Effects of Alloying Elements Addition and Grain Size Refinement on the Microstructures and Magnetic Properties of Ferromagnetic Shape Memory Fe70-xPd30Zx Alloys

• Main Authors: Chien-Feng Lin, 林建鋒
• Other Authors: Jin-Bin Yang
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/02021857722472430042

博士 === 國立高雄第一科技大學 === 工程科技研究所 === 101 === This research paper mainly presents investigation of bulk ferromagnetic shape memory (FSM) Fe70-xPd30Zx (Zx = Rh, Ni) alloys with additions of various trace amounts of Rh, and Ni elements. The influences of the various additions of Rh and Ni elements on the magnetic structures and magnetic properties are investigated in detail. The experimental results indicate that additions of trace elements of Rh (2−4 at.%) to Fe70-xPd30Zx (Zx = Rh) alloy systems can significantly improve the magnetostrictive strains of the alloys. In addition, the Fe70-xPd30Rh2-4 (at.%) alloys through homogenization and strain-forged to a ~40% reduction in thickness then recrystallized thermal annealing at 950–1050 ℃ for proper times show improvements in the following: (a) magnetostrictive strains, (b) magnetostrictive susceptibility (Δλ║s/ΔH), (c) saturation magnetization (Ms), (d) the magnetocrystalline anisotropy energy constant (Ku). SEM and TEM investigations indicate that the high magnetostriction of the strain-forged Fe70-xPd30Rh2-4 alloys through solution treated (ST) and annealed recrystallization can mainly be ascribed to the grain refinement, as well as deformation twins, transformation twins, and transverse twins.However, the strain-forged alloys through ST and aging at 400–550 ℃ for various times. The L10+L1m twin phase decomposition → the stoichiometric L10+L1m+αbct structures lead to the ferromagnetic shape memory effect disappearing. Therefore, the alloys can not be applied in a high temperature and high frequency environments. Based on the above-mentioned disadvantages, therefore, the paper investigated the effects of adding a third alloying element, Ni, to create Fe70-xPd30Zx (Zx = 2, 4, 6, 8 at.% Ni) ferromagnetic shape memory alloys (FSMAs). The Ni replaced a portion of the Fe. The Fe70-xPd30Nix 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 magnetic properties indicated that the greater Ni amount in the Fe70-xPd30Nix 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 Fe70-xPd30Nix (Nix = 6, 8 at.%) alloys, the L10+L1m twin phase decomposition into stoichiometric L10+L1m+αbct structures was suppressed after the 500 ℃/100 h aging treatment. The result was that the Fe70-xPd30Nix (Nix = 6, 8 at.%) alloys maintained a high magnetostriction and magnetostrictive susceptibility (∆λ║s/∆H) after the alloys were aged at 500 ℃ for 100 h. This magnetic property of the Fe70-xPd30Nix (Nix = 6, 8 at.%) alloys make it suitable for application in a high temperature (T>500 ℃) and high frequency environments.