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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Influence of the as-built microstructure on the recrystallization of an additively manufactured Inconel939 Ni-based superalloy

This study investigates the influence of the as-built microstructure on the recrystallization (RX) behavior and mechanical properties of the Ni-based superalloy Inconel 939 produced by laser powder bed fusion (PBF-LB/M). Two distinct as-built microstructures were obtained by varying the hatch distance (h d ): a columnar, strongly textured condition (h d =50, termed h d 50) and an equiaxed, weakly textured condition (h d =70, termed h d 70)). Both were subjected to nine solution treatments combining three temperatures (1100, 1150, and 1200 °C) and three holding times (1, 4, and 8 h). Comprehensive microstructural characterization was conducted to assess grain morphology, texture, grain boundary character, dislocation density, and precipitate distribution. Recrystallization was found to be significantly slower than in cast counterparts, requiring higher temperatures and longer times for completion. The initial microstructure plays a decisive role: full RX was achieved only in hd70 specimens after treatment at 1200 °C for 8 h, whereas hd50 samples exhibited delayed and incomplete RX under identical conditions. This behavior is attributed to the finer grain size and higher fraction of high-angle grain boundaries in hd70, which promote recrystallization. Mechanical testing revealed that hd70 samples subjected to a 1200 °C/8 h treatment followed by standard double ageing show higher yield and tensile strengths across the investigated temperature range than both printed and cast Inconel939 processed under conventional conditions, albeit with slightly reduced ductility. The enhanced mechanical performance is attributed to the larger grain size, which limits grain boundary sliding. These results demonstrate the critical importance of controlling the as-built microstructure and tailoring post-processing strategies to optimize high-temperature performance of PBF-LB/M Inconel939.

Inconel939↗
DOE OSTI2023

Role of geometric dynamic recrystallization in nanocrystalline alloys

Nanocrystalline and near-nano-grained metals are plagued with an overall lack of ductility and formability. This is in part due to their inability to support the dislocation mechanisms or undergo the same types of transformations that conventional coarse-grained metals access in order to increase their workability. Therefore, despite their advanced properties such as high strength, the manufacturing of such fine-grained metals, which exposes them to multi-axial states of stress in operations such as rolling, drawing, extrusion, forging, and bending, has not been possible. In this work, we address this limitation and highlight an important aspect of geometric dynamic recrystallization (GDRX) in nanocrystalline materials as a way to improve manufacturability. In particular, using two different alloy compositions and two different processing techniques, this study points to the fact that if nanocrystalline or near nano metals can be truly stabilized, they can repeatedly undergo the same types of processes that conventional coarse-grained metals endure, increasing both their formability and hence manufacturability. The results reveal that due to a large number of initial high-angle grain boundaries and large applied compressive strains, GDRX is activated in the absence of any discontinuous dynamic recrystallization (DDRX) or continuous dynamic recrystallization (CDRX). This is a unique aspect of stabilized nanocrystalline materials, as traditionally fine-grained metals are not microstructurally stable enough to accommodate such an event.

36 MATERIALS SCIENCE↗
DOE OSTI2023

3D mapping of residual stresses in growing grains of partially recrystallized Gum Metal

The crystallographic orientations and residual stresses within recrystallizing grains in partially recrystallized beta titanium-Gum Metal-were examined non-destructively in 3D using synchrotron Differential Aperture X-ray Microscopy. Contrary to common assumptions, significant local stresses and stress variations are observed within the recrystallizing grains. The results reveal that the development of these local residual stresses depends on the plastic deformation mode and material's elastic constants, rather than grain properties such as size and orientation, or even the material's yield stress. This work provides insights valuable for the design of advanced materials with heterogeneous microstructures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

High-Rate and Low-Temperature Fabrication of Cu(In,Ga)Se 2 Solar Cells Using AgBr Induced Recrystallization

We present results demonstrating a three-stage, high-rate, low-temperature deposition process for Cu(In,Ga)Se 2 solar cells including a recrystallization step after the second stage, catalyzed by AgBr. The entire deposition and recrystallization process takes place below 450 °C in less than 15 min. Device results with efficiencies exceeding 16% are shown. Here, we achieve very high levels of grain growth and a greater than a 5% absolute increase in device performance because of the recrystallization step relative to an identical process not involving AgBr.

