% Encoding: UTF-8
@COMMENT{BibTeX export based on data in FAU CRIS: https://cris.fau.de/}
@COMMENT{For any questions please write to cris-support@fau.de}
@article{faucris.318371980,
abstract = {Cost- and time-demanding trial-and-error methods have been the historical route for alloy development. A combinatorial approach can significantly simplify and accelerate the development process by characterization of composition dependent properties on material libraries, which are specimens or sets of specimens that map out a certain composition space, often employing composition profiles. Herein, a promising production method for such a material library is proposed: laser-remelting of stacked blocks of different compositions is evaluated for its suitability to produce material libraries, using the ternary CrCoNi system for a proof-of-concept. The composition profiles of the successfully created CrCoNi material library were measured by electron probe micro analysis. The intermixing has a length of about 2.5 mm. An analytical model describing the intermixing process is proposed and shows value in the estimation of the intermixing length after the first melting step. The comparison of the experimental microstructure observations from this work and from literature shows mostly good agreement with some deviations related to microsegregation and finite quenching cooling rates, which is supported by thermodynamic calculations regarding phase stability. In the single-phase region, the mechanical properties as measured via microhardness indentation are discussed as potential candidates for model validation.},
author = {Gaag, Tobias and Heidowitzsch, Maximilian and Galgon, Florian and Körner, Carolin and Zenk, Christopher},
doi = {10.1002/adem.202301316},
faupublication = {yes},
journal = {Advanced Engineering Materials},
keywords = {combinatorial alloy development; CrCoNi; high-throughput analysis; material library; multi-principal-element-alloy; phase diagram},
note = {CRIS-Team Scopus Importer:2024-02-16},
peerreviewed = {Yes},
title = {{A} {Novel} {Approach} for {Rapid} {Material} {Library} {Generation} {Using} {Laser}-{Remelting}},
volume = {26},
year = {2024}
}
@article{faucris.207755171,
abstract = {A gamma' strengthened Co-Ti-Cr superalloy is presented with a mass density similar to 14 % below that of typical Co-Al-W-based alloys. The lattice misfit is sufficiently low to form coherent cuboidal gamma' precipitates. Atom probe tomography shows that Cr partitions to the gamma phase, but increases the gamma' volume fraction compared to a binary Co-Ti alloy to more than 60 %. The solubility of Cr in the gamma' phase is significantly higher than expected from previously published values. The gamma' solvus temperature is above 1100 degrees C. The yield strength shows a distinct increase above 600 degrees C surpassing that of Co-9Al-8W (at.%) and conventional Co-base superalloys, even more so when it is normalized by the mass density. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.},
author = {Zenk, Christopher and Povstugar, Ivan and Li, Rui and Rinaldi, Fernando and Neumeier, Steffen and Raabe, Dierk and Göken, Mathias},
doi = {10.1016/j.actamat.2017.06.024},
faupublication = {yes},
journal = {Acta Materialia},
keywords = {Co-base superalloys;Atom probe tomography (APT);High-temperature deformation;X-ray diffraction (XRD);Phase diagram calculation},
pages = {244-251},
peerreviewed = {Yes},
title = {{A} novel type of {Co}-{Ti}-{Cr}-base γ/γ′ superalloys with low mass density},
volume = {135},
year = {2017}
}
@inproceedings{faucris.243059409,
abstract = {Casting of single-crystalline superalloys is known to be difficult due to a variety of challenges. Co-based superalloysCo-base superalloys, however, promise to show quite good castability compared to Ni-based superalloys, as documented in this manuscript. Therefore, an alloy series, which is designed by changing only the Co-to-Ni ratio, is used to address this topic. In addition to the castingCasting behavior, segregationSegregation and recrystallizationRecrystallization behavior were also investigated, since these are closely related to castingCasting challenges. It was found that in the as-cast state, all alloying elements distribute more homogeneously in the Co-rich alloys which is beneficial for castingCasting. CastingCasting of directionally solidified tubes revealed that the Co-rich alloys show a lower susceptibility to hot tearing and predominantly develop cold cracks. Since cold cracking can be addressed by component design, Co-base superalloysCo-base superalloys are suggested to show a better castability compared to Ni-based superalloys. RecrystallizationRecrystallization, however, is more pronounced for the Co-rich alloys. This might become a problem during castingCasting of single-crystalline Co-base components, if high deformation is introduced in the solidified component.},
address = {Cham},
author = {Volz, Nicklas and Zenk, Christopher and Halvaci, Timur and Matuszewska, Katarzyna and Neumeier, Steffen and Göken, Mathias},
doi = {10.1007/978-3-030-51834-9{\_}88},
editor = {Tin S, Hardy M, Clews J, Cormier J, Feng Q, Marcin J, O'Brien C, Suzuki A},
faupublication = {yes},
isbn = {978-3-030-51834-9},
pages = {901-908-908},
peerreviewed = {unknown},
publisher = {Springer International Publishing},
title = {{Castability} and {Recrystallization} {Behavior} of γ′-{Strengthened} {Co}-{Base} {Superalloys}},
year = {2020}
}
@article{faucris.267249836,
abstract = {The development of high-temperature heavy-duty turbine disk materials is critical for improving the overall efficiency of combined cycle power plants. An alloy development strategy to this end involves superalloys strengthened by ‘compact’ γ′-γ” coprecipitates. Compact morphology of coprecipitates consists of a cuboidal γ′ precipitate such that γ” discs coat its six {001} faces. The present work is an attempt to investigate the microstructure and creep behavior of a fully aged alloy exhibiting compact coprecipitates. We conducted heat treatments, detailed microstructural characterization, and creep testing at 1200◦ F (649◦ C) on an IN718-variant alloy. Our results indicate that aged IN718-27 samples exhibit a relatively uniform distribution of compact coprecipitates, irrespective of the cooling rate. However, the alloy ruptured at low strains during creep tests at 1200◦ F (649◦ C). At 100 ksi (689 MPa) load, the alloy fails around 0.1% strain, and 75 ksi (517 MPa) loading causes rupture at 0.3% strain. We also report extensive intergranular failure in all the tested samples, which is attributed to cracking along grain boundary precipitates. The results suggest that while the compact coprecipitates are indeed thermally stable during thermomechanical processing, the microstructure of the alloy needs to be optimized for better creep strength and rupture life.},
author = {Mukhopadhyay, Semanti and Sriram, Hariharan and Zenk, Christopher and Didomizio, Richard and Detor, Andrew J. and Hayes, Robert W. and Viswanathan, Gopal B. and Wang, Yunzhi and Mills, Michael J.},
doi = {10.3390/met11121897},
faupublication = {yes},
journal = {Metals},
keywords = {Compact; Coprecipitates; Creep; ECCI; Grain boundary; IN718; Microstructure; Superalloy},
note = {CRIS-Team Scopus Importer:2021-12-17},
peerreviewed = {Yes},
title = {{Creep} behavior of compact γ′-γ′′ coprecipitation strengthened in718-variant superalloy},
volume = {11},
year = {2021}
}
@article{faucris.238451353,
abstract = {High strain-hardening rates in equiatomic CrCoNi and other multi-principal element alloys have been attributed to deformation twinning. This work shows that small additions of Al and Ti to a CrCoNi alloy deactivate deformation twinning with only minor changes to uniform elongation and ultimate tensile strength. The initial microstructure is free of chemically ordered (Al,Ti)-rich precipitates after solutionizing and quenching. Tensile properties for the alloy are reported and compared to equiatomic CrCoNi, and the post-deformation microstructure is assessed. Density functional theory calculations indicate that energetically unfavorable Al-Al bonds may discourage shearing via partial dislocations, which are necessary for twinning to occur.
