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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Complete the first phase of the comprehensive characterization of repair welding performed on irradiated Ni alloy 182

This report describes the research activities on post-weld evaluation and characterization of the quality and properties of welds made on the first phase of repair welding campaign on irradiated Ni alloy 182. The equipment and capabilities of the campaign were developed jointly by the U.S. Department of Energy, Office of Nuclear Energy, Light Water Reactor Sustainability Program, the Electric Power Research Institute, Long Term Operations Program (and the Welding and Repair Technology Center), and Oak Ridge National Laboratory. Irradiated nickel alloy 182 with doped boron ranging from 5 wppm to 15 wppm, were laser welded in the hot cell. The weld samples were cross-sectioned and characterized. The significant, on-going effort to weld irradiated alloys with high helium concentrations and comprehensively analyze the results will eventually yield validated repair techniques and guidelines for use by the nuclear industry in extending the operational lifetimes of nuclear power plants.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Machine Learning for Automated Weld Quality Monitoring and Control

Resistance Spot Welding (RSW) is a critical process in the automotive industry, valued for its cost-effectiveness, short cycle time, and robustness. However, achieving consistent high-quality joints remains challenging due to the complex interplay of various factors, like materials, processes, and manufacturing uncertainties, etc. Under the collaborative project between Oak Ridge National Laboratory (ORNL) and General Motors (GM), we have developed a robust and expansible machine learning (ML) framework aimed at enhancing quality control in RSW. By harnessing the power of machine learning, we have developed the ability to ensure every aspect of the welding process, from the initial process design stage to the final weld joint quality. The framework operates by analyzing a variety of data streams, including in-line process signals, process parameters, materials, and postprocessed weld joint data. Through this analysis, the models have been trained to detect deviations from optimal quality standards, leveraging their ability to identify signature data patterns and anomalies within in-line signals and construct complex correlations between these signals and weld quality parameters. Meanwhile, the machine learning framework is designed to adapt to a variety of materials, including high strength steels and aluminum alloys, etc. Its flexible architecture facilitates the incorporation of diverse data sources and features, enabling precise modeling and prediction across a broad range of material properties and weld quality variables. The expansible ML frameworks represent a promising transformation in weld quality monitoring and control, empowering industry to achieve high levels of efficiency, consistency, and reliability in manufacturing.

42 ENGINEERING↗
DOE OSTI2018

Dynamic Reflection Behaviors of Weld Pool Surface in Pulsed GTAW

Here in this paper, a method was studied to determine the weld pool penetration based on the dynamic behaviors of the weld pool surface. To this end, relative works were per- formed to observe, measure, and analyze the development of a weld pool through the imaged laser matrix dots and correlate the changes in the imaged dots to the weld pool penetration. It was found that during partial joint penetration, the imaged dot matrix on the weld pool was clear and bright, but became fuzzier and dimmer when critical/complete joint penetration was reached. Results showed this was related to the root damping force in partial penetration, which obstructed the oscillation of the weld pool and made the surface relatively still for imaging. When critical/complete joint penetration was reached, the root damping force was diminished, and thus the pool surface oscillation was stronger, which led to dimmer and fuzzier images. By quantifying the relation between the image grayness variations with the penetration stages, a method was found for the automated control of the welding process.

42 ENGINEERING↗
DOE OSTI2017

Quality status display for a vibration welding process

A method includes receiving, during a vibration welding process, a set of sensory signals from a collection of sensors positioned with respect to a work piece during formation of a weld on or within the work piece. The method also includes receiving control signals from a welding controller during the process, with the control signals causing the welding horn to vibrate at a calibrated frequency, and processing the received sensory and control signals using a host machine. Additionally, the method includes displaying a predicted weld quality status on a surface of the work piece using a status projector. The method may include identifying and display a quality status of a suspect weld. The laser projector may project a laser beam directly onto or immediately adjacent to the suspect welds, e.g., as a red, green, blue laser or a gas laser having a switched color filter.

36 MATERIALS SCIENCE↗
DOE OSTI2018

On Process, Structure, Property Relationships in Impact Welding of Aluminum 6061 and Steel 4130

Vaporizing Foil Actuator Welding process was used to weld 1mm thick aluminum alloy 6061 sheet to 3.2 mm thick 4130 grade steel plate. Temporal evolution of the flyer sheet velocity was recorded at four locations on the flyer sheet using photonic Doppler velocimetry. The welded samples were subjected to mechanical and microstructural characterization. Although the welded interface did not show a very wavy characteristic, the welds had substantial strength. Welds made with a softer temper, T4 alloy were found to be stronger than the one created with a harder, T6 temper alloy. A coupled Lagrangian-Eulerian numerical framework was also utilized to predict the structure of the interface based on the measured velocity profile. The model also depicted absence of large waves although the jetting phenomenon was observed, thereby providing insight into necessary conditions for impact welding.

