||Abdelrahman Abdelmotagaly, Timothy Pickle, Aric Adamson, Zhenzhen Yu, Chad Augustine, Judith Vidal, Benjamin Rafferty, Jeremy Iten
Most of the current advanced concentrated solar power (CSP) plants operate with power towers incorporated with two molten salt tanks for thermal energy storage. These systems deliver thermal energy at a temperature of 565░C for integration with conventional steam-Rankine power cycles. The target of Gen3 CSP is to reduce the cost of CSP-generated power by enhancing the plant efficiency. There is a great potential to achieve this target through increasing the operating temperature higher than 700░ C. On the other hand, the severe service conditions of Gen3 CSP require higher grades of materials to withstand an operation temperature range of 500-750 ℃ while in contact with molten salts, such as Ni-based superalloys. The high material cost imposes a challenge for Gen3 CSP capital cost control. In addition, conventional fabrication methods, such as large-scale machining, forging and casting, for components designed for Gen3 CSP, are cost and time consuming, which adds another barrier for achieving the target economic efficiency of Gen3 CSP. Thus, more cost-effective solutions have to be tailored to reduce the cost of the utilized alloys as well as their manufacturing techniques.
Laser powder bed fusion additive manufacturing (LPBF) was selected for study as an alternative technique for CSP component fabrication. After initial screening for strength, corrosion resistance, and compatibility, H282 and In740H alloys were chosen as candidate materials. Since different locations across the CSP would potentially require similar and dissimilar welding, multiple weld samples were studied including gas tungsten arc welding (GTAW) similar weldments of H282 and In740H AM to their wrought plates, and GTAW dissimilar weldments of H282 and In740H to SS 304H. Digital image correlation (DIC)- assisted thermomechanical testing was performed on transverse weld samples to compare the weld strength to each relative wrought alloy strength. Moreover, cross sectional samples were extracted from the various welds for metallurgical characterization, hardness profile evaluation, and dilution calculations.
Thermomechanical testing of the similar GTAW samples showed that almost all LPBF to wrought welds exceeded 80% of wrought alloy strength for samples tested at 720 ║C and RT. However, H282 LPBF to wrought welds tested at 500║C reached only 77% of wrought H282, due to early fracture associated with weld defects. Also, all tested dissimilar GTAW samples have exceeded 80% strength of wrought SS304H properties. After post-weld aging heat treatment of the H282/ SS304H dissimilar welds, a noticeable coarsening occurred in the Ti, Mo, and Cr carbide particles at the interface between the SS304H and the filler metal, which may affect the failure behavior of these welds adversely.