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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Towards Polymer-Free, Femto-Second Laser-Welded Glass/Glass Solar Modules

This project explores the use of femto-second (fs) lasers to form glass-to-glass welds for hermetically sealed, polymer-free solar modules. Low iron solar glass coupons were welded together without the use of glass filler using a fs laser with dedicated optics to elongate the focal plane parallel to the incident beam. The resulting welds were then stress tested to failure to reveal the critical stress intensity factor, KIc. These values were used in a structural mechanics model of a 1 m by 2 m glass/glass module under a simulated static load test. The results show that the fs laser welds are strong enough for a suitably framed module to pass the IEC 61215 static load test with a load of 5400 Pa. Key to this finding is that the module must be framed and braced, and the glass must be ribbed to allow pockets for the cells and welds inside the border of the module. The result is a module design that is completely polymer-free, hermetically sealed, has improved thermal properties, and is easily recycled.

femto-second laser welded↗
DOE OSTI2018

Influence of Welding Strength Matching Coefficient and Cold Stretching on Welding Residual Stress in Austenitic Stainless Steel

Austenitic stainless steel is widely used in pressure vessels for the storage and transportation of liquid gases such as liquid nitrogen, liquid oxygen, and liquid hydrogen. Cryogenic pressure vessel manufacturing uses cold stretching technology, which relies heavily on welding joint performance, to construct lightweight and thin-walled vessels. Residual stress from welding is a primary factor in cases of austenitic stainless steel pressure vessel failure. In this paper, on the basis of Visual Environment 10.0 finite element simulation technology, the residual stress resulting from different welding strength matching coefficients (0.8, 1, 1.2, 1.4) for two S30408 plates welded with three-pass butt welds is calculated according to thermal elastoplastic theory. In addition, the stress field was calculated under a loading as high as 410 MPa and after the load was released. Path 1 was set to analyze stress along the welding line, and path 2 was set to analyze stress normal to the welding line. The welding strength matching coefficient strongly affected both the longitudinal residual stress (center of path 1) and the transverse residual stress (both ends of path 1) after the welding was completed. However, the coefficient had little effect on the longitudinal and transverse residual stress of path 2. Under the loading of 410 MPa, the longitudinal and transverse stress decreased and the stress distribution, with different welding strength matching coefficients, was less diverse. After the load was released, longitudinal and transverse stress distribution for both path 1 and path 2 decreased to a low level. Cold stretching could reduce the effect of residual stress to various degrees. Transverse strain along the stretching direction was also taken into consideration. The experimental results validated the reliability of the partial simulation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Optimization of a Welding Procedure for Making Critical Aluminum Welds on the LBNF Absorber Core Block

he LBNF Absorber consists of thirteen 6061-T6 aluminum core blocks. The core blocks are water cooled with de-ionized (DI) water which becomes radioactive during beam operations. The cooling water flows through gun-drilled channels in the core blocks. A weld quality optimization was performed to produce National Aeronautical Standard (NAS) 1514 Class I quality welds on the aluminum core blocks. This was not successful in all cases. An existing Gas Tungsten Arc Welding (GTAW) Welding Procedure Specification (WPS) was fine tuned to minimize, in most cases, and eliminate detectable tungsten inclusions in the welds. All the weld coupons however, passed welding inspection as per the piping code: ASME B31.3 Normal Fluid Service. Tungsten electrode diameter, type, and manufacturer were varied. Some of the samples were pre-heated and others were not. It was observed that larger diameter electrodes, 5/32 in., with pre-heated joints resulted in welds with the least number of tungsten inclusions. It is hypothesized that thinner electrodes breakdown easily and get lodged into the weld pool during the welding process. This breakdown is further enhanced by the large temperature differential between the un-preheated sample and the hot electrode.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Effect of Weld Consumable Conditioning on the Diffusible Hydrogen and Subsequent Residual Stress and Flexural Strength of Multipass Welded P91 Steels

