Coherent gamma '-precipitates at singular and rough grain boundaries in a model Ni-base superalloy

Abstract

In a model Ni-base superalloy of Ni-24Co-4Al-4Ti-5Cr-5Mo (by wt pct), the singular and rough grain boundaries that exist at a temperature range between 1050 degreesC and 1200 degreesC can be identified by observing the shapes of coherent gamma'-precipitates by transmission electron microscopy (TEM). Some grain boundaries become locally curved with the impinging spherical gamma'-precipitates. These grain boundaries must be rough. Some grain boundaries maintain their flat shapes even at the contact areas with the gamma'-precipitates and triple junctions. Such flat grain boundary shapes indicate that these grain boundaries are singular. Some grain boundaries have hill-and-valley shapes and some of their segments also show flat shapes with impinging precipitates. These boundary segments must also be singular. The results show that the singular and rough grain boundaries in this alloy can be clearly identified by the shape distortions produced by the impinging gamma'-precipitates.