PNNL

Abstract

The development of high temperature fuel cladding materials to withstand a variety of extreme environments have received much attention. Several potential materials systems that have been identified for the fuel systems and core structural materials application in advanced reactor systems are ferritic/martensitic steel (e.g., HT9), austenitic stainless steels (e.g., 316 LN), oxide-dispersion strengthened steels (e.g., 12 YWT), Ni-based alloys and ceramic-based composites depending on the type of the reactors. Though these material systems have promising properties conducive for radiation-resistant performance, they suffer beyond the design-limit from one or more damage processes such as void swelling, radiation embrittlement, phase instability, corrosion, and limited creep life. A critical necessity exists to design materials systems with better performance than the conventional materials for the advanced reactor systems. Additionally, the drive is further through enabling advanced manufacturing techniques, to decrease the energy used for manufacturing of these components. In this proposed work, a direct customizable thin-walled tubular product will be developed from irradiation-tolerant composite high-entropy alloys (C-HEAs) with enhanced high-temperature strength and compatibility in a variety of corrosive environments. We will use solid phase processing (SPP) methods to enable development of a robust tube manufacturing process with upscale potential for a U.S.-based tube supply chain. Tube fabrication processes for HEA alloys are still in early research and development phases because it is difficult to prevent segregation on the bulk scale. Furthermore, the presence of nanocomposites can further complicate the manufacturing processes because homogenous distribution of the nano features must be confirmed, and feature coarsening must be prevented during the manufacturing processes. ShAPE is a complicated thermomechanical process that involves large material deformation, complex die/billet contact, and copious heat generation to maintain the processing temperature. Process modeling of ShAPE can help understand the associated physics, reveal the process parameter/condition relationship, and design for optimized tooling geometries and process parameters. Based on the preliminary process modeling results, it was shown that the Smoothed Particle Hydrodynamics (SPH) model can predict material flow and morphology, stress-strain state, temperature, extrusion force, and torque of the ShAPE extrusion of HEA tubes with various die designs and process parameters. Using the developed SPH model, the thermomechanical physics associated with the ShAPE extrusion of HEA tubes can be better understood. For example, the steady-state process conditions (e.g., force, torque, multi-point temperature) of the ShAPE extrusion of HEA tubes measured from the experiment (planned for the next couple of months) can be used to further improve the SPH model in terms of cooling boundary conditions, stick-slip contact conditions, and thorough model validations. To date, raw material billets were received, homogenization heat treatment were performed, and microstructural analysis were completed. As part of the corrosion mitigation design strategy, a new invention was developed under a provision patent, to form radially gradient material that can be sued as an input material for the tube manufacturing ShAPE process.