Relationship between colored microstructure under polarized light and shape recovery characteristics on the thermomechanical cycled CuAlNi single crystals

The paper studied the relationship between microstructure and shape recover y characteristics by using colored microstructure analysis under polarized light on the thermomechanical cycled CuAINi single crystals. The two-way sh ape memory effect in quenched thin bar resulted from the preferential forma tion/extinction of martensite variant due to the internal quench stress, an d the variant was formed at an angle of about 45 deg. with the tension dire ction ([001] of the beta phase). Initial thermomechanical cycling under rel atively low stress single variant stress-induced martensite was formed at a n angle of 45 deg. with the tension and its morphology was a lath of parall el twins. More than one group of variants were formed after several trainin g cycles and such variants also caused tilting of some thermally formed acc ommodated martensite. By overheating the trained sample containing stabiliz ed multi-variants of stress-induced martensite, very coarse martensite stru cture with a strong asymmetry was produced, which caused the reverse two-wa y shape memory effect.