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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

High-Speed Friction-Stir Welding To Enable Aluminum Tailor-Welded Blanks

Current joining technologies for automotive aluminum alloys are utilized in low-volume and niche applications, and have yet to be scaled for the high-volume vehicle market. This study targeted further weight reduction, part reduction, and cost savings by enabling tailor-welded blank technology for aluminum alloys at high-volumes. While friction stir welding has been traditionally applied at linear velocities less than one meter per minute, high volume production applications demand the process be extended to higher velocities more amenable to cost sensitive production environments. Unfortunately, weld parameters and performance developed and characterized at low to moderate welding velocities do not directly translate to high speed linear friction stir welding. Therefore, in order to facilitate production of high volume aluminum welded components, parameters were developed with a minimum welding velocity of three meters per minute. With an emphasis on weld quality, welded blanks were evaluated for post-weld formability utilizing a combination of numerical and experimental methods. Evaluation across scales was ultimately validated by stamping full-size production door inner panels made from dissimilar thickness aluminum tailor-welded blanks, which provided validation of the numerical and experimental analysis of laboratory scale tests.

aluminum↗
DOE OSTI2024

Impact of Backing Plate and Thermal Boundary Conditions for High-Speed Friction Stir Welding of 25-mm Thick Aluminum Alloy 7175-T79

Here this study demonstrates high-speed (150 mm/min) single pass friction stir butt joining of 25 mm thick aluminum alloy 7175-T79. To understand the impact of quenching and cooling rate on process responses, joint strength, and grain size distributions across the weld thickness, we performed a series of friction stir welding (FSW) trials in air and with a trailing water spray using steel and composite backing plates (BP). Welds made in air and trailing water spray exhibit significantly different hardness distributions across the nugget, heat affected zone (HAZ), and HAZ minimum hardness as evidenced by detailed microhardness mapping. The effect of trailing water spray (TWS) on joint efficiency overshadows the influence of BP composition due to the vastly different contribution to quenching. TWS also resulted in a multifaceted effect on FSW such as lowering processing temperature, increasing X and Z forces while lowering Y force, and narrow heat affecting zone. Finally, digital image correlation (DIC)-based fracture mode analysis and grain size measurements correlate with the hardness distribution.

42 ENGINEERING↗
DOE OSTI2026

Quantitative characterization of gradient microstructures: A study on friction stir spot processing of pure cobalt

Heterogeneous microstructures in polycrystalline metals can enhance the strength and ductility, outperforming homogeneous structures of similar composition. This study investigates deformed cobalt via friction stir spot processing with varying dwell times to uncover the effects of plastic deformation and heat generation on the formation of morphological, phase, and grain boundary character gradients. A new approach to quantify the morphological gradients in materials, which describes grain morphology in terms of density followed by parametric regression, enables direct quantification of processing depth and gradient sharpness. Results show that longer processing times increase the steepness of morphological gradients and reduce the deformation depth for friction stir spot processing with low plunge depths and high tool rotational speeds. The amount of retained FCC is increased in the shorter processing conditions, primarily due to refined grain size, increased defect content, and reduced heat generation. Crystallographic texture analysis of the HCP phase indicated a dominant B-fiber described by (0001) ∥ shear plane normal in the extreme processing conditions and the formation of a P-fiber, shear direction ∥ ⟨11$\bar2$0⟩ for intermediate dwell times. The texture of the FCC phase for low processing times was a C texture {100}⟨011⟩ where longer processing times were dominated by a [001] fiber texture with a main {110}⟨100⟩ orientation and emergence of a slight [111] fiber in the longest processing condition. The approaches outlined in this work give insight into quantifying gradients and improve the understanding of highly deformed cobalt.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Characterization of microstructure and residual stress following the friction stir welding of dissimilar aluminum alloys

