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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Microstructure Characteristic and Mechanical Properties of High-Strength Mg-Nd-Zn-Zr Alloy Seamless Tube Produced by Integrated Extrusion

Large size seamless tubes of Mg-3.0Nd-0.4Zn-0.4Zr alloy (NZ30K, in weight percent) were prepared by integrating backward extrusion with forward extrusion. Microstructure, mechanical properties, aging behavior and texture of the tubes were investigated. The microstructure of as-extruded tube is characterized by the blend of considerably elongated grains and fine equiaxed grains. The maximum values of yield strength and ultimate tensile strength, i.e., 191 and 245 MPa, were obtained in the as-extruded tubes, and these values were increased to 212 and 267 MPa in the peak-aged tubes (T5), implying an increasing ratio of 9 and 11%, respectively. The peak value of the Vickers’ micro-hardness of the NZ30K tubes extruded at 673, 723 and 753 K are 66, 64 and 60 (kilogram-force per square millimeter), respectively. The texture of NZ30K tube is weak, the primary mechanism behind which is suggested to be the particle-induced nucleation responsible for the promotion of recrystallization.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Single-Point Incremental Force Process Parameters on Forming Characteristics and Microstructure Evolution of AA-6061 Alloy Sheet

Single-point incremental forming (SPIF) process comprises a set of process variables, such as forming tool diameter, vertical pitch, spindle rotation speed, and tool velocity, which may affect the forming behavior of the sheet to be deformed. The objective of this work is to study the effect of SPIF process parameters on forming characteristics and microstructure development for the AA-6061 (T6) aluminum alloy sheet. The SPIF experiments and finite element (FE) simulations were performed at different process parameters to achieve conical shapes from the AA-6061 blanks. The effect of process parameters on forming forces, thickness uniformity in wall region of the cone and surface roughness of the blank was analyzed. A detailed microstructure study was performed to analyze the effect of process variables on microstructure and texture evolution during the SPIF process. This study reveals that the process parameters are likely to influence the texture development especially at high tool diameter and vertical pitch values. Therefore, suitability and consequences of using different combinations of tool diameter and vertical pitch values are discussed for AA-6061 alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Solid state dewetting of thin plasmonic films under focused cw-laser irradiation

Elevated temperatures and large thermal gradients are a significant source of component failure in microelectronics, and is the limiting factor in heat-assisted magnetic recording (HAMR). Here, we have investigated the effect of solid-state dewetting in Au thin films, as a function of local temperature, film thickness, and substrate adhesion. In this work, a localised temperature rise is induced in thin (≤ 50 nm) polycrystalline Au films on SiO 2 substrates via focused continuous-wave laser irradiation at 488 nm. The magnitude and distribution of the total temperature rise is measured using CCD-based thermoreflectance. This also allows a sensitive measurement of the temperature at which dewetting occurs, showing that for thin (≤ 50 nm) Au films without adhesion layers, rapid dewetting can occur at temperatures as low as 50° C. The time decay of the reflected light from the illuminating laser is used to monitor locally the dynamics of solid state dewetting. TEM diffraction analysis shows significant changes in the microstructure and crystallographic texture of the films as far as 10 µm away from the illuminated area. The use of a thin metallic adhesion layer (such as Ti or Cr) is shown to significantly improve the adhesion of the Au to the substrate and reduce the tendency towards dewetting, but does not entirely protect it from changes to the crystallographic texture.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Temperature-dependent dynamic fouling on superhydrophobic and slippery nonwetting copper surfaces

Bioinspired, superhydrophobic and slippery liquid infused surfaces that offer nonwetting characteristics have been explored in recent years for fouling mitigation. However, most of the studies are in the context of biofouling or under static immersion at ambient temperature conditions that are not reflective of the dynamic flow environment in practice. This article presents, for the first time, a systematic study of dynamic fouling of superhydrophobic (SHS) and slippery lubricant-infused surfaces (LIS) over a range of flow and temperature conditions. In this work, copper metallic surfaces were textured via electrodeposition or etching and further functionalized to achieve SHS and, additionally, infiltrated with a lubricant to fabricate LIS. The nonwetting surfaces were studied for their fouling behavior in a rotating Couette flow of a supersaturated calcium sulfate solution at different rotational speed and temperature. Fouling mineral mass accumulation on the different surfaces was measured as a function of time over a period of days using inductively coupled plasma mass spectroscopy and the fouled surfaces were investigated using scanning electron microscopy. Both SHS and LIS showed superior anti-scaling performance at all ranges of variables. An analytical Hill-Langmuir model is presented, for the first time, to describe the time evolution of scaling within 20% accuracy over the range of parameters studied. The study is the first to juxtapose two surface texturing methods, electrodeposition and etching, and two nonwetting surface types, SHS and LIS, subject to a common suite of experiments to elucidate fundamental understanding of mineral fouling on nonwetting surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Engineering grain boundary anisotropy to elucidate grain growth behavior in alumina

