Solid solution dependence of the deformation behavior in Mg–xZn (x = 0, 1, 2 wt%) alloys: In-situ neutron diffraction and crystal plasticity modeling
Not Available
Wang, Huai (ORCID:0000000206168248)↗
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Flux Growth of Cerium Nickel Gallides Studied by In Situ Neutron Diffraction
In this work, reactions of cerium and nickel in excess molten gallium were monitored by neutron diffraction during heating and cooling. The formation of binary intermediates CeGa 2 and Ni 2 Ga 3 was observed during heating. During cooling of the molten mixture from 900 °C, precipitation of BaAl 4 -type CeNi 0.74 Ga 3.26 occurred at 850 °C. Upon cooling to 650 °C, this compound reacted in the flux to form Ce 2 NiGa 10 and then Ce 2 NiGa 12 , the latter of which persisted to room temperature. Making use of this information, subsequent reactions were quenched at 750 °C to isolate crystals of CeNi 0.74 Ga 3.26 for further study. Similar reactions replacing Ce with La and quenching above 750 °C yielded LaNi 0.35 Ga 3.65 crystals. Magnetic susceptibility studies on CeNi 0.74 Ga 3.26 indicate that the cerium is trivalent; the Ce 3+ moments undergo a strongly anisotropic ferromagnetic ordering with moment perpendicular to the c axis below 7 K. Heat capacity data show little evidence of heavy fermion behavior. Resistivity measurements show that both LaNi0.35Ga3.65 and CeNi 0.74 Ga 3.26 exhibit metallic behavior. Density of states calculations support this and indicate that Ni/Ga mixing in the compound stabilizes the structure.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
The role of ternary alloying elements in eutectoid transformation of U-10Mo alloy part II. In and Ex-situ Neutron diffraction-based assessment of eutectoid phase transformation kinetics in U-9.8Mo-0.2X alloy (X = Cr, Ni or Co)
HExploring the effects of minor ternary alloying additions, typically impurity elements, on the phase stability of U-10Mo is important for preventing undesirable phase decomposition during processing or during service. This work examines the influence small ternary additions of Cr, Ni, and Co. Both in-situ and ex-situ neutron diffraction measurements made during and after high temperature (450 – 525°C) exposures were used to better define the influence of these elements on the time-temperature-transformation (TTT) behavior of U-10Mo, providing information which is complementary to electron microscopy investigations of the same alloy systems performed in the first part of this work. Minor additions of Ni and Co decrease the ?-phase stability at all temperatures investigated. Signatures of U6X (X = Ni or Co) compounds were shown to be present in amounts of up to 6 wt% in the heat treated alloys, suggesting that the initial precipitation of this phase may catalyze further ?-phase decomposition. On the other hand, the Cr containing alloys were observed to have nearly the same, and in some cases slower, phase transformation kinetics when compared to the binary U-10Mo control samples. The results of the study have enabled preliminary estimates of the TTT curves for the ternary alloys.
phase transformation, kinetics, discontinuous prec↗
Large Destabilization of (TiVNb)-Based Hydrides via (Al, Mo) Addition: Insights from Experiments and Data-Driven Models
High-entropy alloys (HEAs) represent an interesting alloying strategy that can yield exceptional performance properties needed across a variety of technology applications, including hydrogen storage. Examples include ultrahigh volumetric capacity materials (BCC alloys → FCC dihydrides) with improved thermodynamics relative to conventional high-capacity metal hydrides (like MgH 2 ), but still further destabilization is needed to reduce operating temperature and increase system-level capacity. Here, in this work, we demonstrate efficient hydride destabilization strategies by synthesizing two new Al 0.05 (TiVNb) 0.95–x Mo x (x = 0.05, 0.10) compositions. We specifically evaluate the effect of molybdenum (Mo) addition on the phase structure, microstructure, hydrogen absorption, and desorption properties. Both alloys crystallize in a bcc structure with decreasing lattice parameters as the Mo content increases. The alloys can rapidly absorb hydrogen at 25 °C with capacities of 1.78 H/M (2.79 wt %) and 1.79 H/M (2.75 wt %) with increasing Mo content. Pressure-composition isotherms suggest a two-step reaction for hydrogen absorption to a final fcc dihydride phase. The experiments demonstrate that increasing Mo content results in a significant hydride destabilization, which is consistent with predictions from a gradient boosting tree data-driven model for metal hydride thermodynamics. Furthermore, improved desorption properties with increasing Mo content and reversibility were observed by in situ synchrotron X-ray diffraction, in situ neutron diffraction, and thermal desorption spectroscopy.
