Influence of microstructural changes on corrosion behaviour of thermally aged Ti-6Al-7Nb alloy

Abstract

Solution treatment and ageing (STA) is an effective strengthening method for α + β titanium alloys. This paper reports the effect of solution treatment and aging on the corrosion behaviour of Ti-6Al-7Nb alloy in a simulated body fluid (Ringer's solution). Ti-6Al-7Nb alloy is hot rolled in the α + β field and subjected to solution treatment above and below its beta transus temperature (1283 K). The solution treated specimens are water quenched (WQ), air-cooled (AC), and furnace cooled (FC) at three different rates, and subsequently aged at 823 K for 4 h. Microstructural changes were examined using optical microscopy and phases developed were analyzed using XRD. The influence of microstructure on the corrosion performance of the alloys are discussed in detail based on the Open Circuit Potential (OCP), passive current density and area of repassivation loop values obtained from the cyclic polarization study in Ringer's solution. The passive current density was low (0.5 μA/cm²) for the specimen with duplex microstructure obtained for specimen solution treated at 1223 K, air-cooled, and aged, in comparison with that for as-rolled specimen (1.5 μA/cm²). The corrosion aspects resulting from various heat treatments are discussed in detail.