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Keywords:

  • ferromagnetic shape memory alloys;
  • grain-size effect;
  • martensite phase transformation;
  • melt spinning;
  • Ni[BOND]Mn[BOND]Sn ribbons

Abstract

The present investigation was undertaken to investigate the effect of quenching rate on the microstructure of Ni50Mn50 − xSnx ribbon alloys and its influence on the martensitic starting phase-transition temperature MS. The study was performed on melt-spun ribbons of a ferromagnetic shape memory alloy (FSMA) of composition Ni50Mn37Sn13 produced by varying the speed of the rotating copper wheel between 15 and 50 m s−1. The resulting samples have a chemical composition close to the nominal one and at room temperature crystallize in a cubic single-phase austenite with the highly ordered L21-type crystal structure without a significant variation in the cell parameter. The average grain size varies between 1.4 and 7.3 µm, while MS increased from 212 to 258 K. Our results suggest that in these materials the average grain size of the parent austenite phase limits the size of the martensite variants, giving rise to its stabilization, while a multivariant transformation mode is maintained.