Shape Memory Alloy Synthesis

Optical micrograph of non-heat-treated sample.
Etchant: 2 parts H2SO4 : 1 part 3% H2O2 : 2 parts H2O.
While the striped sections, with a variety of orientations, are most likely the martensitic β′ phase that we were loking for, the presence of orange and silver sections, copper-rich α and aluminum-rich γ1 phases (respectively), indicates that the sample was not quenched rapidly enough to prevent them from forming. An alloy with good shape-memory properties requires a uniform transformation into pure martensite.

Optical micrograph of annealed sample.
Etchant: 2 parts H2SO4 : 1 part 3% H2O2 : 2 parts H2O.
The annealed sample clearly depicts the needle-like, twinned structure of β′ martensite. The different orientations of the grains minimize the strain in the sample; upon deformation, the variants align themselves in one direction and allow the transformation from martensite back to austenite without breaking any bonds.