36 MATERIALS SCIENCE↗
Unraveling magneto-structural coupling of Ni 2 MnGa alloy under the application of stress and magnetic field using in situ polarized neutron diffraction
The magneto-structural evolution of a Ni 2 MnGa single crystal was investigated by in situ polarized neutron diffraction under both magnetic field and mechanical loading. The ability to separate the nuclear and magnetic scatterings by polarized neutrons enables simultaneous observations of the twin reorientation (through twin boundary motion) and magnetic moment configuration. It is found that under a 1.0 T saturating magnetic field, twin reorientation can be activated by compressive stress and is accompanied by a realignment of the magnetic moment, which follows the easy axis of the twin variant. On the other hand, compressive stress as small as 1.0 MPa can freeze the twin reorientation. The evolution of the magnetic scattering amplitudes suggests that the change in magnetization was mainly achieved through the magnetic domain wall motion, while the twin boundary motion was blocked.
36 MATERIALS SCIENCE↗
Determination of single crystal thermal expansion in Uranium-6wt%Niobium shape memory alloy using in-situ diffraction and modeling of textured polycrystalline samples
In-situ neutron diffraction and ex-situ dilatometry experiments were performed on a chemically banded, quenched uranium-6wt% niobium shape memory alloy to study the impact of deformation-(detwinning-) induced texture on the evolution of thermally induced strains (and associated stresses). Thermal heating and cooling cycles between 5K and 473K were performed in-situ with neutron diffraction, and the lattice strain evolution is reported for the observed monoclinic α" phase. Comparisons between the measured diffraction strains and macroscopic dilatometry experiments reveal relationships between micro- and macro-level thermal expansion. Softening of the texture during heating suggests that twin boundary motion can accommodate the large internal thermal strains which are approximately 2% greater than that typically observed during the 175K heating interval used to age more randomly oriented polycrystalline material. Assuming weak constraint of neighboring grains in randomly textured polycrystals, the single crystal thermal expansion tensor is extracted from measurements of lattice strains over the range 5K to 473K. Predictions of polycrystalline thermal expansion, based upon this single crystal thermal expansion tensor, are shown to compare favorably with bulk thermal expansion observations of the as quenched microstructure. However, such a lower-bound estimate is insufficient to explain all aspects of the behavior of the textured material, where the matrix is not isotropic. In conclusion, it is hypothesized that relaxation processes which occur within the quenched microstructure during heating are responsible for the distinct thermal expansion behavior observed during the initial heating cycle compared to cooling and subsequent cycling.
36 MATERIALS SCIENCE↗
Enhancing fatigue life by ductile-transformable multicomponent B2 precipitates in a high-entropy alloy
Catastrophic accidents caused by fatigue failures often occur in engineering structures. Thus, a fundamental understanding of cyclic-deformation and fatigue-failure mechanisms is critical for the development of fatigue-resistant structural materials. Here we report a high-entropy alloy with enhanced fatigue life by ductile-transformable multicomponent B2 precipitates. Its cyclic-deformation mechanisms are revealed by real-time in-situ neutron diffraction, transmission-electron microscopy, crystal-plasticity modeling, and Monte-Carlo simulations. Multiple cyclic-deformation mechanisms, including dislocation slips, precipitation strengthening, deformation twinning, and reversible martensitic phase transformation, are observed in the studied high-entropy alloy. Its improved fatigue performance at low strain amplitudes, i.e., the high fatigue-crack-initiation resistance, is attributed to the high elasticity, plastic deformability, and martensitic transformation of the B2-strengthening phase. This study shows that fatigue-resistant alloys can be developed by incorporating strengthening ductile-transformable multicomponent intermetallic phases.
