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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Microstructure and Mechanical Characterization of Incoloy 925 Welds in the As-Welded and Direct Aged Conditions

The joints of Incoloy 925 obtained from gas tungsten arc welding (GTAW) with pulsating current utilizing ERNiCrMo-3 and ERNiCrMo-10 were investigated under as-welded and direct aged conditions. The microstructure showed the microsegregation of Nb-Mo-, Ti-rich phases in the weld zone of ERNiCrMo-3 in the as-welded condition. Post-weld heat treatment (PWHT) involving direct aging was carried out on the weldments at 732 °C for 4 h followed by air cooling. On direct aging, the tensile strength of the base metal increases by 40% when compared to the as-received ones. The failures were experienced in the parent metal of Incoloy 925 upon tension testing in as-welded conditions. Although the tensile strength was improved considerably, the failures occurred at the fusion zones, for both the fillers in the direct aged conditions. The joint efficiencies of Incoloy 925 welds employing ERNiCrMo-3 and ERNiCrMo-10 were reported as 95 and 86%, respectively. The impact toughness of the weldments in both the as-welded and PWHT conditions was considerably greater compared to that of the candidate metal.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Heat Input on Weld-Bead Geometry, Surface Chemical Composition, Corrosion Behavior and Thermal Properties of Fiber Laser-Welded Nitinol Shape Memory Alloy

Bead-on-plate laser welding was carried out on 1-mm-thick Nitinol sheets at different heat input values. The variations in weld-bead geometry and variations in microstructures across the bead were studied. The effects of heat input on surface layer composition of the welded samples, corrosion properties and phase transformation temperature were examined. From x-ray photoelectron spectroscopy (XPS), it was clear that relative intensity of elemental Ni peak was higher in parent material and the oxidation state of Ti was Ti{sup 4+}. It was further observed from Auger electron spectroscopy (AES) that the Ti to Ni ratio on the top surface of the welded samples was more than 1, and as a result of this the stability of TiO{sub 2} layer was enhanced, which eventually helped to improve the corrosion property of the welded samples. The polarization resistance of the welded samples was increased by more than ten times compared to that of the un-welded samples. From differential scanning calorimetry (DSC), it became evident that phase transformation temperatures got changed due to welding.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Creep Deformation and Rupture Behavior of P92 Steel Weld Joint Fabricated by NG-TIG Welding Process

The creep deformation and rupture behavior of P92 steel weld joint fabricated by narrow-gap TIG (NG-TIG) welding process have been investigated at 923 K over a stress range of 80-140 MPa. The prior-austenite grain size, M{sub 23}C{sub 6} precipitate size and hardness have been found to vary significantly in the weld joint. The reduction in hardness from weld metal to base metal with a trough at the outer edge of heat-affected zone (HAZ) has been observed. Coarsening of M{sub 23}C{sub 6} precipitate, recovery of martensite lath dislocation structure and formation of subgrain structure led to lower hardness in the intercritical HAZ. The creep rupture life of NG-TIG weld joint was lower than the base metal, the difference in creep rupture life between base metal and weld joint has been increased significantly with decrease in applied stress. The fracture location in the joint changed from base metal at high-stress regime to the fine grain (FG) HAZ (Type IV cracking) under lower stress level. Fracture in the FGHAZ evidenced the significant reduction in ductility, localized deformation and extensive localized cavitation. Extensive Laves phase formation with significant loss of solution strengthening contribution from tungsten and coarsening of M{sub 23}C{sub 6} precipitate with prolonged creep exposure led to reduction in hardness and more extensive cavitation in the FGHAZ resulting in premature Type IV failure of the weld joint. Weld strength reduction factor about 0.59 has been evaluated for 10{sup 5} h at 923 K.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Report Summarizing the Effort Required to Initiate Welding of Irradiated Materials within the Welding Cubicle