Ti > W > Mo > Re,
the solid solution strengthening elements Mo, Re and W are displaced
from the γ′-phase by increasing Ti and Ta contents. The investigated
solutes do not directly influence the partitioning behavior of Ru as it
prefers Ni-sites in the γ′-phase. Compressive creep experiments reveal a
correlation between the content of solid solution strengtheners in the
γ-phase and creep performanc},
author = {Gaag, Tobias and Ritter, Nils and Peters, Alexandra and Volz, Nicklas and Gruber, Daniel and Neumeier, Steffen and Zenk, Christopher and Körner, Carolin},
doi = {10.3390/met11111707},
faupublication = {yes},
journal = {Metals},
keywords = {Ni-based superalloys; creep; solid solution strengthening; partitioning behavior; DSC; CALPHAD},
note = {CRIS-Team Scopus Importer:2021-11-05},
peerreviewed = {Yes},
title = {{Improving} the {Effectiveness} of the {Solid}-{Solution}-{Strengthening} {Elements} {Mo}, {Re}, {Ru} and {W} in {Single}-{Crystalline} {Nickel}-{Based} {Superalloys}},
volume = {11},
year = {2021}
}
@article{faucris.218985325,
abstract = {The role of base element (Co or Ni) in γ′-strengthened single-crystalline superalloys was elucidated in the present study. Reaction kinetics during oxidation at 900 °C were assessed by thermogravimetry and measurements of individual layer thicknesses in the multilayered oxide scales. The development of diffusion-limiting barrier layers as well as the extent of sub-scale phase transitions could be directly correlated to the Co/Ni ratio in the alloy. For the first time a surface pretreatment with F was applied to Co-base superalloys. Apparent differences in the efficacy of the halogen effect depending on the Co content in the model alloys were observed.},
author = {Weiser, Martin and Galetz, Mathias C. and Zschau, Hans Eberhard and Zenk, Christopher and Neumeier, Steffen and Göken, Mathias and Virtanen, Sannakaisa},
doi = {10.1016/j.corsci.2019.05.007},
faupublication = {yes},
journal = {Corrosion Science},
keywords = {Co/Ni-base model alloys; Diffusion-limiting scales; EPMA; Halogen effect; Oxidation},
note = {CRIS-Team Scopus Importer:2019-05-28},
peerreviewed = {Yes},
title = {{Influence} of {Co} to {Ni} ratio in γ′-strengthened model alloys on oxidation resistance and the efficacy of the halogen effect at 900 °{C}},
year = {2019}
}
@article{faucris.290027611,
abstract = {Introducing Cu nanoparticles is an effective mechanism for strengthening and toughening Fe-based materials such as ultra-high-strength steels. Herein, the effect of Cu on the mechanical properties of a novel Fe-based alpha/alpha '/alpha '' superalloy is studied. Compared to a Cu-free reference alloy, nanoindentation reveals an increase in hardness, which was associated with the formation of Cu nanoparticles. Both alloys show room temperature (RT) compressive plastic strain at maximum stress greater than 8%, irrespective of the heat-treatment. At RT and at 750 degrees C, the Cu-containing alloy exhibits a slightly higher strength, but the heat treatment has a more significant impact: A configuration of alpha-matrix and intermetallic alpha '/alpha ''-phases forming an interpenetrating network is superior to a state with isolated precipitates. This difference vanishes in monotonic creep experiments, and under the same conditions, the Cu-containing alloy exhibits a twice as high creep rate despite a slightly higher precipitate fraction. This is linked to a higher lattice misfit and faster-coarsening kinetics. Post-mortem transmission electron microscopy analysis of the creep-deformed specimens identifies dislocation bypass as the dominant deformation mechanism. However, the presence of {110} dislocations in the interfacial networks and evidence of dislocation activity within alpha '/alpha '' precipitates suggest the occurrence of shearing events.},
author = {Morales, Luis Angel and Bezold, Andreas and Förner, Andreas and Holz, Hendrik and Merle, Benoit and Neumeier, Steffen and Körner, Carolin and Zenk, Christopher},
doi = {10.1002/adem.202201652},
faupublication = {yes},
journal = {Advanced Engineering Materials},
month = {Jan},
note = {CRIS-Team WoS Importer:2023-03-03},
peerreviewed = {Yes},
title = {{Influence} of {Cu} {Addition} and {Microstructural} {Configuration} on the {Creep} {Resistance} and {Mechanical} {Properties} of an {Fe}-{Based} alpha/alpha '/alpha '' {Superalloy}},
year = {2023}
}
@article{faucris.293799096,
abstract = {The influence of various alloying elements on Co-Al-W based superalloys has been investigated in detail since the discovery of the Co3(Al,W) phase. However, a full picture on the role of the refractory and platinum group elements is still lacking. Accordingly, this work covers the microstructural changes and phase stability in Co9Al9W-X superalloys with 2 at% Zr, Ru, Rh, Pd, Hf, Re, Ir, and Pt. The experimental findings are compared with thermodynamic calculations. Generally, alloying with refractory and platinum group elements preserves γ/γ′ microstructures, but causes the formation of additional intermetallic phases. Electron backscatter diffraction and energy dispersive X-ray spectroscopy reveal that Ru, Ir, and Pt cause discontinuous formation of β (B2) and χ (D019) phases whereas in the Re-containing alloy β and µ (D85) precipitates are present along the grain boundaries. Also unidentified Hf- and Zr-rich phases form in the alloys containing these elements. Additionally, differential scanning calorimetry measurements and scanning electron microscopy analysis indicate an increasing γ′ solvus temperature as well as γ′ volume fraction for most of the refractory and platinum group elements. This can be explained by their γ′/γ partitioning behavior, which has been examined by atom probe tomography.},
author = {Köbrich, Manuel and Förner, Andreas and Volz, Nicklas and Zenk, Christopher and Fries, S. G. and Göken, Mathias and Neumeier, Steffen},