36 MATERIALS SCIENCE↗
Plastic and low-cost axial zero thermal expansion alloy by a natural dual-phase composite
Zero thermal expansion (ZTE) alloys possess unique dimensional stability, high thermal and electrical conductivities. Their practical application under heat and stress is however limited by their inherent brittleness because ZTE and plasticity are generally exclusive in a single-phase material. Besides, the performance of ZTE alloys is highly sensitive to change of compositions, so conventional synthesis methods such as alloying or the design of multiphase to improve its thermal and mechanical properties are usually inapplicable. In this study, by adopting a one-step eutectic reaction method, we overcome this challenge. A natural dual-phase composite with ZTE and plasticity was synthesized by melting 4 atom% holmium with pure iron. The dual-phase alloy shows moderate plasticity and strength, axial zero thermal expansion, and stable thermal cycling performance as well as low cost. By using synchrotron X-ray diffraction, in-situ neutron diffraction and microscopy, the critical mechanism of dual-phase synergy on both thermal expansion regulation and mechanical property enhancement is revealed. These results demonstrate that eutectic reaction is likely to be a universal and effective method for the design of high-performance intermetallic-compound-based ZTE alloys.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Accelerated and heterogeneous corrosion of Cr-doped uranium nitride fuel pellets
The steam oxidation of Cr-doped UN fuel pellets is analyzed during sequential isothermal holds up to 720 °C. In situ neutron diffraction results show how Cr is accommodated in a secondary U 2 CrN 3 phase, leading to the formation of a duplex UN/U 2 CrN 3 microstructure. Under corrosion, the oxidation of the two phases begins at 400 °C for UN and 430 °C for U 2 CrN 3 , respectively. Because the UN phase is preferentially oxidized in the presence of U 2 CrN 3 , addition of Cr in UN based nuclear fuel is found to accelerate the corrosion rate. At 430 °C the oxidation of UN in the UN/U 2 CrN 3 microstructure is ~ 5 times faster than pure UN, increasing to ~19 times faster at 460 °C. The oxidation of U 2 CrN 3 produces UO 2 via the formation of two transient intermediate phases. In situ neutron diffraction enables oxidation processes of UN and U 2 CrN 3 components to be followed separately within the two-phase system.
11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
Deformation and Phase Transformation Processes in Polycrystalline NiTi and NiTiHf High Temperature Shape Memory Alloys
The deformation and transformation mechanisms of polycrystalline Ni49.9Ti50.1 and Ni50.3Ti29.7Hf20 (in at.%) shape memory alloys were investigated by combined experimental and modeling efforts aided by an in situ neutron diffraction technique at stress and temperature. The thermomechanical response of the low temperature martensite, the high temperature austenite phases, and changes between these two states during thermomechanical cycling were probed and reported. In the cubic austenite phase, stress-induced martensite, deformation twinning and slip processes were observed which helped in constructing a deformation map that contained the limits over which each of the identified mechanisms was dominant. Deformation of the monoclinic martensitic phase was also investigated where the microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were compared to the bulk macroscopic response. When cycling between these two phases, the evolution of inelastic strains, along with the shape setting procedures were examined and used for the optimization of the transformation properties as a function of deformation levels and temperatures. Finally, this work was extended to the development of multiaxial capabilities at elevated temperatures for the in situ neutron diffraction measurements of shape memory alloys on the VULCAN Diffractometer at Oak Ridge National Laboratory.
Benafan, Othmane↗
Redox Properties of Hexagonal and Cubic Sr 0.4 Ba 0.6 Mn 0.94 Ti 0.06 O 3−δ Investigated by In Situ Neutron Powder Diffraction
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
In-situ Mechanical Neutron Diffraction Loading Characteristics of GRCop-84 Fabricated by SLM
GRCop-84 is a precipitation strengthened alloy composed of Cu-8Cr-4Nb at % with Cr2Nb precipitates that provide dispersion and precipitation strengthening characteristics and limited solubility in the Cu matrix. The particle role of Cr2Nb(C15Laves) is unusual only contributing 1/3 of strengthening at high temperatures while the matrix provides the remainder. The particles mechanically and thermally stabilize the matrix retaining purity and preventing coarsening and loss of strength. At high temperatures (50-85%TmCu), GRCop-84 provides the best thermal and mechanical properties of available alloys. GRCop-84 is currently in development for reusable launch vehicles including the Space Launch System (SLS) with a focus on fabrication with additive manufacturing (AM) techniques. GRCop-84 is an optimal material for consolidating with AM. The base material is costly, the production times are long, and more geometry control can considerably improve cooling efficiency. Development of AMGR Cop-84 with selective laser melting (SLM) has rapidly progressed due to ease of printing and limited operator adjustment between builds, but the necessary knowledge-base of thermal history and stress state during builds is still under development.
