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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Understanding the Role of Hot Isostatic Pressing Parameters on the Microstructural Evolution of Ti-6Al-4V and Inconel 718 Fabricated by Electron Beam Melting

In this project, Avure and ORNL evaluated the influence of hot isostatic pressing (HIP) and thermal cycling as standalone post processing techniques on the microstructure of electron beam powder bed deposited Ti-6Al-4V and Inconel 718 alloys. Electron beam powder bed deposition is an effective technology for fabricating complex net shape components that cannot be manufactured with conventional processes. However, material deposited by this technology results in columnar grain growth which is detrimental for many applications. For Ti-6Al-4V, it has been found that thermal cycling alone is not sufficient to breakdown the columnar microstructure that is typical of electron beam powder bed technology. HIP, on the other hand, has the potential to be an effective technique to break down the columnar microstructure of Ti-6Al-4V into a more equiaxed and refined β grain structure, and provide a more homogeneous microstructure compared to the thermally cycled samples. Overall, the project showed that hot isostatic pressing reduced/eliminated porosity in both Ti-6Al-4V and Inconel 718 However, based on the unique thermal cycle and the application of pressure in the HIP vessel, Ti-6Al-4V e-beam deposited microstructures were modified from columnar grain growth to equiaxed microstructures; a significant outcome to this collaboration. Inconel 718, on the other hand, shows no change in the macrostructure as a result of the current HIP cycle based on the thermal history, and would require further investigation. Though the results of HIP cycle were very good at changing the microstructure, further development in optimizing the post heat treatments and HIP cycles is required to improve mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of stored strain energy heterogeneity on microstructure evolution of 90% cold rolled AISI 304L stainless steel during interrupted annealing treatment

Highlights: • Study of usefulness of stored strain energy distribution map of the material for variable temperature range. • Advantage of using stored strain energy distribution map • Variation observed in stored energy between isothermal annealing treatment and interrupted annealing treatment. - Abstract: This research work is an attempt to understand the effect of stored strain energy heterogeneity over macro-scale, induced during interrupted annealing treatment, on the micro structural evolution in a heavily cold rolled AISI 304L austenitic stainless steel. The cold rolled AISI 304L stainless steel (SS) samples were subjected to different annealing treatments. The microstructures obtained after each annealing treatment were characterized using optical and electron microscopy techniques. Further, an attempt was made to estimate the stored strain energy by a novel approach of micro hardness measurement both over small scale (area 3600 μm{sup 2}) and large scale (area ~0.25 mm{sup 2}). The stored strain energy was determined using hardness values. Using these data, spatial stored strain energy distribution contour maps were created. They were, in turn, used to characterize the local softening behavior both at micro and macro-scale levels after each interrupted annealing treatment. The results showed that, interrupted annealing treatment induces increased stored strain energy heterogeneity after each annealing interruptions. Also, it was possible to determine recrystallization kinetics of the material using stored strain energy map, which helps in designing annealing cycles for achieving ultrafine grained microstructure.

36 MATERIALS SCIENCE↗
DOE OSTI2014

An investigation on microstructure evolution and mechanical properties during liquid state diffusion bonding of Al2024 to Ti–6Al–4V

Joining mechanism of Ti/Al dissimilar alloys was studied during liquid state diffusion bonding process using Cu/Sn/Cu interlayer at 510 °C under vacuum of 7.5 × 10{sup −5} Torr for various bonding times. The microstructure and compositional changes in the joint zone were analyzed by scanning electron microscopy equipped with energy dispersive spectroscopy and X-ray diffraction. Microhardness and shear strength tests were also applied to study the mechanical properties of the joints. It was found that with an increase in bonding time, the elements of interlayer diffused into the parent metals and formed various intermetallic compounds at the interface. Diffusion process led to the isothermal solidification and the bonding evolution in the joint zone. The results from mechanical tests showed that microhardness and shear strength values have a straight relation with bonding time so that the maximum shear strength of joint was obtained for a bond made with 60 min bonding time. - Highlights: • Liquid state diffusion bonding of Al2024 to Ti–6Al–4V was performed successfully. • Diffusion of the elements caused the formation of various intermetallics at the interface. • Microhardness and shear strength values have a straight relation with bonding time. • The maximum shear strength reached to 36 MPa in 60 min bonding time.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Microstructure evolution of Al/Mg butt joints welded by gas tungsten arc with Zn filler metal

