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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 OSTI2017

Development of Friction Stir Processing for Repair of Nuclear Dry Cask Storage System Canisters

The Nuclear Regulatory Commission has identified chloride-induced stress corrosion cracking (CISCC) of austenitic stainless steel dry cask storage systems (DCSS) as an area of great concern. Friction Stir Processing (FSP) was used to repair laboratory-generated stress corrosion cracking (SCC) in representative stainless steel 304 coupons. Results of this study show FSP is a viable method for repair and mitigation CISCC. This paper highlights lessons learned and developed techniques relative to FSP development for crack repair in sensitized thick section stainless steel 304. These include: development of process parameters, welding at low spindle speed, use of weld power and temperature control and optimization of these controls. NDE and destructive analysis are also presented to demonstrate effectiveness of the developed methods for SCC crack repair.

Friction Stir↗
DOE OSTI2017

Solid-State Joining of Thick-Section Dissimilar Materials using a New Friction Stir Dovetailing (FSD) Process

Solid-state joining of thick section aluminum to steel plate has been achieved using a new process called Friction Stir Dovetailing (FSD). In FSD, a custom designed pin tool is used to flow a lower melting point material (AA6061) into dovetail grooves machined into the surface of an underlying higher melting point material (Rolled Homogeneous Armor – RHA). Repeating dovetails form a mechanical interlocking structure akin to metallic Velcro. In this study, AA6061 sections ranging in thickness from 1.5” to 3.0” are joined to 0.5” thick RHA plates. The effectiveness of FSD is demonstrated through tensile test data which shows specimens failing in the processed aluminum rather than at the joint interface. Numerical simulations are presented which highlight the importance of optimizing dovetail geometry. The effect of process parameters on joint strength, microstructure, and hardness are also discussed.

dissimilar metals joining↗
DOE OSTI2016

Development of Friction Stir Welding Technologies for In-Space Manufacturing

Friction stir welding (FSW) has emerged as an attractive process for fabricating aerospace vehicles. Current FSW state-of-the-art uses large machines that are not portable. However, there is a growing need for fabrication and repair operations associated with in-space manufacturing. This need stems from a desire for prolonged missions and travel beyond low-earth orbit. To address this need, research and development is presented regarding two enabling technologies. The first is a self-adjusting and aligning (SAA) FSW tool that drastically reduces the axial force that has historically been quite large. The SAA-FSW tool is a bobbin style tool that floats freely, without any external actuators, along its vertical axis to adjust and align with the workpiece s position and orientation. Successful butt welding of 1/8 in. (3.175 mm) thick aluminum 1100 was achieved in conjunction with a drastic reduction and near elimination of the axial process force. Along with the SAA-FSW, an innovative in-process monitor technique is presented in which a magnetoelastic force rate-of-change sensor is employed. The sensor consists of a magnetized FSW tool that is used to induce a voltage in a coil surrounding the tool when changes to the process forces occur. The sensor was able to detect 1/16 in. (1.5875 mm) diameter voids. It is concluded that these technologies could be applied toward the development of a portable FSW machine for use in space.

42 ENGINEERING↗
DOE OSTI2024

Additive friction stir deposition induced stress ripples in aluminum alloy

In additive manufacturing, modification of the viscosity of softened or molten metal plays a significant role in the development of mechanical properties distribution. Similar to soft polymers, molten or softened metal usually exhibits vastly different viscoelastic properties. During scratching tests, viscoelastic polymers undergo spatiotemporal stress development and relaxation, causing stress ripples to form on their surfaces. Here, it is observed that friction stir-based solid-state manufacturing can yield similar stress ripples on softened aluminum alloys due to the linear motion of the deposition tool. Softened aluminum alloys exhibit viscoelastic and viscoplastic responses similar to polymeric material during the solid-state deposition process. In the final product, residual stress ripples appear on the surface of the metal alloy due to periodic residual stress relaxation, leading to oscillatory behavior from the bulk mechanical properties of the material. The orientation of the in-built stress pattern formed in the bulk of the additively manufactured metal alloy underneath the visually evident onion ring-like surface pattern formation is diametrically in the opposite direction. The experimentally observed results are consistent with analytical calculation and numerical simulations in terms of behaviors.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A comparative analysis of residual stresses from friction stir processing of aluminum cast 380 and wrought 7075 alloy sheets: experimental characterization and modeling