The advanced welding facility within a hot cell at the Radiochemical Engineering Development Center of Oak Ridge National Laboratory (ORNL), which has been jointly funded by the U.S. Department of Energy (DOE), Office of Nuclear Energy, Light Water Reactor Sustainability Program and the Electric Power Research Institute, Long Term Operations Program and the Welding and Repair Technology Center, is in the final phase of development. Research and development activities in this facility will involve direct testing of advanced welding technologies on irradiated materials in order to address the primary technical challenge of helium induced cracking that can arise when conventional fusion welding techniques are utilized on neutron irradiated stainless steels and nickel-base alloys. This report details the effort that has been required since the beginning of fiscal year 2017 to initiate welding research and development activities on irradiated materials within the hot cell cubicle, which houses welding sub-systems that include laser beam welding (LBW) and friction stir welding (FSW) and provides material containment within the hot cell.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Computerized adaptive control weld skate with CCTV weld guidance project

This report summarizes progress of the automatic computerized weld skate development portion of the Computerized Weld Skate with Closed Circuit Television (CCTV) Arc Guidance Project. The main goal of the project is to develop an automatic welding skate demonstration model equipped with CCTV weld guidance. The three main goals of the overall project are to: (1) develop a demonstration model computerized weld skate system, (2) develop a demonstration model automatic CCTV guidance system, and (3) integrate the two systems into a demonstration model of computerized weld skate with CCTV weld guidance for welding contoured parts.

Wall, W. A.↗
NASA NTRS1979

Weld bead reinforcement removal: A method of improving the strength and ductility of peaked welds in 2219-T87 aluminum alloy plate

The results of a study to determine the degree to which the ductility and tensile properties of peaked welds could be enhanced by removing the reinforcing bead and fairing the weld nugget into the adjacent parent metal are presented. The study employed 2219-T87 aluminum alloy plate, tungsten inert gas (TIG) welding, and 2319 filler wire. The study concluded that significant improvements in peak weld, ultimate strength, and ductility can be obtained through removal and fairing of the weld reinforcing bead. The specimens so treated and tested in this program exhibited ultimate strength improvements of 2 to 3 percent for peak angles of 5.8 to 10 degrees and 10 to 22 percent for welds with peak angles of 11.7 to 16.9 degrees. It was also determined that removal of the weld bead enhanced the ability of peaked welds to straighten when exposed to cyclic loading at stress levels above the yield strength.

Lovoy, C. V.↗
DOE OSTI2016

Characterization of as-welded microstructure of heat-affected zone in modified 9Cr–1Mo–V–Nb steel weldment

Non-equilibrium microstructure of the heat-affected zone (HAZ) in the as-welded modified 9Cr–1Mo–V–Nb pipe steel (P91) weldment deposited by gas tungsten arc welding (GTAW) and flux core arc welding (FCAW) has been characterized by field-emission scanning electron microscope (FESEM) and electron backscatter diffraction (EBSD). The heterogeneous structures in the sub-layers of the as-welded HAZ are attributable to phase transformations caused by the welding thermal cycles and the local structure variations in the as-received base metal. Coarse-grained heat-affected zone (CGHAZ) has a prior austenite grain (PAG) size of 20 μm. Fine uniformly-distributed precipitates and a higher fraction of MX carbonitrides are observed in the CGHAZ. Fine-grained heat-affected zone (FGHAZ) consists of the finest grains (1.22 μm measured by EBSD, 5 μm PAG size), coarse undissolved M{sub 23}C{sub 6} carbides within the PAG boundaries and fine nucleated M{sub 23}C{sub 6} particles within the martensite laths. Inter-critical heat-affected zone (ICHAZ) consists of partially austenitized grains and over-tempered martensite laths. EBSD kernel average misorientation (KAM) map in the FGHAZ close to the ICHAZ illustrates the greatest local strain variations with a moderate normalized KAM value of 0.92°. The majority (88.1%) of the matrix grains in the CGHAZ are classified as deformed grains by EBSD grain average misorientation (GAM) evaluation. The FGHAZ close to the ICHAZ has the most recrystallized grains with an area fraction of 14.4%. The highest density variation of precipitates within grains in the FGHAZ originates from the inhomogeneous chemistry in the base metal. - Highlights: •A comprehensive characterization of the as-welded HAZ of P91 weldment is conducted. •Structural features in the each layer of the HAZ are quantified by EBSD. •Structural heterogenities in HAZ are due to welding cycle and base metal structure. •FGHAZ contains the finest grain structure and largest precipitate density variation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Suggestion of an Indicator to Evaluate Material Deposition in Resistance Spot Welding: Weld–Surface Interaction Index

