NSUF 24-5069: Influence of laser welding on deformation mechanisms in irradiated and weld-repaired Ni-Cr alloys

The objective of this project is to evaluate the influence of laser welding on the deformation mechanisms in Ni-Cr alloys intended for advanced reactor applications, and for potential to use laser welding to repair these alloys following irradiation. Ni-Cr alloys are widely used for structural components in light water reactors (LWRs) and are leading candidates for structures and vessels of advanced reactors. This class of alloys is known for its high temperature creep strength, oxidation resistance, and relative passivity in molten salts. Given these favorable attributes and broad applicability across current and future reactor designs, it is critical to establish reliable and repeatable processes for joining of new Ni-Cr components as well as weld repair of in-service (i.e., irradiated) Ni-Cr components. Unfortunately, most established joining processes (e.g., arc welding and friction stir welding) result in significant alteration of the microstructures, compromising the favorable mechanical properties and environmental resilience for which Ni-Cr alloys are engineered. In the case of weld repair of an irradiation-embrittled, cracked component in-service, the weld heat input can result in significant coarsening of gas bubbles, exacerbating cracking. Alternatively, low heat-input laser welding is a promising candidate for joining Ni-Cr alloys due to its smaller heat affected zone and fast cooling rates that limits the microstructure coarsening, reduction in mechanical properties, and compromised irradiation resistance. Previous studies of laser welding have revealed a significant influence on the deformation mechanisms in f.c.c. structured materials, specifically deformation-induced martensitic transformations. In a prior study of 304 stainless steel, laser welding resulted in significant grain size reduction within the fusion zone, which proved to be stronger than the surrounding bulk material, resulted in an ~40% increase in ductility, and dramatically reduced the martensitic deformation-induced phase transformation. In a weld-repair scenario, laser welding of previously irradiated 304L SS caused annealing of irradiation-induced cavities, which makes the activation of deformation-induced martensitic transformations more difficult. Since the possibility of deformation-induced martensitic transformations in Ni-Cr alloys has recently been demonstrated, there is a need to evaluate these deformation mechanisms in laser welded Ni-Cr alloys for both weld fabrication and weld repair scenarios. The ability to finely control heat input via laser welding offers the opportunity to achieve smaller grains in the fusion zone, likely improving overall irradiation resistance. Plus, it will be important to understand if laser welding in f.c.c.-based Ni-Cr alloys can retain strength while limiting the martensitic transformations that otherwise have the potential to limit ductility. To address this knowledge gap, our proposal involves a two-pronged approach to evaluate the combined effects of laser welding and irradiation on the microstructure and deformation mechanisms in Ni-Cr Alloy 625. First, unirradiated samples of the material will be laser-welded (using optimized parameters) and subsequently irradiated with protons. Next, samples of the same alloy that were previously irradiated in ATR will be laser-welded using the same process and parameters to simulate a weld-repair scenario. Each specimen will be comparably characterized to clearly understand the influence of each process on the microstructure, deformation-mechanisms, and strengthening mechanisms of the material.

추가 정보

필드	값
Award Announced Date	2024-08-15T09:38:04.417
Awarded Institution	University of Idaho
Facility Tech Lead	Alina Montrose, Catou Cmar, Kevin Field, Kory Linton
Irradiation Facility	Michigan Ion Beam Laboratory
PI	Matthew Swenson
PI Email	[email protected]
Project Type	RTE
RTE Number	None