14 SOLAR ENERGY↗
DOE OSTI2020

Rafting-Enabled Recovery Avoids Recrystallization in 3D-Printing-Repaired Single-Crystal Superalloys

The repair of damaged Ni-based superalloy single-crystal turbine blades has been a long-standing challenge. Additive manufacturing by an electron beam is promising to this end, but there is a formidable obstacle: either the residual stress and γ/γ' microstructure in the single-crystalline fusion zone after e-beam melting are unacceptable (e.g., prone to cracking), or, after solutionizing heat treatment, recrystallization occurs, bringing forth new grains that degrade the high-temperature creep properties. Here, a post-3D printing recovery protocol is designed that eliminates the driving force for recrystallization, namely, the stored energy associated with the high retained dislocation density, prior to standard solution treatment and aging. The post-electron-beam-melting, pre-solutionizing recovery via sub-solvus annealing is rendered possible by the rafting (i.e., directional coarsening) of γ' particles that facilitates dislocation rearrangement and annihilation. The rafted microstructure is removed in subsequent solution treatment, leaving behind a damage-free and residual-stress-free single crystal with uniform γ' precipitates indistinguishable from the rest of the turbine blade. Finally, this discovery offers a practical means to keep 3D-printed single crystals from cracking due to unrelieved residual stress, or stress-relieved but recrystallizing into a polycrystalline microstructure, paving the way for additive manufacturing to repair, restore, and reshape any superalloy single-crystal product.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A thermodynamic evaluation of metal halides for the recrystallization of Cu(In,Ga)Se 2

CdTe films are deposited at low temperatures and recrystallized to photovoltaic device quality using CdCl 2 treatments, leading to competitive manufacturing costs. Cu(In,Ga)Se 2 (CIGS) typically requires high-temperature, low-rate depositions to produce high-efficiency devices, resulting in higher costs. A similar metal halide treatment of CIGS has been demonstrated by us previously for some metal halide sources. To understand and optimize the process, a thermodynamic evaluation of candidate metal halides for such treatments is presented as a guide for their selection. By comparing bond dissociation energies, mono- and di-halide compounds are proposed to be ideal compounds to act as transport agents. Known recrystallization and temperature reduction benefits by Ag alloying suggests that Ag-halides should be used to aid transport of all species. The high vapor pressure and mobility of Ga compounds still poses a problem for metal halide treatment resulting in Ga etching and removal of intentional Ga gradients. Less severe but similar issues with In compounds may occur. As a result, Cu compounds have low vapor pressures which may limit transport, however, Cu is highly mobile in CIGS and recrystallization still occurs.

14 SOLAR ENERGY↗
DOE OSTI2025

High-pressure high-temperature melting and recrystallization of nanolamellar high-entropy alloys

Additively manufactured (AM) High Entropy Alloys (HEAs) are notable for their exceptional high-yield strength and large tensile ductility. The nanolamellar Eutectic HEA (EHEA) AlCoCrFeNi 2.1 was fabricated by laser powder bed fusion (L-PBF) in the as-printed form (EHEA1) and subsequently annealed at 1000oC (EHEA2) and 600oC (EHEA3) to achieve a broad range of mechanical properties. EHEA2 and EHEA3 samples were studied using Scanning transmission electron microscopy (STEM), energy dispersive X-ray diffraction (EDXRD) at high-pressures and high temperatures, nanoindentation hardness and modulus measurements. According to EDXRD EHEA2 and EHEA3 are composed of B2 and L1 2 phases. High-pressure high-temperature EDXRD studies show melting for EHEA2 at 1698 ± 25 K at a pressure of 6.5 GPa and melting for EHEA3 at 1598 ± 25 K at a pressure of 5.8 GPa. Post-melt and recrystallized samples were recovered at ambient conditions, and XRD analysis showed retention of B2 and L1 2 phases, although a new σ phase appeared for both EHEA2 and EHEA3 samples due to high-pressure and high-temperature melting and recrystallization experiment. SEM analysis also demonstrated the preservation of the nanolamellar morphology. Nanoindentation studies revealed that recrystallized EHEAs retain their original mechanical property hierarchy, with EHEA3 being 47% harder than EHEA2, largely related to higher content of B2-phase and retention of nanolamellar morphology. We also present Pressure-Volume-Temperature (P-V-T) data for 3-D printed and annealed eutectic high entropy alloys and extract mechanical and thermal properties data.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Depth-dependent recovery of thermal conductivity after recrystallization of amorphous silicon