doi = {10.1016/j.jallcom.2023.169542},
faupublication = {yes},
journal = {Journal of Alloys and Compounds},
keywords = {Atom probe tomography, thermodynamic calculations; Co-base superalloys; Differential scanning calorimetry; Electron backscatter diffraction; Energy dispersive X-ray spectroscopy},
note = {CRIS-Team Scopus Importer:2023-03-24},
peerreviewed = {Yes},
title = {{Influence} of refractory and platinum group metals on the microstructure and thermo-physical properties of {Co}-{Al}-{W}-based superalloys},
volume = {947},
year = {2023}
}
@article{faucris.207755977,
abstract = {The element Re is known to be a very potent strengthener concerning the creep properties of Ni-base superalloys. In this paper the influence of Re on the properties of new gamma'-strengthened Co-base superalloys is addressed. Atom probe tomography reveals that Re partitions preferentially to the gamma phase, but not as pronounced as in ni-base superalloys. Nanoindentation and micro-pillar compression tests of the gamma' phase indicate an increase of the hardness and the critical resolved shear stress caused by a considerable concentration of Re in the gamma' phase. Creep investigations show that the positive effect of Re is by far not as pronounced as in Ni-base superalloys. Several effects, which can contribute to this behavior, such as the lower Re concentration in gamma and hence a slightly reduced effective diffusion coefficient, a smaller diffusion barrier of Re in Cocompared to Ni, a slightly lower lattice misfit and gamma' volume fraction of the Re-containing alloy, are discussed.},
author = {Kolb, Markus and Zenk, Christopher and Kirzinger, Anna and Povstugar, Ivan and Raabe, Dierk and Neumeier, Steffen and Göken, Mathias},
doi = {10.1557/jmr.2017.242},
faupublication = {yes},
journal = {Journal of Materials Research},
pages = {2551-2559},
peerreviewed = {Yes},
title = {{Influence} of rhenium on γ′-strengthened cobalt-base superalloys},
volume = {32},
year = {2017}
}
@article{faucris.310158408,
abstract = {Outstanding inherent environmental resistance is a precondition for the use of superalloys in high-temperature applications. Besides high Al and Cr levels, also refractory metal concentrations (W and Ta) are reported to affect protective scale formation, as these elements are expected to affect the chemical activity and also the transport of protective scale formers within the alloy. In this study, we elucidate the high-temperature oxidation behavior of 3 Co-based (Co/Ni ratio: 1.4) and 3 Ni-based (Co/Ni ratio: 0.7) superalloys differing in W and Ta levels. Time-resolved thermogravimetric analysis (TGA) in synthetic air at 1050 °C and 1150 °C for 100 h, scanning electron microscopy analysis (SEM), thermodynamic calculations using the CALPHAD software Thermo-Calc, and diffusion couple experiments were conducted to assess the impact of the Co/Ni ratio and the refractory metal content on the oxidation performance. The results indicate that a low W content (3 vs. 5 at.%) and a high Ta content (2.1 vs. 1.5 at.%) beneficially affect the oxidation resistance, as alumina scale formation is facilitated.},
author = {Hagen, Sebastian and Haußmann, Lukas and Wahlmann, Benjamin and Gebhardt, Franz and Abu-Khousa, B. and Weiser, Martin and Neumeier, Steffen and Zenk, Christopher and Virtanen, Sannakaisa},
doi = {10.1007/s11085-023-10183-1},
faupublication = {yes},
journal = {High Temperature Corrosion of Materials},
keywords = {Cobalt-base superalloys; High-temperature oxidation; Protective scales; Refractory metals},
note = {Created from Fastlane, Scopus look-up},
peerreviewed = {Yes},
title = {{Influence} of the {W} and {Ta} content on the {High}-{Temperature} {Oxidation} {Resistance} of {Multinary} {Co}/{Ni}-{Based} {Superalloys} at 1050 °{C} and 1150 °{C}},
year = {2023}
}
@article{faucris.313461875,
abstract = {Understanding the influence of γ′ and secondary-phase fractions on the mechanical properties of superalloys is very important to optimize these high-strength materials. So far, this has not been systematically investigated for the novel class of Co-based superalloys. In this study, a Co–Al–W–Ta model alloy series was designed with compositions of γ/γ′ on the tie-line and an increasing γ′ volume fraction of up to 70% after heat treatment at 900 °C, while a few alloys are unexpectedly out of γ/γ′ two-phase region with an additional secondary phase fraction of up to 15%. The high-temperature strength and creep properties were evaluated by compression tests up to 1050 °C and compressive creep experiments at 950 °C, respectively. At temperatures of up to 1050 °C, an increasing γ′ volume fraction consistently increased the yield strength, which was not dramatically changed by the presence of secondary phases. Significant work hardening was found in alloys with γ′ volume fractions of 65–70% during compression testing, but not in alloys with either a lower γ′ volume fraction (<50%) or a high fraction of secondary phases (~15%). Similar to the yield strength, the creep strength also increased continuously with the γ′ volume fraction, but was greatly reduced with an increasing fraction of secondary phases. The best creep performance at 950 °C and 200 MPa was found in the alloy with the highest γ′ volume fraction and no secondary phases. At higher creep stresses, rafting contributed significantly to the hardening and, again, the alloy with a high γ′ volume fraction and a small amount of secondary phases exhibited the highest strength.},
author = {Xue, Fei and Bezold, Andreas and Volz, Nicklas and Kirchmayer, Andreas and Zenk, Christopher and Neumeier, Steffen and Göken, Mathias},
doi = {10.3390/cryst13071095},
faupublication = {yes},
journal = {Crystals},
keywords = {Co-based superalloys; compression test; creep; rafting; stacking faults; transmission electron microscopy},
