Microstructure changes in two phase β+ γ Co-Ni-Al ferromagnetic shape memory alloys in relation to Al/Co ratio |
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| Authors: | W Maziarz J Dutkiewicz R Santamarta E Cesari |
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| Institution: | (1) Institute of Metallurgy and Materials Science of the Polish Academy of Sciences, 25 Reymonta Str., 30059 Krakow, Poland;(2) Departament de Física, Universitat de les Illes Balears, Cra. de Valldemossa, km 7.5, (Illes Balears), 07122 Palma de Mallorca, Spain |
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| Abstract: | The microstructure of Co35 + x-Ni40 - x-Al25 (x = 0, 2.5, 5.0) ferromagnetic shape memory alloys annealed at 1200 °C and water quenched has been investigated by optical
(OM) and analytical transmission electron microscopy (TEM). The microstructure consists of elongated grains of martensite
and γ phase. Annealing twins were found frequently in the γ phase. The volume fraction of γ phase has been determined to be
about 40%. TEM observations show twinned L10 martensite with {111}-type twinning plane and tetragonality c/a = 0.85 in all investigated alloys. Determination of the composition
of β phase, allows to calculate Al/Co and e/a ratio in the range 7.68–8.40 in correlation with its Ms temperatures between
66 and 167 °C, respectively. An increase in the Al/Co ratio together with a decrease of Ni content in β phase causes a decrease
of the e/a ratio, which promotes a decrease of martensitic transformation temperatures. |
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