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DOE OSTI2017

Shock and Microstructural Characterization of the α-ω Phase Transition in Titanium Crystals

In this paper, a multicrystal comprised of a small number of large crystals of high-purity titanium and a [ 0001 ] oriented high-purity single crystal titanium sample were shock loaded using gas gun plate impact experiments. Tests were performed at stresses above the α − ω phase transition stress (for high-purity polycrystalline specimens) to observe the behavior of oriented crystals under similar conditions. Post-mortem characterization of the shocked microstructure was conducted on the single crystal sample to measure textures, and quantify phases and twinning. The apparent activation of plastic and transformation mechanisms was dependent upon crystal orientation. Specifically, the [ 0001 ] crystal showed a higher Hugoniot elastic limit than the [ 10 1 ¯ 0 ] or [ 3 1 ¯ 4 ¯ 4 ] orientations. The slope of velocity as a function of time was lower in the [ 0001 ] orientation than the other orientations during plastic deformation, indicating sluggish transformation kinetics for the α to ω phase transition for the [ 0001 ] oriented crystal. Finally, microtexture measurements of a recovered [ 0001 ] oriented single crystal revealed the presence of retained ω phase after unloading, with orientations of the constituent phase fractions indicative of the forward α→ω transition, rather than the reverse ω→α transition, suggesting that the material never achieved a state of 100% ω phase.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Predicting intragranular misorientation distributions in polycrystalline metals using the viscoplastic self-consistent formulation

In a recent paper, we reported the methodology to calculate intragranular fluctuations in the instantaneous lattice rotation rates in polycrystalline materials within the mean-field viscoplastic self-consistent (VPSC) model. Here, this paper is concerned with the time integration and subsequent use of these fluctuations to predict orientation-dependent misorientation distributions developing inside each grain representing the polycrystalline aggregate. To this end, we propose and assess two approaches to update the intragranular misorientation distribution within the VPSC framework. To illustrate both approaches, we calculate intragranular misorientations in face-centered cubic polycrystals deformed in tension and plane-strain compression. These predictions are tested by comparison with corresponding experiments for polycrystalline copper and aluminum, respectively, and with full-field calculations. It is observed that at sufficiently high strains some grains develop large misorientations that may lead to grain fragmentation and/or act as driving forces for recrystallization. Finally, the proposed VPSC-based prediction of intragranular misorientations enables modeling of grain fragmentation, as well as a more accurate modeling of texture using a computationally efficient mean-field approach, as opposed to computationally more expensive full-field approaches.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Surface and subsurface characterization of laser-interference structured Ti6Al4V

Ti6Al4V specimens were exposed to high-energy laser pulses of 1.24 J/cm 2 fluences per pulse using a two-beam optical configuration to attain laser-interference. In addition to the formation of periodic surface textures by laser-interference, scanning electron microscope (SEM) images demonstrated several microstructural changes on the surface processed. Moreover, the surface and subsurface of Ti6Al4V specimens were characterized for the as-received and laser-interference processed conditions using x-ray photoelectron spectroscopy (XPS) and electron energy dispersive spectroscopy (EDS). The XPS data showed that this laser technique is effective at removal of surface contaminants for Ti6Al4V. The XPS analysis also revealed the formation of an oxy-nitride layer on the laser treated material. Finally, the microstructure analysis indicates that grain refinement, dendrite and twin structures were found near the surface due to laser processing.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Sr immobilization in irradiated Portland cement paste exposed to carbonation

Cement based materials are widely used as binding matrices for radionuclides in low and intermediate level waste management applications. We studied the effect of irradiation and carbonation under atmospheric condition on the leaching of Sr from Portland cement paste. Samples were exposed to gamma irradiation or subjected to thermal treatment under either inert or atmospheric conditions. Leaching tests were performed and supplemented by post-leaching characterization including local chemical analysis (LA-ICPMS) crystallographic analysis (XRD), and EPMA imaging. The combination of these methods enabled us to link between the crystallography, texture and composition of the treated samples and their ability to retain Sr ions. Results show that carbonation was the main factor determining the retention of Sr ions, whereas irradiation did not have a significant effect. Moreover, carbonation has a positive effect on the retention of Sr ions in the matrix with the formation of a carbonated zone.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2019

