Corelation between the microstructure, microhardness and corrosion resistance of Ti-5Al-2.5Fe

Abstract

The electrochemical impedance spectroscopy (EIS) and the polarization techniques have been used to study the corrosion behaviour of different samples of Ti-5Al-2.5Fe after undergoing specific heat treatments at 1025°C. The analysed alloy is a α + β alloy and contain a mixture of α (hexagonal close-packed structure) and β (body-centred cubic structure) phases at room temperature. The microstructure of the titanium alloy is strongly influenced by the processing history and heat treatment. The effect of cooling rate on the microstructure of Ti- 5Al-2.5Fe annealed above the β transus was analysed and was found that as the cooling rate increases, the lamellar hexagonal close-packed (hcp) crystal structure becomes finer. The microhardness of the titanium alloy (at 15 seconds, 200 grams) shows that there is a difference of about 100 in the Vickers microhardness of the α and β phases and that the microhardness of both of the phases increases with the increasing of the thermal treatment time. The experimental results emphasised that the heat treatment, cooling rate, microstructure and microhardness, as well as corrosion behaviour, are strongly enhanced. A long time heat treatment and a low cooling rate generate an homogeneous structure with high corrosion resistance and higher microhardness.