Mao, Yu↗
DOE OSTI2022

Friction Stir Welding – an Advanced Approach to Repair Nuclear Power Plant Components

Solid phase joining technique friction stir welding (FSW) has been shown to mitigate helium-related issues in fusion welding of irradiated steels. Here, we present detailed characterization results of the first friction stir weld of an irradiated 304L stainless steel (SS) coupon contained 5.2 atomic parts per million (appm) helium. Scanning electron microscopy (SEM) was used to characterize a cross section specimen removed from the friction stir weld. No macro helium induced crack was observed at the analyzed cross-section, and only 1 – 1.5 µm size pores were found in the stir zone (SZ) and the thermal-mechanical affected zone (TMAZ). Moreover, some minor helium aggregations (Maximum ~20 µm in length) appeared along grain boundaries inside the TMAZ. Thereafter, miniature tensile specimens were extracted from the SZ, TMAZ and heat affected zone (HAZ), and base metal (BM) and tested. All welded specimens showed high total elongations (> 60%) and strengths (> 75% BM strengths). Overall, the weld made by FSW showed much better results comparing with traditional fusion welding on irradiated SS.

Tang, Wei↗
DOE OSTI2019

Modeling of the Heat-Affected and Thermomechanically Affected Zones in a Ti-6Al-4V Inertia Friction Weld

Inertia friction welding has been used across the aerospace, automotive, and power-generation industries for the fabrication of complex axisymmetric components for over forty years. The process involves one axisymmetric piece being held stationary and another piece being brought into contact set to rotate about its axis of symmetry by a flywheel with the system under an applied load across the joint. Plasticization at the joint interface through the frictional heating sees the two pieces bond together. The titanium alloy Ti-6Al-4V has been widely studied for inertia welding applications. A successful selection of processing parameters (flywheel energy and mass, applied load) allows an inertia welding process which produces a very high-integrity weld, with a minimal heat-affected zone (HAZ) and thermomechanically affected zone (TMAZ), formed as a narrow band at the interface and extending further into the material. The width of this narrow band of heated material is dependent upon the process parameters used. A series of experimental inertia friction welds were performed using Ti-6Al-4V, and a finite element (FE) modeling framework was developed using the FE code Deform in order to predict the widths of the HAZ and TMAZ at the weld interface. The experimentally observed HAZ boundaries were correlated with the thermal fields from the FE model, while TMAZ boundaries were correlated with the Von Mises plastic strain fields.

42 ENGINEERING↗
DOE OSTI2018

Effects of the Electron Beam Welding Process on the Microstructure, Tensile, Fatigue and Fracture Properties of Nickel Alloy Nimonic 80A

The purpose of this study was to evaluate rotary bending high-cycle fatigue properties and crack growth of Nimonic 80A-based metal and electron beam-welded joints. All the tests were performed at room temperature. Fracture surfaces under high-cycle fatigue and fatigue crack growth were observed by scanning electron microscopy. Microstructure, hardness and tensile properties were also evaluated in order to understand the effects on the fatigue results obtained. It was found that the tensile properties, hardness and high-cycle fatigue properties of the welded joint are lower than the base metal. The fracture surface of the high-cycle fatigue shows that fatigue crack initiated from the surface under the high stress amplitude and from the subsurface under the low stress amplitude. The effect of the welding process on the statistical fatigue data was studied with a special focus on probabilistic life prediction and probabilistic lifetime limits. The fatigue crack growth rate versus stress intensity factor range data were obtained from the fatigue crack growth tests. From the results, it was evident that the fatigue crack growth rates of the welded are higher than the base metal. The mechanisms and fracture modes of fatigue crack growth of welded specimens were found to be related to the stress intensity factor range ΔK. In addition, the effective fatigue crack propagation thresholds and mismatch of welded joints were described and discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Strain Rate-Dependent Tensile Deformation Behavior of Fiber Laser-Welded Butt Joints of Dual-Phase Steels