PyProcar: A Python library for electronic structure pre/post-processing

The PyProcar Python package plots the band structure and the Fermi surface as a function of site and/or s,p,d,f - projected wavefunctions obtained for each k-point in the Brillouin zone and band in an electronic structure calculation. This can be performed on top of any electronic structure code, as long as the band and projection information is written in the PROCAR format, as done by the VASP and ABINIT codes. PyProcar can be easily modified to read other formats as well. This package is particularly suitable for understanding atomic effects into the band structure, Fermi surface, spin texture, etc. PyProcar can be conveniently used in a command line mode, where each one of the parameters define a plot property. In the case of Fermi surfaces, the package is able to plot the surface with colors depending on other properties such as the electron velocity or spin projection. Furthermore, the mesh used to calculate the property does not need to be the same as the one used to obtain the Fermi surface. A file with a specific property evaluated for each k-point in a k-mesh and for each band can be used to project other properties such as electron–phonon mean path, Fermi velocity, electron effective mass, etc. Another existing feature refers to the band unfolding of supercell calculations into predefined unit cells.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2022

Understanding syringeability and injectability of high molecular weight PEO solution through time-dependent force-distance profiles

Opioid medications play a vital role in treating moderate to severe pain. Unfortunately, many drug misusers and abusers attempt to alter the formulations or properties of these drugs by manipulation, (e.g., crushing, chewing, smoking, snorting, injecting). The intravenous (IV) route is most dangerous to abusers, as the drugs directly enter the circulatory system and produce intense euphoria. To obtain a full understanding of the impact of syringe factors (e.g., needle gauge size, needle length, syringe barrel size), on the ease of injection, we undertook a comprehensive assessment of syringeability and injectability of manipulated abuse-deterrent formulations (ADFs). A texture analyzer-based testing method was developed for the measurement of the resistance force of pulling, holding, and pushing phases of injections. Results showed that the finer needle gauge sizes required higher injection force to withdraw drug solutions. In addition, the syringed liquid volume was highly dependent on needle gauge size, holding time, and sample viscosity. In most cases, a lower needle gauge number and a longer holding time increased the syringed volume. Needle length was highly correlated to injection force (R 2 = 0.99). Using longer needles to inject drug solution requires greater force. Furthermore, large barrel size was correlated to pushing force (R 2 = 0.99); thus, increasing the difficulty of pushing the plunger of a large syringe with one hand. Lastly, relationships between injection force, sample viscosity, and testing conditions were elucidated using a mathematical model, which could be used in the future to assess and predict injection force of solution samples.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2023

Microstructure and high temperature properties of tungsten processed via electron beam melting additive manufacturing

There is considerable interest in the adoption of additive manufacturing for processing refractory metals. The layer-wise fabrication approach enables opportunities for producing complex geometries which cannot be otherwise be achieved via powder metallurgy. However, the processing science is still in its nascent stages and structure–property relations are relatively unexplored. Fundamental research is needed to further develop the technology and enable the fabrication of refractory metals for high temperature applications. Here we focus on the processing of pure tungsten using electron beam melting additive manufacturing. Experimentally we develop a suitable processing window for achieving high density crack free material. Microstructural analysis reveals that the microstructure generally consists of a columnar structure with a (111) build direction fiber preference, although, fiber switching was observed. Process induced deformation is believed to drive the formation of subgrains whose boundaries exhibit a high dislocation density. Additionally, high temperature tensile testing reveals that the material exhibits excellent properties closer to that of annealed tungsten. Significant mechanical anisotropy was observed to be present which is likely driven by strong crystallographic texture.

