Martensitic transformations which occurred in these alloys were investigated by means of electrical resistivity measurements, X-ray diffraction analysis and transmission electron microscopy. It was found that both alloys transformed via 2 steps during cooling: from the high-temperature cubic phase (B2-type) to orthorhombic martensite (B19-type) and then to monoclinic martensite (B19’-type). During cooling, plates of orthorhombic martensite nucleate at certain sites in the cubic matrix. While the plates of orthorhombic martensite were growing, plates of the monoclinic martensite nucleated in the orthorhombic martensite and grew by consuming it. Transformation from orthorhombic martensite to monoclinic martensite occurred by shear on the (001)o plane, in the [100]o direction. A plate of the monoclinic martensite which grew in this way consisted of thin plates of (001)m compound twin, due to alternating shearing in the [100]o and [1¯00]o directions.

T.Fukuda, T.Saburi, T.Chihara, Y.Tsuzuki: Materials Transactions, 1995, 36[10], 1244-8