Resistance spot welding (RSW) is still leading joining process in the automotive industry due to the simplicity and speed of the process. On the other hand, galvanized steel sheets provide improvement in corrosion resistance of the auto body. Material deposition has an influence on the corrosion resistance and weld strength; however, in the literature very little effort has been made to identify any weld–surface interaction numerically. In this study, a numerical approach called “Weld–Surface Interaction Index” (I{sub WSI}) has been introduced to investigate the effect of material deposition on the corrosion sensitivity of the welding zone and its periphery. A systematic investigation was carried out to better understand the effects of an electrode cap–galvanized steel sheet interface on the corrosion resistance of spot-welded steel. The chemical composition of DP600 steel sheet and Z-Trode electrode cap was analyzed by using a spectrometer. The specimens were then joined by using same caps up to 1200 welds. SEM–EDS analysis was also performed on the chosen specimens to determine the weight percentages (wt.%) of Fe, Zn and Cu. EDS analysis results and coefficient of variation wt.% of Fe, Zn and Cu were used to compose I{sub WSI} formula. In the proposed formula, wt.% of Zn represented resistivity of the cover to corrosion, while wt.% of Fe represents the vulnerability.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Welding Speed on Zigzag Line Feature and Tensile Property of a Friction-Stir-Welded Al-Zn-Mg Aluminum Alloy

The zigzag line has significant and complicated effects on the mechanical properties of friction-stir-welded aluminum alloys. The zigzag line feature and its affecting characteristic on joint property are largely related to welding speed. In this paper, an Al-Zn-Mg aluminum alloy was butt friction-stir-welded, and the effects of welding speed on zigzag line feature and joint property were studied in detail in order to reveal the intrinsic correlations between the critical process parameter and the weld quality and, consequently, to provide guidance for the process optimization. The results indicate that at high welding speed of 300 mm/min, the loose and dilute distribution of the oxide layer fragments induces the relatively ambiguous zigzag line feature; the joint does not fail through the zigzag line during tensile test and shows superior tensile properties. With decreasing welding speed to 175 and 50 mm/min, the zigzag line feature is not weakened by the severer tool stirring action, as widely reported by previous studies, but is strengthened gradually due to the enhancement of the collective flow and more concentrated redistribution of broken oxide particles, leading to joint failure at zigzag lines and the degradation of tensile properties of joints.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Heat Input and Cold Wire Feeding Rate on Pitting Corrosion Resistance of Submerged Arc Welding Duplex Stainless Steel Welds

Welding thermal cycles may severely impair duplex stainless steel (DSS) performance, especially local pitting resistance and toughness. The restricted welding energy between 0.5 and 2.5 kJ mm{sup −1} represents a limiting factor for productivity increase in DSS welding, and the addition of cold wire is an interesting alternative to increase the welding deposition rate without adding extra heat. The aim of this work is to evaluate the influence of the cold wire feeding rate (CW) and heat input (HI) on pitting corrosion behavior of DSS UNS S32304 bead-on-plate welds obtained by submerged arc welding (SAW). Cyclic potentiodynamic polarization was carried out in transverse weld sections using 1 mol L{sup −1} NaCl solution at room temperature. Most pitting corrosion spots were located on the heat-affected zone (HAZ), and the pitting potentials were lower than the base metal due to higher ferrite fractions and the presence of chromium nitrides. Considering the same CW, the HI increasing reduced E{sub pit} for 1.6, 1.9, 2.2 kJ mm{sup −1}, but increased E{sub pit} for 2.7 kJ mm{sup −1}, due to a balance between the HAZ width and the austenite fraction.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Investigation of the oxide film on 308L weld surface produced during welding process

