HIGH RESOLUTION ELECTRON MICROSCOPY STUDIES OF TWIN BOUNDARY STRUCTURES IN B19′ MARTENSITE IN THE Ti-Ni SHAPE MEMORY ALLOY

摘要

The boundary structure of the <011> Type Ⅱ, {111} Type Ⅰ, {011} Type Ⅰ, (100) compound and (001) compound twins in the B19′ martensite in the Ti-Ni shape memory alloy was observed in the edge-on state by high resolution electron microscopy (HREM). The lattice images of the Type Ⅰ and the compound twins exhibit the well-defined crystallographic features of those boundaries. Lattice image of the <011> Type Ⅱ twin taken from the unique η_1 axis suggests that neither ledge nor step structures are present at the irrational boundary.