Transient liquid phase bonding of ferritic oxide-dispersion-strengthened alloys
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Ferritic oxide-dispersion-strengthened (ODS) alloys are of particular interest in the nuclear industry due to their superior properties, including oxidation resistance, creep resistance, and radiation-induced swelling resistance, compared to austenitic stainless steels and conventional superalloys.[1–4] The development of an appropriate joining technique is especially crucial for ODS alloys in order to produce a microstructure that is comparable to that of the parent metal, which is free from yttria agglomerates, second-phase particles, and unwanted fine secondary recrystallized grains. The transient liquid phase (TLP) bonding[5,6] shows potential for maintaining parent metal microstructure in bonds between substrates with stable oxide layers. The TLP bonding with different substrate orientations was performed using MA956 (Fe-20Cr-4.5Al-0.5Ti-0.5Y2O3, wt pct), both in the fine and coarse grain conditions, and PM2000 (Fe-20Cr-5.5Al-0.5Ti-0.5Y2O3, wt pct), in the fine grain condition. The 11-mm 10-mm 2-mm-thick samples were cut normal (transverse) and parallel (longitudinal) to the direction of extrusion, surface ground to a flatness of around 1 m, and then cleaned in an acetone bath. Fine boron interlayers of 1 m, 500 nm, and 250 nm thickness deposited using physical vapor deposition (PVD) were used in the bonding trials; forming a liquid by eutectic reaction with the iron-base substrates. For comparison, bonding was also conducted using a 25-m-thick iron-based (Fe-16B5Si, wt pct) foil as an interlayer at 1190 °C (above the melting point of the foil). The TLP bonding was performed in a Gleeble (Duffers Scientific Inc., Troy, NY, USA) 1500 thermomechanical processing system in a vacuum of less than 2 103 Pa at 1250 °C under compressive stresses of up to VENU G. KRISHNARDULA, Doctoral Candidate, NOFRIJON I. SOFYAN, Doctoral Candidate, WILLIAM F. GALE, Alumni Professor and Executive Director, Air Transportation Center of Excellence for Airline Cabin Environment Research, and JEFFREY W. FERGUS, Associate Professor, are with the Materials Research and Education Center, Auburn University, Auburn, AL 36849. Contact e-mail: [email protected] Manuscript submitted March 28, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
20 MPa to extrude the excess liquid formed at the bond line. Postbond heat treatments (PBHTs) were performed in a radiantly heated vacuum furnace at 1300 °C for up to 8 hours or 1385 °C for 2 hours for MA956 and PM2000 bonds, i.e., at the respective recrystallization temperatures of the substrate materials. The samples were then etched in a solution consisting of 2 g copper chloride, 40 mL hydrochloric acid, and 40 to 80 mL methanol for 2 to 10 seconds. The microstructural features were then examined by light microscopy and scanning electron microscopy (SEM), the latter employing a JEOL* JSM-840 instrument operated *JEOL is a trademark of Japan Electron Optics Ltd., Tokyo.
at 20 kV and energy-dispersive X-ray spectroscopy (EDS). The use of substrate material in the unrecrystallized fine grai
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