Effects of Ni Addition on the Microstructures and Magnetic Properties of Fe70-xPd30NixHigh-Temperature Ferromagnetic Shape Memory Alloys

Abstract

This study investigated the effects of adding a third alloying element, Ni, to create Fe 70-x Pd₃?Ni x (x = 2, 4, 6, 8 at.% Ni) ferromagnetic shape memory alloys (FSMAs). The Ni replaced a portion of the Fe. The Fe 70-x Pd₃?Ni x alloys were homogenized through hot and cold forging to gain a ~38% reduction in thickness, next they were solution-treated (ST) with annealing recrystallization at 1100 ℃ for 8 h and quenched in ice brine, and then aged at 500 ℃ for 100 h. Investigation of the microstructures and magnetostriction indicated that the greater Ni amount in the Fe 70-x Pd₃?Ni x alloys reduced saturation magnetostriction at room temperature (RT). It was also observed that it was more difficult to generate annealed recrystallization. However, with greater Ni addition into the Fe 70-x Pd₃?Ni x (x = 6, 8 at.% Ni) alloys, the L1?+L1 m twin phase decomposition into stoichiometric L1?+L1 m +α bct structures was suppressed after the 500 ℃/100 h aging treatment. The result was that the Fe 70-x Pd₃?Ni x (x = 6, 8 at.% Ni) alloys maintained a high magnetostriction and magnetostrictive susceptibility (Δλ || s /ΔH) after the alloys were aged at 500 ℃ for 100 h. This magnetic property of the Fe 70-x Pd₃?Ni x (x = 6, 8 at.% Ni) alloys make it suitable for application in a high temperature (T ＞ 500 ℃) and high frequency environments.