The depth-dependent recovery of silicon thermal conductivity was achieved after the recrystallization of silicon that had been partially amorphized due to ion implantation. Transmission electron microscopy revealed nanoscale amorphous pockets throughout a structurally distorted band of crystalline material. The minimum thermal conductivity of as-implanted composite material was 2.46 W m −1 K −1 and was found to be uniform through the partially amorphized region. X-ray diffraction measurements reveal 60% strain recovery of the crystalline regions after annealing at 450 °C for 30 min and almost full strain recovery and complete recrystallization after annealing at 700 °C for 30 min. In addition to strain recovery, the amorphous band thickness reduced from 240 to 180 nm after the 450 °C step with nanoscale recrystallization within the amorphous band. A novel depth-dependent thermal conductivity measurement technique correlated thermal conductivity with the structural changes, where, upon annealing, the low thermal conductivity region decreases with the distorted layer thickness reduction and the transformed material shows bulk-like thermal conductivity. Full recovery of bulk-like thermal conductivity in silicon was achieved after annealing at 700 °C for 30 min. After the 700 °C anneal, extended defects remain at the implant projected range, but not elsewhere in the layer. Previous results showed that high point-defect density led to reduced thermal conductivity, but here, we show that point defects can either reform into the lattice or evolve into extended defects, such as dislocation loops, and these very localized, low-density defects do not have a significant deleterious impact on thermal conductivity in silicon.

Huynh, Kenny↗
DOE OSTI2024

Effect of Processing Parameters on Recrystallization During Hot Isostatic Pressing of Stellite-6 Fabricated Using Laser Powder Bed Fusion Technique

Crack-free Stellite-6 alloy was fabricated using the laser powder bed fusion technique equipped with a heating module as the first attempt. Single tracks were printed with a build plate heated to 400 °C to identify the processing window. Based on the melt pool dimensions, two combinations (sample A: 300 W/750 mm/s and sample B: 275 W/1000 mm/s) were identified to print the cubes. The as-printed microstructure comprised FCC-Co dendrites with M7C3 in the interdendritic region. W-rich M6C particles were found in the overlapping regions between the melt pools, matching the Scheil simulations. However, gas pores were observed due to the higher nitrogen and oxygen content of the feedstock requiring hot isostatic pressing (HIP) at 1250 °C and 150 MPa for 2 h. Sample A was partially recrystallized with slightly coarsened M7C3, while sample B underwent complete recrystallization followed by grain growth along with higher coarsening of the M7C3 after HIP. The varying recrystallization behavior can be attributed to the difference in residual stresses and grain aspect ratio in the as-built condition dictated by laser power and scanning speed. The microhardness after HIP was slightly higher than its wrought counterpart, indicating no severe impact of post-processing on the properties of Stellite-6 alloy.

Sridar, Soumya (ORCID:0000000306775408)↗
DOE OSTI2021

Dynamic recrystallization of a wrought magnesium alloy: Grain size and texture maps and their application for mechanical behavior predictions

Effect of dynamic recrystallization (DRX) on the grain refinement and texture modification was studied by conducting a series of hot compression on AZ31B Mg alloy. Processing-grain size-texture maps were established as a function of temperature, strain rate, strain, and the Zener-Hollomon parameter (Z). Moreover, influence of simultaneous changes in the grain size and texture on tensile yield strength and ductility of the hot-worked Mg alloy was studied using the grain size and texture maps established. The processing-grain size map showed that the DRX grain size decreased with the increase in Z, also revealing various characteristics ranging from a grain growth, grain refinement, to a bimodal distribution of ultrafine grains and partially recrystallized grains. The effect of twinning on the grain refinement was also evident at high Z conditions. The processing-texture map revealed that the initial fiber texture was altered significantly to a shear, off-normal, or extension-twin texture with the increase in Z. The Schmid-factor maps were calculated to identify a dominant deformation mode during a subsequent tensile deformation of the hot-worked samples. Finally, a corresponding Hall-Petch relationship for each dominant deformation mode was used to establish tensile yield-strength maps, which agree well with the measured data.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ice Recrystallization Inhibition Activity of Soy Protein Hydrolysates

