Publications
440 results found
Wu X, Makineni SK, Liebscher CH, et al., 2020, Unveiling the Re effect in Ni-based single crystal superalloys, Nature Communications, Vol: 11, Pages: 1-13, ISSN: 2041-1723
Single crystal Ni-based superalloys have long been an essential material for gas turbines in aero engines and power plants due to their outstanding high temperature creep, fatigue and oxidation resistance. A turning point was the addition of only 3 wt.% Re in the second generation of single crystal Ni-based superalloys which almost doubled the creep lifetime. Despite the significance of this improvement, the mechanisms underlying the so-called “Re effect” have remained controversial. Here, we provide direct evidence of Re enrichment to crystalline defects formed during creep deformation, using combined transmission electron microscopy, atom probe tomography and phase field modelling. We reveal that Re enriches to partial dislocations and imposes a drag effect on dislocation movement, thus reducing the creep strain rate and thereby improving creep properties. These insights can guide design of better superalloys, a quest which is key to reducing CO2 emissions in air-traffic.
Rivas NA, Babayigit A, Conings B, et al., 2020, Cryo-focused ion beam preparation of perovskite based solar cells for atom probe tomography, PLoS One, Vol: 15, Pages: 1-14, ISSN: 1932-6203
Focused-ion beam lift-out and annular milling is the most common method used for obtaining site specific specimens for atom probe tomography (APT) experiments and transmission electron microscopy. However, one of the main limitations of this technique comes from the structural damage as well as chemical degradation caused by the beam of high-energy ions. These aspects are especially critical in highly-sensitive specimens. In this regard, ion beam milling under cryogenic conditions has been an established technique for damage mitigation. Here, we implement a cryo-focused ion beam approach to prepare specimens for APT measurements from a quadruple cation perovskite-based solar cell device with 19.7% efficiency. As opposed to room temperature FIB milling we found that cryo-milling considerably improved APT results in terms of yield and composition measurement, i.e. halide loss, both related to less defects within the APT specimen. Based on our approach we discuss the prospects of reliable atom probe measurements of perovskite based solar cell materials. An insight into the field evaporation behavior of the organic-inorganic molecules that compose the perovskite material is also given with the aim of expanding the applicability of APT experiments towards nano-characterization of complex organo-metal materials.
He J, Makineni SK, Lu W, et al., 2020, On the formation of hierarchical microstructure in a Mo-doped NiCoCr medium-entropy alloy with enhanced strength-ductility synergy, SCRIPTA MATERIALIA, Vol: 175, Pages: 1-6, ISSN: 1359-6462
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- Citations: 60
Evertz S, Kirchlechner I, Soler R, et al., 2020, Electronic structure based design of thin film metallic glasses with superior fracture toughness, MATERIALS & DESIGN, Vol: 186, ISSN: 0264-1275
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- Citations: 14
Ackerman AK, Vorontsov VA, Bantounas I, et al., 2020, Interface characteristics in an α+β titanium alloy, Physical Review Materials, Vol: 4, ISSN: 2475-9953
The alpha/beta interface in Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) is investigated viacentre of symmetry analysis, both as-grown and after 10% cold work.Semi-coherent interface steps are observed at a spacing of 4.5 +/-1.13 atoms inthe as-grown condition, in good agreement with theory prediction (4.37 atoms).Lattice accommodation is observed, with elongation along [-1 2 -1 0]alpha andcontraction along [1 0 -1 0]alpha . Deformed alpha exhibited larger, lesscoherent steps with slip bands lying in {110}beta. This indicates dislocationpile-up at the grain boundary, a precursor to globularisation, offering insightinto the effect of deformation processing on the interface, which is importantfor titanium alloy processing route design.
Schweinar K, Nicholls RL, Rajamathi CR, et al., 2020, Probing catalytic surfaces by correlative scanning photoemission electron microscopy and atom probe tomography, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 8, Pages: 388-400, ISSN: 2050-7488
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- Citations: 17
Yu Y, Zhou C, Zhang S, et al., 2020, Revealing nano-chemistry at lattice defects in thermoelectric materials using atom probe tomography, MATERIALS TODAY, Vol: 32, Pages: 260-274, ISSN: 1369-7021
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- Citations: 64
Lim J, Kim SH, Armengol RA, et al., 2020, Atomic-Scale Mapping of Impurities in Partially Reduced Hollow TiO<inf>2</inf> Nanowires, Advanced Materials, Vol: 59, Pages: 5700-5704, ISSN: 0935-9648
The incorporation of impurities during the chemical synthesis of nanomaterials is usually uncontrolled and rarely reported because of the formidable challenge in measuring trace amounts of often light elements with sub-nanometer spatial resolution. And yet, these foreign elements (introduced by doping, for example) influence functional properties. We demonstrate how the hydrothermal growth and a partial reduction reaction on hollow TiO2 nanowires leads to the introduction of parts per millions of boron, sodium, and nitrogen. This doping explains the presence of oxygen vacancies and reduced Ti states at the surface, which enhance the functional properties of TiO2. Our results were obtained on model metal oxide nanomaterials and they shed light on a general process that leads to the uncontrolled incorporation of trace impurities in TiO2, thereby, having a strong effect on applications in energy-harvesting.