Current grain growth models have evolved to account for the relationship between grain boundary energy/mobility anisotropy and the five degrees of grain boundary character. However, the role of grain boundary networks on overall growth kinetics remains poorly understood. To experimentally investigate this problem, a highly textured Al 2 O 3 was fabricated by colloidal casting in a strong magnetic field to engineer a unique spatial distribution of grain boundary character. Microstructural evolution was quantified and compared to an untextured sample. From this comparison, a prevalence of (0001)/(0001) terminated grain boundaries with anisotropic networks were identified in the textured sample. These boundaries and their networks were found to be driving grain growth at a faster rate than predicted by models. These findings will allow better modelling of grain growth in real systems by experimentally exploring the impact thereon of grain boundary plane anisotropy and relative energy/mobility differences between neighboring boundaries.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Role of surface wetting on tribological behavior for laser nanotextured steel using ionic liquid lubricants

Here, this research evaluates the effect of surface wettability on the tribological performance through ball-on-flat tribology testing. The substrate material, M2 tool steel, is laser processed and then functionalized with fluorocarbon and nitrile chemistry to achieve distinct oleophobicity and oleophilicity, respectively, but with a similar nanoscale surface texture. The baseline lubricant is poly-alpha-olefin (PAO) oil, and ionic liquids (ILs) are used as additives for this study. The interaction between the nanoscale textured steel surface and ionic liquid-based oils is investigated. A set of reciprocating wear tests are performed to investigate the tribological behavior of the tribo-system consisting of the surface-engineered, flat M2 tool steel specimen and a standard, surface-polished steel ball. Results show that the oleophobic flat surface results in a lower friction, while the oleophilic surface modification leads to a better wear protection to the flat surface. Ammonium-based IL provides the highest friction reduction, while the phosphonium-based ILs provide an improved wear protection.

36 MATERIALS SCIENCE↗
DOE OSTI2020

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↗
DOE OSTI2017

Microstructural control of FeCrAl alloys using Mo and Nb additions

The effects of Mo and Nb additions on the microstructure and mechanical properties of two FeCrAl alloys were studied in this paper. Fine and uniform recrystallized grain structures (~ 20–30 μm) were achieved in both alloys through suitable annealing after warm-rolling. The formation of Fe 2 Nb-type Laves phase precipitates in the Nb-containing FeCrAl alloy effectively stabilized the deformed and recrystallized microstructures. The Mo-containing FeCrAl alloy exhibited strong γ texture fiber after annealing at 650–900 °C, whereas the annealed Nb-containing FeCrAl alloy had much weaker texture. Finally, both strength and ductility decreased as the grain size increased in both alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Multiscale mechanical behavior and microstructure evolution of extruded magnesium alloy sheets: Experimental and crystal plasticity analysis

Highlights: • Experimental stress-strain responses were reproduced by CPFE simulation based on Voronoi grains on three strain paths. • Textures predicted by simulation were in accordance with the ones measured by EBSD at the strain of 0.085. • Deformation heterogeneity in slip-dominated cases was found more significant than that in twin-favored case. • For slip-dominated cases, both high m′ value and high SFs in adjacent grains are responsible for strain localization. - Abstract: A phenomenological crystal plasticity finite element (CPFE) model based on Voronoi grains was applied to reproduce basic deformation features of a hot-extruded magnesium alloy sheet under various strain paths. Corresponding experimental investigations, including mechanical tests, electron back scattered diffraction (EBSD) measurements and optical observation, were also carried out as either a validation or a supplement of the numerical results. Predicted average stress-strain responses and texture evolution are in good accordance with measured ones. Furthermore, deformation heterogeneity at the mesoscopic and intergranular scale were investigated based on the proposed model. At the mesoscale, the heterogeneity in the slip-dominated cases tends to develop continuously, whereas the heterogeneity is retarded in twin-favored deformation. At the intergranular scale, it is concluded from the slip-dominated case that a high slip-transfer parameter and high Schmid factors (SFs) of principal slip systems in adjacent grains could accommodate higher local strain.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Coincidence site lattice boundary mechanism for the preferred growth of Goss and Cube grains during annealing in an Al-Cu-Mg alloy

