SURFACE PHASE-TRANSITIONS DURING MARTENSITIC TRANSFORMATIONS OF SINGLE-CRYSTAL CO

The phase transitions of close-packed surfaces that accompany the mart ensitic transformations between the hexagonal close-packed and face-ce ntered cubic structures of single-crystal Co are observed in real spac e and in real time with secondary-electron imaging. Simultaneous measu rement of the bulk resistivity is used to identify the onset of the bu lk transformation. The surface transitions show a broader thermal hyst eresis than that of the resistivity, indicating that the martensitic t ransformation is initiated in the bulk and proceeds slowly to the surf ace.