Identifying and developing ice recrystallization inhibitors from sustainable food proteins such as soy protein isolate (SPI) can lead to practical applications in both pharmaceutical and food industries. Here, the objective of this study was to investigate the ice recrystallization inhibition (IRI) activity of SPI hydrolysates, and this was achieved by using an IRI activity-guided fractionation approach and relating IRI activity to interfacial molecular activity measured by vibrational sum frequency generation (VSFG). In addition, the impact of molecular weight (MW) and enzyme specificity was analyzed using three different proteases (Alcalase, trypsin, and pancreatin) and varying hydrolysis times. Using preparative chromatography, hydrolysates from each enzyme treatment were fractionated into five different MW fractions (F1–F5), which were then characterized by high-performance liquid chromatography (HPLC). All SPI hydrolysates had IRI activity, resulting in a 57–29% ice crystal diameter reduction when compared to native SPI. The F1 fraction (of 4–14 kDa) was most effective among all tested hydrolysates, while the lower MW peptide fractions lacked activity. One sample (SPI-ALC 20-F1) had a 52% reduction of ice crystal size at a lower concentration of 2% compared to the typical 4% used. SFG showed a difference in H-bonding and hydrophobic interactions of the molecules on the water/air interface, which may be linked to IRI activity. This study demonstrates for the first time the ability of SPI hydrolysates to inhibit ice crystal growth and the potential application of SFG to study molecular interaction at the interface that may help illustrate the mechanism of action.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Vapor Treatment and In-situ Recrystallization by Copper Chloride on Cu(In,Ga)Se 2 Thin Film

Deposition of CIGS semiconductor thin films was performed at low temperature and high rate by three-stage coevaporation process on molybdenum coated glass substrate. Here, a vapor treatment was done in between the second and third stage by flashing CuCl 2 for 5 mins at 400 °C. A large change in morphology and crystal structure was observed after the treatment. XRD and SEM showed that small grains transformed into large grains. A smoother Ga profile was observed by SIMS measurements for the treated films as compared to as-deposited films. Furthermore, the Na profile was also modified in the recrystallized samples, with a lower content after recrystallization.

14 SOLAR ENERGY↗
DOE OSTI2023

Post-growth Recrystallization by Halides for High Throughput CIGS Photovoltaics

The objective of this project in broad terms was to address the capital equipment expense associated with Cu(In,Ga)Se 2 (CIGS) as a material for photovoltaic devices. This project has demonstrated a new method for processing CIGS using metal halides to recrystallize and enhance the quality of the final materials. A wide spectrum of metal halides were examined. Of these Cu and In chlorides and AgBr were found to be most effective; and, of these, AgBr was found to produce exemplary results. Cu and In chlorides were found to produce undesirable changes in film composition. The project demonstrated over 16% efficiency in a CIGS device deposited at 10x the standard rate of ~1 μm/hr and with a >100°C reduction in maximum temperature to 450°C. The entire deposition of the absorber layer including the recrystallization step required only 15 minutes, which is a 4x decrease in processing time.

14 SOLAR ENERGY↗
DOE OSTI2024

Direct observation of annealing-driven recrystallization behavior in magnesium alloy at low strain condition

Grain-twin interactions are significant in texture modification under thermodynamic driving force. In this study, annealing-driven twinning/detwinning behavior, grain growth, and corresponding texture evolution in a pre-deformed AZ31 magnesium alloy were systematically tracked and investigated via in-situ heating synchrotron X-ray diffraction and quasi in-situ electron backscattered diffraction techniques. A twinning texture is generated in the pre-deformed sample due to the activation of {$10\bar{1}2$} tensile twinning. During annealing, dislocation annihilation occurs between 100 and 280 °C, and recrystallization occurs above 280 °C, manifesting as the initial residual matrix and twins being competitively swallowed by each other, forming a bimodal texture. The recrystallization process is completed by boundary movement, which depends on the energy difference across the boundary. In addition, it is found that the grain boundaries favor movement towards the side with higher stored energy, regardless of the boundary type or the boundary energy.

In-situ observation↗
DOE OSTI2020

Solid-State Recrystallization Pathways of Sodium Aluminate Hydroxy Hydrates

Crystallization of Al-bearing solid phases from highly alkaline Na 2 O:Al 2 O 3 :H 2 O solutions commonly necessitates an Al 3+ coordination change from tetrahedral to octahedral, but intermediate coordination states are often difficult to isolate. Here, a similar Al 3+ coordination change process is examined during the solid-state recrystallization of sodium oxohydroxoaluminate hydrate (MSA) to nonasodium bis(hexahydroxy aluminate) trihydroxide hexahydrate (NSA) at ambient temperature. While the MSA structure contains solely polymerized tetrahedral Al 3+ , the NSA structure is a molecular aluminate salt solely based upon monomeric octahedral Al 3+ . Spontaneous recrystallization of MSA and excess sodium hydroxide hydrate into NSA over 3 days of reaction time was clearly evident in X-ray diffractograms and in Raman spectra. In situ 27 Al multiple quantum MAS NMR spectroscopy showed no evidence of intermediate aluminates, suggesting that intermediates, such as pentacoordinate Al 3+ , are short-lived and require more highly time resolved spectroscopies to detect. Such research is advancing upon detailed mechanistic understanding of Al 3+ coordination change mechanisms in these highly alkaline systems, with relevance to aluminum refining, corrosion sciences, and nuclear waste processing.

