Thermally induced microstructural transformations and anti-corrosion properties of Co<inf>70</inf>Fe<inf>5</inf>Si<inf>10</inf>B<inf>15</inf> amorphous alloy

Abstract

The amorphous Co70Fe5Si10B15 alloy was studied in terms of thermal and corrosion resistance as well as thermally induced structural transformations, using several structural and thermal analysis techniques and electrochemical measurements. It was shown that the alloy is thermally stable up to around 510 °C. Anodic polarization curves of the as-prepared alloy revealed its high corrosion resistance in 0.5 M NaCl, HCl and NaOH solutions. Multistep structural stabilization through the crystallization is manifested as two well defined DSC peaks corresponding to formation of fcc Co, hcp Co, Co23B6, and Co2Si phases, whose microstructural parameters were studied after thermal treatment at different temperatures in the range 25–800 °C. TEM and EDX analyses suggested the presence of minor Co-Si phases as well in the crystallized alloy and deformation twinning in the Co23B6 grains. The microstructural transformations exhibited significant influence on the magnetic moment of the alloy. Kinetics of non-isothermal crystallization was studied on the bases of isoconversional principle. Determination of kinetic triplets of individual crystallization steps, based on deconvolution of the complex DSC peaks applying Fraser-Suzuki function, enabled assessment of thermal stability of the alloy and kinetic predictions at different temperatures.