P91 steel weld joint was prepared using the shielded metal arc welding process and four different conditions of weld consumable that provide the different levels of diffusible hydrogen in deposited metal. In the present research, the effects of diffusible hydrogen content on the flexural strength, lower critical stress, and tensile strength of P91 steel welds were also determined with respect to different electrode conditions. To investigate the effect of diffusible hydrogen on multipass welding, top and root side flexural tests were performed. The residual stresses (axial stress and transverse stress) were also measured using the blind hole drilling method for different conditions of welding consumable. The peak value of residual stresses was measured at the center of the weld fusion zone. The maximum value of transverse stress was measured to be 355 MPa for case II (6.21 mL/100 g of diffusible hydrogen), while the maximum axial stress was about 218 MPa for case IV (12.43 mL/100 g of diffusible hydrogen). A three-dimensional finite element simulation was also performed to predict the residual stress distribution and thermal profile along the welded joint. The experimentally determined residual stresses correlated well with the numerically estimated residual stresses. The diffusible hydrogen content was not observed to have any significant effect on the residual stresses. The corrected residual stress values were also predicted by considering the plasticity-induced error. However, the flexural performance of the welded joint was affected by the diffusible hydrogen content. The top and root flexural strength was measured to be optimum for the low level of diffusible hydrogen content, and the values decreased with an increase in diffusible hydrogen content.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment

Highlights: • The formation and spheroidization of the eutectic-like carbides are found in the Hastelloy N alloy during welding and PWHT. • All precipitates in the joints before and after the PWHT are identified as a M{sub 6}C type carbide with different morphology. • The diffusion of main element of Mo leads to the decrease of lattice parameter of the carbide during the welding and PWHT. - Abstract: The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M{sub 6}C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M{sub 6}C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M{sub 6}C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M{sub 6}C carbides, which results in a decrease of the lattice parameter.

36 MATERIALS SCIENCE↗
DOE OSTI2017

The Evolution of the Weld Metal Microstructures in Dissimilar Titanium Welds Based on Al and Mo Equivalents

CO{sub 2} laser welding of Ti-15V-3Cr-3Al-3Sn to Ti-4.5Al-3V-2Fe-2Mo was conducted in the study. The notched fracture and microstructures of the weld metal (WM) with various post-weld aging treatments were studied. In the as-welded sample, the WM comprised only β phase, which was relatively soft and ductile. Moreover, the phase constituent of the as-welded WM was related to the Al and Mo equivalents and further compared with other welds. The microstructural morphologies and microhardness of the WMs of dissimilar welds exhibited significant changes after post-weld aging at distinct temperatures. Increasing the Al equivalent ([Al]{sub EQ}) of the WM caused an increased response to age-hardening during post-weld aging treatments. When the aging temperature was increased from 426 to 593 °C, the α precipitates in the WM grew in size, causing a decrease in hardness, but an improvement in toughness.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Tensile Behavior of Electron Beam-Welded and Post-Weld Vacuum-Annealed Nb-10% Hf-1% Ti Refractory Alloy Weldments

Nb-10% Hf-1% Ti refractory alloy is a high performance material extensively used for high temperature applications. Electron beam welding is one of the most widely used techniques to join refractory and reactive alloys. Bigger sizes of nozzles for rocket propulsion applications can be either made through deep drawing and flow turning route or by roll bending and welding route both using sheets/plates as input material for fabrication. The latter is a more economical option for mass production of the hardware using such exotic and expensive alloys. In view of this, both as-welded (AW) coupon and weld plus post-weld vacuum-annealed (AW + VA) coupon have been prepared to study their mechanical behavior. It has been observed that tensile strength and ductility have not been reduced in both these conditions vis-à-vis the base metal, confirming weld efficiency of the alloy to be ~ 100%. Microhardness is found to be 150-160 VHN in the base metal and 200-225 VHN in the weld fusion zone in AW condition, which became uniform (145-155 VHN) throughout the weldment in AW + VA condition. Microstructure of the weldment in AW condition is found to be consisting of grains solidified by epitaxial mode from base metal toward the weld centre. In AW + VA condition, improvement in tensile elongation is observed, which is found to be due to the presence of homogenized grains/more uniform microstructure near the heat-affected zone as compared to the steep gradient in grain size in different zones in the weld in AW condition.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Welding Parameters on Junction Structure and Fracture Behavior of Friction-Stir-Welded Joints of 2024 Aluminum Alloys

