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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Postweld Heat Treatment on Toughness of Electric- Resistance Welded X70 Steel

In this report the effect of postweld heat treatment (PWHT) on Charpy V-notch impact toughness of a highfrequency electric-resistance welded (HF-ERW) grade X70 pipeline steel is investigated. PWHT thermal cycles are simulated using the Gleeble on the as-welded specimens. Microstructure, along with crystallographic texture and microhardness, is characterized in specimens that are impact tested at –5°C (23°F), –30°C (–22°F), and –45°C (–49°F). The impact toughness values show a wide scatter band and decrease with the increasing peak temperature of the PWHT. For higher peak temperatures, the microstructure of the heat-affected zone (HAZ) gradually changed from equiaxed ferrite to bainitic ferrite. Furthermore, the prior austenite grain size (PAGS) increases with the increasing peak temperature. The density of high-angle grain boundaries decreases, and the fraction of cleavage planes {100} parallel to the impact fracture plane increases for higher peak temperatures of the PWHT

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nanoindentation Investigation of Chloride-Induced Stress Corrosion Crack Propagation in an Austenitic Stainless Steel Weld

Transgranular chloride-induced stress corrosion cracking (TGCISCC) is a mounting concern for the safety and longevity of arc welds on austenitic stainless steel (AuSS) nuclear waste storage canisters. Recent studies have shown the key role of crystallography in the susceptibility and propagation of TGCISCC in SS weldments. Given that crystallography underlies mechanical heterogeneities, the mechanical-crystallographic relationship during TGCISCC growth must be understood. In this study, welded SS 304L coupons are loaded in four-point bend fixtures and then boiled in magnesium chloride to initiate TGCISCC. Nanoindentation mapping is paired with scanning electron microscopy (SEM) electron backscatter diffraction (EBSD) to understand the correlation between grain orientation, grain boundaries, and hardening from TGCISCC propagation. The nanoindentation hardness of individual grains is found to not be a controlling factor for TGCISCC propagation. However, intragranular hardness is generally highest immediately around the crack due to localized strain hardening at the crack tip. This work shows that nanoindentation techniques can be useful in understanding CISCC behaviors when paired with electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Analysis of High-Power Diode Laser Heating Effects on HY-80 Steel for Laser Assisted Friction Stir Welding Applications

In this research, several conditions of high power diode laser heated HY-80 steel were characterized to determine the viability of using such lasers as a preheating source before friction stir welding in order to reduce frictional forces thereby reducing tool wear and increasing welding speeds. Differences in microstructures within heat affected zones were identified at specific laser powers and traverse speeds. Vickers hardness values were recorded and analyzed to validate the formation of additional martensite in diode laser heated regions of HY-80 steel. Conditions that produced little to no additional martensite were identified and relationships among high power diode laser power, traverse speed, and martensite formation were determined. The development of heat affected zones, change in grain structure, and creation of additional martensite in HY-80 can be prevented through the optimization of laser amperage and transverse speed.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Joining of 14YWT and F82H by Friction Stir Welding

The feasibility of using friction stir welding (FSW) to join specimens of the advanced oxide dispersion strengthened (ODS) 14YWT nanostructured ferritic alloy (NFA) and a plate of F82H tempered martensitic steel (TMS) was investigated. The sample used in the FSW experiment consisted of spot welding four specimens 14YWT prepared from prior tested dual notch fracture toughness bend bars in a corresponding slot that was machined in the F82H plate. The FSW run was successfully performed on the sample using a polycrystalline boron nitride tool (PCBN) that resulted in joints showing good bonding between butt joints of 14YWT specimens and 14YWT specimens and F82H plate. The joints were characterized by light microscopy and SEM analysis and were observed to be relatively narrow in width. The ultra-fine grain size associated with 14YWT increased by a factor of up to 3 while that of F82H was refined by a considerable amount in the thermomechanically affected zones (TMAZ) due to FSW. In addition, porosity was observed in the TMAZ of 14YWT on the advancing side of the FSW joint and at the interface between F82H and 14YWT. Vickers hardness (VH) measurements showed a decrease of ~120 VH from ~500 VH (~20% decrease) for 14YWT and an increase of ~220 VH from ~220 VH (~100% increase) for F82H in the FSW zones. Further refinements in the FSW process will be required to minimize defects including porosity.