Residual stresses are often overlooked in friction stir processing (FSP), but their significant impact on fatigue performance necessitates their consideration in optimizing processing parameters. The first step in this effort is understanding how process conditions influence residual stress distributions, especially across different alloys. This study focuses on determining and explaining the through-thickness residual stress variations and the effect of process temperature on the residual stress magnitude in wrought AA7075 and cast AA380.0 alloys. Additionally, for AA380.0, the impact of a second FSP pass was investigated. To achieve this, hole-drilling electronic speckle pattern interferometry (ESPI) and the thermal pseudo-mechanical (TPM) model within finite element analysis were employed to study the 3D distributions of in-plane residual stresses in processed samples under various conditions. A key finding was the varying impact of process temperatures on residual stress magnitudes. Higher process temperatures reduced stresses in AA380.0 but increased them in AA7075. Additionally, the through-thickness stress distributions differed between the two alloys. Further analysis revealed that yield stresses are crucial in explaining these phenomena and the effects of additional FSP passes. Further, this fundamental understanding will be vital in guiding the efforts to mitigate residual stresses and assess their impact on the performance of FSP aluminum alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Neural lumped parameter differential equations with application in friction-stir processing

Lumped parameter methods aim to simplify the evolution of spatially-extended or continuous physical systems to that of a “lumped” element representative of the physical scales of the modeled system. For systems where the definition of a lumped element or its associated physics may be unknown, modeling tasks may be restricted to full-fidelity physics simulations. Here, in this work, we consider data-driven modeling tasks with limited point-wise measurements of otherwise continuous systems. We build upon the notion of the Universal Differential Equation (UDE) to construct data-driven models for reducing dynamics to that of a lumped parameter and inferring its properties. The flexibility of UDEs allow for composing various known physical priors suitable for application-specific modeling tasks, including lumped parameter methods. The motivating example for this work is the plunge and dwell stages for friction-stir welding; specifically, (i) mapping power input into the tool to a point-measurement of temperature and (ii) using this learned mapping for process control.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

On an Anomaly in the Modeling of Electromagnetic Stirring in Continuous Casting

Early, yet still often-cited, mathematical models for electromagnetic stirring (EMS) in continuous casting are re-examined and found to contain a surprising anomaly: the solutions obtained were not unique. Analysis for the case of a round billet under rotary EMS shows how to avoid this behavior, whilst still making use of the experimental data that motivated the original models. The relevance of this result for current-day modeling of EMS is highlighted, particularly in the context of modulated EMS.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Experimental Study of the Mold Flow Induced by a Swirling Flow Nozzle and Electromagnetic Stirring for Continuous Casting of Round Blooms

This study focuses on an experimental investigation of the fluid flow in round bloom continuous casting using a 1:3 model of the industrial casting process. A swirling flow nozzle, represented by the specific design of the RHI Magnesita GYRONOZZLE, is used to produce a swirling motion in the cylindrical mold. The test section is integrated into the Mini-LIMMCAST facility at HZDR, which is operated at room temperature using the ternary alloy GaInSn. Systematic measurements of horizontal and vertical velocity profiles are performed by means of the Ultrasound Doppler Velocimetry. The second part of the study focuses on the interaction between the flow driven by the GYRONOZZLE and concurrent electromagnetic stirring in the mold (M-EMS) by applying rotating magnetic fields (RMFs) at different magnetic flux densities. The effect of the GYRONOZZLE on the flow pattern inside the mold is examined with and without superimposed RMFs and compared to those of a standard single-port nozzle. The measurements reveal that the GYRONOZZLE induces a swirling flow in the whole mold. It is further shown that the influence of a simultaneously applied RMF is mainly restricted to the lower part of the mold since the transport of angular momentum to the top is suppressed by the jets pouring out from the GYRONOZZLE.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Introducing the Planar Laser-Induced Fluorescence Technique (PLIF) to Measure Mixing Time in Gas-Stirred Ladles

