It was recalled that martensite phases with the 9R or 18R structure were found in many ß-phase Hume-Rothery alloys. Their stacking sequence was hardly ever perfect, and a high density of randomly distributed basal stacking faults were often observed. Apart from the basal plane faults, the presence of other planar defects, such as type-I or type-II, had been reported. In order to clarify the precise nature of the type-I and type-II defects, a high-resolution electron microscopic investigation was carried out. A type-I defect in 18R martensite was shown to be a dislocation extension zone that was bounded by 2 partials with Burgers vectors of 1/12[2¯30] and 1/3[100]. The type-II defect was not fault which was internal to the martensite plate, but was rather a stack of plates A and C; like the A/C-type coupling in normal transmission electron microscopy. The rare observation of the type-II defect was attributed to the fact that the slice was too thin to exist for self-accommodation.

High-Resolution Electron Microscopic Observation of Non-Basal Planar Defects in 18R Martensite in a Cu-Zn-Al Alloy. J.X.Zhang, Y.F.Zheng, W.Cai, L.C.Zhao: Journal of Materials Science Letters, 1998, 17[19], 1657-9