note = {CRIS-Team Scopus Importer:2023-11-03},
peerreviewed = {Yes},
title = {{Influence} of the γ′ {Volume} {Fraction} on the {High}-{Temperature} {Strength} of {Single} {Crystalline} {Co}–{Al}–{W}–{Ta} {Superalloys}},
volume = {13},
year = {2023}
}
@article{faucris.210836693,
abstract = {The mechanical properties of gamma'-strengthened Co-Ni-Al-W-Cr model superalloys extending from pure Ni-base to pure Co-base superalloys have been assessed. Differential scanning calorimetry measurements and thermodynamic calculations match well and show that the gamma' solvus temperature decreases with increasing Co-content The gamma/gamma' lattice misfit is negative on the Ni- and positive on the Co-rich side. High Ni-contents decelerate the oxidation kinetics up to a factor of 15. The creep strength of the Ni-base alloy increases by an order of magnitude with additions of Co before it deteriorates strongly upon higher additions despite an increasing gamma' volume fraction. (C) 2015 Elsevier Ltd. All rights reserved.},
author = {Zenk, Christopher and Neumeier, Steffen and Engl, Nicole and Fries, Suzana G. and Dolotko, Oleksandr and Weiser, Martin and Virtanen, Sannakaisa and Göken, Mathias},
doi = {10.1016/j.scriptamat.2015.09.018},
faupublication = {yes},
journal = {Scripta Materialia},
keywords = {Cobalt;Nickel;Superalloy;Creep;Neutron diffraction},
pages = {83-86},
peerreviewed = {Yes},
title = {{Intermediate} {Co}/{Ni}-base model superalloys - {Thermophysical} properties, creep and oxidation},
volume = {112},
year = {2016}
}
@article{faucris.277556039,
abstract = {Fe–Co–B–Si–Nb bulk metallic glasses are prone to the formation of micro-cracks during laser powder bed fusion (LPBF) additive manufacturing. Introducing ductile Cu into Fe–Co–B–Si–Nb bulk metallic glass alloy system rich with Fe and Co could be a promising solution to reduce or even eliminate micro-cracks since there is almost no miscibility of Cu in Fe and Co. In this work, processing, microstructure and mechanical properties of Cu-containing {(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 (at.%) bulk metallic glass composites (BMGCs) under different laser power and scanning speed by LPBF are investigated in detail. A moderate area energy density facilitates the fabrication of highly dense (relative density: up to ∼99.5%) and almost crack-free (crack density: ∼0.1 mm−1) FeCoBSiNb–Cu bulk samples. These bulk samples possess an interpenetrating composite microstructure mainly composed of an amorphous Fe(Co)-rich phase and a crystalline Cu-rich phase. A crystalline Cu-rich phase is distributed relatively homogeneously in an amorphous phase and helps to reduce and even eliminate micro-crack formation during LPBF processing. Also, the Cu-rich phase has the effect of a heat sink and thus speeds up heat dissipation, facilitating the formation of an amorphous phase. The microhardness of the ductile Cu-rich phase and the hard amorphous Fe(Co)-rich phase in the interpenetrating composite microstructure was evaluated. Compressive tests at room temperature indicate that the dense bulk samples exhibit a relatively high fracture strength and a large fracture strain. Additionally, bulk samples with lack-of-fusion pores show a larger fracture strain although their fracture strength is lower than that of dense bulk samples. It is concluded that the LPBF-processed FeCoBSiNb–Cu BMGCs constitute a promising wear-resistant material to be used for example as bearing materials.},
author = {Luo, Ning and Huber, Florian and Ciftci, Nevaf and Wahl, Larissa and Bezold, Andreas and Neumeier, Steffen and Uhlenwinkel, Volker and Travitzky, Nahum and Schmidt, Michael and Zenk, Christopher and Körner, Carolin},
doi = {10.1016/j.msea.2022.143405},
faupublication = {yes},
journal = {Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing},
keywords = {Bulk metallic glass composites; Fe-based amorphous alloy; Laser powder bed fusion; Mechanical properties; Microstructure; Solidification},
note = {CRIS-Team Scopus Importer:2022-07-08},
peerreviewed = {Yes},
title = {{Laser} powder bed fusion of {FeCoBSiNb}-{Cu} bulk metallic glass composites: {Processing}, microstructure and mechanical properties},
volume = {849},
year = {2022}
}
@article{faucris.106593784,
abstract = {A continuous γ/γ' two-phase field has been identified extending between the ternary Co-Al-W system to the binary Co-Ti system. The lattice misfits of two phase γ/γ' alloys from the Co-Al-W-Ti quaternary system were measured by X-ray diffraction and found to be positive and vary linearly with composition. Differential scanning calorimetry measurements showed that the solidus and liquidus temperatures decrease from the W and Al rich end to the Ti rich end, whilst the γ' solvus temperature increases. Long term heat treatments identified the occurrence of discontinuous precipitation at the grain boundaries in many of the alloys studied. The high temperature strength and creep resistance of the quaternary alloys in the intermediate composition range surpassed those of the binary and ternary alloys. © 2014 Elsevier Ltd. All rights reserve},
author = {Zenk, Christopher and Neumeier, Steffen and Stone, H. J. and Göken, Mathias},
doi = {10.1016/j.intermet.2014.07.006},
faupublication = {yes},
journal = {Intermetallics},
keywords = {B. Age-hardening; B. Thermal stability; B. Yield stress; D. Microstructure; F. Differential scanning calorimetry; F. Diffraction/sacterring (electron, neutron and X-ray)},
pages = {28-39},
peerreviewed = {Yes},
title = {{Mechanical} properties and lattice misfit of γ/γ' strengthened {Co}-base superalloys in the {Co}-{W}-{Al}-{Ti} quaternary system},
volume = {55},
year = {2014}
}
@article{faucris.265400521,
