ICME Development of a Cold Spray Enabled Corrosion Resistant Bimetallic Structure for Nuclear Reactors

The bimetallic structure concept consisting of a corrosion resistant surface layer joined on top of an ASME code-approved substrate becomes a promising solution to address the corrosion issue of ASME substrate materials in molten salt environment. Specifically, refractory materials such as molybdenum, tungsten, and alloys containing them are found to be most resistant in molten salt environment and hence they have great potential to be used as the salt-facing surface layer. Due to the well-recognized difficulties of welding/printing refractory materials i.e., oxidation, brittle phase formation, cracking, etc.), cold spray, a deposition technology that minimizes material heating, avoids undesired thermal effects and maintains dimension stability, is an ideal approach for fabricating the bimetallic components. Under this SBIR program, QuesTek Innovations LLC, a leader in the field of Integrated Computational Materials Engineering ICME) and 2016 Tibbetts Award recipient, will apply its computational materials design methodologies to design cold sprayable, molten salt resistant, refractory-based e.g., Mo) powder compositions, in order to enable application of cold spray technology in fabricating bimetallic structures that consist of a salt resistant surface layer and an ASME code-certified substrate. Solvus Global, a leading company dedicated to advanced cold spray technology, will assist in conducting cold spray trials, optimizing spray parameters, and producing proof-of-concept coupons to demonstrate processing feasibility and joint performance. Prof. Vilupanur Ravi at Cal Poly Pomona, a distinguished professor with extensive experience in materials degradation in molten salt environment, will be the molten salt corrosion expert in our team to guide powder design and conduct molten salt corrosion test. H.C. Starck, a global leader in refractory metal products will produce powders and, as a commercialization partner, can support a strong path for commercialization of technology developed under this program. Idaho National Lab has expressed interest in our proposed technology and provided a letter of support. In the Phase I program, focus will be placed on cold spraying a Mo-based corrosion resistant surface layer onto a 316H stainless steel substrate ASME code-approved paradigm material) with the primary technical objective being computational design and experimental validation of a Mo-based powder composition that can be efficiently cold sprayed on 316H with satisfactory corrosion resistance and interfacial bond in experimental validation. Molten salt corrosion resistance of candidate powder compositions will be evaluated by immersion corrosion test at CPP. Cold-sprayed Mo/316H samples will be produced by optimized spray parameters and tested by accelerated heat treatment, thermal cycling, and standard adhesive strength test as proof-of-concept demonstration in Phase I. The impacts of irradiation on materials, although critical for reactor applications, lies outside the scope of Phase I due to limited funding and time, but can be added into the scope of Phase II if desired. Based on the results from the Phase I efforts, we envision that the objectives of Phase II may encompass refining the powder specs composition, size, impurity, shape, etc.), scaling-up selected cold spray designs, and validating additional material properties more comprehensively, such as more complex and realistic molten salt corrosion test, structural properties e.g., creep and fatigue), processibility e.g., capability of forming into tubular components), among others relevant to the reactor application and long term component integrity. Additional surface layer compositions e.g., W-based) may also be explored.