Friction-stir-welding (FSW) has gained importance as an effective way to join dissimilar materials due to its solid-state nature. However, FSW produces substantial residual stresses in aluminum welding, often deteriorating the component's structural performance and reliability. In the current study, the d-spacing (inter-atomic distance) of several locations on a battery tray and stress-free reference samples are measured with neutron diffraction to calculate the residual stresses in a lap 6061 to A365 dissimilar friction-stir-weld. Furthermore, the present study connects the measured residual stress to microstructure properties through electron backscatter diffraction (EBSD) and optical microscopy analyses. The EBSD results indicate that the FSW operation affects the grains’ orientation, thereby producing location-specific directionally varying elasticity across the weldment. Further, this varied elasticity creates unique d-spacing profiles even in the stress-free material. Additionally, the resulting stressed and stress-free d-spacing profiles show dependencies on the FSW tool geometry, traverse direction, and rotational direction. Lastly, this study suggests that the final component residual stress can be influenced by the sequence of multi-pass welds contributing to a rise in temperature in the presence of a completed weld relaxing its residual stress.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Coulombic friction in metamaterials to dissipate mechanical energy

Product designs from a wide range of industries such as aerospace, automotive, biomedical, and others can benefit from new metamaterials for mechanical energy dissipation. In this study, we explore a novel new class of metamaterials with unit cells that absorb energy via sliding Coulombic friction. Remarkably, even materials such as metals and ceramics, which typically have no intrinsic reversible energy dissipation, can be architected to provide dissipation akin to elastomers. The concept is demonstrated at different scales (centimeter to micrometer), with different materials (metal and polymer), and in different operating environments (high and low temperatures), all showing substantial dissipative improvements over conventional non-contacting lattice unit cells. Further, as with other ‘programmable’ metamaterials, the degree of Coulombic absorption can be tailored for a given application. Additionally, an analytic expression is derived to allow rapid first-order optimization. This new class of Coulombic friction energy absorbers can apply broadly to many industrial sectors such as transportation (e.g. monolithic shock absorbers), biomedical (e.g. prosthetics), athletic equipment (e.g. skis, bicycles, etc.), defense (e.g. vibration tolerant structures), and energy (e.g. survivable electrical grid components).

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effect of die design on microstructure and mechanical joint strength in friction self-piercing riveted AA7055-T76 and AA7055-T76

In the present study, a unique friction self-piercing riveting (F-SPR) was applied to join high-strength, low-ductility aluminum alloy (AA) 7055-T76 and AA7055-T76 to mitigate a cracking issue. Also, the effect of die design on both joint formation and the mechanical joint performance were investigated. A crack-free joint was achieved when joining AA7055-T76 and AA7055-T76 by F-SPR. As the bottom diameter of the die increased, the mechanical interlocking distance initially increased then became almost saturated. At the same time, the solid-state bonding gradually disappeared, and the lap-shear fracture changed from bottom aluminum fracture to rivet pull-out with partial bottom aluminum fracture. The average maximum lap-shear joint strength of 11.57 kN and cross tension of 5.65 kN were achieved from the D2 die design owing to the combined contributions from high mechanical interlocking distance and good solid-state bonding at the joint interface. Ultrafine grain refinement was observed at the region next to the rivet shank outer surface and along the materials flow line between the top and bottom aluminum sheet in the rivet cavity. Further, because of the same joint-process parameters, the hardness profile at the joints made by different dies did not show obvious differences. As the distance from the base metal to the rivet outer surface decreased, frictional heat caused the hardness to initially decrease from 190 to 150 HV in the heat-affected zone. Hardness increased up to 175 HV in the thermomechanical affected zone (TMAZ-I) owing to large plastic deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effects of process parameters on friction self-piercing riveting of dissimilar materials

In the present work, a recently developed solid state joining technique, Friction self-piercing riveting (F-SPR), has been applied for joining high strength aluminum alloy AA7075-T6 to magnesium alloy AZ31B. The process was performed on a specially designed machine where the spindle can achieve the motion of sudden stop. Effects of rivet rotating rate and punch speed on axial plunge force, torque, joint microstructure and quality have been analyzed systematically. During F-SPR, higher rotating rate and slower punch speed can reduce axial force and torque, which correspondingly results in a slightly smaller interlock between rivet leg and joined materials. Improved local flowability of both aluminum and magnesium alloys under a higher rotating speed results in a thicker aluminum layer surrounding the rivet leg, where formation of Al-Mg intermetallics was observed. Equivalent joint strength obtained in this study are higher than the yield strength of the AZ31 Mg alloy. One of the tensile failure modes is the rivet fracture, which is due to local softening of rivet leg from frictional heat. Lastly, other two failure modes include rivet pullout and shear through of bottom sheet.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effect of friction stir welding and post-weld heat treatment on a nanostructured ferritic alloy

