The mechanisms of eutectoid decomposition are important because of the widespread use of alloys which exhibit a eutectoid transformation. However, the transformation remains a matter of controversy for a number of reasons. The Ti-Co system is examined in order to test current understanding of eutectoid decomposition.
The high temperature beta phase can transform on cooling into several products - alpha plates, a non-lamellar mixture of alpha and Ti2Co which can be designated bainite, lamellar pearlite, spheroidal pearlite and Ti2Co allotriomorphs. In this study the high temperature beta phase was decomposed in hypoeutectoid, eutectoid and hypereutectoid alloys, for a range of undercoolings. The microstructure and crystallography of the transformation products was characterised by reflected light microscopy, SEM, XRD and TEM. The classification of the transformation products is discussed.