Highlights: • Double layer film formed under welding of no shielding was first deeply studied. • Micro-cracks and nano-scale gaps were found in outer and inner layer. • Outer layer was composed of Fe{sub 2}O{sub 3}, inner layer included Fe{sub 3}O{sub 4} and FeCr{sub 2}O{sub 4.} • Cr deficiency of film related to the volatilization of CrO{sub 3} over 1000 °C. • Oxidation rule of 308L weld during GTAW was found based on thermodynamics. The oxide film formed during welding on the inner surface of 308L weld was investigated. The morphology, composition and structure of the oxide film were characterized by optical microscopy, scanning electron microscopy, laser Raman spectroscopy, X-ray diffraction, Auger electron spectroscopy and transmission electron microscopy. The results indicated that the oxidation degree of the weld metal was generally uniform from the weld center to the fusion line. Micro-scale cracks were found on the outer surface of the oxide film and nano-scale gaps scattered on the inner oxide film-weld interface. The oxide film exhibited a duplex structure including outer and inner layers. The outer layer, made of tightly bound particles, was mainly composed of Fe{sub 2}O{sub 3} oxide particles with a diameter of 50–150 nm. And the inner layer, made of relative loosely bound particles, was mainly composed of Fe{sub 3}O{sub 4} and FeCr{sub 2}O{sub 4} oxide particles with a diameter of 10–50 nm. The corresponding oxidation behavior and mechanism of the oxide film were also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Weld Strength and Heat Affected Zone Size in Friction Welded NFA and CostE

Friction welding (FW) enables joining of dissimilar metals parts up to the limits of their strength. CostE and NFA are two high-temperature steel alloys used in land-based power generation. These alloys were joined with FW, and the effect of process parameters on post-welded structure and tensile strength was studied. Weld energy primarily determined the heat-affected zone (HAZ) thickness in both alloys. The highest joint efficiencies – up to 96% – resulted from contact strengthening of thin NFA HAZ regions, but too thin of a HAZ resulted in an unreliable joint. Conversely, thick HAZ regions consistently lowered the weld strength. Optimal welding conditions occur with sufficient energy to create a full bond but not so much to notably lower weld strength.

friction welding, rotary friction welding, nanostr↗
DOE OSTI2021

Solid-State Welding of the Nanostructured Ferritic Alloy 14YWT Using a Capacitive Discharge Resistance Welding Technique

Joining nanostructured ferritic alloys (NFAs) has proved challenging, as the nano-oxides that provide superior strength, creep resistance, and radiation tolerance at high temperatures tend to agglomerate, redistribute, and coarsen during conventional fusion welding. In this study, capacitive discharge resistance welding (CDRW)—a solid-state variant of resistance welding—was used to join end caps and thin-walled cladding tubes of the NFA 14YWT. The resulting solid-state joints were found to be hermetically sealed and were characterized across the weld region using electron microscopy (macroscopic, microscopic, and nanometer scales) and nanoindentation. Microstructural evolution near the weld line was limited to narrow (~50–200 μm) thermo-mechanically affected zones (TMAZs) and to a reduction in pre-existing component textures. Dispersoid populations (i.e., nano-oxides and larger oxide particles) appeared unchanged by all but the highest energy and power CDRW condition, with this extreme producing only minor nano-oxide coarsening (~2 nm → ~5 nm Ø). Despite a minimal microstructural change, the TMAZs were found to be ~10% softer than the surrounding base material. These findings are considered in terms of past solid-state welding (SSW) efforts—cladding applications and NFA-like materials in particular—and in terms of strengthening mechanisms in NFAs and the potential impacts of localized temperature–strain conditions during SSW.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Welding for testability: An approach aimed at improving the ultrasonic testing of thick-walled austenitic and dissimilar metal welds

