Interaction between liquid lead-bismuth eutectic and aluminized Inconel 625 superalloy at 600 and 850 °C

Abstract

Aluminide coating layer was formed on Inconel 625 superalloy using pack aluminizing process and subsequent diffusion heat treatment. The corrosion tests of the aluminized alloy 625 tubes were carried out in static lead-bismuth eutectic alloy at 600 and 850 °C for 200 h and 72 h, respectively in the flowing argon maintaining 1 ppm of oxygen. The as-coated and corrosion tested alloy samples were characterized using scanning electron microscopy, energy dispersive spectrometry and electron back scattered diffraction techniques. A single aluminide layer containing β-NiAl phase was successfully formed by optimizing the aluminizing process parameters. Aluminized alloy 625 showed excellent corrosion resistance against liquid Pb-Bi at 600 °C, and the formation of a protective alumina rich continuous scale on NiAl layer. However, depletion of Cr from the NiAl coating, and inward penetration of Pb-Bi through the aluminide layer was observed at 850 °C.