Berlin 2008 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 43: Phase Transitions IV

MM 43.1: Talk

Thursday, February 28, 2008, 16:00–16:15, H 0107

Effect of composition and heat treatment on martensitic transformation and magnetic properties in Ni-Fe-Ga-Co magnetic shape memory alloys — •Jian Liu, Nils Scheerbaum, Dietrich Hinz, and Oliver Gutfleisch — IFW Dresden, Institute for Metallic Materials, P.O. Box 270116, D-01171 Dresden, Germany

Ni-Fe-Ga-Co is a promising alloy system for magnetic shape memory alloy applications, due to its good ductility, mobile twin boundaries and high transformation temperatures. Here, the martensitic transformation and magnetic properties in a large composition range with Ni54-xFe20Ga26Cox, Ni54-xFe19Ga27Cox, Ni56-xFe17Ga27Cox and Ni54-xFe18Ga28Cox (x = 0, 2, 4) are investigated. The martensitic transformation temperature Tm and the Curie temperature Tc can be tailored in a wide range by changing composition and heat treatment (ageing temperature, time and cooling rate), Tm ~ -100 to 100 C and Tc ~ 10 to 130 °C. A coupling of martensitic and magnetic transformations at a relatively high temperature (~ 90 °C) is found for Ni52Fe17Ga27Co4. In this composition, increasing the degree of atomic order by long ageing and slow cooling decreases Tm but keeps Tc unchanged. Compared to ageing at 300 °C, after ageing at 400 °C there is no obvious change in Tm and Tc, but the transformation hysteresis is increased and the transformation interval is decreased significantly. However, the presence of γ precipitates induced by ageing at 500 °C suppresses the occurrence of the martensitic transformation itself.