Austenitic and dissimilar welds in thick walled components show a coarse grained, dendritic microstructure. Therefore, ultrasonic testing has to deal with beam refraction, scattering and mode conversion effects. As a result, the testing techniques typically applied for isotropic materials yield dissatisfying results. Most approaches for improvement of ultrasonic testing have been based on modeling and improved knowledge of the complex wave propagation phenomena. In this paper, we discuss an alternative approach: is it possible to use a modified welding technology which eliminates the cause of the UT complications, i.e. the large-grained structure of the weld seams? Various modification parameters were tested, including: TIG current pulsing, additional DC and AC magnetic fields, and also additional external vibrations during welding. For all welds produced under different conditions, the grain structure of the weld seam was characterized by optical and GIUM microstructure visualizations on cross sections, wave field propagation measurements, and ultrasonic tests of correct detectability of flaws. The mechanical properties of the welds were also tested.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Electron Beam Welding and Characterization of 21-6-9 Stainless Steel Annealed Plate and Welds

This report summarizes the electron beam (EB) welding and characterization work performed on annealed 21-6-9 stainless steel plate during the 2011-2012 time period. The work was directed at producing legacy autogeneous EB welds with the use of the Enhanced Modified Faraday Cup (EMFC) EB diagnostic to characterize the beam, and measuring the resulting tensile and hardness properties of the weld relative to annealed 21-6-9 stainless steel base metal. Different tensile bar configurations were produced, and the results were analyzed to determine how well the stress-strain behavior of small tensile samples compares to standard sized tensile samples for the same material. Additional comparisons were made between cross-weld tensile samples with and without weld steps to determine how the unwelded portion of a step joint affects the measured tensile behavior. Base metal tensile data was further used to calibrate a spherical indentation method to estimate uniaxial tensile behavior using a nanoindenter. The calibrated method was then used to generate the first engineering stress-strain curve for EB welded 21-6-9 stainless steel. Additional analysis was performed to determine Steinberg-Guinan and Johnson-Cook model parameters to represent both the annealed 21-6-9 SS base metal and the EB weld metal stress-strain behaviors under quasi static strain rate conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Open Source Laser Polymer Welding System: Design and Characterization of Linear Low-Density Polyethylene Multilayer Welds

The use of lasers to weld polymer sheets provides a means of highly-adaptive and custom additive manufacturing for a wide array of industrial, medical, and end user/consumer applications. This paper provides an open source design for a laser polymer welding system, which can be fabricated with low-cost fused filament fabrication and off-the-shelf mechanical and electrical parts. The system is controlled with free and open source software and firmware. The operation of the machine is validated and the performance of the system is quantified for the mechanical properties (peak load) and weld width of linear low density polyethylene (LLDPE) lap welds manufactured with the system as a function of linear energy density. The results provide incident laser power and machine parameters that enable both dual (two layers) and multilayer (three layers while welding only two sheets) polymer welded systems. The application of these parameter sets provides users of the open source laser polymer welder with the fundamental requirements to produce mechanically stable LLDPE multi-layer welded products, such as heat exchangers.

Laureto, John↗
NASA NTRS1981

A summary of tests on Invar welded with 308L and 8N12 welding rods

The cost and difficulty in obtaining Invarod, the recommended welding rod to weld Invar, nessitated the investigation of substituting more readily available rods that would meet the cryogenic design criteria for the National Transonic Facility (NTF). Two weld rods, 308L and 8N12, were chosen as promising candidates. Four welded specimen plates were made; two plates for each type of weld rod. One plate from each of the 308L and 8N12 weldings was thermally cycled 50 times between 366 K and 89 K while the two remaining plates were not thermally cycled. Specimens were machined from all four plates for three types of tests: tensile, charpy impact, and guided-bend. The methods in making the specimen plates, conduction of the tests, test results, and conclusions leading to the selection of a weld rod are presented.

Cox, J. W.↗
NASA NTRS1986

Seam tracking performance of a Coaxial Weld Vision System and pulsed welding

This report describes a continuation of a series of tests on the Coaxial Weld Vision System at MSFC. The ability of the system to compensate for transients associated with pulsed current welding is analyzed. Using the standard image processing approach for root pass seam tracking, the system is also tested for the ability to track the toe of a previous weld bead, for tracking multiple pass weld joints. This Coaxial Weld Vision System was developed by the Ohio State University (OSU) Center for Welding Research and is a part of the Space Shuttle Main Engine Robotic Welding Development System at MSFC.

Gangl, K. J.↗