Weld quality in the context of process control and internal conditions is studied. Several different alloys are welded including plain carbon steel, high-temperature steels, and several traditional and advanced superalloys. Across all studied weld systems, the following conditions led to stronger welds: higher forces and feedrates, lower temperatures, and moderate or limited upsets. In the best cases, post-weld strengths were nearly equal to basemetal strength. Tradition holds that large and symmetric upsets are necessary for good welds, but this study contradicts that notion. The fundamental requirements for bonding are two sufficiently clean surfaces in intimate contact. Only minimal upset is necessary to achieve that. In welding alloy 718, only 1 mm of feed (or ~0.4 mm of sample upset) was necessary to achieve $>$95\% of basemetal strength. In an advanced superalloy with low ductility, very low upsets were required in order to achieve high joint strength. For this low-ductility alloy, using a containing geometry increased both the internal pressure and ductility of this alloy, leading to a much larger window of sound welding conditions and stronger welds overall. In several dissimilar alloy systems, the relationship between force/feedrate and upset asymmetry varied between each alloy, but a more symmetric upset did not correlate to stronger welds. Advanced process control in FW was also performed with closed-loop temperature control and open-loop predictive cooling rate control. Using this technique, martensitic microstructures associated with a fast natural cooling rate were avoided, and a pearlitic microstructure was obtained. The yield and tensile strength of the weld was not adversely affected, and both were within range of published values for the basemetal.
| Identifer | oai:union.ndltd.org:BGMYU2/oai:scholarsarchive.byu.edu:etd-9705 |
| Date | 24 September 2019 |
| Creators | Taysom, Brandon Scott Boyer |
| Publisher | BYU ScholarsArchive |
| Source Sets | Brigham Young University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
| Rights | https://lib.byu.edu/about/copyright/ |
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