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Electron microscopy study of 2H and 18R martensites in Cu–11.92wt% Al–3.78wt% Ni shape memory alloy

“…Martensite formed on cooling is 18R in a low Al alloy and is 2H in a high Al alloy. In alloys with compositions near the phase boundary between these two martensites, both can coexist [8][9][10]. On the other hand, both kinds of martensite show different transformation characteristics.…”

“…Both orthorhombic and hexagonal axes are used for describing planes and directions in the 2H martensite. This structure is characterized by an AB stacking sequence and where the inhomogeneous shear occurs by twinning [6,9,15].…”

Synthesis and properties of Cu–Al–Ni shape memory alloy strips prepared via hot densification rolling of powder preforms

“…The presence of fine and coarse striations are typical features of b' (18R, monoclinic) and c' (2H, orthorhombic) martensites respectively. 25 Therefore, it appears that the present material consists of both types of martensite, i.e. b' and c'.…”

Micro-structural analysis of self-accommodating martensites in Cu–11.92wt%Al–3.78wt%Ni shape memory alloy

“…Martensite formed on cooling is 18R in a low Al alloy and is 2H in a high Al alloy. In alloys with compositions near the phase boundary between these two martensites, both can coexist (Sugimoto et al, 1995;Liu et al, 1997). Besides, the crystal structure of the thermally induced martensitic phase in CuAlNi alloys changes with heat treatment, for example varying the quenching rate or annealing time, or homogenizing or aging at different temperatures.…”