36 MATERIALS SCIENCE↗

DOE OSTI2021

In situ study on the compression deformation of MoNbTaVW high-entropy alloy

The excellent mechanical properties of high-entropy alloys (HEAs) make them promising materials for advances in science and technology. However, the underlying mechanism of plastic deformation is not well understood. In situ experiments are urgently required to provide a fundamental understanding of the plastic deformation under high pressure. We performed in situ synchrotron X-ray diffraction (XRD) experiments to study compression deformation behavior of the HEA MoNbTaVW in a radial diamond anvil cell (rDAC). Our results show that the strength and ratio of the stress-to-shear modulus values are ~1.5 and 3 times that of pure tungsten (W), respectively. MoNbTaVW showed plastic deformation above 5 GPa and displayed a much stronger texture. In this work, we found that the active dislocation behavior is mainly responsible for the high strength in MoNbTaVW under compression. This unique technique opens a new avenue to investigate the in situ mechanical properties and their mechanism in other types of HEAs.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Advanced magnetic X-ray spectro-microscopies to characterize mesoscopic magnetic materials

Here, this article provides a brief overview of advanced magnetic X-ray spectro-microscopies that are widely used in characterizing mesoscopic magnetic materials. Common to those techniques are various X-ray magnetic dichroism effects that are used as magnetic contrast mechanism. A particular interest is to use those techniques to image the underlying microscopic spin structures in magnetic materials with high spatial resolution and to ultimately resolve their full 3D mesoscale characteristics with elemental sensitivity, as well as their ultrafast dynamics upon excitations with field and current pulses. Recent research examples using various magnetic X-ray spectro-microscopies are presented to showcase their specific features with a focus on imaging novel topological spin textures, such as vortices, skyrmions and Hopfions, which are considered as potential building blocks towards low power, high-speed and high-density magnetic devices that could transform information technologies and potentially be used in biomedical applications. Future developments with magnetic X-ray spectro-microscopies harness the full coherence of next generation X-ray sources and could open the path towards single shot imaging with spatial and temporal resolutions down to fundamental magnetic length and time scales.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Effects of sample bias on adhesion of magnetron sputtered Cr coatings on SiC

Swelling of SiC at 300 C due to in-service neutron irradiation causes tensile residual stresses in coatings which are expected to adversely affect the performance of coated SiC composite fuel cladding for light water reactors. Matching the coating swelling with the substrate, a solution common for thermal expansion, is not practical in the case of neutron irradiation. Biasing samples during magnetron sputtering deposition induces compressive residual stress which may counteract this. In this study, chromium coatings were deposited on SiC by DC magnetron sputtering with no external heating at bias voltages of –50V, –75V, and –100V. The effects of the bias voltage on morphology, residual stress, microstrain, texture, and adhesion are shown. The low deposition temperature resulted in the coating microstructure evolution following an energetic particle bombardment dominated trend. Additionally, at the two lower bias voltages knock-on implantation dominated increasing the residual stress and microstrain while at the highest bias voltage, thermal spike migration allowed for defect relaxation. When the knock-on induced compressive residual stress exceeded 0.8 GPa microcrack formation in the SiC substrate decreased coating adhesion. While no microcracks formed at the lowest bias voltage, insufficient atomic mobility during coating growth lead to voids forming in the coating. A balance is needed to form void-free coatings that have high compressive residual stress.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Improving precipitation hardening behavior of Mg−Zn based alloys with Ce−Ca microalloying additions

The precipitation hardening behavior of newly developed Mg−Zn−Ca−Ce alloys, with modified texture and improved ductility, is studied to delineate the microstructural characteristics that lead to effective hardening upon ageing treatments. Advanced electron microscopy and atom probe techniques are used to analyze the structural characteristics in relevance to the hardening potential. It has been found that the formation of a new basal precipitate phase, which evolves from a single atomic layer GP zone, and is finely distributed in both under-aged and peak-aged microstructures, has a significant impact in the improvement of the hardening response compared with the base Mg−Zn alloys. It has also been found that the β′{sub 1} rod precipitates, commonly formed during ageing treatments of Mg−Zn alloys, have their size and distribution significantly refined in the Ca−Ce containing alloys. The role of alloy chemistry in the formation of the fine basal plate GP zones and the refinement in β′{sub 1} precipitation and their relationships to the hardening behavior are discussed. It is proposed that Ca microalloying governs the formation of the GP zones and the enhancement of hardening, particularly in the under-aged conditions, but that this is aided by a beneficial effect from Ce. - Highlights: • Ce−Ca microalloying additions improve hardening in Mg−Zn, over Ce or Ca alone. • Improved hardening is due to refined β′{sub 1} rods, and fine basal plate precipitates. • Atom probe tomography identifies Ca in both β′{sub 1} and the fine basal plates. • The fine basal plates originate as ordered monolayer GP zones with 1:1 Zn:Ca (at.%). • With ageing GP zones become more Zn-rich and transform to the fine basal plates.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Analysis of heterogeneities in strain and microstructure in aluminum alloy and magnesium processed by high-pressure torsion