The microstructure and tensile deformation behavior of the fiber laser-welded similar and dissimilar dual-phase (DP) steel joints over a wide range of strain rates from 10{sup −3} to 10{sup 3} s{sup −1} were investigated for the further applications on the lightweight design of vehicles. The high strain rate dynamic tensile deformation process and full-field strain distribution of the base metals and welded joints were examined using the digital image correlation method and high-speed photography. The strain rate effects on the stress–strain responses, tensile properties, deformation, and fracture behavior of the investigated materials were analyzed. The yield stress (YS) and ultimate tensile strength (UTS) of the dissimilar DP780/DP980 welded joints were lying in-between those of the DP780 and DP980 base metals, and all materials exhibited positive strain rate dependence on the YS and UTS. Owing to the microstructure heterogeneity, the welded joints showed relatively lower ductility in terms of total elongation (TE) than those of the corresponding base metals. The strain localization started before the maximum load was reached, and the strain localization occurred earlier during the whole deformation process with increasing strain rate. As for the dissimilar welded joint, the strain localization tended to occur in the vicinity of the lowest hardness value across the welded joint, which was in the subcritical HAZ at the DP780 side. As the strain rate increased, the typical ductile failure characteristic of the investigated materials did not change.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Pulse MIG Welding of 6061-T6/A356-T6 Aluminum Alloy Dissimilar T-joint

Dissimilar T-joints between 4-mm-thick wrought 6061-T6 and cast A356-T6 aluminum alloy plates are made with pulse metal inert gas welding (P-MIG) process, and the weld geometry, microstructure and mechanical properties of the joints are investigated. The average tensile load of the joints is 9488 N at travel speed 12 mm/s and welding current 165 A with 6061 aluminum alloy as web plate and A356 aluminum alloy as flange plate. The weld zone (WZ) is composed of dendrite zone and columnar zone, which is wide at bottom of weld making it become a weak zone. Besides, grain boundary (GB) liquation, consisting of GB eutectic and solute-depleted α-Al, occurs in the partially melted zone on 6061 aluminum alloy side. The T-joint with highest tensile load fails at the root of WZ and the flange plate near the weld with different fracture modes.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Numerical and Experimental Analysis of Dissimilar Repair Welding Residual Stress in P91 Steel Considering Solid-State Phase Transformation

Repair welding is a popular method to repair the cracked zones of pipes in power plants. However, residual stresses induced by repair welding are inevitably generated and have a significant effect on the performance of repair-welded components during service. The purpose of this research is to investigate the effects of solid-state phase transformation (SSPT) on the repair welding residual stress distribution of multi-layer and multi-pass welding in P91 steel. Based on thermal elastic-plastic theory, a three-dimensional thermal–metallurgical–mechanical finite element model considering the SSPT is established, and shielded metal arc welding (SMAW) heat input is modelled as one double elliptical heat source. The effect of phase transformation on residual stress is investigated by considering effects with and without phase transformation in the database of materials. The results show that transverse compressive stress and a low longitudinal stress area are generated in the final pass due to martensite transformation. Compared with different zones along the thickness direction, the effect of SSPT is greater around the outer surface than around the internal fusion zone. The rationality of the developed finite element model is verified by the experimental method, and good agreement is obtained between those results from the numerical analysis and experimental methods.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Neutron diffraction illustrates residual stress behavior of welded alloys used as radioactive confinement boundary

Corrosion-resistant welded alloys are frequently used as a leak-tight boundary in critical applications that require confinement of hazardous and/or radioactive substances, including an increasing population of spent nuclear fuel (SNF) canisters. The behavior of residual stresses generated as a result of irregular elastic–plastic deformation during processes such as welding is one of today's key issues to a full understanding of the aging mechanisms that may compromise the confinement boundary. Whether such processes and any subsequent weld repairs, not subjected to post-weld heat treatment, would negatively affect the initial material by introducing through-thickness tensile stresses remains an open question. Here we report the first residual stress measurements using neutron diffraction on the welded joints of a SNF canister. We found significant tensile residual stresses in the as welded sample, indicating that initiation and through-thickness growth of cracks may be possible. Following repair, we observed a stress redistribution and introduction of beneficial compressive stresses. We anticipate our results will improve understanding of confinement susceptibility to aging and guide improvements in repair techniques.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Microstructural analysis of laser weld fusion zone in Haynes 282 superalloy