Based on the idea of alloying welding seam, Gas tungsten arc welding method with pure Zn filler metal was chosen to join Mg alloy and Al alloy. The microstructures, phases, element distribution and fracture morphology of welding seams were examined. The results indicate that there was a transitional zone in the width of 80-100 {mu}m between the Mg alloy substrate and fusion zone. The fusion zone was mainly composed of MgZn{sub 2}, Zn-based solid solution and Al-based solid solution. The welding seam presented distinct morphology in different location owning to the quite high cooling rate of the molten pool. The addition of Zn metal could prevent the formation of Mg-Al intermetallics and form the alloyed welding seam during welding. Therefore, the tensile strengths of joints have been significantly improved compared with those of gas tungsten arc welded joints without Zn metal added. Highlights: Black-Right-Pointing-Pointer Mg alloy AZ31B and Al alloy 6061 are welded successfully. Black-Right-Pointing-Pointer Zinc wire is employed as a filler metal to form the alloyed welding seam. Black-Right-Pointing-Pointer An alloyed welding seam is benefit for improving of the joint tensile strength.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Probing the Influence of Thermally Induced Structural Changes on the Microstructural Evolution in Shale using Multiscale X-ray Scattering Measurements

Various pathways to accelerate the recovery of hydrocarbons from unconventional subsurface environments have been proposed, including the use of high-temperature fluids. However, the influence of temperature on the structural and microstructural changes in complex subsurface materials characterized by compositional and morphological heterogeneity are not very well understood. In this study, in operando ultrasmall angle, small angle, and wide-angle X-ray scattering (USAXS/ SAXS/WAXS) measurements were performed to link the structural and morphological changes in shale when heated from 30 to 1150 °C. The structural changes observed from the wide-angle X-ray scattering measurements were complemented by the changes in the porosity, particle size, and surface morphology. Overall, we report the combined USAXS/SAXS measurements showed enhanced smoothness in the pore–solid interface on heating. The dehydroxylation of illite and calcination of calcium carbonate were noted prior to the formation of denser and sintered silicate and alumino-silicate phases such as Mg 2 SiO 4 (forsterite), Fe 0.3 Mg 0.7 (SiO 3 ) (enstatite), and Al 2.35 Si 0.64 O 4.82 (mullite).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2010

Microstructural evolution during dynamic deformation of cubic metals: copper

Shockwave shape can influence dynamic damage evolution. Features such as rise time, pulse duration, peak shock pressure, pull back, and release rate are influenced as wave shape changes. However, their individual influence on dynamic damage evolution is not well understood. Specifically, changing from a square to triangular or Taylor wave loading profile can alter the release kinetics from peak shock pressure and the volume of material sampled during release. This creates a spatial influence. In high purity metals, because damage is often linked to boundaries within the microstructure (grain or twin), changing the volume of material sampled during release, can have a drastic influence on dynamic damage evolution as the number of boundaries or defects sampled is altered. In this study, model-driven dynamic experiments have been conducted on eu with four different grain sizes to examine, for a given shockwave shape, how the spatial effect of boundary distribution influences dynamic damage evolution. Both two and three dimensional damage characterization techniques have been utilized. This study shows the critical influence of spatial effects, in this case boundary density, on dynamic damage evolution. As the boundary density decreases, the damage evolution transitions from nucleation controlled to growth controlled. It also shows that specific boundaries, those with high Schmid factor orientations on either side, maybe a necessary condition for void formation.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Impact of Materials Processing on Microstructural Evolution and Hydrogen Isotope Storage Properties of Pd-Rh Alloy Powders.