Highlights: • Both Goss and Cube grains are recrystallized out of Brass matrix. • Boundary character between Brass and Goss grains was Σ9, and that between Brass and Cube was Σ5. • Σ9 and Σ5 boundaries only transitionally appeared during recrystallization. • Temperature had decisive effect on the formation and mobility of CSL boundaries. • Σ9 and Σ5 boundaries with high index planes were highly mobile. - Abstract: The formation mechanism of recrystallized textures in an Al-Cu-Mg alloy was investigated by means of three dimensional orientation distribution functions (ODFs) and in-situ electron back-scattered diffraction (EBSD). The results showed that in the hot-rolled alloy with a very sharp Brass texture but weak Copper and S orientations, both Goss and Cube grains were recrystallized out of parent Brass matrix. In-situ EBSD analysis revealed that characteristic boundary between Brass and Goss grains to be Σ9, while that between Brass and Cube grains to be Σ5. Frequency of Σ9 and Σ5 boundaries increased quickly at early stage and then reduced gradually with the process of recrystallization. Annealing at a higher temperature (320 °C) was found to be beneficial for the formation of Σ9 boundary, while at lower one (300 °C), Σ5 boundary became dominant. Besides, with temperature decreasing from 320 to 300 °C, the mobility of Σ9 boundaries was greatly degraded, but relatively, Σ5 boundaries still behaved highly mobile. Principally, the preferred growth of recrystallized Goss and Cube grains was respectively attributed to the high mobility of Σ9 and Σ5 boundaries with high index planes that the square sum of plane index was larger than 3.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure of titanium on complex deformation paths: Comparison of ECAP, KOBO and HE techniques

Highlights: • Method for producing CP titanium rods for medical implants is searched. • Three processing methods producing ultra-fine grain titanium are compared. • Microstructure and textures are examined and analysed. • Mechanical characteristics are determined based on microhardness and tensile tests. • Hydrostatic extrusion (HE) leads to the best properties of titanium rods for medical implants. - Abstract: In this work samples of commercial purity grade 2 titanium were severely deformed by three different extrusion techniques: equal-channel angular pressing (ECAP), extrusion through oscillating die (KOBO), and hydrostatic extrusion (HE). Resulting microstructures and mechanical properties of processed titanium samples are studied and compared with regard to potential application as a material for dental implants. The obtained results demonstrate the effect of different strain paths, involved by three applied deformation methods, on microstructure refinement, mechanical properties and textures of the studied material. Heterogeneous microstructures with bimodal grain size distributions are observed for all deformation techniques in the examined material, however differences in their internal structures and grain boundary distributions point to different grain refinement mechanisms. The fraction of ultra-fine grains is the highest in titanium deformed by HE. Also the internal grain fragmentation is the most important after HE deformation. This leads to the best mechanical and microstructural properties obtained in this type of deformation. Consequently, the HE process seems to be very interesting for production of material for medical implants.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Multi-scale and multi-technic microstructure analysis of a linear friction weld of the metastable-β titanium alloy Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti17) towards a new Post-Weld Heat Treatment

Highlights: • Soft joint showing sharp macro-zones and marked by asymmetrical process effects • Gradient of thermomechanical loads identified through progressive stages of transformation • Highly textured recrystallized β grains at the joint core with distorted β lattice • Lattices, phase fractions, microstructures and hardness homogenized after heat treatment - Abstract: Linear Friction Welding (LFW) is a solid-state joining process producing narrow joints mainly developed for the aircraft industry. The Thermo-Mechanical Processing (TMP) loads imposed on the material cause complex microstructure transformations. This study aimed at characterizing the local microstructures and crystallographic configurations to identify the mechanisms impacting the stability and the mechanical properties of a Ti17 LFW joint with the objective of establishing an innovative homogenizing Post-Weld Heat Treatment (PWHT). The process caused a narrow zone of ±2 mm from the friction interface to reach the isothermal α → β transformation temperature under a heating rate of 500 K/s followed by quenching (−100 K/s). The TMP resulted in the formation a ±3 mm wide soft Process Affected Zone (PAZ) delimited by three characteristic zones: the Welding Line (WL width ≈ 400 μm), The Thermo-Mechanically Affected Zone (TMAZ width ≈ 1 mm) and the Heat Affected Zone (HAZ). β TMP resulted in the total dissolution of the α phase in the joint core (WL + TMAZ) and formed strongly textured {110}<111> β recrystallized grains in the WL by continuous dynamic recrystallization of squeezed prior-β grains in the TMAZ. α + β TMP led to a gradual loss of hardness in the HAZ whose microstructure is similar to the one of the base material (BM) but is subject to gradual α laths dissolution due to the local temperatures experienced during LFW. A PWHT consisting in a β annealing followed by an α + β ageing resulted in a uniformly hardened weld with a homogenized Widmanstätten microstructure in the whole assembly.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Annealing-induced microstructural evolution and mechanical anisotropy improvement of the Mg-Gd-Y-Zr alloy processed by hot ring rolling