Lenz M, Wu M, He J, et al., 2020, Atomic Structure and Chemical Composition of Planar Fault Structures in Co-Base Superalloys, Pages: 920-928, ISSN: 2367-1181
We report atomic structures and chemical compositions of defects associated to planar faults in a creep deformed Co-base superalloy and discuss their formation and contribution to plastic deformation. The multinary single crystalline Co-base superalloy was creep deformed under tension along [ 001 ] -direction at 850 °C and 400 MPa. The creep microstructure comprises a high density of planar defects. Solute segregation to superlattice intrinsic stacking faults (SISF) is characterized via EDXS analysis of a statistically relevant number of faults and compared at different creep stages. The amount of solute segregation shows negligible difference at different creep stages indicating that segregation directly occurs during planar fault formation and does not significantly evolve afterward. Based on the observation and analysis of Frank partial dislocations with a/3⟨111⟩ Burgers vectors terminating SISF, we discuss a new route to SISF formation via dislocation climb. Additionally, two more complex fault structures are analyzed, and potential formation mechanisms are discussed. The first of these structures is a terminating end of an SISF where an a/3⟨112⟩ partial dislocation splits up into two closely spaced a/6⟨112⟩ partials separated by an SESF. The second structure consists of two parallel SISFs connected by an anti-phase boundary (APB). All deformation mechanisms described in this study show an involvement of solute segregation directly affecting formation and propagation of creep defects by changing planar fault energies and chemical environments of dislocations. Solute segregation is therefore expected to be a key to future alloy design by enabling control of creep deformation mechanisms in specific temperature and stress regimes.
Doñate-Buendia C, Streubel R, Kürnsteiner P, et al., 2020, Effect of nanoparticle additivation on the microstructure and microhardness of oxide dispersion strengthened steels produced by laser powder bed fusion and directed energy deposition, Pages: 41-45, ISSN: 2212-8271
In this contribution, the effect of nanoparticle additivation on the microstructure and microhardness of oxide dispersion strengthened steels (ODS) manufactured by laser powder bed fusion (L-PBF) and directed energy deposition (DED) additive manufacturing (AM) is studied. The powder composites are made of micrometer-sized iron-chromium-alloy based powder which are homogenously decorated with Y2O3 nanoparticles synthesized by pulsed laser fragmentation in water. Consolidated by L-PBF and DED, an enhanced microhardness of the AM-built ODS sample is found. This increase is related to the significant microstructural differences found between the differently processed samples.
Zhao H, Gault B, De Geuser F, et al., 2020, Grain boundary segregation and precipitation in an Al-Zn-Mg-Cu alloy, 17th International Conference on Aluminium Alloys (ICAA), Publisher: E D P SCIENCES, ISSN: 2261-236X
Hariharan A, Lu L, Risse J, et al., 2019, Misorientation-dependent solute enrichment at interfaces and its contribution to defect formation mechanisms during laser additive manufacturing of superalloys, PHYSICAL REVIEW MATERIALS, Vol: 3, ISSN: 2475-9953
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- Citations: 59
Kasian O, Geiger S, Li T, et al., 2019, Degradation of iridium oxides <i>via</i> oxygen evolution from the lattice: correlating atomic scale structure with reaction mechanisms, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 12, Pages: 3548-3555, ISSN: 1754-5692
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- Citations: 124
Katnagallu S, Stephenson LT, Mouton I, et al., 2019, Imaging individual solute atoms at crystalline imperfections in metals, New Journal of Physics, Vol: 21, Pages: 1-10, ISSN: 1367-2630
Directly imaging all atoms constituting a material and, maybe more importantly, crystalline defects that dictate materials' properties, remains a formidable challenge. Here, we propose a new approach to chemistry-sensitive field-ion microscopy (FIM) combining FIM with time-of-flight mass-spectrometry (tof-ms). Elemental identification and correlation to FIM images enabled by data mining of combined tof-ms delivers a truly analytical-FIM (A-FIM). Contrast variations due to different chemistries is also interpreted from density-functional theory (DFT). A-FIM has true atomic resolution and we demonstrate how the technique can reveal the presence of individual solute atoms at specific positions in the microstructure. The performance of this new technique is showcased in revealing individual Re atoms at crystalline defects formed in Ni–Re binary alloy during creep deformation. The atomistic details offered by A-FIM allowed us to directly compare our results with simulations, and to tackle a long-standing question of how Re extends lifetime of Ni-based superalloys in service at high-temperature.