Hoelzer, David T↗
DOE OSTI2016

Solid cartridge for a pulse weld forming electrode and method of joining tubular members

A cartridge assembly is disclosed for a pulse welding a first tube supported on a mandrel to a second tube. An outer tool is assembled over the second tube and a stored charge is discharged in the cartridge assembly. The cartridge comprises an annular conductor and a solid casing enveloping the conductor. The stored charge is electrically connected to the conductor and discharged through the conductor to compress the second tube and pulse weld the second tube to the first tube.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Friction stir weld tools having fine grain structure

Tools for friction stir welding can be made with fewer process steps, lower cost techniques, and/or lower cost ingredients than other state-of-the-art processes by utilizing improved compositions and processes of fabrication. Furthermore, the tools resulting from the improved compositions and processes of fabrication can exhibit better distribution and homogeneity of chemical constituents, greater strength, and/or increased durability. In one example, a friction stir weld tool includes tungsten and rhenium and is characterized by carbide and oxide dispersoids, by carbide particulates, and by grains that comprise a solid solution of the tungsten and rhenium. The grains do not exceed 10 micrometers in diameter.

36 MATERIALS SCIENCE↗
DOE OSTI2017

System for evaluating weld quality using eddy currents

Electromagnetic and eddy current techniques for fast automated real-time and near real-time inspection and monitoring systems for high production rate joining processes. An eddy current system, array and method for the fast examination of welds to detect anomalies such as missed seam (MS) and lack of penetration (LOP) the system, array and methods capable of detecting and sizing surface and slightly subsurface flaws at various orientations in connection with at least the first and second weld pass.

42 ENGINEERING↗
DOE OSTI2022

Methods for thermal welding of wind turbine blades

Disclosed herein are methods, devices, and systems for manufacturing wind turbine blades which in some instances require using new blade joint designs. The blade joint designs described herein may allow for contact in places where welds will be made, which allows for existing manufacturing tolerances to be used while still enabling the use of thermal welding for wind turbine blades.

17 WIND ENERGY↗
DOE OSTI2021

Some Physics Fundamentals of High Energy Density Welding

The purpose of this section of this document is to provide a brief summary of the physics aspects of high energy density welding (HEDW). One reason for this is to help elucidate some of the differences between EBW and LBW. A fundamental understanding of these differences can help guide an appropriate choice of process for a particular application.

42 ENGINEERING↗
DOE OSTI2018

Welding Defect Classification from Simulated Ultrasonic Signals

Nondestructive testing is widely used to detect and to size up discontinuities embedded in a material. Among the several ultrasonic techniques, time of flight diffraction (TOFD) combines high speed inspection, high sizing reliability and low rate of incorrect results. However, the classification of defects through ultrasound signals acquired by the TOFD technique depends heavily on the knowledge and experience of the operator and thus, this classification is still frequently questioned. Besides, this task requires long processing time due to the large amount of data to be analyzed. Nevertheless, computational tools for pattern recognition can be employed to analyze a high amount of data with large efficiency. In the present work, simulation of ultrasound propagation in two-dimensional media containing, each one, different kinds of modeled discontinuities which mimic defects in welded joints were performed. Clustering (k-means) and classification (principal component analysis and k-nearest neighbors) algorithms were employed to associate each simulated ultrasound signal with its corresponding modeled defects. The results for each method were analyzed, discussed and compared. The results are very promising.

42 ENGINEERING↗
DOE OSTI2018

Laser Welding-Brazing of Immiscible AZ31B Mg and Ti-6Al-4V Alloys Using an Electrodeposited Cu Interlayer

Metallurgical bonding between immiscible system AZ31B magnesium (Mg) and Ti-6Al-4V titanium (Ti) was achieved by adding Cu interlayer using laser welding-brazing process. Effect of the laser power on microstructure evolution and mechanical properties of Mg/Cu-coated Ti joints was studied. Visually acceptable joints were obtained at the range of 1300 to 1500 W. The brazed interface was divided into three parts due to temperature gradient: direct irradiation zone, intermediate zone and seam head zone. Ti{sub 3}Al phase was produced along the interface at the direct irradiation zone. Ti-Al reaction layer grew slightly with the increase in laser power. A small amount of Ti{sub 2}(Cu,Al) interfacial compounds formed at the intermediate zone and the (α-Mg + Mg{sub 2}Cu) eutectic structure dispersed in the fusion zone instead of gathering when increasing the laser power at this zone. At the seam head zone, Mg-Cu eutectic structure was produced in large quantities under all cases. Joint strength first increased and then decreased with the variation of the laser power. The maximum fracture load of Mg/Cu-coated Ti joint reached 2314 N at the laser power of 1300 W, representing 85.7% joint efficiency when compared with Mg base metal. All specimens fractured at the interface. The feature of fracture surface at the laser power of 1100 W was characterized by overall smooth surface. Obvious tear ridge and Ti{sub 3}Al particles were observed at the fracture surface with increase in laser power. It suggested atomic diffusion was accelerated with more heat input giving rise to the enhanced interfacial reaction and metallurgical bonding in direct irradiation zone, which determined the mechanical properties of the joint.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure Evolution and Mechanical Properties of High-Speed Friction Stir Welded Aluminum Alloy Thin Plate Joints