The planar laser-induced fluorescence (PLIF) technique was implemented to measure mixing time in a 1/17 water model of a 200-ton ladle furnace. The results were compared to those obtained using the conventional method of pH probes. PLIF determinations were done at two different planes, and pH probe determinations were performed at two different locations. The results suggest that mixing times measured by PLIF are similar to those obtained under optimal conditions by the pH probe and that PLIF technique is more accurate and less sensitive to the location of the measurement than the pH probe method. In addition, the particle image velocimetry (PIV) technique was used to measure the effect of the immersed probe on the fluid-dynamic structure of the system. The presence of the probe affects greatly fluid dynamics and consequently the mixing behavior, which could explain the differences found in its mixing time measurements at different probe locations. This study shows the feasibility of the PLIF technique used to measure mixing time in physical models of gas-stirred ladles; it is not intrusive and allows the visualization of the mixing phenomena in a complete plane of the system.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Investigation on the Surface Vortex Formation During Mechanical Stirring with an Axial-Flow Impeller Used in an Aluminum Process

The present study investigated the mechanism of surface vortex formation in an aluminum melt vessel stirred by an axial-flow impeller mechanically. The oxide film is formed at the aluminum melt/air interface, and the movement of the interface entrains the oxide film and inclusions. Hence, the transient movement of melt–air interface is significant. The present study conducted a water model experiment and numerical simulation focusing on the movement of gas–liquid interface. The present study found that the oxide film can be entrained by two phenomena: (1) local surface vortex and (2) sloshing near the vessel wall. The local surface vortex is formed due to the pressure distribution around the impeller, and the sloshing is caused by macroinstabilities, which is generated by the discharged flow of axial-flow impeller. Besides, the shape of gas–liquid interface is dependent on the impeller shape. The axial-flow impeller gives rise to steeply curved shape of gas–liquid interface near the impeller shaft.

36 MATERIALS SCIENCE↗
DOE OSTI2016

An Alternative Frictional Boundary Condition for Computational Fluid Dynamics Simulation of Friction Stir Welding

For better application of numerical simulation in optimization and design of friction stir welding (FSW), this paper presents a new frictional boundary condition at the tool/workpiece interface for computational fluid dynamics (CFD) modeling of FSW. The proposed boundary condition is based on an implementation of the Coulomb friction model. Using the new boundary condition, the CFD simulation yields non-uniform distribution of contact state over the tool/workpiece interface, as validated by the experimental weld macrostructure. It is found that interfacial sticking state is present over large area at the tool-workpiece interface, while significant interfacial sliding occurs at the shoulder periphery, the lower part of pin side, and the periphery of pin bottom. Due to the interfacial sticking, a rotating flow zone is found under the shoulder, in which fast circular motion occurs. The diameter of the rotating flow zone is smaller than the shoulder diameter, which is attributed to the presence of the interfacial sliding at the shoulder periphery. For the simulated welding condition, the heat generation due to friction and plastic deformation makes up 54.4 and 45.6% of the total heat generation rate, respectively. In conclusion, the simulated temperature field is validated by the good agreement to the experimental measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Pouring Temperature and Electromagnetic Stirring on Porosity and Mechanical Properties of A357 Aluminum Alloy Rheo-Diecasting

