Abstract
Nickel-titanium B19’ martensite is a strongly plastically anisotropic material with only one available slip system, which is the [100](001)M slip. Despite this, B19’ martensite polycrystals can be homogeneously plastically formed, reaching up to very high plastic strains. The absence of other slip systems is compensated by plastic twinning, in particular by the frequently appearing irreversible (20-1)M twins. However, these twins act on the same (010)M lattice plane as the plastic slip, and thus, do not seem to be a very suitable complement to the slip in terms of the Von Mises criterion. In fact, exactly the same strains as by the (20-1)M twins can be achieved also by the [100](001)M slip itself, and thus, a question arises, whether they can be understood as plastic twins in the conventional sense.