Lopez-Galilea I, Ruttert B, He J, et al., 2019, Additive manufacturing of CMSX-4 Ni-base superalloy by selective laser melting: Influence of processing parameters and heat treatment, ADDITIVE MANUFACTURING, Vol: 30, ISSN: 2214-8604
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- Citations: 45
Wei Y, Peng Z, Kuhbach M, et al., 2019, 3D nanostructural characterisation of grain boundaries in atom probe data utilising machine learning methods, PLoS One, Vol: 14, Pages: 1-19, ISSN: 1932-6203
Boosting is a family of supervised learning algorithm that convert a set of weak learners into a single strong one. It is popular in the field of object tracking, where its main purpose is to extract the position, motion, and trajectory from various features of interest within a sequence of video frames. A scientific application explored in this study is to combine the boosting tracker and the Hough transformation, followed by principal component analysis, to extract the location and trace of grain boundaries within atom probe data. Before the implementation of this method, these information could only be extracted manually, which is time-consuming and error-prone. The effectiveness of this method is demonstrated on an experimental dataset obtained from a pure aluminum bi-crystal and validated on simulated data. The information gained from this method can be combined with crystallographic information directly contained within the data, to fully define the grain boundary character to its 5 degrees of freedom at near-atomic resolution in three dimensions. It also enables local atomic compositional and geometric information, i.e. curvature, to be extracted directly at the interface.
Massey CP, Dryepondt SN, Edmondson PD, et al., 2019, Corrigendum to Multiscale investigations of nanoprecipitate nucleation, growth, and coarsening in annealed low-Cr oxide dispersion strengthened FeCrAl powder (Acta Materialia (2019) 166 (1–17), (S135964541830939X), (10.1016/j.actamat.2018.11.062)), Acta Materialia, Vol: 180, ISSN: 1359-6454
The authors regret that the scale bars in Figure 4 for the visualized atom probe tomography control volumes are mislabelled and should be in units of nanometers, not micrometers. The authors would like to apologise for any inconvenience caused. Corrected Image:
Harding I, Mouton I, Gault B, et al., 2019, Carbon partitioning and microstructure evolution during tempering of an Fe-Ni-C steel, SCRIPTA MATERIALIA, Vol: 172, Pages: 38-42, ISSN: 1359-6462
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- Citations: 7
Li L, Li Z, da Silva AK, et al., 2019, Segregation-driven grain boundary spinodal decomposition as a pathway for phase nucleation in a high-entropy alloy, ACTA MATERIALIA, Vol: 178, Pages: 1-9, ISSN: 1359-6454
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- Citations: 81
Kontis P, Chauvet E, Peng Z, et al., 2019, Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys, ACTA MATERIALIA, Vol: 177, Pages: 209-221, ISSN: 1359-6454
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- Citations: 125
Massey CP, Hoelzer DT, Edmondson PD, et al., 2019, Stability of a model Fe-14Cr nanostructured ferritic alloy after long-term thermal creep, Scripta Materialia, Vol: 170, Pages: 134-139, ISSN: 1359-6462
The successful development of advanced materials such as nanostructured ferritic alloys (NFA) for next generation nuclear reactor concepts and ultra-supercritical steam power plants requires information on long term thermal creep. To support this initiative, this work examines the NFA MA957 (Fe-14Cr-1.0Ti-0.3Mo + 0.3Y2O3 in wt%) crept to 61,251 h at 825 °C and 70 MPa, the longest creep test available to date for this material. Using atom probe tomography and electron microscopy, it is shown that the grain size and nanoprecipitate size/composition are unaffected following this 7 yr creep test, although significant porosity is noted throughout the microstructure attributed to microvoid coalescence and growth.