In this paper, the effect of welding speed and tool rotation speed on the junction structure and fracture behavior of friction-stir-welded joints was investigated with use of 2024 aluminum alloys of 3.2 mm thick. Results show that the formation of junction structure is more affected by tool rotation speed than by welding speed due to the differences of heat input levels. When welding speed is at 100 mm/min and tool rotation speed is in the range of 400-600 r/min, the joint junction structure causes complete bonding with no welding defects. While under improper welding parameters, the junction structure causes the precipitate aggregation on the bonding line and the partial bonding with the appearance of both tunnel defects and kissing bond defects. Meanwhile, the results of tensile tests show that the tensile fracture of all FSW joints occur at the weld center. The failure mode of joints with defects-free junction structure characterized by shear fracture is ductile. While the failure mode of joints with defects-existent junction structure characterized by layered fracture surface is brittle. Furthermore, that heterogeneous microstructure, precipitate aggregation and welding defects converge inside the junction structure is the main factor affecting the tensile properties and fracture behavior of the friction-stir-welded joint.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Effect of Weld Metal Composition on Microstructural and Mechanical Properties of Dissimilar Welds Between Monel 400 and Inconel 600

The current work was carried out to characterize welding of Inconel 600 superalloy and Monel 400. In the present study, gas tungsten arc welding (GTAW) with four types of filler metals (ENiCu, ENiCu-7, ENiCr-3 and ENiCrFe-3) was utilized. The filler metals were categorized into two groups based on the presence of Cr and Nb in their chemical composition. This paper describes the selection and application of welding consumables in manufacturing dissimilar metal combinations. It was found that (Nb/Cr) ratio and Fe content can affect on the size and amount of carbides. During solidification of ENiCr-3 and ENiCrFe-3 filler metals, Nb leaves dendritic cores and is rejected to inter-dendritic regions because of its high tendency for segregation. However, No brittle Laves phase was detected in the welds. The interface between weld metal and base metal and gradual changes in alloying elements were also investigated by scanning electron microscopy. EDX analysis was also applied for different samples. Microhardness measurements and tensile test were performed on the joints. The average hardness value in the weld metal obtained from ENiCrFe-3 is higher than the other welds. ENiCu-7 weld exhibited the highest tensile strength of 540 MPa and percent elongation of 53% in contrast to ENiCrFe-3 weld with the lowest tensile strength (518 MPa) and percent elongation (39%).

36 MATERIALS SCIENCE↗
DOE OSTI2020

Modular In-Chamber Electron Beam Welding – Process Planning: Welding, Cladding, Inspection, and Manufacturing

Electron beam welding (EBW) is commonly employed by industry today to join relatively thin section components. Industrial sectors which utilize the technology include; automotive, aircraft, aerospace, defense, medical, oil & gas, etc. The ability to produce single pass, thick section (up to 6 inches, 150mm) welds has also been available for more than 40 years; however, the technology has not been deployed for civil nuclear manufacturing and fabrication such as reactor pressure vessels, steam generators, or pressurizers. Instead, thick section joining is performed much in the same manner it has been for decades using submerged arc or gas tungsten arc welding processes. Recent research performed under U.S. Department of Energy (DOE) project DE-NE0008629 has demonstrated that the overall welding time to produce one major reactor pressure vessel (RPV) girth weld can be reduced from weeks to less than 90 minutes, while maintaining exceptional quality and inspection characteristics. The subject project (DE-NE0008846) investigates a modular in-chamber (MIC) EBW approach which allows various RPV sections to be joined within a “modular” chamber. The MIC-EBW approach utilizes individual modules that can be stacked and de-stacked to various heights to enable production girth welds to be performed at a given elevation. This report describes the various processing methodology necessary to complete major girth weldments for the NuScale Power small modular reactor including welding development, manufacturing, production sequence, inspection, and cladding.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Intelligent Weld Manufacturing: Role of Integrated Computational Welding Engineering

A master welder uses his sensory perceptions to evaluate the process and connect them with his/her knowledge base to take the necessary corrective measures with his/her acquired skills to make a good weld. All these actions must take place in real time. Success depends on intuition and skills, and the procedure is labor-intensive and frequently unreliable. The solution is intelligent weld manufacturing. The ultimate goal of intelligent weld manufacturing would involve sensing and control of heat source position, weld temperature, weld penetration, defect formation and ultimately control of microstructure and properties. This involves a solution to a problem (welding) with many highly coupled and nonlinear variables. The trend is to use an emerging tool known as intelligent control. This approach enables the user to choose a desirable end factor such as properties, defect control, or productivity to derive the selection of process parameters such as current, voltage, or speed to provide for appropriate control of the process. Important elements of intelligent manufacturing are sensing and control theory and design, process modeling, and artificial intelligence. Significant progress has been made in all these areas. Integrated computational welding engineering (ICWE) is an emerging field that will aid in the realization of intelligent weld manufacturing. The paper will discuss the progress in process modeling, microstructure, properties, and process control and automation and the importance of ICWE. Also, control and automation strategies for friction stir welding will be discussed.

