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Electron beam welding processes have highly accurate control of both spatial and temporal heating profiles which provide unique capabilities in dissimilar metals joining. In this work, electron beam welds were made between commercially pure nickel and iron to determine the effect of fusion zone composition on solidification behavior and microstructure evolution. The weld was made with a beam deflected in a circular pattern to enable joining and promote mixing. The beam traveled at a shallow angle of approximately 1 deg to the joint interface starting in the nickel and finishing in the iron. The shallow angle created a weld with a composition gradient along its 110 mm length. The solidification behavior and final weld microstructure were characterized using both light optical microscopy and scanning electron microscopy. Electron backscatter diffraction was used to determine the phase fractions in the fusion zone. A change in solidification mode from face-centered cubic austenite to body-centered cubic ferrite was observed as a function of fusion zone composition. Weld cross-sections containing 65.5 wt pct Fe and 76.9 wt pct Fe had a two-phase fcc + bcc microstructure. Using the compositions and phase fractions, the two-phase region was estimated to be between 56.4 and 79.7 wt pct Fe. Martensite was observed in cross-sections containing between 76.9 wt pct Fe and 98.1 wt pct Fe, which was confirmed using hardness measurements.
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The Effects of Target Thicknesses and Backing Materials on a Ti-Cu Collision Weld Interface Using Laser Impact Welding
This study demonstrates that the thickness of the target and its backing condition have a powerful effect on the development of a wave structure in impact welds. Conventional theories and experiments related to impact welds show that the impact angle and speed of the flyer have a controlling influence on the development of wave structure and jetting. These results imply that control of reflected stress waves can be effectively used to optimize welding conditions and expand the range of acceptable collision angle and speed for good welding. Impact welding and laser impact welding are a class of processes that can create solid-state welds, permitting the formation of strong and tough welds without the creation of significant heat affected zones, and can avoid the gross formation of intermetallic in dissimilar metal pairs. This study examined small-scale impact using a consistent launch condition for a 127 µm commercially pure titanium flyer impacted against commercially pure copper target with thicknesses between 127 µm and 1000 µm. Steel and acrylic backing layers were placed behind the target to change wave reflection characteristics. The launch conditions produced normal collision at about 900 m/s at the weld center, with decreasing impact speed and increasing angle moving toward the outer perimeter. The target thickness had a large effect on wave morphology, with the wave amplitude increasing with target thickness in both cases, peaking when target thickness is about twice flyer thickness, and then falling. The acrylic backing showed a consistently smaller unwelded central zone, indicating that impact welding is possible at a smaller angle in that case. Strength was measured in destructive tensile testing. Failure was controlled by the breakdown of the weaker of the two base metals over all thicknesses and backings. This demonstrates that laser impact welding is a robust method for joining dissimilar metals over a range of thicknesses.
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- Award ID(s):
- 2133630
- PAR ID:
- 10530899
- Publisher / Repository:
- Metals (MDPI)
- Date Published:
- Journal Name:
- Metals
- Volume:
- 14
- Issue:
- 3
- ISSN:
- 2075-4701
- Page Range / eLocation ID:
- 342
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The need for joining dissimilar materials is increasing rapidly in manufacturing industries. Therefore, a successful weld of dissimilar metals by Friction Stir Welding (FSW) process becomes a topic of interest for many investigators. FSW research topics have been used for Manufacturing Engineering students at Virginia State University as undergraduate research projects. The purpose of this study was to investigate intermetallic characteristics between aluminum and copper at the transition zone in the FSW process. The effects of process parameters on heat affected zone (HAZ) have been examined to find the optimal tool rotational speed, axial force, and transverse speed. A metallographic study was conducted to investigate the quality of intermetallic bonding at the interfaces. It was observed that using optimized process parameters for experimental setup resulted in a very good quality of the welds.more » « less
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We present the first results of laser-driven flyer plate experiments on a nanocrystalline copper-tantalum (NC–Cu–Ta) alloy. A pulsed Nd:YAG laser (1.2 J/pulse, 10 ns) is used to accelerate an Al foil disk (25 μm × ∼800 μm) off a glass substrate at velocities of 0.8 and 2.4 km/s through a small air gap and impact the NC–Cu–Ta target. The flyer velocities were determined from a high-speed video and extensive post-impact analyses were conducted using advanced electron microscopy revealing the formation of a band structure leading to a non-trivial upper bound for the breakdown of an extremely stable NC-microstructure and physical-properties.more » « less
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Dissimilar metal welds (DMWs) are routinely used in the oil and gas industries for structural joining of high-strength steels to eliminate the need for post-weld heat treatment (PWHT) in field welding. Hydrogen-assisted cracking (HAC) can occur in DMWs during subsea service under cathodic protection. DMWs of two material combinations, 8630 steel/FM 625 and F22 steel/FM 625, produced with two welding procedures, non-temper bead (BS1) and temper bead (BS3), in the as-welded and PWHT conditions were investigated in this study. These DMWs were subjected to metallurgical characterization and testing with the delayed hydrogen cracking test (DHCT) to identify the effects of base metal composition, welding and PWHT procedures on their HAC susceptibility. The HAC susceptibility was ranked using the time to failure in the DHCT at loads equivalent to 90% of the base metal yield strength (YS) and the apparent stress threshold for HAC. A criterion for resistance to HAC in the testing conditions of DHCT was also established. The results of this study showed that 8630/FM 625 DMWs were more susceptible to HAC than the F22/FM 625 DMWs. PWHT did not sufficiently reduce the HAC susceptibility of the 8630/FM 625 and F22/FM 625 BS1 welds. DMWs produced using BS3 performed better than BS1 DMWs. The post-weld heat-treated F22/FM 625 BS3 DMW passed the HAC resistance criterion.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/met14030342
