Novel Joining Technique for Oxide-Dispersion Strengthened Iron Aluminide Alloys
Oxide dispersion strengthened ferritic steels are irreplaceable in modern technology due to their unique resistance against creep. In order to enable the wider use ODS materials, it is necessary to develop reliable methods of joining them. The conventional welding methods (arc, plasma, laser, or electron beam) inevitably lead to fluid formation, which, in turn, results in coarsening of the fine oxide particles and thus loss of their ability to confer creep resistance. Direct diffusion bonding has not been successful due to a tenacious alumina scale which forms on the alloy surfaces. Also, usage of interlayers did not result in strong joints, since no interlayers possess the unique properties of ODS ferritic steel. Plasma-assisted joining is one of the methods that can solve this problem. During bonding, plasma discharges break the oxide scale and intensify the mass transfer. This allows bonding at lower temperatures, thus avoiding disturbance of the microstructure. In order to provide strong butt joints in ODS ferritic steel, unrecrystallized pieces should be bonded. Plasma-assisted butt joining, followed by a recrystallization heat treatment, results in full secondary recrystallization with grain growth across the bonding line. This provides UTS values at 1000oC usually ranging from 70 MPa / 10.1 ksi to 77 MPa / 11.1 ksi. This constitutes from 78 to 86% of the UTS achievable by solid MA-956 at 1000oC. The best result was 88 MPa / 12.8 ksi, which amounts to 98% of the solid MA-956 UTS at 1000oC. Tube bonding of commercially available recrystallized ODS ferritic steel with plasma-assisted sealing resulted in failure at 49 MPa / 7.1 ksi in 377 hours during step-loading testing at 1000oC. This joint strength falls within the usual range for the strength of solid ODS ferritic steel tubes.
- Research Organization:
- Materials & Electrochemical Research (MER) Corporation
- Sponsoring Organization:
- USDOE - Office of Energy Research (ER)
- DOE Contract Number:
- FG03-00ER83041
- OSTI ID:
- 907744
- Report Number(s):
- DOE/ER/83041-F; MER #90452 - DE-FG03-00ER83041
- Resource Relation:
- Related Information: Was SBIR-protected, but the protection period passed some years ago.
- Country of Publication:
- United States
- Language:
- English
Similar Records
Joining Techniques for Ferritic ODS Alloys
Overview of ODS Alloy Development