Abstract
Transmission electron microscopy and diffraction studies have been carried out on the martensite in a Kovar (Fe-27.5 wt%Ni-17.2 wt%Co). In the martensite, transformation twins were observed parallel to the {112} planes, and a mid-rib of 0.5∼1 μ width was observed with a different contrast from the neighboring region. The orientation relationship between martensite and austenite matrix and the habit plane of martensite plate were of the Nishiyama’s relation and of the {3, 15, 10} type, respectively. These results are the same as those in Fe-Ni alloys, suggesting that the crystallographic properties of martensite are not affected by the addition of Co atom.
Very thin martensite platelets were also observed in the austenite matrix. They had the same crystallographic properties as those of the fully grown thick plates and contained striations parallel to the intersection of the plane of platelet with the plane of transformation twin. These results suggest that the martensite plate does not pass through a transition structure but grows fully without any change from the beginning. The fully grown martensites contained line or planar imperfections of another system besides the transformation twins of the {112} planes.