abstract = {In this work, laser metal deposition (LMD), a direct energy deposition (DED) additive manufacturing technology, is used to prepare Zr59.3Cu28.8Al10.4Nb1.5 bulk metallic glass composites (BMGCs). Phase constitutions and thermal behavior of LMD-processed Zr–Cu–Al–Nb samples are examined using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The microstructure evolution parallel to the build direction is characterized in detail utilizing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron probe microscopy analysis (EPMA) and electron backscatter diffraction (EBSD). Young's modulus and hardness in typical microstructures are evaluated employing nanoindentation. Within each deposited layer, a periodic microstructure, exhibiting crystalline features of three distinctly different morphologies, is observed, depending on the location within that layer. Along the build direction, the dominating microstructure of the melt pool evolves from a nearly featureless amorphous state over fine nanocrystals to coarse nanocrystals while the morphology of most micro-scale dendritic crystals changes from flower-shaped to columnar, simultaneously a coarse microstructure appearing in upper layers. The fine Al-rich phases gradually coarsen directionally parallel to the build direction. Furthermore, the correlation between microstructure and mechanical properties is investigated. This work enhances our knowledge about microstructural characteristics and mechanical properties of BMGCs in-situ fabricated by DED additive manufacturing.},
author = {Luo, Ning and Galgon, Florian and Krauß, Sebastian and Morales, Luis A. and Merle, Benoit and Zenk, Christopher and Körner, Carolin},
doi = {10.1016/j.intermet.2021.107393},
faupublication = {yes},
journal = {Intermetallics},
keywords = {Bulk metallic glass composites; Crystallization; Laser metal deposition; Microstructure; Nanoindentation},
month = {Jan},
note = {Created from Fastlane, Scopus look-up},
peerreviewed = {Yes},
title = {{Microstructural} evolution and mechanical properties in {Zr}–{Cu}–{Al}–{Nb} bulk metallic glass composites prepared by laser metal deposition},
volume = {140},
year = {2022}
}
@article{faucris.106595544,
abstract = {The microstructure and mechanical properties of a series of Cr-CrTa-based alloys with nominal compositions (90-x)Cr-9Ta-xSi, where x = 4, 6, 10 and 14 at%, have been investigated. The alloys predominantly consisted of a microstructure of primary C14 CrTa Laves phase dendrites and a eutectic intergrowth of an A2 Cr rich solid solution and the Laves phase. The Laves phase was seen to adopt the C14 polytype in all ternary alloys, with no evidence of transformation to the C15 polytype. Fine, solid-state precipitates of the Laves phase were also observed within the solid solution. At higher silicon contents, a third intermetallic phase, CrSi, with the A15 crystal structure, was also identified. The overall hardness of the alloys at room temperature increased with Si content and hence, the volume fraction of the Laves phase. Compression tests were conducted on samples of the alloys at 1000 and 1100 °C under a strain rate of 10 s in air. Amongst the ternary alloys, the alloy with 14 at% Si showed the highest yield strength of ~440 MPa at 1000°C and ∼290 MPa at 1100°C. The yield strength of the alloy with 6 at% Si was also found to reduce monotonically with increasing temperature from ambient to 1100°C. Transmission electron microscopy of the post-compression microstructures revealed that deformation was primarily accommodated by the A2 Cr-rich solid solution, with a high density of dislocations in the phase compared to that in the intermetallic phase. Within the C14 Laves phase, deformation was seen to be mediated by the movement of a/3-type synchro-Shockley partial dislocations, consistent with previous studies, bounding stacking faults on the basal plan},
author = {Bhowmik, Ayan and Neumeier, Steffen and Barnard, Jon S. and Zenk, Christopher and Göken, Mathias and Rae, Catherine M. F. and Stone, Howard J.},
doi = {10.1080/14786435.2014.971086},
faupublication = {yes},
journal = {Philosophical Magazine},
keywords = {deformation; dislocation; electron microscopy; intermetallics; Laves phase; transmission},
pages = {3914-3944},
peerreviewed = {Yes},
title = {{Microstructure} and mechanical properties of {Cr}-{Ta}-{Si} {Laves} phase-based alloys at elevated temperatures},
volume = {94},
year = {2014}
}
@article{faucris.110986744,
author = {Zenk, Christopher and Bauer, Alexander and Goik, Philip and Neumeier, Steffen and Stone, Howard J. and Göken, Mathias},
doi = {10.1007/s11661-016-3408-8},
faupublication = {yes},
journal = {Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science},
keywords = {High Temperature},
note = {WW1::1060},
pages = {2141-2149},
peerreviewed = {No},
title = {{Microstructure}, {Lattice} {Misfit}, and {High}-{Temperature} {Strength} of γ′-{Strengthened} {Co}-{Al}-{W}-{Ge} {Model} {Superalloys}},
volume = {47},
year = {2016}
}
@article{faucris.285682222,
abstract = {The design freedom in Laser Metal Deposition provided by the absence of a powder bed enables the fabrication of Functionally Graded Materials through Additive Manufacturing. For the first time, two suitable γ-TiAl alloys (TiAl48Cr2Nb2, TiAl45Nb4C) are combined in direct and gradual transitions to generate different microstructure morphologies and, consequently, different mechanical properties within a component after an identical heat treatment. The influence of alloy composition, microstructure type, and material transition on the tensile properties and fracture toughness is analyzed through miniature testing. Miniature tensile tests show no orientation dependency in regard to the build direction and the composition/microstructure transition is not found to be a preferred fracture site. The miniature fracture toughness tests reveal that already small composition changes—insufficient to alter the microstructure configuration—can have a significant effect on the cracking behavior. Graphical abstract: [Figure not available: see fulltext.]},
