Diffusion Welding of Alloys for Molten Salt Service - Status Report

Abstract

This report addresses present work concerned with heat exchanger development for molten salt service, including the AHTR (Advanced High Temperature Reactor), which uses molten salt for cooling and process heat transfer. These results are an outgrowth of recent work done under the Next Generation Nuclear Plant (NGNP) Project, which was concerned with the diffusion welding of Alloys 800H, 617, and similar materials for oxidation resistance at operating temperatures up to 900°C. The molten salt systems discussed herein use other alloys such as Alloy N and 242, which show corrosion resistance to molten salt at nominal operating temperatures up to 700°C. These alloys were diffusion welded, typically at 1150°C for 3 hours under applied loads of ~5 MPa using the Gleeble thermo-mechanical testing machine. Thermocalc/DICTRA models were developed to predict diffusion, and compositions of welds with a 15 µm nickel foil interlayer were measured after welding for comparison. Calculated and experimental values were in good agreement. Test specimens were prepared for exposing diffusion welds to molten salt environments. Alloy N and 242 were found to be weldable by diffusion welding, with ultimate tensile strengths about 90% of base metal values.