Low-Cost Alloys for High-Temperature SOFC System Components

Under this SBIR program, QuesTek Innovations LLC will apply its computational alloy design methodology and experience with high-Cr stainless ferritic alloy and oxidation modeling to create a novel low-cost alloy for SOFC with low Cr volatility and high oxidation resistance that is also weldable, to resolve a major technical challenge in SOFC commercialization. QuesTek has partnered with FuelCell Energy (FCE), a global leader in the manufacture and commercialization of stationary fuel cell power plants. FuelCell Energy has more than 30 years of experience in fuel cell research and commercialization, whose products including the Direct FuelCell have successfully generated over 900 million kW hours of electricity in 50 locations worldwide. QuesTek has generated two unique alloy micro-structural concepts to achieve cost-effectiveness, oxidation resistance and low Cr volatility in its new alloys: 1) Alumia-forming ferritic alloy that develops a thermally grown oxide (TGO) layer with slow growth kinetics that serves as a Cr diffusion barrier on the alloy substrate and provides additional oxidation resistance. One of the concerns of this approach is the reduced room-temperature toughness due to high aluminum content 2) in-situ spinel forming ferritic alloy that grows a spinel oxide layer on top of Cr2O3 to reduce Cr vaporization rate, similar to custom alloys such as Crofer 22. Spinel system(s) with minimal Cr solubility and diffusivity will be incorporated into the alloy designs. In this Phase I program, QuesTek will demonstrate the feasibility to achieve both high oxidation resistance and low Cr-volatility by implementing its oxidation model, which is based on Calculation of Phase Diagram (CALPHAD) multi-component tools. QuesTek may also invoke reliable mechanistic process-structure-property models to accurately predict other important properties such as weldability and fracture toughness. QuesTek will investigate the potential of the identified microstructural concepts via the development and application of computational materials models that will be validated at laboratory-scale. Based upon the laboratory-scale results, QuesTek will design prototype alloys using its integrated suite of material design models. QuesTek will demonstrate the feasibility of the initial designs by producing 15 lb sub-scale prototype ingot and evaluate them against program goals including Cr- volatility, oxidation resistance, creep resistance, weldability and cost. The prototypes will be characterized specifically on chromium loss rate, oxide growth rate, oxide morphology, heat treatment response, solidification behavior, etc. Microstructural and property characterization data will feedback into QuesTek property and process modeling tools for further refinement. Based on the results from the Phase I prototype alloys, and on input from project stakeholders (including the DOE and OEM stakeholders), the objective of Phase II is to finalize the alloy design and demonstrate improved oxidation resistance and suppressed chromium volatility. Working with one of its suppliers, QuesTek will have prototype ingots manufactured to specification at larger size scale. Low-Cr volatility, oxidation resistance, thermal fatigue resistance and weldability will be demonstrated in the intermediate scale material in simulated SOFC service environment. In Phase III our investigations will be expanded (in conjunction with our OEM partners) to include component level testing and qualification. Application of the alloy to additional components with similar requirements will be identified and pursued.