A transmission electron microscopic study was made of mechanical twinning. A large number of [00•1] dislocations (which were rarely seen in the matrix), and a new type of stacking fault, were found within deformation twins in both materials. Matrix dislocations were observed to interact actively with the tips of twin embryos and the step ledges of growing twin lamellae. Twin embryos which were bounded by straight coherent and inclined semi-coherent boundaries were observed. These results, and the morphological variations of twin lamellae during deformation, did not agree with twinning dislocation theories. They instead supported a step-wise nucleation and growth mechanism which had been proposed for deformation twinning in hexagonal close-packed structures.

S.G.Song, G.T.Gray: Acta Metallurgica et Materialia, 1995, 43[6], 2339-50