Nanostructured ferritic alloys (NFAs) are new generation materials for use in high temperature energy systems, such as nuclear fission or fusion reactors. However, joining these materials is a concern, as their unique microstructure is destroyed by traditional liquid-state welding methods. The microstructural evolution of a friction stir welded 14YWT NFA was investigated by atom probe tomography, before and after a post-weld heat treatment (PWHT) at 1123K. The particle size, number density, elemental composition, and morphology of the titanium-yttrium-oxygenenriched nanoclusters (NCs) in the stir and thermally-affected zones were studied and compared with the base metal. No statistical difference in the size of the NCs was observed in any of these conditions. After the PWHT, increases in the number density and the oxygen enrichment in the NCs were observed. Therefore, these new results provide additional supporting evidence that friction stir welding appears to be a viable joining technique for NFAs, as the microstructural parameters of the NCs are not strongly affected, in contrast to traditional welding techniques.

36 MATERIALS SCIENCE↗
DOE OSTI2022

No ball milling needed: Alternative ODS steel manufacturing with gas atomization reaction synthesis (GARS) and friction-based processing

Oxide dispersion strengthened (ODS) steels are promising structural materials for future fusion reactors. The high-density (~10 23 /m 3 ) of highly stable Y-(Ti)-O nano-oxides provide high sink strength for radiation resistance and high-temperature (> 650 °C) creep strength. Concomitantly, helium management is enabled by trapping high density (~10 23 /m 3 ) of small (< 3 nm) helium bubbles in the vicinity of nano-oxides. However, conventional route of making ODS steels involves prolonged ball milling, canning, degassing, and laborious thermo-mechanical processing (TMP). Such route, especially the batch-by-batch ball milling step, faces persistent challenge with scalability and high costs. Gas atomization reaction synthesis (GARS) method has demonstrated the potential of making precursor ODS steel powders without ball milling, but the nano-oxide density was around 10 21 /m 3 in the final consolidated form by conventional TMP. Taking advantage of GARS precursor powder, we use friction-based processing, including friction consolidation and extrusion, to manufacture ODS steel with further improved nano-oxide characteristics. Here, preliminary results showed that Y/Ti/O species were intimately mixed and rapidly reacted to form nano-oxides with a number density of ~10 22 /m 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2023

High performance aluminum-air flow batteries through double-face architecture and laser-modified and friction-stir processed 3D anode

Aluminum-air batteries (AAB) are regarded as one of the most promising beyond-lithium high-energy-density storage candidates. Here, this paper introduces a three-dimensional (3D) Al 7075 anode enabled by femtosecond laser and friction-stir process which, along with a special double-face anode architecture provides world-class performance. Electrochemical characterizations prove that the corrosion resistance of the modified 3D Al 7075 FSP anode was enhanced, and electrochemically active surface area (ECSA) was increased compared with that of normal Al 7075 anode. Friction-stir processing reduced the mean grain size from 30 μm to 3 μm. The discharge performance of 3D Al 7075 FSP anode is shown to be quite stable, and the average values of energy density are significantly increased from 2256 mWh g –1 to 2941 mWh g –1 at 100 mA cm –2 . In a double-face flowing Al-air battery system, the 3D Al 7075 FSP anode exhibited significantly better electrocatalytic performance (discharge voltage of 0.76 V at 400 mA cm –2 , and power density of 337.8 mW cm –2 ) than that of a commercial Al 7075 anode.