author = {Galgon, Florian and Melzer, Daniel and Zenk, Christopher and Dzugan, Jan and Körner, Carolin},
doi = {10.1557/s43578-022-00801-0},
faupublication = {yes},
journal = {Journal of Materials Research},
keywords = {Directed energy deposition; Fracture toughness; Functionally graded materials; Laser metal deposition; Miniature testing; Tensile testing; Titanium aluminides},
note = {CRIS-Team Scopus Importer:2022-11-25},
peerreviewed = {Yes},
title = {{Miniature} mechanical testing of {LMD}-fabricated compositionally & microstructurally graded γ titanium aluminides},
year = {2022}
}
@article{faucris.276066823,
abstract = {Ferritic superalloys with an α/α′ (A2/B2) microstructure constitute an auspicious materials system for high-temperature application and could help satisfy the need for more sustainable creep resistance materials. An exciting way to improve their creep resistance further through alloy development and microstructure engineering is introducing a hierarchical network consisting of α, α′, and α″ (L21). This work investigates the formation and evolution of this microstructure in Fe-Al-Ni-Co(Cr-Mo-Ti-Cu) alloys. It has been identified that the substitution of Fe by Cr leads to the stabilization of γ (fcc, A1) at intermediate temperatures. This amount of γ was found to decrease in the presence of Mo, and the transformation is entirely avoidable by carefully adjusting the α - and γ-stabilizing elements. The observations in quinary and senary alloys led to the development of two promising hierarchical α/α′/α″ alloys with additions of Co and Cu. Both solutes are enriched in the precipitates and are expected to act as strengthening elements. Microstructural analysis of the particle size evolution in the range of 800–950 °C indicates that the precipitates undergo a non-classical ripening process at early stages with coarsening exponent deviating from the t1/3-relationship predicted by the Lifshitz-Slyozov-Wagner (LSW) theory for multicomponent alloys. Furthermore, after furnace cooling from 950 °C, a pronounced reprecipitation phenomenon was found to occur not only in the matrix but also inside the primary precipitates.},
author = {Morales Victoria, Luis and Luo, Ning and Li, K. and Zenk, Christopher and Körner, Carolin},
doi = {10.1016/j.jallcom.2022.164996},
faupublication = {yes},
journal = {Journal of Alloys and Compounds},
keywords = {Ferritic superalloys; Microstructure evolution; Phase transitions; Precipitation; Thermal analysis},
note = {CRIS-Team Scopus Importer:2022-05-27},
peerreviewed = {Yes},
title = {{On} stabilizing an α/α′/α″ microstructure in ferritic superalloys},
volume = {911},
year = {2022}
}
@article{faucris.230052332,
abstract = {We investigated the solute diffusional behavior active during compressive creep deformation at 150 MPa / 975 °C of a Co-Al-W-Ta single crystal superalloy in the [001] orientation. We report the formation of shear-bands that involves re-orientation of γ/γʹ rafts to {111} from {001} planes, referring to as γ/γ′ raft-rotation. In the shear-band regions, we observed abundant micro-twins, stacking faults (SFs), disordered zones within the γʹ termed as ‘γ pockets’ and also few geometrically-close-packed (GCP) phases. We used a correlative approach blending electron microscopy and atom probe tomography to characterize the structure and composition of these features. The SFs were identified as intrinsic and exhibit a W enrichment up to 14.5 at.% and an Al deficiency down to 5.1 at.%, with respect to the surrounding γʹ phase. The micro-twin boundaries show a solute enrichment similar to the SFs with a distinct W compositional profile gradients perpendicular from the boundaries into the twin interior, indicating solute diffusion within the micro-twins. The γ-pockets have a composition close to that of γ but richer in W/Ta. Based on these observations, we propose (i) a solute diffusion mechanism taking place during micro-twinning, (ii) a mechanism for the γ/γʹ raft-rotation process and evaluate their influence on the overall creep deformation of the present Co-based superalloy.},
author = {He, Junyang and Zenk, Christopher and Zhou, Xuyang and Neumeier, Steffen and Raabe, Dierk and Gault, Baptiste and Makineni, Surendra Kumar},
doi = {10.1016/j.actamat.2019.11.035},
faupublication = {yes},
journal = {Acta Materialia},
keywords = {Atom probe tomography; Co-based superalloy; Creep deformation; Transmission electron microscopy; γ/γʹ rafting},
note = {CRIS-Team Scopus Importer:2019-12-03},
pages = {86-99},
peerreviewed = {Yes},
title = {{On} the atomic solute diffusional mechanisms during compressive creep deformation of a {Co}-{Al}-{W}-{Ta} single crystal superalloy},
volume = {184},
year = {2020}
}
@article{faucris.201118476,
abstract = {
We propose here a deformation-induced diffusive phase transformation mechanism occurring during shearing of γ′ ordered phase in a γ/γ′ single crystalline CoNi-based superalloy. Shearing involved the creation and motion of a high density of planar imperfections. Through correlative electron microscopy and atom probe tomography, we captured a superlattice intrinsic stacking fault (SISF) and its associated moving leading partial dislocation (LPD). The structure and composition of these imperfections reveal characteristic chemical – structural contrast. The SISF locally exhibits a D019 ordered structure coherently embedded in the L12 γ′ and enriched in W and Co. Interestingly, the LPD is enriched with Cr and Co, while the adjoining planes ahead of the LPD are enriched with Al. Quantitative analysis of the three-dimensional compositional field in the vicinity of imperfections sheds light onto a new in-plane diffusion mechanism as the LPD moves on specific {111} planes upon application of stress at high temperature.