Highlights: • Growth of SRX grains in GBR is random, while that of TBR is anisotropic. • The new texture component in annealed MR weakens the anisotropy obviously. • T6 treatment leads to an excellent comprehensive mechanical property. - Abstract: Hot ring rolling (HRR) is widely used to fabricate large-size seamless ring-shape components. However, this process produces a severe mechanical anisotropy, which is not acceptable in practical industrial application and should be avoided. This paper reports the annealing-induced microstructural evolution and mechanical anisotropy improvement of HRRed Mg-8.12Gd-1.82Y-0.35Zr alloy ring. Results show that annealing treatment could improve the microstructural homogeneity of the ring owing to the occurrence of static recrystallization (SRX). SRX grains are preferentially formed at twin boundaries and initial grain boundaries due to high dislocation density, high level of stored energy, and stress concentration. Twin boundaries, to some extent, can suppress the migration of SRX grain boundaries. In addition, occurrence of SRX weakens the texture intensity and basal pole inclination, leading to a decrease in the mechanical anisotropy of the ring. Considering the weakened anisotropy, comparable strength, and improved ductility, annealing + aging (T6), compared with direct aging (T5), is a more suitable heat treatment schedule for the HRRed Mg-8.12Gd-1.82Y-0.35Zr alloy ring.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A critical assessment of deformation twinning and epsilon martensite formation in austenitic alloys during complex forming operations

Highlights: • The formation of ε-martensite in TRIP steel reduces formability. • In austenitic alloys, stress induced transformation in addition to twinning and slip does not affect the twinning behaviour. • The volume fraction of twins exhibits variation depending on the strain pathway due to differences in texture development. - Abstract: The effect of mechanical twinning and ε-martensite formation on the formability of austenitic alloys in complex strain pathways has been examined. One of the alloys studied deformed by deformation twinning and slip (TWIP), and this alloy was examined with two grain sizes. The second alloy showed three concurrent deformation modes (slip, TWIP and ε-martensite TRIP). The TWIP/TRIP alloy showed a markedly reduced formability compared to similar alloys, and this has been attributed to a combination of the early development of strain localizations, and the stress-induced formation of ε-martensite. It is suggested that the TRIP effect may not be desirable in high formability sheet steels if the transformation product is ε-martensite. Microstructural examination revealed that the different strain paths develop different twin volume fractions. Plasticity modelling has shown this to be the result of differences in texture development in the different strain paths. In microstructures where slip, TWIP and TRIP can operate concurrently, the stress to activate twinning is unaffected by the additional deformation mode becoming operative.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of initial orientation on dynamic recrystallization of a zirconium alloy during hot deformation

Highlights: • The dynamic recrystallization process is enhanced by the operation of slip. • Continuous dynamic recrystallization is promoted by the rotation of grains. • Texture induced hardening hides the softening induced by dynamic recrystallization. - Abstract: The present study investigated the influence of the initial orientation on the dynamic recrystallization (DRX) behavior of a Zr-1Sn-0.3Nb alloy. A hot-rolled and annealed Zr sheet was compressed along two directions: along the normal direction so that the grains' -axis was nearly parallel to the loading direction (0° sample) and along the transverse direction so that the grains' -axis was nearly perpendicular to the loading direction (90° sample). The samples were compressed at 700 °C at a strain rate of 1 s{sup −1}. The microstructures at different strains were characterized by the electron backscatter diffraction (EBSD) technique, and conventional dislocation analysis using transmission electron microscope (TEM) was performed. A threshold value of grain orientation spread (GOS) equaled to 5° was used to distinguish the dynamically recrystallized grains from the deformed matrix. The results revealed that the DRX behavior strongly depended on the initial orientation. The Schmid factor analysis and TEM observation confirmed that pyramidal slip operated from the first stage of deformation in the 0° sample but not in the 90° sample. For the 0° sample, in the early and medium stages of deformation, due to the high stored energy caused by the operation of pyramidal slip, DDRX was mainly contributed to the formation of new fine grains. However, in the later stage of deformation, the DRX mechanism changed from DDRX to CDRX. In the 90° sample, although DDRX featured by grain boundary bulging occurred, the main DRX mechanism was CDRX in the whole deformation processing. Moreover, texture induced hardening in the early stage of deformation hides the softening induced by DDRX.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evolution of microstructure and microtexture during hot deformation in an advanced P/M nickel base superalloy