Sound friction stir welded (FSW) joints of 6061-T6 aluminum alloy sheets with an 0.8 mm thickness were obtained at conventional speed (2000 rpm, 300 mm/min) and high speed (11,000 rpm, 1500 mm/min). The recrystallization mechanism, precipitate evolution, mechanical properties and fracture behavior were investigated in detail. Microstructure analyses revealed that the grain structure evolution in the nugget zone (NZ) was dominated by continuous dynamic recrystallization. In the process of FSW, high speed facilitates the formation of finer equiaxed recrystallized grains, higher density of dislocations and substructures, and a larger number of precipitates in the NZ compared to the conventional speed, which further significantly improves the hardness and tensile strength of the joints. The maximum tensile strength was obtained with 292.6 MPa, 83.2% for the 6061-T6 aluminum alloy and 122.6% for the conventional-speed FSW joints. This work provides an effective method for preparing FSW aluminum alloy thin plate joints with excellent mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced Strength of 304 SS-Ti6Al4V Laser-Welded Joints Containing Composite Interlayers

This paper investigates the microstructural characterization of the fracture propagation edge during laser beam welding of Ti6Al4V and 304 stainless steel using Cu, V, and Ni interlayers as a single Cu interlayer and composite interlayer structures with different Cu interlayer thicknesses. This study attempts to increase the Ti-SS joint strength through the use of the composite interlayers. X-ray diffraction characterization based on a 0.5-mm-thick Cu interlayer showed that the SS/Cu/Ti joint contained considerable brittle IMCs; however, the fracture surface of the SS/Cu-V/Ti composite interlayer sample did not contain any Fe-Ti IMCs or Cr{sub 2}Ti. EBSD observation indicated that the crack propagated transgranularly from solidified CuTi in the interdendritic regions of the FeTi compounds in the composite interlayer sample; however, the crack propagated intergranularly along Fe{sub 2}Ti grain boundaries in the single interlayer sample. The investigation based on a 1-mm-thick Cu interlayer showed that the SS/Ni-Cu1/Ti sample was stronger than the SS/Cu1/Ti sample due to a lack of CuTi at 3.5 kW. The tensile strength of the SS/Cu1-V/Ti joint was greater than that of the SS/Ni-Cu1/Ti joint due to the formation of ductile NiTi instead of brittle NiTi{sub 2}. The microstructures of the fracture edges after tensile testing illustrated that the eutectic CuTi + CuTi{sub 2} fractured at the SS/Cu1/Ti joint after tensile testing, while CuTi{sub 2} and eutectoid αTi + CuTi{sub 2} compounds fractured during the tensile experiment at the SS/Ni-Cu1/Ti and SS/Cu1-V/Ti joints, respectively. Investigations based on both the 0.5- and 1-mm-thick Cu interlayers showed that the tensile strength and elongation of the composite interlayer joints at a laser power of 3.5 kW were greater than those of the single interlayer joints.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influencing mechanism of pre-existing nanoscale Al 5 Fe 2 phase on Mg–Fe interface in friction stir spot welded Al-free ZK60–Q235 joint

Al-free ZK60 magnesium (Mg) alloy sheet was selected as substrate material of Mg–steel pinless friction stir spot welding (FSSW), avoiding the effect of the Al element in the substrate on the alloying reaction of Mg-iron (Fe) interface. The sound FSSW joint of ZK60 Mg alloy and Q235 steel with a hot-dipped aluminum (Al)-containing zinc (Zn) coating was successfully realized. The detailed microstructural examinations proved that Al 5 Fe 2 phase at the Mg-Fe interface came from the pre-existing Al 5 Fe 2 phase in the coating and acted as the transition layer for promoting the metallurgical bonding of Mg and Fe. The interfaces with well-matched lattice sites among Fe, Al 5 Fe 2 and Mg were formed during FSSW. A low energy interface with good match of lattice sites ((002) Al5Fe2 //(110) Fe , [110] Al5Fe2 //[13] Fe ) between Al 5 Fe 2 and Fe was identified. For the interface between Al5Fe2 and Mg, an orientation relationship of ( 6 2 ¯ 2 ) A l 5 F e 2 / / ( 3 1 ¯ 1 ¯ 2 ¯ ) M g and [ 1 5 ¯ 8 ¯ ] A l 5 F e 2 / / [ 2 4 ¯ 23 ] M g was observed. The tensile–shear load of the ZK60–steel joint could reach 4.6 kN. Moreover, the joint fracture occurred at the interface between the Al5Fe2 layer and the Mg alloy substrate, suggesting the brittle fracture characteristic.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructure and mechanical properties of resistance-spot-welded joints for A5052 aluminum alloy and DP 600 steel