42 ENGINEERING↗
DOE OSTI2024

Optimization of a Welding Procedure for Making Critical Aluminum Welds on the LBNF Absorber Core Block

The LBNF Absorber consists of thirteen 6061-T6 aluminum core blocks. The core blocks are water cooled with de-ionized (DI) water which becomes radioactive during beam operations. The cooling water flows through gun-drilled channels in the core blocks. A weld quality optimization was performed to produce National Aeronautical Standard 1514 Class I quality welds on the aluminum core blocks. This was not successful in all cases. An existing Gas Tungsten Arc Welding Procedure Specification was fine tuned to minimize, in most cases, and eliminate detect-able tungsten inclusions in the welds. All the weld coupons, however passed welding inspection as per the piping code: ASME B31.3 Normal Fluid Service. Tungsten electrode diameter, type, and manufacturer were varied. Some of the samples were pre-heated and others were not. It was observed that larger diameter electrodes, 5/32 in., with pre-heated joints resulted in welds with the least number of tungsten inclusions. It is hypothesized that thinner electrodes breakdown easily and get lodged into the weld pool during the welding process. This breakdown is further enhanced by the large temperature differential between the un-preheated sample and the hot electrode.

43 PARTICLE ACCELERATORS↗
NASA NTRS2012

Effects of Fusion Tack Welds on Self-Reacting Friction Stir Welds

In order to know whether fusion tack welds would affect the strength of self-reacting friction stir seam welds in 2195-T87 aluminum alloy, the fracture stresses of 144 tensile test coupons cut from 24 welded panels containing segments of friction stir welds were measured. Each of the panels was welded under unique processing conditions. A measure of the effect of the tack welds for each panel was devised. An analysis of the measures of the tack weld effect supported the hypothesis that fusion tack welds do not affect the strength of self-reacting friction stir welds to a 5% level of confidence.

Nunes, A. C., Jr.↗
DOE OSTI2021

Evaluation of residual stresses in isothermal friction stir welded 304L stainless steel plates

Friction stir welding was performed on 304L SS plates in order to heal simulated cracks created by electrical discharge machining. Two different tool temperatures (825 and 725 °C) were chosen for this study. Both neutron diffraction and X-ray diffraction techniques were employed to evaluate the residual stresses along two orthogonal reference directions, longitudinal (syy) and transverse (sxx). The former technique was also used to measure residual stresses at various depths. It was found that, at 1 mm depth from the top surface inside the stir zone (SZ), the longitudinal component was tensile in nature while the transverse component was compressive. The nature and magnitude of the residual stress fields, and the position of the peak residual stresses were found to vary with the weld depth. The SZ of the 725 °C weld exhibited higher peak stress than 825 °C weld mainly due to a lack of stress relief at the lower temperature.

Friction stir welding, Steel↗
DOE OSTI2022

A New Perspective of Post-Weld Baking Effect on Al-Steel Resistance Spot Weld Properties through Machine Learning and Finite Element Modeling

The root cause of post-weld baking on the mechanical performance of Al-steel dissimilar resistance spot welds (RSWs) has been determined by machine learning (ML) and finite element modeling (FEM) in this study. A deep neural network (DNN) model was constructed to associate the spot weld performance with the joint attributes, stacking materials, and other conditions, using a comprehensive experimental dataset. The DNN model positively identified that the post-weld baking reduces the joint performance, and the extent of degradation depends on the thickness of stacking materials. A three-dimensional finite element (FE) model was then used to investigate the root cause and the mechanism of the baking effect. It revealed that the formation of high thermal stresses during baking, from the mismatch of thermal expansion between steel and Al alloy, causes damage and cracking of the brittle intermetallic compound (IMC) formed at the interface of the weld nugget during welding. This in turn reduces the joint performance by promoting undesirable interfacial fracture when the welds were subjected to externally applied loads. The FEM model further revealed that increase in structural stiffness, because of increase in steel sheet thickness, reduces the thermal stresses at the interface caused by the thermal expansion mismatch and consequently lessens the detrimental effect of post-weld baking on the joint performance.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Predicting laser weld reliability with stochastic reduced-order models. Predicting laser weld reliability

