L. G. Bujoreanu, S. Stanciu, R. I. Comaneci, C. Lohan, The Gheorghe Asachi Technical University from Iasi, Iasi, Romania; M. Meyer, NETZSCH, Selb/ Bavaria, Germany; V. Dia, S.C.MITTAL STEEL Iasi S.A., Iasi, Romania
It is well-known that one way shape memory effect (SME) in Fe-Mn-Si based shape memory alloys (SMAs) is related to the thermally-induced reversion of ε (hexagonal close packed, hcp) stress induced martensite (SIM) to γ (face centered cubic , fcp) austenite. In the case of a Fe-Mn-Si-Cr-Ni SMA this reverse martensitic transformation was analyzed in regards to the critical temperature for the beginning of austenite formation (As) and the percentage of permanent deformation recovered by heating (SME). For this purpose, a dilatometric study, dynamic mechanical analyzer (DMA) measurements and scanning electron microscopy (SEM) observations were employed aiming to determine a relationship between permanent strain, ε SIM, As and SME.
Summary: An Fe-Mn-Si-Cr-Ni shape memory alloy was cast, homogenized and solution treated in order to obtain epsilon (hexagonal close packed, hcp) martensite. Since one way shape memory effect (SME) is related to the reversion to gamma (face centered cubic, fcc) austenite of epsilon stress induced (SIM) martensite on heating, the cylindrical specimens were elongated to different permanent strains, at room temperature. In this states, the specimens were analysed by dilatometry and dynamic mechanical analyser (DMA) in order to determine critical transformation temperatures for both martensite formation and reversion as well as for antiferromagnetic transition. Finally the scanning electron microscopy (SEM) studies were performed in order to confirm the formation of epsilon SIM. The studies were conducted in order to determine a relationship between permanent strain, critical start temperature for martensite reversion and the amount of resulting SME.
