No Stress PFC Bonding Technology

Electric power generation regularly necessitates the conversion of heat into useful work. Except for some renewable forms, all energy production involves high-temperature. In cases such as fusion, fission, gas-turbine, and fuel cells, the operating temperatures can be very high. Working parts exposed to these environments are thermally stressed. The material joints found in multi-component parts must be designed to address the effects of high-temperature joining in addition to these harsh service conditions. SOC is proposing a novel bonding technology that is designed to reduce residual stress arising from high- temperature bonding of dissimilar materials. In this technology, a bonding material is formed as a blended composite such that its thermal expansion rate changes continuously from high-to-low across the bonding gap. In such a graded composite, the expansion rate nearest each surface closely matches that of the respective parent materials. In Phase I, this composite bonding technology will be evaluated for the manufacture of critical fusion energy components. Magnetically confined fusion components are exposed to higher heat flux and neutron irradiation than fission reactor components. For the next generation fusion reactors, tungsten and specialty, low-activation steels have been identified as the most likely construction materials for plasma facing components (PFC). In this study, the strength and toughness of continuously graded tungsten and mild-steel composites will be compared to that achieved by brazing with a commercial alloy commonly used to bond tungsten and steel. The optimum property gradient for strength and toughness will be determined by mechanical and microstructural analyses. This universal bonding approach, using a continuously graded coefficient of thermal expansion, can significantly benefit the design of high-temperature components made by joining dissimilar materials. Many energy-related technologies could benefit from new, robust bonding methods. The attachment of tungsten hard faces onto earth-boring drills, joining plate-fin assemblies in Intermediate Heat Exchangers (IHX) for Next Generation Nuclear Plants (NGNP), and sealing high-temperature gas separation equipment are a few examples.