Cryomilled Pd - 10Rh was investiga ted as potential solid - state storage material of hydrogen. Pd - 10Rh was first atomized, and then subsequently cryomilled. The cryomilled Pd - 10Rh was then examined using microstructural characterization techniques including op tical microscopy, electron microscopy, and X - ray diffraction. Pd - 10Rh particles were significantly flattened, increasing the apparent surface area. Microstructural refinement was observed in the cryomilled Pd - 10Rh, generating grains at the nanom etric scale through dislocation - based activity. Hydrogen sorption properties were also characterized, generating both capacity as well as kinetics measurements. It was found that the microstructural refinement due to cryomilling did not play a significant role on hyd rogen sorption properties until the smallest grain size (on the order of %7E25 nm) was achieved. Additionally, the increased surface area and other changes in particle morphology were associated with cryomilling changed the kinetics of hydrogen absorption.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Chemical, Molecular, and Microstructural Evolution of Kerogen during Thermal Maturation: Case Study from the Woodford Shale of Oklahoma

Integrated elemental, spectroscopic (infrared spectroscopy and X-ray absorption near-edge structure), and gas intrusion (helium pycnometry and nitrogen adsorption) analyses are used to characterize the bulk chemical, molecular, and physical microstructures of kerogen spanning a thermal maturity transect (vitrinite reflectance, Ro, from 0.5% to 2.6%) across the Woodford Shale of the Anadarko Basin, Oklahoma. The integration takes advantage of novel procedures to prepare kerogen isolates that preserve both the chemical and physical properties of the organic matter in the bulk shale. The Woodford kerogens follow the expected trends in H/C and O/C coordinates during thermal maturation for type II kerogen. Infrared spectra show that loss of hydrogen from kerogen is related to cracking of hydrogen-rich aliphatic (alkyl) carbon structures from aromatic carbons. Within the range of Ro values < 1.5%, peripheral aromatic carbons remain highly substituted with alkyl (methyl and methylene) and probably heteroatom functional groups. At Ro values > 1.5%, these substitutions are substantially removed and replaced by hydrogen. The evolution of carbon structures inferred from the IR spectra is supported by known carbon bond dissociation energies for carbonaceous materials. Total organic sulfur and sulfur-XANES data show that sulfur in Woodford kerogens is dominated by aromatic sulfur (thiophene) and that reactive, aliphatic sulfur (sulfide) is eliminated at low degrees of thermal stress (Ro ≤ 0.9%). At higher thermal stress, sulfur speciation is stable and dominated by thermally stable thiophene. The physical properties of Woodford kerogens evolve during thermal maturation in a manner consistent with their molecular characteristics. Skeletal density of kerogen increases during maturation in a manner that is linearly correlated to its atomic H/C ratio and inferred aromatic carbon content. The specific surface area of kerogen also increases during maturation, reflecting the development of internal pores within the kerogen skeletal framework as aliphatic carbon structures are preferentially cracked and expelled from solid kerogen. The quantitative chemical and structural changes expressed by the Woodford kerogens during thermal maturation, including their hydrogen and carbon content, carbon speciation, and skeletal density, are shown by comparison to not be measurably different for other type II kerogens from numerous oil- and gas-producing shale plays, indicating that thermal stress acts to drive maturation of type II kerogen in a similar way globally.

58 GEOSCIENCES↗
DOE OSTI2019

Microstructure Evolution and Improved Creep Behavior of Mg-Al-Si Alloy Matrix Composite Reinforced with SiC Nanoparticles

The Mg-9Al-1Si matrix composite reinforced with SiC nanoparticles is fabricated by semisolid stirring-assisted ultrasonic vibration, which contains finer grains and a more uniform microstructure compared to that of the Mg-9Al-1Si alloys. The sizes of the Mg{sub 17}Al{sub 12} and Mg{sub 2}Si phases decreased continuously as the volume fraction of n-SiCp increased from 0 to 1% and then increased apparently when the volume fraction of n-SiCp increased to 1.5%. The steady-creep rates of the 1 vol.% n-SiCp/Mg-9Al-1Si are approximately two times lower than those of the Mg-9Al-1Si matrix alloy at 200 °C under applied stress of 70 MPa due to the strengthening effect of the nanosized SiCp. The reason for the improved creep properties is mainly attributed to the obvious grain boundary strengthening, the Orowan strengthening mechanism, the load transfer effect, and the pinning effect of the n-SiCp and the refined Mg{sub 17}Al{sub 12} and Mg{sub 2}Si phases.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Dynamic recrystallization kinetics and microstructure evolution of an AZ91D magnesium alloy during hot compression