Minneci, R.↗
Progression of creep deformation from grain boundaries to grain interior in Al-Cu-Mn-Zr alloys
Creep mechanisms are studied in θ'-Al 2 Cu-strengthened Al-Cu-Mn-Zr alloys at 300 and 350°C for (i) ACMZ, a base alloy without further alloying elements and (ii) RR350, a commercial alloy with additions of Ni and Co forming distinct grain-boundary precipitates. At high stresses, creep is dominated by dislocations bypassing θ' precipitates within grains via the Orowan mechanism, as evidenced by (i) very high stress exponent (n~20-25) and (ii) α-Al and θ' lattice strains (measured via in-situ neutron diffraction) evolving during creep in a manner consistent with load transfer from the plastically-deforming α-Al matrix to elastically-deforming θ' precipitates. At intermediate stresses, both alloys exhibit a n~3 regime, where α-Al and θ' lattice strains scale near-linearly with applied stress while remaining largely unaffected by strain accumulation, indicating that Orowan looping or dislocation pile-up around θ' is now inactive within the grains. Rather, dislocation motion occurs solely in θ'-precipitate-free zones (θ'-PFZ) where high dislocation densities are observed via TEM after creep deformation. Plastic flow at θ'-PFZ and/or localized pipe diffusion are expected to enable grain-boundary sliding (GBS), which is proposed as the rate-limiting mechanism in the n~3 regime. Ni/Co-rich precipitates at RR350 grain-boundaries, with negligible θ'-PFZ around them, share load (as determined via neutron diffraction) with the α-Al matrix more effectively than θ-Al 2 Cu precipitates at ACMZ grain-boundaries, with wide surrounding θ'-PFZ. So, high creep resistance in the n~3 GBS regime of RR350 is enabled by coarsening-resistant grain-boundary precipitates, forming without concomitant development of weak θ'-PFZ, which effectively share load with the grains.
36 MATERIALS SCIENCE↗
In situ monitoring of dislocation, twinning, and detwinning modes in an extruded magnesium alloy under cyclic loading conditions
This work investigates the microscopic deformation mechanisms of an extruded, precipitation-strengthened AZ80 magnesium (Mg) alloy subjected to strain-controlled low-cycle fatigue using in situ neutron diffraction measurements. Results demonstrate that the plastic deformation during cyclic loading is dominated by the alternating {10.2} extension twinning and detwinning mechanisms. The observed deformation mode is strongly texture and precipitate dependent. For the initial texture, the tested material has two major texture components which result in the occurrence of extension twinning during both compression and reverse tension in the first two cycles. The prolonged detwinning process in the following cycles is proposed to relieve the shear stress field of {00.2} grains, leading to the disappearance of twinning. The precipitation strengthening results in an increase of the critical resolved shear stress (CRSS) by similar to 33 MPa for the extension twinning in this AZ80 alloy. Here, the synergistic effects of the initial texture, precipitation strengthening, and load sharing of various grain families and phases contribute to the complicated evolution of dominant deformation mechanisms, among which elevated dislocation activities are believed to be responsible for the relatively poor low-cycle-fatigue lifetime when compared to other Mg alloys.