The microstructure and mechanical properties of resistance-spot-welded A5052 aluminum alloy and DP 600 dual-phase steel joint were studied. The fusion zone (FZ) and heat-affected zone (HAZ) of DP 600 exhibited lath martensite and ferrite-martensite structures, respectively. The microstructure of FZ and HAZ in the A5052 side was composed of cellular crystals and the boundary region of FZ exhibited a columnar crystal morphology. A Fe{sub 2}Al{sub 5} intermetallic compound (IMC) layer with 3.3 μm thickness was found adjacent to the DP 600 side, whereas a needle-shaped Fe{sub 4}Al{sub 13} IMC layer with length of 0.67 μm to 15.8 μm was found adjacent to the aluminum alloy side. The maximum tensile shear load of the A5052/DP 600 joint was 5.5 KN, with a corresponding molten nugget diameter of 6.3 mm. The fracture morphology of the optimized A5052/DP 600 joint was mainly an elongated dimple fracture accompanied by cleavage fracture. - Highlights: •A5052 and DP 600 with large gaps in properties were investigated by RSW. •The microstructures of RSW joints in DP 600/A5052 were examined detailedly. •The micro/macro-characteristics and strength relations of joints were analyzed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The relationship between low-temperature toughness and secondary crack in low-carbon bainitic weld metals

Highlights: • The crack propagation plane was identified with the decreasing possibility of {110}/{100}, {112} and {123}. • Crack path deviates at some middle-angle misorientation boundaries with high strain concentration. • The most effective barrier to arrest crack in Ni0 and Ni2 is the boundaries of inter-Bain in a CPP packet, while in Ni4 the boundaries of inter-CPP and intra-Bain packets impede crack propagation. - Abstract: This paper aims to reveal the relationship among low-temperature toughness, microstructure and secondary crack from both microstructural and crystallographic perspectives. Instrumented Charpy tests were carried out in the upper platform, transition temperature range, as well as at lower temperatures. Quantitative fractographic analysis, microstructural characterization and secondary crack observation were conducted on half of the impact specimen. Crystallographic features were identified in the secondary crack proximity, e.g. variant selection, orientation relationship, cleavage plane of the corresponding crack matrix. Some results in literature are confirmed. Nickel addition is beneficial to hindering crack propagation as a result of microstructure improvement. The most effective barrier for crack propagation is high-angle misorientation boundaries between Bain packets and the boundaries of ferrite matrix with the microstructure of granular bainite. Additionally, high-angle misorientation boundaries between closed-packed plane packets arrest cracks in the mixed microstructure of fine lath bainite and intricate acicular ferrite. Most preferred crack propagation planes are {110} and {100} in our low carbon bainitic weld metals, with the decreasing possibility of {112} and {123}.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Structure and properties of fixed joints formed by ultrasonic-assisted friction-stir welding

This paper deals with structure and properties of aluminum alloy 7475 and its joints obtained by friction stir welding including under ultrasonic action. Microhardness measurements show that ultrasonic action increases strength properties of the joints. Optical and transmission electron microscopy reveals that this effect is related to the precipitation of tertiary coherent S-and T-phase particles.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Impact of tool wear on joint strength in friction stir spot welding of DP 980 steel

Friction stir spot welding has been shown to be a viable method of joining ultra high strength steel (UHSS), both in terms of joint strength and process cycle time. However, the cost of tooling must be reasonable in order for this method to be adopted as an industrial process. Recently a new tool alloy has been developed, using a blend of PCBN and tungsten rhenium (W-Re) in order to improve the toughness of the tool. Wear testing results are presented for two of these alloys: one with a composition of 60% PCBN and 40% W-Re, and one with 70% PCBN and 30% W-Re. The sheet material used for all wear testing was 1.4 mm DP 980. Lap shear testing was used to show the relationship between tool wear and joint strength. The Q70 tool provided the best combination of wear resistance and joint strength.

36 MATERIALS SCIENCE↗