Highlights: • Microstructural evolution of PM superalloy sensitive to temperature and strain rate. • Highest DRX with finer grained structure at higher temperatures and strain rates. • Dominance of DDRX showed by serrated grain boundaries and misorientation gradient. • Weak microtextural evolution inclined towards [110] fiber compression texture seen. In the present study, the effect of hot deformation parameters on the microstructural evolution is investigated for an experimental powder metallurgy nickel superalloy. The hot isostatically pressed (HIPed) alloy is isothermally hot compressed at constant true strain rate over wide temperatures (1000 °C, 1050 °C, 1100 °C, 1150 °C) and strain rates (0.001 s{sup −1}, 0.01 s{sup −1}, 0.1 s{sup −1}, 1 s{sup −1}) regimes. Electron Back-Scattered Diffraction (EBSD) characterization of the hot deformed samples is carried out to evaluate the microstructural evolution, grain boundary characteristics, and microtextural behaviour. The strong dependence of dynamic recrystallization characteristics on the hot deformation conditions is divulged through EBSD derived colour inverse pole figure maps endorsed by grain/twin boundary characteristics and misorientation gradient. Dynamic recrystallization (DRX) is maximized at higher deformation temperatures, whereas limited DRX is observed at lower deformation temperatures, especially at higher strain rates. The dominance of discontinuous dynamic recrystallization (DDRX) is manifested through bulged/serrated grain boundaries resulting in the formation of necklace microstructure corroborated by grain boundary cumulative misorientation gradient. Although random microtexture is revealed in both deformed and recrystallized microstructures, the tendency towards the formation of 110 fiber compression texture is apparently evident.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Ultrasonic additive manufacturing of zirconium: Pilot results

Ultrasonic additive manufacturing (UAM) was successfully applied to the Zirconium material system to create a three-dimensional component prototype. The UAM process resulted in grain size refinement and significant localized deformation. Electron backscatter diffraction analysis revealed activated slip systems only applicable at high deformation temperatures, while texture analysis showed a decrease in measurable texture of the UAM build in comparison to the initial Zr-foil. Average tensile strengths in the X (sonotrode travel), Y (vibration), and Z (build) directions averaged 435 MPa, 458 MPa, and 359 MPa, respectively, demonstrating the viability of UAM for Zr-based materials. Furthermore, the delamination of some Z specimens along foil boundaries during loading suggests an interplay between interfacial Ti impurities introduced during welding and the spatial dependence of weld quality for this material system.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Sn on Martensitic Beta Ti Alloys

The influence of Sn composition in Ti-17 at.% Nb alloys is studied by cyclic tension and in-situ synchrotron X-ray diffraction. It is essentially found that Sn stabilizes β-phase and effectively suppresses the formation of ω-phase. Along with β-phase stability, we detect lowering of the austenite and martensite transformation temperature by ~ 100 K/at.% and 88 K/at.%, respectively. Increasing Sn decreases the martensitic transformation strain in Ti-Nb alloys by ~ 1.4%/at.%, larger than that in Ti-Zr-Nb-Sn systems. The influence of Sn in martensitic Ti is anisotropic: causing larger reduction in lattice parameter b and higher decreases in elastic moduli of grain families that are aligned close to the b -axis. Lastly, a {013} α'' , {031} α'' ,{122} α'' and {211} α'' quadruple texture was observed in martensitic Ti wire. At the early stage of deformation, detwinning quickly rotated {013} α'' and (211} α'' , towards {031} α'' and {122} α'' components. After that, the strength of {031} α'' continued to increase, while the strength of {122} α'' texture was gradually decreased by dislocation slip as deformation continued.

36 MATERIALS SCIENCE↗