36 MATERIALS SCIENCE↗
Ce- and Ni-Codoped Double PrBaMn 2 O 5 Perovskite as a Ceramic SOFC Anode
This study explores the efficacy of cerium introduction, both on its own and in combination with nickel, into PrBaMn 2 O 5+δ (PBM) structures to enhance solid oxide fuel cell (SOFC) anodes. We synthesized Pr 1–x Ce x BaMn 2 O 5+δ compositions for x values of 0.05 (PrCe5) and 0.1 (PrCe10), as well as a nickel-doped variant (PrCe5Ni), assessing their performance under H 2 – 3% H 2 O reducing conditions pertinent to SOFC anode operations. Our findings reveal that the PrCe5 composition exhibits a thermal expansion coefficient (TEC) that not only improves upon that of the Ce-free counterpart but also aligns closely with the TEC standards of prevalent SOFC electrolytes. A notable advancement was achieved with the application of a 3.5 μm gadoliniadoped ceria (GDC) buffer layer through physical vapor deposition, effectively mitigating chemical interactions between PBM-based anodes and yttria-stabilized zirconia (YSZ) electrolytes, a concern highlighted by in situ neutron diffraction analyses. Electrochemical impedance spectroscopy, conducted over 220 h in a H 2 –3% H 2 O atmosphere at 750 °C, demonstrated that the optimal 3.5 μm thickness of the GDC buffer layer significantly minimizes the area-specific resistance (ASR) degradation rate to 0.002 Ω cm 2 /h, markedly outperforming both thinner (1 μm) and thicker (8 μm) GDC layers, which showed higher degradation rates of 0.15–0.2 Ω cm 2 /h due to the diffusion of Ba ions or delamination. Moreover, cerium doping fosters superior microstructural stability and obviates barium diffusion, thereby suggesting an enhanced durability of the doped anodes over their lifespan. Integrating nickel into the PrCe5 structure halved the ASR to 0.5 Ω cm 2 at 750 °C, situating it well within the ideal performance range for SOFC anodes. Furthermore, the enhancement brought about by simultaneously doping PBM with cerium and nickel, which fundamentally relies on the critical contributions of defect chemistry and crystal structure, highlights the significance of these fields in creating sophisticated materials for energy related applications.
25 ENERGY STORAGE↗
Microstructure Evolution of U–Zr System in A Thermal Cycling Neutron Diffraction Experiment: Extruded U–10Zr (wt. %)
Microstructure evolution of 1073 K extruded U–10Zr (wt. %) fuel during thermal cycling (303–1073 K with a ~9 hour hold at 873 K during cooling) was investigated using in situ neutron diffraction. Analysis was performed using Rietveld texture and crystal structure refinements from time–of–flight neutron diffraction data, with a focus on the evolution of textures and lattice parameters as a function of temperature. The α–U phase exhibits lattice contraction with increasing temperature along the b lattice direction and lattice expansion in the other directions while the other phases exhibit lattice expansion with temperature in all directions. Contrary to the established phase diagram, the β–U phase is absent at the temperatures of the thermal cycling. (001) α and (110) γ plane normals are observed with a strong preferred orientation along the extrusion direction. Finally, the variant selection of (001) α ||(110) γ is observed for the first time.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
Utilizing integrated neutron diffraction and elastoplastic self-consistent crystal plasticity model to quantitatively assess the strengthening mechanism in Al–12.5Ce and Al–12.5Ce–0.4Mg alloys
An integrated in-situ neutron diffraction and elastic plastic self-consistent crystal plasticity (EPSC-CP) modeling scheme is performed on a binary Al–12Ce alloy and a ternary Al–12Ce–0.4Mg alloys. Using this scheme, the constitutive parameters, i.e. elastic constants and slip system parameters of individual phases can be calibrated which can be used in microstructure-based CP models to predict materials performance. From this study, it is shown that the elastic constants of Al 11 Ce 3 intermetallics calculated from density function theory calculation in the literature are rather accurate. When applied to the EPSC-CP model, the lattice strains of both the binary and ternary alloys are correctly predicted as compared with experiments, and large lattice strain differences between Al (100) plane and Al 11 Ce 3 (010) plane are demonstrated. The slip system parameters calibrated by the scheme shows that the addition of 0.4 wt% Mg in the alloy has little influence on the critical resolved shear stress of initial dislocation glide in the Al matrix which caused plastic yield in the material. This can be explained by the very dilute Mg solute content in the Al solid solution, causing large spacing of Al–Mg lattice misfit sites and little impact on resistance of dislocation glide at initial yield. The 0.4 wt% Mg addition, on the other hand, has a large influence on the hardening term in the slip system parameters, indicating those Al–Mg misfit sites do help dislocation accumulation during the deformation. The impact of dilute Mg addition on the Al slip system parameters is also reflected in the flow behavior of the ternary alloy: little impact on the yield stress, but a large impact on working hardening and tensile strength of the materials which is consistent with the literature.
36 MATERIALS SCIENCE↗