High Temperature Corrosion Behaviour of Ti-46.6Al-1.4Mn-2Mo in Environments of Low Oxygen and High Sulphur Potentials at 750 and 900deg C

摘要

In this paper, the oxidation and sulphidation behaviour of a TiAl-based intermetallic, Ti-46.6Al-1.4Mn-2Mo (atpercent) with duplex and laminar microstructures, was investigated in environments of H_2/H_2S/H_2O at 750 and 900deg C. The corrosion kinetics of the intermetallic were determined by means of discontinuous gravimetry and the as-received and exposed samples were characterised using SEM, EDX and XRD. The weight gain/time data in the oxygen and sulphur containing environment used indicated parabolic kinetics with Kp approx 10~(-12) g~2/cm~4/s at 750deg C and cubic kinetics at 900deg C. The increase in exposure temperature did not significantly change the corrosion behaviour of the materials. The material showed the development of a multilayered scale consisting of an outermost TiO_2 layer beneath which an Al_2O_3 layer existed; the formation of MnS and Al_2S_3 was observed to occur between the oxide layers and substrate. This paper will discuss the significance of these results and consider the mechanisms responsible for degradation of this type of intermetallics in high sulphur and low oxygen environment with reference to their limit of temperature tolerance.