Laser welds are prevalent in complex engineering systems and they frequently govern failure. The weld process often results in partial penetration of the base metals, leaving sharp crack-like features with a high degree of variability in the geometry and material properties of the welded structure. Furthermore, accurate finite element predictions of the structural reliability of components containing laser welds requires the analysis of a large number of finite element meshes with very fine spatial resolution, where each mesh has different geometry and/or material properties in the welded region to address variability. We found that traditional modeling approaches could not be efficiently employed. Consequently, a method is presented for constructing a surrogate model, based on stochastic reduced-order models, and is proposed to represent the laser welds within the component. Here, the uncertainty in weld microstructure and geometry is captured by calibrating plasticity parameters to experimental observations of necking as, because of the ductility of the welds, necking – and thus peak load – plays the pivotal role in structural failure. The proposed method is exercised for a simplified verification problem and compared with the traditional Monte Carlo simulation with rather remarkable results.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of Local Post Weld Heat Treatment on Tensile Properties in Friction Stir Welded 2219-O Al Alloy

To improve the formability of the aluminum alloy welds and overcome the size limitation of the bulk post weld heat treatment (BPWHT) on large size friction stir welded joints, a local post weld heat treatment method (LPWHT) was proposed. In this method, the resistance heating as the moving heat source is adopted to only heat the weld seam. The temperature field of LPWHT and its influence on the mechanical properties and formability of FSW 2219-O Al alloy joints was investigated. The evaluation of the tensile properties of FSW samples was also examined by mapping the global and local strain distribution using the digital image correlation methodology. The results indicated that the formability was improved greatly after LPWHT, while the hardness distribution of the FSW joint was homogenized. The maximum elongation can reach 1.4 times that of as-welded joints with increase the strength and the strain of the nugget zone increased from 3 to 8% when annealing at 300 °C. The heterogeneity on the tensile deformation of the as-welded joints was improved by the nugget zone showing large local strain value and the reason was given according to the dimple fracture characteristics at different annealing temperatures. The tensile strength and elongation of LPWHT can reach 93.3 and 96.1% of the BPWHT, respectively. Thus, the LPWHT can be advantageous compared to the BPWHT for large size welds.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure Evolution and Mechanical Properties of Keyhole Repair Welds in AA 2219-T851 Using Refill Friction Stir Spot Welding

The search for a suitable friction-based keyhole repair technique that fulfills the requirements for high-quality repair welds has become an important research topic, especially for aerospace applications. In order to provide and analyze an universal keyhole repair method for lightweight metals, refill friction stir spot welding is applied to through-hole repairs in 3- and 6-mm-thick sheets of precipitate hardening AA 2219-T851. Keyholes with a diameter of 7.5 mm were repair welded achieving a defect-free microstructure. The correlation between the microstructural evolution imposed by the repair process and the resulting mechanical properties is shown. A comprehensive analysis of the precipitate evolution in peak-aged AA 2219 during RFSSW is presented. Thermal cycle measurements revealed high heating rates and peak temperatures of up to 520 °C in the weld center. The thermal cycle caused mainly dissolution and minor equilibrium phase formation in the stirred zone. In the HAZ, overaging of the strengthening precipitates dominates with minor dissolution and equilibrium phase formation only in the direct proximity of the SZ. Microstructural analysis revealed typical weld zone formation with inhomogeneous grain size distribution in the SZ. The resulting mechanical properties are dominated by an inhomogeneous hardness distribution with lowest hardness in the TMAZ at 5 mm from the center of the weld. During tensile loading main yielding and the final fracture occur in the area of lowest strength. Tensile testing showed yield strength of 40 to 46% and UTS of 28 to 25% below BM values in 3- and 6-mm-thick sheets, respectively. The sheet thickness and post-weld natural aging were found to influence the mechanical properties of the weld significantly.

36 MATERIALS SCIENCE↗