Development of Co-Ni-Ga Ferromagnetic Shape Memory Alloys with Enhanced Properties
Polycrystalline ingots of Co70-xNixGa30 (22 ≤ x ≤ 25) alloys were prepared by a sequence of arc melting high purity Co, Ni and Ga in argon atmosphere, followed by homogenization at 1150°C under a pressure of 10-3 Pa, and quenching in ice water. Structural characterisation of the quenched alloys was carried out to verify the presence of the martensite phase at room temperature. The martensite start (Ms), martensite finish (Mf), austenite start (As) and austenite finish (Af) temperatures for the alloys were determined using a differential scanning calorimeter. The ferromagnetic to paramagnetic phase transition temperature (TC) of the alloys was determined using an indigenously developed ac susceptometer. All the alloys are FSMAs with Ms, Af and TC above room temperature. The composition dependence of the properties of these alloys could be understood on the basis of the e/a (electrons to atom) ratio and the Co/Ni ratio. Presence of γ-phase precipitates along with the β-phase in these alloys enhances the ductility as well as influences the physical properties of these alloys.
António Torres Marques, António Fernando Silva, António Paulo Monteiro Baptista, Carlos Sá, Fernando Jorge Lino Alves, Luís Filipe Malheiros and Manuel Vieira
S. Sarma and A. Srinivasan, "Development of Co-Ni-Ga Ferromagnetic Shape Memory Alloys with Enhanced Properties", Materials Science Forum, Vols. 587-588, pp. 650-653, 2008