Effects of rotation speed on microstructure and transition temperatures in Ni–Fe–Al melt-spun ribbons

The influence of quenching rate on the magnetic and martensitic properties of Ni–Fe–Al β phase alloys, with Al content less than 25 at.%, was investigated through melt-spinning. Rapidly solidified ribbons with different rotation speeds were fabricated for comparison. Microstructure observation and X-ray diffraction measurements revealed that lower quenching rate produced a β + γ two phase structure, whereas higher rate could produce a single β phase in a certain range of composition. The solid solution range of the β phase can be extended to lower Al content range by preventing the precipitation of the γ phase with an appropriate quenching rate. In Ni75−xFexAl25 ferromagnetic shape memory alloys, the magnetic transition temperatures (TC) are limited to below 250 K in conventional processing, which is a disadvantage for practical applications. In the ribbons with lower Al content and higher quenching rate, both TC and martensitic transformation temperatures (TM) became simultaneously around room temperature. The TM and TC showed a linear dependence with average electron concentration e/a and the magnetic valence Zm, respectively.