Dubosq R, Rogowitz A, Schweinar K, et al., 2019, A 2D and 3D nanostructural study of naturally deformed pyrite: assessing the links between trace element mobility and defect structures, CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, Vol: 174, ISSN: 0010-7999
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- Citations: 20
Mianroodi JR, Shanthraj P, Kontis P, et al., 2019, Atomistic phase field chemomechanical modeling of dislocation-solute-precipitate interaction in Ni-Al-Co, ACTA MATERIALIA, Vol: 175, Pages: 250-261, ISSN: 1359-6454
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- Citations: 44
Massey CP, Hoelzer DT, Seibert RL, et al., 2019, Microstructural evaluation of a Fe-12Cr nanostructured ferritic alloy designed for impurity sequestration, Journal of Nuclear Materials, Vol: 522, Pages: 111-122, ISSN: 0022-3115
Fast reactor fuel cladding candidate materials require proficiency in extreme environments consisting of high temperatures and irradiation doses in excess of 150 displacements per atom (dpa). Nanostructured oxide dispersion strengthened (ODS) alloys have been developed extensively for this purpose due to their notable high temperature strength, creep resistance, and irradiation resistance. However, their properties can deteriorate if interstitial impurities such as C and N are not well controlled during the fabrication process. A new Fe-12Cr nanostructured ODS alloy OFRAC (Oak Ridge Fast Reactor Advanced Fuel Cladding) with solute additions of Mo, Ti, and Nb has been developed to provide the desired properties mentioned above while simultaneously sequestering impurities within the matrix. After extrusion at 850 °C, the as-extruded microstructure consists of an average 490 nm grain size and a high number density (6.8 × 1023 m-3) of 2.2 nm diameter (Y,Ti,O) nanoclusters distributed homogeneously in the matrix. Atom probe tomography investigations suggest non-stochiometric compositions for the smallest nanoclusters. In addition, a second population of nanometer scale (Nb,Ti) rich carbonitrides is also present in the microstructure that captures the potentially detrimental C and N impurity atoms present in the matrix. Atom probe tomography results indicate elemental segregation of Cr, Mo, and Nb to grain boundaries in the as-extruded material, consistent with previous investigations of solid solution strengthening by solute additions. The ability of OFRAC to sequester impurities introduced from the powder metallurgical approach to nanostructured ferritic alloy development, compounded with its beneficial mechanical properties, makes this alloy a competitive candidate for fast reactor applications. This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains a
Zhu M, Song W, Konze PM, et al., 2019, Direct atomic insight into the role of dopants in phase-change materials, Nature Communications, Vol: 10, Pages: 1-10, ISSN: 2041-1723
Doping is indispensable to tailor phase-change materials (PCM) in optical and electronic data storage. Very few experimental studies, however, have provided quantitative information on the distribution of dopants on the atomic-scale. Here, we present atom-resolved images of Ag and In dopants in Sb2Te-based (AIST) PCM using electron microscopy and atom-probe tomography. Combing these with DFT calculations and chemical-bonding analysis, we unambiguously determine the dopants’ role upon recrystallization. Composition profiles corroborate the substitution of Sb by In and Ag, and the segregation of excessive Ag into grain boundaries. While In is bonded covalently to neighboring Te, Ag binds ionically. Moreover, In doping accelerates the crystallization and hence operation while Ag doping limits the random diffusion of In atoms and enhances the thermal stability of the amorphous phase.
Springer H, Zhang JL, Szczepaniak A, et al., 2019, Light, strong and cost effective: Martensitic steels based on the Fe – Al – C system, Materials Science and Engineering: A, Vol: 762, ISSN: 0921-5093
We introduce a novel alloy design concept for density reduced ultra-high strength steels. It is based on the effects of C to increase martensite strength and the Al-solubility in austenite, in conjunction with Al to increase the martensite start temperature and to reduce density. This alloy combination results in inherently strong but light martensitic microstructures, whose mechanical properties (i.e. strength and ductility) can be readily adjusted over a wide range by applying straightforward and established heat treatments. The concept is validated on an Fe – 8 Al – 1.1C (wt.%) alloy subjected to quench and tempering treatments. The steel exhibits relatively low yield strength (~600 MPa) and reasonable ductility (~ 15% elongation) after hot rolling and soft annealing, but can be brought to a maximum hardness of 62 HRC after quenching and tempering at 250 °C. These attractive mechanical properties are coupled with a low density (6.95 g cm–3) and high elastic stiffness (Young's modulus 199 GPa). These lightweight martensitic steels are cost-effective structural materials for weight-critical applications, promising unprecedented specific strength. Advanced characterisation presented herein allows us to derive the fundamental underpinnings of carbide precipitation and phase transformation, and outline and discuss perspectives for refining the alloy composition and processing parameters.
Dear FF, Kontis P, Gault B, et al., 2019, Combined APT, TEM and SAXS Characterisation of Nanometre-Scale Precipitates in Titanium Alloys, Microscopy and Microanalysis, Vol: 25, Pages: 2516-2517, ISSN: 1431-9276
Kürnsteiner P, Hariharan A, Jung HY, et al., 2019, Application of atom probe tomography to complex microstructures of laser additively manufactured samples, Microscopy and Microanalysis, Vol: 25, Pages: 2514-2515, ISSN: 1431-9276
Palanisamy D, Raabe D, Gault B, 2019, On the compositional partitioning during phase transformation in a binary ferromagnetic MnAl alloy, ACTA MATERIALIA, Vol: 174, Pages: 227-236, ISSN: 1359-6454
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- Citations: 25
Rodenbough PP, Mao Z, Gault B, 2019, How to write a compelling (materials) science paper, MATERIALIA, Vol: 6, ISSN: 2589-1529
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