25 ENERGY STORAGE↗
DOE OSTI2015

Friction stir welding joint of dissimilar materials between AZ31B magnesium and 6061 aluminum alloys: Microstructure studies and mechanical characterizations

Friction stir welding is an efficient manufacturing method for joining dissimilar alloys, which can dramatically reduce grain sizes and offer high mechanical joint efficiency. Lap FSW joints between dissimilar AZ31B and Al 6061 alloy sheets were made at various tool rotation and travel speeds. Rotation and travel speeds varied between 560–1400 r/min and 16–40 mm/min respectively, where the ratio between these parameters was such that nearly constant pitch distances were applied during welding. X-ray diffraction pattern (XRD), optical microscopy images (OM), electron probe microanalysis (EPMA) and scanning electron microscopy equipped with an energy-dispersive X-ray spectroscopy (SEM-EDS) were used to investigate the microstructures of the joints welded. Intermetallic phases including Al{sub 12}Mg{sub 17} (γ) and Al{sub 3}Mg{sub 2} (β) were detected in the weld zone (WZ). For different tool rotation speeds, the morphology of the microstructure in the stir zone changed significantly with travel speed. Lap shear tensile test results indicated that by simultaneously increasing the tool rotation and travel speeds to 1400 r/min and 40 mm/min, the joint tensile strength and ductility reached a maximum. Microhardness measurements and tensile stress–strain curves indicated that mechanical properties were affected by FSW parameters and mainly depended on the formation of intermetallic compounds in the weld zone. In addition, a debonding failure mode in the Al/Mg dissimilar weld nugget was investigated by SEM and surface fracture studies indicated that the presence of intermetallic compounds in the weld zone controlled the failure mode. XRD analysis of the fracture surface indicated the presence of brittle intermetallic compounds including Al{sub 12}Mg{sub 17} (γ) and Al{sub 3}Mg{sub 2} (β). - Highlights: • Dissimilar Al/Mg joint was obtained by lap friction stir welding technique. • Effect of rotation and travel speeds on the formation of intermetallic compounds • Microstructure and chemical studies including metallography, XRD, SEM-EDS, and EPMA • Mechanical property tests such as stress–strain curves, failure load and hardness • IMCs as Al{sub 3}Mg{sub 2} and Al{sub 12}Mg{sub 17} were identified in weld nugget and at Al/Mg interface.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Interfacial microstructure and properties of copper clad steel produced using friction stir welding versus gas metal arc welding

A preliminary study compares the feasibility and microstructures of pure copper claddings produced on a pressure vessel A516 Gr. 70 steel plate, using friction stir welding versus gas metal arc welding. A combination of optical and scanning electron microscopy is used to characterize the grain structures in both the copper cladding and heat affected zone in the steel near the fusion line. The friction stir welding technique produces copper cladding with a grain size of around 25 μm, and no evidence of liquid copper penetration into the steel. The gas metal arc welding of copper cladding exhibits grain sizes over 1 mm, and with surface microcracks as well as penetration of liquid copper up to 50 μm into the steel substrate. Transmission electron microscopy reveals that metallurgical bonding is produced in both processes. Increased diffusion of Mn and Si into the copper cladding occurs when using gas metal arc welding, although some nano-pores were detected in the FSW joint interface. - Highlights: • Cladding of steel with pure copper is possible using either FSW or GMAW. • The FSW yielded a finer grain structure in the copper, with no evidence of cracking. • The FSW joint contains some evidence of nano-pores at the interface of the steel/copper. • Copper cladding by GMAW contained surface cracks attributed to high thermal stresses. • The steel adjacent to the fusion line maintained a hardness value below 248 HV.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructure and wear characterization of aluminum matrix composites reinforced with industrial waste fly ash particulates synthesized by friction stir processing

