Precipitation Morphologies of Grain Boundary Chromium Carbides in Alloy690TT

摘要

The correlation between grain boundary type characterized by coincidence site lattice (CSL) model andrnchromium carbide morphology in Alloy 690TT was investigated utilizing transmission electron microscopy (TEM).rnThe chromium carbides precipitated in Alloy 690TT were identified as Cr-rich M_(23)C_6 by TEM analysis. Thernprecipitation of chromium carbides was suppressed at the low angle grain boundaries with less than 15 degrees ofrnmisorientation angle between the adjoining grains. Also, carbides were seldom observed on nearly exact CSLrnboundaries such as ∑ 11 and ∑ 15, including coherent twin boundaries (∑ 3_c). On the other hand, coarse and discreterncarbides were precipitated along the random high angle grain boundaries, and needle-like ones were evolved on thernincoherent twin boundaries (∑ 3_i). The precipitation behaviors of chromium carbides are explained based on the grainrnboundary energy, which could be a variable for certain grain boundary types.