Analytical electron microscopy and spectroscopy analyses of the fusion zone (FZ) microstructure in autogenous laser beam welded Haynes 282 (HY 282) superalloy were performed. The micro-segregation patterns observed in the FZ indicate that Co, Cr and Al exhibited a nearly uniform distribution between the dendrite core and interdendritic regions while Ti and Mo were rejected into the interdendritic liquid during the weld solidification. Transmission electron diffraction analysis and energy dispersive X-ray microanalysis revealed the second phase particles formed along the FZ interdendritic region to be Ti-Mo rich MC-type carbide particles. Weld FZ solidification cracking, which is sometimes associated with the formation of {gamma}-{gamma}' eutectic in {gamma}' precipitation strengthened nickel-base superalloys, was not observed in the HY 282 superalloy. Modified primary solidification path due to carbon addition in the newly developed superalloy is used to explain preclusion of weld FZ solidification cracking in the material. - Highlights: Black-Right-Pointing-Pointer A newly developed superalloy was welded by CO{sub 2} laser beam joining technique. Black-Right-Pointing-Pointer Electron microscopy characterization of the weld microstructure was performed. Black-Right-Pointing-Pointer Identified interdendritic microconstituents consist of MC-type carbides. Black-Right-Pointing-Pointer Modification of primary solidification path is used to explain cracking resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Effect of Nd:YAG laser welding on microstructure and hardness of an Al-Li based alloy

Butt joints of 3.0 mm thick sheets of an Al-Li based alloy have been produced using Nd:YAG laser welding without filler metals. The hardness distribution and microstructure of the alloy and welded joints were investigated. The changes in the grain shapes, grain orientations, microtexture, and precipitates of the fusion zone were analyzed using optical microscope, electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results show that Nd:YAG laser welding leads to a change of the microhardness, grain shape, grain orientations, and a disappearance of the microtexture and precipitates. A narrow band of EQZ along the fusion boundary and a predominantly equiaxed dendritic structure are developed in the fusion zone. The formation of the predominately equiaxed dendritic grains is due to a heterogeneous nucleation mechanism aided by equilibrium A1{sub 3}Zr phases as well as the growth of pre-existing nuclei created by dendrite fragmentation, or by grain detachment resulted from Nd:YAG laser welding processes. In addition, Nd:YAG laser welding produces lower Vickers hardness than that of the base metal due to the decrease in the in quantity of {delta} Prime precipitates in the fusion zone. - Graphical Abstract: The grain shapes, grain orientations, microtexture, and precipitates of the solidified fusion zone were investigated and compared with the base metal using optical microscope, electron back scattered diffraction (EBSD) and transmission electron microscope (TEM). EBSD orientation map of laser welded joint in 5A90 alloys is presented in Fig. 3. It clearly shows that a narrow band EQZ along the fusion boundary and the predominantly equiaxed grains have been developed in the fusion zone of 5A90 alloys. Also, it is clear that the microstructure of the base metal is characterized by laminated grains with preferred orientations, whereas the fusion zone is predominately equiaxed grains in different colors having random orientations. Highlights: Black-Right-Pointing-Pointer The predominantly equiaxed dendritic structure is developed in the fusion zone. Black-Right-Pointing-Pointer The fusion zone with equiaxed grains shows random orientations and microtexture. Black-Right-Pointing-Pointer The loss in hardness in the fusion zone is due to the decrease in {delta} Prime precipitates. Black-Right-Pointing-Pointer The non-epitaxial growth occurs at fusion boundary. Black-Right-Pointing-Pointer The equilibrium A1{sub 3}Zr phases maybe the nuclei of new grains in the fusion zone.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of laser welding parameters on the austenite and martensite phase fractions of NiTi

Although laser welding is probably the most used joining technique for NiTi shape memory alloys there is still a lack of understanding about the effects of laser welding parameters on the microstructural induced changes: in both the heat affected and fusion zones martensite may be present, while the base material is fully austenitic. Synchrotron X-ray diffraction was used for fine probing laser welded NiTi joints. Through Rietveld refinement the martensite and austenite phase fractions were determined and it was observed that the martensite content increases towards the weld centreline. This is related to a change of the local transformation temperatures on these regions, which occurs due to compositional variation in those regions. The martensite phase fraction in the thermally affected regions may have significant implications on functional properties on these joints. - Highlights: •Synchrotron X-ray diffraction was used for fine probing of the microstructure in laser welded NiTi joints. •Rietveld refinement allowed to determine the content of martensite along the heat affected and fusion zones. •The martensite content increases from the base material towards the weld centreline.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Formation mechanisms of periodic longitudinal microstructure and texture patterns in friction stir welded magnesium AZ80

