Abstract
The in situ sintering bonding of oxide dispersion strengthened superalloys MA956 and MA754 was carried out using a pulsed electric current sintering (PECS) technique. Insert layers consisting of MA956 and MA754 powders were positioned between the respective bonding alloys, and PECS bonding was then carried out at 1023–1415 K for 0–64.8 ks applying a bonding pressure of 40–70 MPa. The number of pores between particles in the bond layer diminished with holding time. The densification behaviour of the bond layer during the PECS bonding process could be expressed by a kinetic equation with the sequential rate determining steps of plastic flow (creep) and volume diffusion. Transmission electron microscopy observations revealed that oxide strengthening particles of Y2O3 were dispersed finely and uniformly not only inside the powder particles but also at the prior particle boundaries. The creep rupture lives of MA956 and MA754 joints bonded at 1323 K for 54.0 ks and 1373 K for 64.8 ks were about 70% of that of the base metal in the longitudinal direction. The heat conduction analysis suggested that the rapid densification in PECS bonding could be attributed to the promotion of sintering by the local Joule heat generation (local increase in temperature) at the necked region. It was deduced that the superior mechanical properties of PECS bonded joints resulted from the fine and uniform dispersion of strengthening oxides in the bond layer.
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