Abstract
An Fe-38Ni-13Co-4.7Nb-1.5Ti-0.5Si alloy is a controlled low thermal expansion superalloy with a good resistance to SAGBO (Stress Accelerated Grain Boundary Oxidation) embrittlement at elevated temperatures by an intensional Si addition. The precipitation of second phases, ε phase, η phase and so on, in this superalloy is investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry. A time-temperature-transformation diagram for the ε phase is presented.The crystal structure and the lattice parameters of the ε phase and the orientation relationship with the alloy matrix g are determined. It is shown that the η phase is not a stable phase as well as γ' phase, but cellular η phase is the most stable precipitation phase in this alloy.