Many studies of friction stir welding have shown that periodicity of metal flow around the tool pin may result in the formation of periodic differences in microstructure and texture in the weld nugget area correlated with the weld pitch. The current work investigates the periodicity of magnesium weld microtexture in the nugget region and its association with material flow using optical and electron microscopy. Two welds created in AZ80 at different processing conditions are presented in detail, one illustrating periodic longitudinal texture change, and one showing for the first time that periodic variations in texture, grain size, or composition are not defining features of periodic nugget flow. While nugget texture is dominated by shear deformation, it was found here to be affected to a lesser degree by compaction of material behind the welding tool, which led to reduction in intensity of the shear texture fiber. The decreased tendency for magnesium based alloys to form periodic patterns as compared to aluminum based alloys is explained with reference to the shear textures. - Highlights: •It is shown here that periodic material flow in the nugget does not necessitate longitudinal texture patterns. •Longitudinal texture patterns are shown to be present or absent in Mg AZ80 based on processing conditions. •Texture in the nugget is mainly dictated by shear deformation, but has measurable effects from other deformation modes. •Explanation of why longitudinal texture change is frequently reported in aluminum but not magnesium alloys is provided. •A new vector visualization of material flow based on EBSD data analysis is shown.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Interfacial structure and bonding mechanism of weld seams during porthole die extrusion of aluminum alloy profiles

Highlights: • Interfacial structures and bonding mechanisms of extrusion welds were studied. • Interfacial grain boundaries, amorphous layers and voids were found. • Bonding mechanisms in the absence/presence of a gas-pocket were proposed. • Voids closure, oxide films breaking and grain boundaries migration were discussed. - Abstract: Fine nanostructures of bonding interfaces of weld seams formed by porthole die extrusion in the absence/presence of a gas-pocket behind the bridge of the extrusion die were systematically studied to understand the underlying interfacial bonding mechanisms. Interfacial grain boundaries, nanoscale amorphous layers, and three kinds of new interfacial structures were found. Specifically, it was found that, in the absence of a gas-pocket behind the bridge, there are two distinctly different interfacial structures. For the first kind of bonding interface, interfacial grain boundaries exist in contact areas and micro-voids exist in non-contact areas. For the second kind of bonding interface, there are no interfacial grain boundaries in contact areas and only nanoscale micro-voids exist in non-contact areas. In the presence of a gas-pocket behind the bridge, nanoscale voids and amorphous layers exist at the bonding interface. It was also found that the formation of gas-pockets can be avoided by increasing the depth of the welding chamber, and the increase of the welding chamber's depth and extrusion speed also contributes to the volume reduction of micro-voids and the migration of grain boundaries at the bonding interface, so as to improve the welding quality of weld seams. Based on the experimental findings, two interfacial bonding mechanisms corresponding to the absence/presence of a gas-pocket are proposed. The specific behavior of micro-asperities contact, micro-voids closure, oxide films breaking and interfacial grain boundaries migration are described, and the solid-state bonding process during porthole die extrusion is revealed from the micro-nano scales.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Evaluation of Zn-rich coatings for IMC reaction control in aluminum-magnesium dissimilar welds

Highlights: • Thermodynamic and diffusion simulations have estimated the Zn conc. required to change the IMC reaction in Al-Mg dissimilar welding. • The selected coating alloy was effective in changing the Al-Mg reaction path by forming τ-(Al,Zn){sub 49}Mg{sub 32} as a substitute for β-Al{sub 3}Mg{sub 2}. • Refill™ friction stir spot welds produced with the coating alloy exhibited a thinner reaction layer and an increase in lap shear strength. - Abstract: The dissimilar welding of Al to Mg is very challenging owing to the rapid formation of an intermetallic (IMC) reaction layer at the joint interface, typically comprised of the binary phases γ-Al{sub 12}Mg{sub 17} and β-Al{sub 3}Mg{sub 2}. A potential metallurgical solution has been explored that aimed to change the reaction path by using Al-Zn alloy coatings to promote alternative IMCs with a slower growth rate. To determine the optimum composition for the coating, combined CALPHAD thermodynamic calculations and diffusion simulations were used to estimate the minimum Zn concentration (20 at.%) required to suppress the formation of the faster growing Al{sub 3}Mg{sub 2} phase. This prediction was verified by both static diffusion and Refill™ friction stir spot welding (FSSW) experiments. In each case the selected coating alloy was effective in changing the Al-Mg reaction path by forming the τ-(Al,Zn){sub 49}Mg{sub 32} phase as a substitute for β-Al{sub 3}Mg{sub 2}. However, in static heat treatments there was no reduction in the IMC reaction layer thickness due to the new phase having similar growth kinetics to the β-Al{sub 3}Mg{sub 2} phase it replaced. Nevertheless, Refill™ friction stir spot welds prepared with the new AL-Zn coating alloy exhibited a thinner reaction layer and an increase in lap shear strength. This benefit was attributed to the Zn addition reducing the joint interface liquation temperature, which resulted in a lower peak weld temperature and less IMC reaction; although an increase in local eutectic melting limited the improvement observed.

36 MATERIALS SCIENCE↗