true stress reaches 790 MPa during compression, the α2 phase undergoes rigid-body rotation to accommodate the plastic deformation of the adjacent γ phase, initiating texture evolution that ultimately forms a distinct fiber texture.}, language = {en} } @misc{WangWangLiangetal., author = {Wang, Li and Wang, Yihao and Liang, Xiaopeng and Liu, Bin and He, Junyang and Oehring, Michael and Pyczak, Florian and Liu, Yong}, title = {Revealing the unique evolution and splitting behavior of carbides at atomic-scale in TiAl alloys : the role of elastic interactions and chemical fluctuations}, series = {Acta materialia}, volume = {296}, journal = {Acta materialia}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {1359-6454}, doi = {10.1016/j.actamat.2025.121277}, pages = {1 -- 17}, abstract = {Cubic perovskite-Ti3AlC carbides are essential strengthening particles in TiAl alloys, especially for application above 800 °C where coarsening is expected to occur. However, these carbides can decompose into small sub-particles upon extended annealing, and the underlying atomic-scale mechanisms, especially structural and compositional changes, driving this unique splitting remain unclear. This study revisits this behavior in a Ti-45Al-5Nb-0.75C alloy utilizing probe-corrected transmission electron microscopy, atom probe tomography and first-principle calculations. The results reveal that the elastic interactions significantly influence carbide evolution. While needle-like carbides transform to intact plates during aging, those in high-density regions tend to coalesce or align along elastically softest γ-matrix directions, forming low-energy plate-like carbide conglomerates. With extended annealing, periodic chemical fluctuations driven by lattice misfit, especially along the needles induce splitting. Simultaneously, a γi-phase with a larger tetragonality and a 90°-rotated c-axis relative to the γ matrix emerges between the sub-particles, which exhibits near-zero lattice mismatch with carbides along [001], combined with mass-center shifts of carbides, further stabilizing the split configurations. This study provides atomic-scale insights into the evolution and stability of strengthening precipitates in systems with tetragonal misfit, and offers new strategies for improving creep properties of TiAl alloys by tailoring carbide configurations.}, language = {en} }