ABNORMAL GRAIN-GROWTH IN OXIDE DISPERSION STRENGTHENED NI-BASE SUPERALLOY

To examine the predominant factor controlling abnormal grain growth of Ni-base oxide dispersion strengthened superalloys, microstructures were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Three kinds of particles were recognized; (1) fine, round shape of yttria particles of 10 to 80 nm in diameter, (2) large, round shape of Al and Ti oxide particles of 80 to 200 nm diameter, (3) flake shape of Cr rich phase with sizes of 0.2 to 0.4-mu-m in width and 0.4 to 2.5-mu-m in length. It was found that the major pinning obstacles of abnormal grain growth were the Cr-rich phase.