Highlights: • DRX kinetic model is developed for the aged AZ91D magnesium alloy. • The DRX behavior in different strained regions was investigated. • Four morphologies of the second phase were proposed during the hot compression tests. • The nucleation mechanisms of the DRX grains were clarified. - Abstract: The flow behavior of as-cast AZ91D magnesium alloy was evaluated by isothermal compression tests within the temperatures of 220 °C, 260 °C, 300 °C, 340 °C, and 380 °C, and the strain rates of 0.001, 0.01, 0.1, 1 and 10s{sup −1}. Based on the stress-strain curve and hyperbolic sine function, the thermal activation energy and the strain rate sensitivity of the material were determined to be 142.2726 kJ·mol{sup −1} and 0.142, respectively. The S type evolution of the dynamic recrystallization with the increasing strain that dynamic recrystallization (DRX) model obtained from stress and strain data. There was a good consistency between the proposed DRX kinetics model and microstructure observation results. Combining isothermal compression specimens with finite element and scanning electron microscopy (SEM) analysis indicated that the sample can be divided into rarely recrystallized region, partially recrystallized region and completely recrystallized region, which falls within the dense deformation zone, free deformation zone and severe deformation zone, respectively. The different forms of the β-Mg{sub 17}Al{sub 12} phase induced by compression tests were confirmed by SEM. Nucleation mechanisms of the DRX were discussed with reference to the transmission electron microscope (TEM) analysis results.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Elevated temperature microstructure evolution of a medium-entropy CrCoNi superalloy containing Al,Ti

A new medium-entropy superalloy was produced based on the compositions of equiatomic CrCoNi and Ni-base superalloy Inconel 740H. Initial alloy design was performed using Thermo-Calc. The aging response and microstructural stability were assessed following heat treatment at temperatures between 600 and 900 °C and durations up to 100 h. Aging from a fully recrystallized state resulted in negligible grain growth and produced γ’ and σ phases. The same phases were present after aging from a cold-rolled state, but partially recrystallized microstructures resulted in multi-modal size distributions and heterogeneous spatial arrangements. Finally, room temperature hardness measurements were used to correlate aging conditions with quantitative precipitate measurements and mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure Evolution of Ultra-Fine-Grained AZ31 B Magnesium Alloy Produced by Submerged Friction Stir Processing

Ten-millimeter-thick strain-hardened AZ31B-H24 magnesium sheets were subjected to friction stir processing (FSP) in air and submerged friction stir processing (SFSP) under water to investigate their microstructures and microhardness properties. Different rotational speeds of 500, 630, 800, and 1000 rpm and traverse speeds of 50, 100, 200, and 350 mm/min were employed for processing the materials. For SFSPed samples, the rotational speed of 500 rpm and 200 mm/min of traverse speed resulted in an ultra-fine-grained structure with a minimum grain size of about 400-500 nm, which is half compared to that of FSPed. It was found that both processes led to variation of crystallographic orientation, and enhancing the rotational speed and lowering the traverse speed promoted the development of a {0002} basal texture. The microhardness of SFSPed material increased significantly up to 110% (~ 95 Hv), while the microhardness was 45% (~ 65 Hv) higher than the base metal (~ 45 Hv) for FSPed material.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Microstructural evolution during solution treatment of Co-Cr-Mo-C biocompatible alloys

