Microstructure changes in two phase beta plus gamma Co-Ni-Al ferromagnetic shape memory alloys in relation to Al/Co ratio

作者：Maziarz W^*; Dutkiewicz J; Santamarta R; Cesari E

来源：The European Physical Journal - Special Topics, 2008, 158: 137-142.

DOI：10.1140/epjst/e2008-00666-2

The microstructure of Co(35+x) - Ni(40-x) - Al(25) (x = 0, 2.5, 5.0) ferromagnetic shape memory alloys annealed at 1200 degrees 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 gamma phase. Annealing twins were found frequently in the gamma phase. The volume fraction of gamma phase has been determined to be about 40%. TEM observations show twinned L1(0) martensite with {111}- type twinning plane and tetragonality c/a = 0.85 in all investigated alloys. Determination of the composition of beta 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 degrees C, respectively. An increase in the Al/Co ratio together with a decrease of Ni content in beta phase causes a decrease of the e/a ratio, which promotes a decrease of martensitic transformation temperatures.

• 出版日期2008-5