ribbons with SISF loops embedded in ABPs are observed in tension, extrinsic SFs are revealed in compression. At ∼ 5 % creep strain SISFs confined to the γ' phase dominate in tension, whereas extrinsic SFs and microtwins extending across both phases are the prevalent planar faults in compression. In addition, dense networks of regular a/2<101> matrix dislocations develop at the γ/γ' interfaces in both loading scenarios. In tensile creep and early compressive creep the direct contribution of planar faults to plastic deformation is minor and does not exceed 10 % of the measured plastic strain. In contrast, thickening of microtwins appears to become an efficient deformation channel in the later stages of compressive creep. A pronounced asymmetry regarding the rafting kinetics is observed as well resulting in a P-type rafted and topologically inverted microstructure after ∼ 5 % creep in tension while hardly any rafting has occurred under compression. The pronounced rafting and related recovery processes are likely responsible for the inferior creep behavior in tension. Finally, two novel diffusion-assisted degradation mechanisms related to microtwins are shown to be active: an expansion of the γ phase into γ' precipitates along microtwins and the formation of γ phase nuclei at planar fault intersections inside γ'. Both phenomena are hypothesized to be triggered by segregation of γ-formers like Co and Cr to twin boundarie}, author = {Lenz, Malte and Eggeler, Yolita and Müller, Julian and Zenk, Christopher and Volz, Nicklas and Wollgramm, Philip and Eggeler, Gunther and Neumeier, Steffen and Göken, Mathias and Spiecker, Erdmann}, doi = {10.1016/j.actamat.2018.12.053}, faupublication = {yes}, journal = {Acta Materialia}, keywords = {Cobalt-base superalloy; creep; asymmetry; electron microscopy; planar faults}, pages = {597-610}, peerreviewed = {Yes}, title = {{Tension}/{Compression} asymmetry of a creep deformed single crystal {Co}-base superalloy}, volume = {166}, year = {2019} } @inproceedings{faucris.243060119, abstract = {The system Co–Ti–Cr was recently identified as a very promising base for low mass-density Co-based superalloys. This study presents the influence of quaternary alloying additions on the thermophysical and mechanical properties of a Co–11Ti–15Cr model superalloyModel superalloy. Al, Ta, Re, and W were selected as a starting point for alloy developmentAlloy development as they represent important alloying elements in both Ni-based and Co–Al–W-based superalloys. Microstructure analysis reveals that the addition of only 1 at.% of either of these elements causes the formation of different undesired intermetallic phases in addition to γ and γ′ phases, which is in agreement with thermodynamic calculations. However, a diffusion couple between the Co–Ti–Cr and a Co–Al–W–Ta alloy suggests that the tolerance for alloying elements without destabilizing the γ/γ′ two-phase microstructure is higher when they are present in a certain ratio. Energy-dispersive X-ray spectroscopy shows that Cr and Re are enriched in the γ phase, whereas Ti and W preferentially partition to γ′. All alloying elements increase the yield strength at room temperature, but are disadvantageous at 1000 °C. Re and W retain their strengthening effect up to 900 °C.}, address = {Cham}, author = {Zenk, Christopher and Volz, Nicklas and Bezold, Andreas and Huber, Laura-Kristin and Eggeler, Yolita and Spiecker, Erdmann and Göken, Mathias and Neumeier, Steffen}, doi = {10.1007/978-3-030-51834-9{\_}89}, editor = {Tin S, Hardy M, Clews J, Cormier J, Feng Q, Marcin J, O'Brien C, Suzuki A}, faupublication = {yes}, isbn = {978-3-030-51834-9}, pages = {909-919-919}, peerreviewed = {unknown}, publisher = {Springer International Publishing}, title = {{The} {Effect} of {Alloying} on the {Thermophysical} and {Mechanical} {Properties} of {Co}–{Ti}–{Cr}-{Based} {Superalloys}}, year = {2020} } @article{faucris.201089791, abstract = {
A set of
advanced single crystalline γ´ strengthened Co-base superalloys with at least
nine alloying elements (Co, Ni, Al, W, Ti, Ta, Cr, Si, Hf, Re) has been
developed and investigated. The objective was to generate multinary Co-base
superalloys with significantly improved properties compared to the original
Co-Al-W-based alloys. All alloys show the typical γ/γ´ two-phase
microstructure. A γ´ solvus temperature up to 1174 °C and γ´ volume fractions between
40 and 60 pct at 1050 °C could be achieved, which is significantly higher
compared to most other Co-Al-W-based superalloys. However, higher contents of
Ti, Ta, and the addition of Re decrease the long-term stability. Atom probe tomography
revealed that Re does not partition to the γ phase as strongly as in Ni-base
superalloys. Compression creep properties were investigated at 1050 °C and 125
MPa in <001> direction. The creep resistance is close to that of first
generation Ni-base superalloys. The creep mechanisms of the Re-containing alloy
was further investigated and it was found that the deformation is located
preferentially in the γ channels although some precipitates are sheared during
early stages of creep. The addition of Re did not improve the mechanical
properties and is therefore not considered as a crucial element in the design
of future Co-base superalloys for high temperature applications. Thermodynamic calculations
describe well how the alloying elements influence the transformation
temperatures although there is still an offset in the actual values. Furthermore,
a full set of elastic constants of one of the multinary alloys is presented, showing
increased elastic stiffness leading to a higher Young’s modulus for the investigated
alloy, compared to conventional Ni-base superalloys. The oxidation resistance