Three different Co-Cr-Mo-C alloys conforming to ASTM F75 standard were poured in an industrial environment and subjected to a conventional solution treatment at 1225 Degree-Sign C for several time intervals. The microstructural changes and transformations were studied in each case in order to evaluate the way in which treatment time influences the secondary phase fraction and clarify the microstructural changes that could occur. To assess how treatment time affects microstructure, optical microscopy and image analyzer software, scanning electron microscopy and energy dispersion spectrometry analysis were employed. The main phases detected in the as-cast state were: {sigma}-phase, M{sub 6}C, and M{sub 23}C{sub 6} carbides. The latter presented two different morphologies, blocky type and lamellar type. Despite being considered the most detrimental feature to mechanical properties, {sigma}-phase and lamellar carbides dissolution took place in the early stages of solution treatment. M{sub 23}C{sub 6} carbides featured two different behaviors. In the alloy obtained by melting an appropriate quantity of alloyed commercial materials, a decrease in size, spheroidization and transformation into M{sub 6}C carbides were simultaneously observed. In the commercial ASTM F75 alloy, in turn, despite being the same phase, only a marked decrease in precipitates size was noticed. These different behaviors could be ascribed to the initial presence of other phases in the alloy obtained from alloyed materials, such as {sigma}-phase and 'pearlitic' carbides, or to the initial precipitate size which was much larger in the first than in the commercial ASTM F75 alloy studied. M{sub 6}C carbides dissolved directly in the matrix as they could not be detected in samples solution-treated for 15 min. - Highlights: Black-Right-Pointing-Pointer Three different Co-Cr-Mo alloys were poured under an industrial environment. Black-Right-Pointing-Pointer Transformation of existing phases followed during conventional solution treatment. Black-Right-Pointing-Pointer In as-cast/treated samples, phases were identified by color metallography, SEM and EDS. Black-Right-Pointing-Pointer M{sub 23}C{sub 6} {yields} M{sub 6}C transformation was corroborated by SEM and EDS analysis. Black-Right-Pointing-Pointer Carbide spheroidization was also detected prior a noticeably carbide size decreasing.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of rapid heating and cooling combined with deformation at ultrahigh strain rates on the microstructure evolution of pure titanium shaped charge liner

Highlights: • A slug prepared from pure titanium SCL was recovered after detonation deformation at an ultrahigh strain rate over 10{sup 5} s{sup −1}. • The α → β → α phase transformation occurred in Ti SCL during the ultrahigh-strain -rate deformation. • The microstructures of the recovered slug included lamellar α grains, equiaxed α grains, and jagged α grains. - Abstract: A slug prepared from pure titanium shaped charge liners was recovered after detonation deformation at an ultrahigh strain rate over 10{sup 5} s{sup −1} and high strain over 500%. Optical microscopy, electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM) were employed to investigate the microstructure of the Ti shaped charged liner before and after the detonation deformation. The microstructures of the recovered slug include lamellar α grains, equiaxed α grains within localized shear bands, and jagged α grains. EBSD results indicated that the grain orientation distribution is random and no texture was observed in the slug. TEM observation revealed that the α → β → α phase transformation occurred owing to the rapid heating and cooling combined with deformation at ultrahigh strain rates in the Ti shaped charge liner. No melting phenomenon was observed during the deformation process. The deformation process consisted of the explosive detonation stage combined with rapid heating and the subsequent penetration stage combined with rapid cooling. In the explosive detonation stage, the α → β phase transformation instantaneously occurred via a martensitic mechanism. In the penetration stage, the high-temperature slug in β state was cooled rapidly and showed different deformation behaviors in three different areas.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Microstructural evolution during transient liquid phase bonding of Inconel 738LC using AMS 4777 filler alloy

IN-738LC nickel-based superalloy was joined by transient liquid phase diffusion bonding using AMS 4777 filler alloy. The bonding process was carried out at 1050 Degree-Sign C under vacuum atmosphere for various hold times. Microstructures of the joints were studied by optical and scanning electron microscopy. Continuous centerline eutectic phases, characterized as nickel-rich boride, chromium-rich boride and nickel-rich silicide were observed at the bonds with incomplete isothermal solidification. In addition to the centerline eutectic products, precipitation of boron-rich particles was observed in the diffusion affected zone. The results showed that, as the bonding time was increased to 75 min, the width of the eutectic zone was completely removed and the joint was isothermally solidified. Homogenization of isothermally solidified joints at 1120 Degree-Sign C for 300 min resulted in the elimination of intermetallic phases formed at the diffusion affected zone and the formation of significant {gamma} Prime precipitates in the joint region. - Highlights: Black-Right-Pointing-Pointer TLP bonding of IN-738LC superalloy was performed using AMS 4777 filler alloy. Black-Right-Pointing-Pointer Insufficient diffusion time resulted in the formation of eutectic product. Black-Right-Pointing-Pointer Precipitation of B-rich particles was observed within the DAZ. Black-Right-Pointing-Pointer The extent of isothermal solidification increased with increasing holding time. Black-Right-Pointing-Pointer Homogenizing of joints resulted in the dissolution of DAZ intermetallics.

36 MATERIALS SCIENCE↗