Two distinct bulk light metals were opted to study the shear strain evolution and associated heterogeneities in texture/microstructure development during torsional straining by high pressure torsion (HPT): a face centered cubic Al alloy (A5086) and a hexagonal commercial purity Mg. Relatively thick disk samples - four times thicker than usually employed in HPT process - were processed to 180° and 270° rotations. With the help of X-ray tomography, the shear strain gradients were examined in the axial direction. The results showed strongly localized shear deformation in the middle plane of the disks in both materials. These gradients involved strong heterogeneities in texture, microstructure and associated hardness, in particular through the thickness direction at the periphery of the disk where the interplay between significant strain hardening and possible dynamic recrystallization could occur. - Highlights: •HPT processing was conducted on bulk specimens thicker than the usual thin-disks. •The Al alloy (A5086) and commercial purity magnesium samples were compared. •Distributions of strain and microhardness were evaluated in the radial and axial direction. •Plastic deformation is highly localized in the middle plane at outer edge in both materials. •Different DRX rates governed the differences in microstructure and hardening behavior.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Evolution of twinning in extruded AZ31 alloy with bimodal grain structure

Twinning in extruded AZ31 alloy with a bimodal grain structure is studied under compression along the extrusion direction. This study has combined in-situ measurements during the compression tests by Synchrotron Radiation Diffraction and Acoustic Emission techniques and the evaluation of the microstructure and texture in post-mortem compression samples deformed at different strains. The microstructure of the alloy is characterized by the coexistence of large areas of fine dynamic recrystallized grains and coarse non-recrystallized grains elongated along extrusion direction. Twinning occurs initially in large elongated grains before the macroscopic yield stress which is controlled by the twinning in equiaxed dynamically recrystallized grains. - Highlights: • The AZ31 extruded at low temperature exhibits a bimodal grains structure. • Twinning takes place before macroscopic yielding in coarse non-DRXed grains. • DRXed grains controls the beginning of plasticity in magnesium alloys with bimodal grain structure.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Effect of strain on evolution of dynamic recrystallization in Nb-1 wt%Zr-0.1 wt%C alloy at 1500 and 1600 °C

Uniaxial compression tests were carried out on Nb-1 wt%Zr-0.1 wt%C alloy at temperature of 1500 and 1600 °C and strain rate of 0.1 s{sup −1} to study the evolution of dynamic recrystallization with strain. Electron back scatter diffraction was used to quantify the microstructural evolution. Nb-1Zr-0.1C alloy showed a necklace structure at a strain of 0.9 when deformed at 1500 °C and at strain of 0.6 when deformed at 1600 °C, both at strain rate of 0.1 s{sup −1}. This suggested the occurrence of dynamic recrystallization. At 1500 °C and strain of 0.9 the local average misorientation and the grain orientation spread was low confirming the presence of dynamic recrystallization at this deformation condition. At both 1500 and 1600 °C and all measured strains the recrystallized grains had a strong fiber component of <001>. - Highlights: • Necklace formation of dynamically recrystallized grains occurred at strain of 0.6 and 0.9 for 1500 and 1600 °C, respectively. • Equiaxed microstructures were seen with increase in strain for both 1500 and 1600 °C. • At large strains the predominant recrystallized texture evolved to <001> pole.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Size dependence of microstructure of AlSi10Mg alloy fabricated by selective laser melting