Semisolid slurry of A357 aluminum alloy was prepared using a temperature-controllable electromagnetic stirrer and rheo-diecast at different temperatures. The effects of pouring temperature and electromagnetic stirring (EMS) on the porosity in rheo-diecast samples, as well as the relation between porosity and mechanical properties, were investigated. The results show that pouring temperature and EMS had minor influences on rheo-diecast microstructure but marked influence on the porosity. With decreasing slurry pouring temperature, the porosity decreased first and then increased, whereas the maximum pore ratio (ratio of shape factor to diameter of the largest pore) increased first and then decreased. The maximum pore ratio determines the level of tensile strength and elongation, and higher mechanical properties can be obtained with smaller and rounder pores in samples. The mechanical properties of the rheo-diecast samples increased linearly with increasing maximum pore ratio. The maximum pore ratio was 1.43 µm{sup −1}, and the minimum porosity level was 0.37% under EMS condition for the rheo-diecast samples obtained at a pouring temperature of 608 °C. With this porosity condition, the maximum tensile strength and elongation were achieved at 274 MPa and 4.9%, respectively. It was also revealed that EMS improves mechanical properties by reduction in porosity and an increase in maximum pore ratio.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Corrosion and Electrochemical Behavior of Sn-2Ag-0.5Cu Lead-Free Solders Solidified with Magnet Stirring

In this study, permanent magnet stirring (PMS) was applied to modify the crystallographic texture and corrosion resistance of Sn-2Ag-0.5Cu (SAC205) solders. The results indicate that PMS transforms the lamellar structure into equiaxed grains. Following the initiation corrosion process, the crystallographic texture shows a new class of grains that consists of single-crystal morphology with {111}{sub Sn} facets before applying PMS. This could result in severe corrosion of β-Sn crystals with non-uniform corrosion rate caused by the orientation effect of (111). The corrosion rate for SAC205 solder, measured by immersion tests in 3.5% NaCl solution at 25 °C, was significantly decreased from 31 to 8 mpy after applying PMS. This change in corrosion resistance of SAC205 solder can be attributed to the improved anodic and cathodic reaction activities caused by the modification of microstructure and crystallographic texture. The mechanism of pitting and sequential corrosion events is fully explained and discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A Combined Experimental and Modeling Approach to Investigate the Performance of Joint Between AZ31 Magnesium and Uncoated DP590 Steel Using Friction Stir-Assisted Scribe Technique

In this study, friction stir assisted scribe technique is used to achieve a viable joint between AZ31 magnesium alloy and uncoated DP590 steel. Here, the mechanical properties and performance of the joint are investigated using finite element modeling and electron microscopy. The joint strength can be ascribed to two factors, the mechanical interlocking and the metallurgical bonding of two materials at their interface. The contribution of both factors is intended, and the metallurgical bonding is studied to understand the basic joining phenomenon.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Friction Stir Welding and Processing

With nearly twenty years of international research and collaboration in friction stir welding (FSW) and processing industrial applications have spread into nearly every feasible market. Currently applications exist in aerospace, railway, automotive, personal computers, technology, marine, cutlery, construction, as well as several other markets. Implementation of FSW has demonstrated diverse opportunities ranging from enabling new materials to reducing the production costs of current welding technologies by enabling condensed packaging solutions for traditional fabrication and assembly. TMS has sponsored focused instruction and communication in this technology area for more than fifteen years, with leadership from the Shaping and Forming Committee, which organizes a biannual symposium each odd year at the annual meeting. A focused publication produced from each of these symposia now comprises eight volumes detailing the primary research and development activities in this area over the last two decades. The articles assembled herein focus on both recent developments and technology reviews of several key markets from international experts in this area.

friction stir welding↗
DOE OSTI2021

Tool-workpiece stick-slip conditions and their effects on torque and heat generation rate in the friction stir welding

