Crystal Structure of Stress-Induced and Thermal Martensites in 63.1 At.% Ni--Al Alloy

It was established that thermal martensite in 63.1 At.% Ni--Al alloy possesses a seven-layer structure which may be regarded as a Llo type having two regular stacking faults/each seven layers. Stress-induced martensites possess the same crystal structure. However, when the tensile axis lies along < 100 > SIM is oriented in such a way that the shear stress acting in its basal plane results in an additional shift of the basal planes, causing formation of a Llo single crystal. For a < 110 > tensile axis, the basal plane of SIM is parallel to the tension direction and the shear component is equal to zero. This makes an additional shift impossible which is why the final structure remains a 5.2 stacking sequence. 12 ref.--AA