PRECIPITATION IN INCOLOY ALLOY 909

The precipitation of second phases in Incoloy 909 has been studied usi ng optical microscopy, scanning electron microscopy, and transmission electron microscopy. The compositions and crystal structures of severa l second phases were determined by analytical electron microscopy. A t ime-temperature-transformation diagram was constructed. The Si additio n was found to promote the precipitation of an Fe2Nb type Laves phase during casting and thermal processing, and the formation of Si rich or thorhombic phase at high aging temperatures. Both types of precipitate are considered to enhance the rupture properties of the alloy.