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Current fusion reactor designs often use a tungsten (W) to copper joint as part of the cooling structure in the plasma-facing components. Future fusion reactors may operate at temperatures above the operating window for copper. Therefore, robust joints between W and advanced steels are desired for fabricating plasma-facing components. A W-steel composite or functionally graded material is advantageous to minimize the stresses at the interface because of the thermal expansion coefficient mismatch between W and steel. Here, two methods of creating W-steel composites are examined: hot rolling and ultrasonic welding. Both methods utilize W foil because it has a ductile to brittle transition temperature below room temperature. Three initial thicknesses of W foil were utilized to fabricate the composites, 25 µm, 100 µm, and 250 µm. Before composite fabrication, each foil thickness has a different crystallographic texture and different grain size distribution. The differences in W foil properties resulted in different properties of the composites. The hot rolling method is a standard processing method and results in a significant intermetallic bond layer between the steel and the tungsten. The ultrasonic welding method is advantageous because it is a solid-state joining technique that reduces the thickness of intermetallic formed. However, ultrasonic welding of refractory metals presents other challenges such as a tendency of the W foils to shatter or delaminate during processing. The composites were analyzed with scanning electron microscopy and energy dispersive X-ray spectroscopy. Tensile and hardness tests were performed on the composites.
This work was supported by the Office of Fusion Energy Sciences, U.S. Department of Energy, under contract DE-AC05-00OR22725 with UT-Battelle, LLC.
| Eligible for student paper award? | No |
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