is significantly improved compared to the ternary Co-Al-W compound. A complete
thermal barrier coating system was applied successfull},
author = {Volz, Nicklas and Zenk, Christopher and Cherukuri, Rahul and Kalfhaus, Tobias and Weiser, Martin and Makineni, Surendra Kumar and Betzing, Christian and Lenz, Malte and Gault, Baptiste and Fries, Suzana G. and Schreuer, Juergen and Vassen, Robert and Virtanen, Sannakaisa and Raabe, Dierk and Spiecker, Erdmann and Neumeier, Steffen and Göken, Mathias},
doi = {10.1007/s11661-018-4705-1},
faupublication = {yes},
journal = {Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science},
pages = {1-11},
peerreviewed = {Yes},
title = {{Thermophysical} and {Mechanical} {Properties} of {Advanced} {Single} {Crystalline} {Co}-base {Superalloys}},
year = {2018}
}
@inproceedings{faucris.207764809,
author = {Hammerschmidt, T. and Koßmann, J. and Zenk, Christopher and Neumeier, Steffen and Göken, Mathias and Lopez-Galilea, I. and Mujica Roncery, L. and Huth, S. and Kostka, A. and Theisen, W. and Drautz, R.},
booktitle = {13th International Symposium on Superalloys, SUPERALLOYS 2016},
doi = {10.1002/9781119075646.ch10},
faupublication = {yes},
isbn = {9781118996669},
keywords = {Intermetallic precipitates; Ni-base superalloys; Co-base superalloys; Topologically close-packed phases; Solidification; Structure map},
pages = {89-96},
peerreviewed = {Yes},
publisher = {Minerals, Metals and Materials Society},
title = {{The} role of local chemical composition for {TCP} phase precipitation in {Ni}-base and {Co}-base superalloys},
year = {2016}
}
@inproceedings{faucris.207765135,
author = {Zenk, Christopher and Neumeier, Steffen and Kolb, Markus and Volz, Nicklas and Fries, S. G. and Dolotko, O. and Povstugar, I. and Raabe, D. and Göken, Mathias},
booktitle = {13th International Symposium on Superalloys, SUPERALLOYS 2016},
doi = {10.1002/9781119075646.ch103},
faupublication = {yes},
isbn = {9781118996669},
keywords = {Creep; Lattice misfit; Atom probe tomography; Co-base superalloys; Partitioning behavior},
pages = {971-980},
peerreviewed = {Yes},
publisher = {Minerals, Metals and Materials Society},
title = {{The} role of the base element in γ′ strengthened cobalt/nickel-base superalloys},
year = {2016}
}
@article{faucris.106606324,
abstract = {The nature and stability of intermetallic phases in a multi-component γ/γ′ Co-base superalloy is investigated. At least three kinds of unwanted intermetallic phases form due to the segregation of Al, Ta, Ti, Si, and Hf during casting in the interdendritic areas in addition to γ and γ′. One of the intermetallic phases that shows a blocky shape, contains high content of Ta, Hf, and Ti and has been identified as a topologically close-packed Laves phase. A B2 phase appears as relatively big pools and in some cases contains needle-shaped precipitates with high content of Al and Ti. The thermal stability of these intermetallic phases is studied in this work under defined heat treatments. The needle-shaped precipitates already dissolve at 1000°C, whereas the B2 phase is dissolved only at higher temperatures of 1200°C. Small amounts of Laves phases remained stable during aging at 1200°C for 25h. The prediction of phases as well as their stability is also checked by the CALPHAD method. The TCNi5 database, containing the description of Co3(Al,W), predicts the presence of the observed intermetallic phases; however, the predicted main transformation temperatures for these phases differ from the experimentally obtained values. This work studies the nature and stability of three intermetallic phases - Laves, B2 and needle-shaped precipitates - in a multi-component γ/γ′ Co-base superalloy, named ERBO-Co0. These phases are generated during casting at the interdendritic areas. Experimental characterization of intermetallic phases is contrasted with thermodynamic calculations, which predicts the presence of the identified phase},
author = {Lopez-Galilea, Inmaculada and Zenk, Christopher and Neumeier, Steffen and Huth, Stephan and Theisen, Werner and Göken, Mathias},
doi = {10.1002/adem.201400249},
faupublication = {yes},
journal = {Advanced Engineering Materials},
pages = {741-747},
peerreviewed = {unknown},
title = {{The} thermal stability of intermetallic compounds in an as-cast {SX} co-base superalloy},
volume = {17},
year = {2015}
}
@article{faucris.259817332,
abstract = {A systematic study of the compression creep properties of a single-crystalline Co-base superalloy (Co-9Al-7.5W-2Ta) was conducted at 950, 975 and 1000°C to reveal the influence of temperature and the resulting diffusion velocity of solutes like Al, W and Ta on the deformation mechanisms. Two creep rate minima are observed at all temperatures indicating that the deformation mechanisms causing these minima are quite similar. Atom-probe tomography analysis reveals elemental segregation to stacking faults, which had formed in the γ′ phase during creep. Density-functional-theory calculations indicate segregation of W and Ta to the stacking fault and an associated considerable reduction of the stacking fault energy. Since solutes diffuse faster at a higher temperature, segregation can take place more quickly. This results in a significantly faster softening of the alloy, since cutting of the γ′ precipitate phase by partial dislocations is facilitated through segregation already during the early stages of creep. This is confirmed by transmission electron microscopy analysis. Therefore, not only the smaller precipitate fraction at higher temperatures is responsible for the worse creep properties, but also faster diffusion-assisted shearing of the γ′ phase by partial dislocations. The understanding of these mechanisms will help in future alloy development by offering new design criteria.