Joining Techniques for Ferritic ODS Alloys

Abstract

This report presents results of research on advanced joining techniques for ferritic oxide-dispersion strengthened alloys MA956 and PM2000. The joining techniques studied were resistance pressure welding (also known as pressure forge welding), transient liquid phase bonding, and diffusion bonding. All techniques were shown to produce sound joints in fine-grained, unrecrystallized alloys. Post-bond heat treatment to produce a coarse-grained, recrystallized microstructure resulted in grain growth across the bondline for transient liquid phase and diffusion bonds, giving microstructures essentially identical to that of the parent alloy in the recrystallized condition. The effects of bond orientation, boron interlayer thickness, and bonding parameters are discussed for transient liquid phase and diffusion bonding. The report concludes with a brief discussion of ODS joining techniques and their applicability to GEN IV reactor systems.

Summary of Prior Work on Joining of Oxide Dispersion-Strengthened Alloys

“…12. 31 As indicated, the simulated end cap had a land with an outer diameter (2 mm) slightly larger than the internal diameter of simulated tubing, and a tapered section to expand the tube on insertion. The restraining ring provided the backing force for plastic deformation of the interface, and had an internal diameter machined to match the computed outside diameter of the tubing after expansion by the inserted end cap.…”

“…This processing variant utilized the capability for controlled axial and torsional motion afforded by a torsional Gleeble unit to provide increased levels of deformation at the interfaces to be joined 31 (see, also, Section 10.3 on Inertia-Driven Friction Welding). Despite difficulties in developing fixturing to provide accurate alignment of the components, procedures were developed that produced reasonably well-aligned joints in fine-grained PM2000 (see Fig.…”

“…Optimized bonding parameters reportedly resulted in room temperature bending strengths of 75% of the base alloy. Krishnardula et al 31 examined diffusion bonding parameters for both MA956 and PM2000 in both the unrecrystallized (fine-grained) and secondary-recrystallized (large, elongated grained) conditions. The as-received, fine-grained MA956 was in the form of square-section bar (approximately 11 mm on a side), whereas the recrystallized alloy was a bar approx.…”

“…56,57 In a study in support of the US DOE's Generation IV Gas Fast Reactor program, researchers at Auburn University investigated the TLP bonding of MA956 (fine-grained and recrystallized) and PM2000 (fine grained). 31,52,58,59,60 The interlayer used was pure B, chosen because of its high diffusion rate in ferritic steels (no data specific to ODS alloys). The Fe-B eutectic temperature is 1174°C, and the eventual aim was to deposit interlayers of FeSiB alloys using electron beam physical deposition (EBPVD).…”