Friction stir welding (FSW) has found increased applications in automotive and aerospace industries due to its advantages of solid-state bonding, no fusion and melting, and versatility in various working conditions and material combinations. However, the relationship among processing parameters, material properties, and bonding extent and fidelity remains largely empirical, primarily because of the lack of the mechanistic understanding of the tool-workpiece frictional behavior that affects our subsequent understanding of microstructural evolution and interface bonding formation. While the tool-workpiece stick-slip condition is believed to dictate the resulting torque and heat generation rate during the welding process, it remains rare and elusive to conduct a quantitative experimental measurement of such interfacial field. On the other hand, numerical simulations based on Computational Fluid Dynamics (CFD) rely on ad hoc assumptions of interfacial pressure and shear-stress conditions, but predictions can only be validated via the medium- and far-range temperature field which is known to be insensitive to the interfacial frictional behavior. This work first presents a comparison among two CFD-based simulation methodologies and the Coupled Eulerian Lagrangian (CEL) model in finite element method, the last of which uses the Coulomb friction so that the stick-slip is naturally developed. Based on the Hill-Bower similarity relationship in the contact analysis, an analytical model is developed here to prove why a constant stick-slip fraction will be developed in the steady state, to correlate the stick-slip fraction to processing parameters such as the tool spin rate, and further to derive dimensionless functions for torque and heat-generation-rate predictions. Pros and cons of various numerical approaches in predicting stick-slip are discussed, and our analytical model has been found to agree well with our numerical simulation and literature experimental results. These analyses provide the critical strain-rate and temperature fields that are needed for the bonding analysis in our future work.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Real-time evolution of texture and temperature during friction stir processing of a magnesium alloy: An operando neutron diffraction study

The real-time development of texture and the evolution of temperature during friction stir processing (FSP) of a Mg alloy were investigated using an operando neutron diffraction measurement. A novel approach was applied in this study where the real-time, quasi-steady state measurements performed as a function of position during FSP are converted to a Lagrangian dataset that reveals the transient behavior as a function of time. The in-situ FSP was carried out under two different thermo-mechanical processing conditions represented by the Zener-Hollomon parameter, Z. Further, the results show that: (i) a shear texture develops from the initial strong basal texture with the peak temperature reaching about 774 K during a low-Z processing and (ii) a strong off-normal texture develops with a peak temperature of 616 K during a high-Z processing. Moreover, time-temperature-texture diagrams were established to reveal the real-time development of the texture during the processing for both the low Z and high Z processing conditions. The changes in texture will be discussed in terms of plastic deformation mechanisms active during various stages of the FSP under the two different processing conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Friction stir gradient alloying: A high-throughput method to explore the influence of V in enabling HCP to BCC transformation in a γ-FCC dominated high entropy alloy

The compositional possibilities in high entropy alloys (HEAs) is very vast and effective strategies are needed to establish potential alloy chemistries. In this study, friction stir gradient alloying (FSGA), a recently-introduced high-throughput (HT) technique incorporating compositional and microstructural gradients, was used to explore the possibility of introducing a bcc transformation domain in γ-fcc dominated TRIP HEA Fe 38.5 Mn 20 Cr 15 Co 20 Si 5 Cu 1.5 (at.%) by vanadium addition. FSGA has accelerated the process of attaining the composition-microstructure library and the results suggest that vanadium addition of ~1 at.% results in nucleation of α-bcc. Additionally, this is the first observation of ε-hcp to α-bcc transformation in a TRIP HEA and supports the Olson-Cohen model of martensitic transformation (γ-fcc → ε-hcp → α-bcc). ε-hcp is nucleated with a pyramidal orientation by the formation of planar faults on the {111} close-packed planes of γ-fcc, and α-bcc is nucleated in the vicinity of ε-hcp along the {111} γ-fcc trace. There are indications for the formation of basal orientated ε-hcp from intersecting ε-hcp planes orientated for the pyramidal slip. Thus, the study shows the nucleation and growth of the α-bcc phase attributed to the dual effects of chemistry and strain and potential co-existence of all the three phases.

36 MATERIALS SCIENCE↗