Highlights: • Plate-shaped samples with various widths were fabricated via selective laser melting. • The hardness of AlSi10Mg samples slightly decreased with decreasing sample width. • The alloy sample size had a slight effect on microstructure of the α-Al matrix. • Precipitation of Si phase in α-Al matrix was enhanced by reducing the sample size. • The softening by reducing sample size is likely due to their slower cooling rate. - Abstract: In order to investigate the size dependence of microstructure of the AlSi10Mg alloy fabricated by selective laser melting (SLM) combined with a powder bed technique, plate-shaped AlSi10Mg alloy samples with various widths (ranging from approximately 10 mm to 0.3 mm) were produced in this study. All the fabricated samples exhibited characteristic microstructural morphologies consisting of melt pools with columnar α-Al grains surrounded by fine eutectic Si particles, whereas their sample sizes had a relatively small effect on the texture and average grain size of the α-Al matrix. However, the formation of fine Si precipitates inside the columnar α-Al grains was observed more often for the smaller-sized samples, which could be a possible dominant contributor to the observed softening of the sample by reducing sample size. The obtained results were utilized for discussing the size dependence of the strength of the SLM-manufactured porous alloy samples.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Microstructural evolution and growth behavior of intermetallic compounds at the liquid Al/solid Fe interface by synchrotron X-ray radiography

Highlights: • A layered and tongue-like η phase was in-situ observed by synchrotron radiation X-ray radiography. • The coalescence of η phase bottom resulted in dissolution, further increasing the growth rate. • The θ phase growth behavior with different morphologies during cooling was analyzed. - Abstract: The growth of Inter-Metallic Compounds (IMCs) with dissolution was investigated on the liquid Al/solid Fe interconnection by using synchrotron radiation real-time imaging technology. At the initial stage of holding at 850 °C, a layer of the η-Fe{sub 2}Al{sub 5} phase formed at the interface, and tongue-like η grew into α-Fe. The tongue-like η phase had a stronger (001) texture than the layered phase. The coalescence of tongue-like η started at the bottom, followed by the dissolution of IMCs, which leads to a further increase in its growth rate. During solidification stage, the dotted, needle-like and flake θ-FeAl{sub 3} phases were sequentially formed.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Influence of finish rolling temperature on the microstructure and mechanical properties of Mg-8.5Al-0.5Zn-0.2Mn-0.15Ag alloy sheets

Highlights: • The microstructure is strongly depending on the finish rolling temperature. • Extensive shear zones parallel distributed across the sheets. • The formation process of shear zones in RH and RL are different. • Shear zones decide the mechanical anisotropy of the whole sheet. - Abstract: Mg-8.5Al-0.5Zn-0.2Mn-0.15Ag (wt%) magnesium sheets were produced with various final rolling temperatures, and their microstructures and mechanical properties were characterized. It was found that low final rolling temperature (LT) resulted in stronger heterogeneity, stronger basal texture and higher strength compared with the high final rolling temperature (HT). Considerable shear zones were observed within both the LT and HT sheets, even though their microstructures, formation mechanisms and mechanical properties were different. Preliminary analysis suggests that the shear zones exert great influence on the mechanical anisotropy of whole sheets.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Interfacial microstructure evolution and weld formation during ultrasonic welding of Al alloy to Cu

Highlights: • Surface oxide layer was fractured and dispersed around the weld interface during ultrasonic welding of Al alloy to Cu. • Mechanical mixing around the weld interface was caused by compressive deformation with ultrasonic vibration. • Once micro-bonds were generated between Al and Cu, shear deformation occurred around the weld interface. • Enhanced Cu diffusion into Al in the severely deformed region significantly contributed to the weld formation. - Abstract: Dissimilar welds of Al alloy 1050 to Cu were prepared via ultrasonic spot welding in order to understand the formation of welds and interfacial microstructures. To observe oxide layer behavior at the weld interface, the anodized Al alloy 1050 was also welded to Cu. Mechanical mixing and material flow during ultrasonic welding broke and dispersed the oxide layers into the Al matrix. This material flow is attributed to compressive deformation that occurred due to ultrasonic vibrations. Direct bonding in the Al/Cu region increased with welding time. Once micro-bonds were generated between Al and Cu, the Al matrix in the vicinity of the weld interface was severely deformed in the direction of the ultrasonic vibrations. Consequently, a recrystallized microstructure with shear texture was formed in the Al matrix. Deformation heating and severe shear deformation formed Al{sub 2}Cu intermetallic compound layers at the weld interface. The growth rate of the Al{sub 2}Cu layer was much faster than had previously been estimated based upon the peak temperature and ultrasonic welding heating time. This is likely due to the increased rate of Cu diffusion into Al in the severely deformed region.

36 MATERIALS SCIENCE↗