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

3D In-situ Stop Action Study of Recrystallization in Additively Manufactured 316L Stainless Steel: Reconstruction Optimization and Observations

A volume of an additively manufactured 316L stainless steel sample has been tracked during its recrystallization using near-and far-field High Energy Diffraction Microscopy (HEDM) and absorption tomography at Advanced Photon Source beamline 1-ID. A nearfield compatible in situ furnace allows monitoring of Bragg diffraction signals as they evolve out of a weak and diffuse background while the sample temperature is approximate to 1250 degrees C. The sample is rapidly cooled to room temperature after observation of significant signal evolution and ti similar to 0.035 mm(3) is mapped by the near-field method. Four cycles of heat treatment follow the structure from a state of small, isolated grains through impingement of domains to near completion of recyrstallization. Here, the experiment and reconstructions are described, and recrystallized fractions, twin domains, and distributions of grain boundary types are discussed.

Liu, He↗
DOE OSTI2024

Influence of Nb alloying on Nb recrystallization and the upper critical field of Nb 3 ⁢Sn

Nb 3 Sn conductors are important candidates for high-field magnets for particle accelerators, and they continue to be widely used for many laboratory and NMR magnets. However, the critical current density, J c , of present Nb 3 Sn conductors declines swiftly above 12-15 T. State-of-the-art Ta- and Ti-doped strands exhibit upper critical field, H c2 , values of ~ 24-26.5 T (4.2 K) and do not reach the FCC target J c , which serves as the present stretch target for Nb 3 Sn development. As recently demonstrated, to meet this goal requires enhanced vortex pinning but an independent and supplementary approach is to significantly enhance H c2 . In this study, we have arc-melted multiple Nb alloys with added Hf, Zr, Ta and Ti and drawn them successfully into monofilament wires to investigate the possibilities of H c2 enhancement through alloying. H c2 (T) was measured for all samples in fields up to 16 T and some up to 31 T. We have found that all alloys show good agreement with the standard Werthamer, Helfand, and Hohenberg (WHH) fitting procedure without the need to adjust the paramagnetic limitation parameter (α) and spin-orbit scattering parameter (λ so ). The evaluation of dH c2 /dT near T c , which is proportional to the electronic specific heat coefficient γ and the normal state resistivity ρn, allows a better understanding of the induced disorder introduced by alloying in the A15 phase. So far, we have observed that Hf alloying of pure Nb can enhance H c2 (0) by 3-4 T to ~28 T, while adding just 1 at. %Hf or Zr into a Nb4Ta base alloy can raise H c2 (0) to ~31 T. Very importantly we find that Hf and Zr raise the alloy recrystallization temperature above the usual A15 reaction temperature range of 650°C – 750°C, thus ensuring denser A15 phase nucleation in the Nb alloy grain boundaries, possibly leading to a more homogeneous A15 phase Sn content and refined A15 grain size. Furthermore, the potential for further advancements in Nb 3 Sn properties is explored in relation to the recrystallization of the Nb alloy and the factors controlling the upper critical field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Unveiling the Interplay: Cold Work, Recrystallization, and Flux Expulsion in SRF Cavities

The fabrication of SRF cavities from sheet materials includes deep-drawing, electron beam welding, chemical and mechanical polishing, high-temperature heat treatment, and material diffusion. The performance of these cavities is frequently limited by magnetic flux trapping giving rise to additional rf loss. In this presentation, we thoroughly examine how recrystallization influences flux expulsion in SRF cavities, using cold-worked niobium sheets from various suppliers. Our findings reveal that cold-worked sheets enhance flux expulsion, especially at lower heat treatment temperatures, by promoting improved recrystallization. In particular, a traditionally fabricated Nb cavity half-cell from an annealed poly-crystalline Nb sheet after an 800 C heat treatment leads to a bi-modal microstructure that ties in with flux trapping and inefficient flux expulsion. This non-uniform microstructure is related to varying strain profiles along the cavity shape. A novel approach to prevent this non-uniform microstructure is presented by fabricating a 1.3 GHz single cell Nb cavities with a cold-worked sheet and subsequent heat treatment leading to better flux expulsion after 800 C/3h

Dhakal, P. [Old Dominion Univ., Norfolk, VA (Unite↗