Structural Changes Associated with the Pseudoelastic Response of Fe-based Shape Memory Alloys
Lohan, Monica Nicoleta
Comăneci, Radu Ioachim
The pseudoelastic responses of two types of iron base shape memory alloys (SMAs) were introduced and discussed. The former was based on Fe-Mn-Si system, obtained by classical (CM) and by powder metallurgy (PM) manufacturing. The latter was based on Fe-Ni-Co system being processed by a non conventional technology comprising melt spinning and heat treatment. In the case of FeMnSibased SMAs, CM specimens obviously experienced larger ductility and a more pronounced pseudoelastic response while PM specimens were stiffer and underwent larger work-hardening. On the other hand, melt spun FeNiCo-based SMAs revealed an outstanding superelasticity in the case of micro-indentation tests. By means of scanning electron microscopy (SEM) observations, a martensitic morphology was identified in FeMnSi-based SMAs while FeNiCo-based SMAs revealed an austenitic structure. The presence of both α’ and ε martensites was confirmed in FeMnSibased SMAs by means of X-ray diffraction (XRD). In fully austenitic melt-spun and aged FeNiCo-based SMAs, no martensite was indentified on XRD patterns. These results sustain the conclusion that FeMnSi-based SMAs, that contain pre-existing martensite, experienced a pseudoelastic behavior caused by crystallographic reorientation of martensite plate variants while austenitic FeNiCo-based SMAs experienced a reversible stress-induced martensitic transformation, at room temperature.
- 2014 fascicula9 nr3