Fly ash (FA) is a waste product of coal combustion in thermal power plants which is available in massive quantities all over the world causing land pollution. This paper reports the characterization of AA6061 aluminum matrix composites (AMCs) reinforced with FA particles synthesized using friction stir processing (FSP). The volume fraction of FA particles was varied from 0 to 18 in steps of 6. The prepared AMCs were characterized using optical microscopy (OM), scanning electron microscopy (SEM) and electron backscattered diagram (EBSD). The wear rate was estimated using a pin-on-disc wear apparatus. FA particles were observed to be distributed homogeneously in the AMC irrespective of the location within the stir zone. The EBSD micrographs revealed remarkable grain refinement in the AMC. The incorporation of FA particles enhanced the microhardness and wear resistance of the AMC. The strengthening mechanisms of the AMC were discussed and correlated to the observed microstructures. The wear mechanisms were identified by characterizing the wear debris and worn surfaces. - Highlights: •Industrial waste fly ash was used to produce aluminum matrix composites. •Friction stir processing was used to produce AA6061/Fly Ash composite. •Fly ash particles refined the grains of aluminum matrix. •Fly ash particles enhanced the hardness and wear resistance. •Successful utilization of fly ash to make aluminum composites reduces land pollution.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructure, texture, and mechanical properties of friction stir welded commercial brass alloy

Microstructural evolution during friction stir welding of single-phase brass and corresponding mechanical properties were investigated. For this purpose, 2 mm thick brass plate was friction stir welded at a rotational speed of 450 rpm and traverse speed of 100 mm/min. The microstructure of the joint was studied using optical microscopy, scanning electron microscopy equipped with electron back scattered diffraction system, and scanning transmission electron microscopy. The mechanical properties were measured using hardness and tensile tests. The formation of subgrains and their transformation into new grains in conjunction with existence of A{sub 1}{sup ⁎}, A{sub 2}{sup ⁎} and C texture components revealed that the continuous dynamic recrystallization plays a dominant role in the microstructural evolution. However, grain boundary bulging, along with the formation of twin boundaries, and presence of the G texture component showed that the discontinues dynamic recrystallization may participate in the new grain formation. Furthermore, the different strengthening mechanisms, which caused the higher strength of the joint, were discussed. - Highlights: •Microstructural evolution during FSW of a single phase brass was investigated. •CDRX and DDRX were the main mechanisms of the grain structure formation during FSW. •GDRX and SRX were not contributed in grain structure formation. •The lamellas TBs were formed in the SZ of the joints. •Grain boundary, dislocation, and texture effects resulted in higher strength.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Microstructural variation through weld thickness and mechanical properties of peened friction stir welded 6061 aluminum alloy joints

The current study examined the effect of microstructure variation on the development of mechanical properties in friction stir welded joints of 6061-T6 aluminum alloy, which were subsequently processed by shot peening (SP). Following to FSW, fatigue specimens were extracted perpendicularly to the welding direction. Surface Skimming to 0.5 mm from crown and root sides of the joint was made and SP was later applied on the two sides using ceramic shots of two different Almen intensities of 0.18 mmA and 0.24 mmA. Microstructural examination by electron back scattered diffraction (EBSD) indicated variation in the grain refinement of the weld zone, with coarsest grains (5 μm) at the crown side and finest grains (2 μm) at the root side. Reduction of microhardness to 60 HV occurred in the weld zone for samples in FSW condition. Application of SP promoted significant strain hardening at the crown side, with Almen intensities of 0.24 mmA providing maximum increase in microhardness to 120 HV. On the contrary, only a maximum microhardness of 75 HV was obtained at the root side. The difference in strain hardening capability at the two sides was strongly dependent on grain size. The two Almen intensities produced similar distribution of compressive residual stresses in the subsurface regions that led to enhance the fatigue strength to the level of base metal for N ≥ 10{sup 5} cycles. Yet, the increase in fatigue strength was more pronounced with increasing Almen intensity to 0.24 mmA, demonstrating further enhancement by strain hardening. - Highlights: • Grain refinement was observed after friction stir welding of AA 6061-T6. • Reduction in microhardness and fatigue strength were obtained after welding. • Variation in grain refinement led to different hardening behavior after peening. • Shot peening induced beneficial compressive residual stresses. • Shot peening and surface skimming markedly improved the fatigue performance.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ultrafine grained structure and improved mechanical properties of low temperature friction stir spot welded 6061-T6 Al alloys

Highlights: • Friction stir spot welding of Al alloy was successfully done at low rotation speed. • The highest welding temperature was lower than 200 °C. • The average grain size of less than 500 nm was formed in the stir zone. • No hardness reduction of the HAZ region could be detected. • Shear tensile tests of the welds revealed a maximum shear load of about 5400 N. - Abstract: In this study, 1 mm thick 6061-T6 aluminum alloy plates were subjected to friction stir spot welding (FSSW) at a very low rotation speed of 30, 40 and 50 rpm, aiming to prevent the hardness reduction in the heat affected zone (HAZ) of this precipitate hardening Al joints. Two kinds of rotating tools, namely, one with a 1 mm long probe and the other one with a flat shoulder without a probe, were used and the corresponding force applied to the rotating tools was ranged from 4 to 8 tons. Under this special welding condition, the highest welding temperature was measured lower than 200 °C. As a result, no hardness reduction of the HAZ region could be detected and an ultrafine grain structure with a high density of dislocations was formed in the stir zone. The average grain size obtained in the stir zone was less than 500 nm for all the welds, which was much smaller than that in conventional FSSW processed 6061-T6 Al joints. In addition, no hook-like bonding ligaments were formed in the joints due to the very different material flows and the shear tensile tests showed that the spot welds prepared by the low speed FSSW can reach a maximum shear load of about 5400 N, much higher than those prepared by the conventional FSSW technique.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Twining and dynamic recrystallization in austenitic Alloy 718 during friction welding

Highlights: • DDRX was the primary grain refinement mechanism in friction welding of Alloy 718. • Two models were developed to explain the twin formation mechanism. • Intragranular twins were caused by grain boundary growth incidents. • Intergranular twin boundaries were ascribed to boundary growth stagnation. - Abstract: Quantitative boundary misorientation analysis verified that discontinuous dynamic recrystallization (DDRX) was the primary grain refinement mechanism in friction welding of Alloy 718. Two models were developed to explain the formation mechanism of intragranular twins and intergranular twins, respectively. Intragranular twins were caused by grain boundary growth incidents. After twin initiation, the twin boundary migrated toward the plastic-deformed grain interior to reduce the stored energy. Additionally, intergranular twin boundaries were ascribed to boundary growth stagnation. When boundary growth stagnation occurred, twin boundaries could form and altered the orientation of the boundary migration front, so that boundary migration could progress, leaving a single twin boundary behind.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Interfacial bonding mechanism and mechanical properties of micro friction stir blind riveting for multiple Cu/Al ultra-thin layers

Highlights: • Micro Friction Stir Blind Riveting is developed for joining multilayer ultra-thin dissimilar materials. • Interfacial bonding mechanism for different interfaces is identified. • Proposed technique offers better mechanical performance than conventional micro riveting process. • The relationship between each interfacial bonding mechanism and improved mechanical property is elucidated. - Abstract: In this research, bonding mechanisms and mechanical properties were investigated for a newly developed multilayer dissimilar material joining technique, micro friction stir blind riveting (viz. μFSBR), where the multilayer micro joint was made consisting of one Cu layer and three Al layers (each layer having 0.203 mm thickness) connected through Al rivet. Different microscopy techniques were employed (i.e. scanning electron microscopy and transmission electron microscopy) to unearth the bonding mechanisms of the three interfaces (i.e. Al rivet and Cu sheet interface, Cu sheet and Al sheet interface, and Al rivet and Al sheet interface) which revealed intricate yet distinct bonding phenomenon for each interface. A nano-scale diffusion layer in addition to two-way material flow consequential heterogeneous lamellar structures and mechanical interlocking was formed at the Al rivet and Cu sheet interface; Cu particles diffused into a non-uniform thickness thin oxide layer at the Cu sheet and Al sheet interface; and Al sheet experienced grain refinement near the interface close to Al rivet with a nano-scale gap. These observations revealed that both mechanical and metallurgical bonding occurred simultaneously in μFSBR. The formation of different bonding mechanisms resulted in superior bonding strength and absorbed energy compared to conventional micro blind riveting joints, which was further confirmed through layer by layer tensile tests.

36 MATERIALS SCIENCE↗