Effect of Diffusion Condition for Aluminizing on TiAl Based Alloy

Abstract

Diffusion treatments of TiAl-based alloys (49.1 at% Al) aluminum coated by thermal spray were carried out at the temperature range of 700°C-1100°C. The influence of the diffusion condition for the formation of intermetallic phases in the coating has been investigated. In the initial stage of diffusion treatment, TiAl3 was formed on the outermost surface by the diffusion between liquid aluminum and the substrate. In addition, an intermediate layer comprised of Ti2Al5 (at 1100°C), TiAl2 and Al diffused layer (Al-rich TiAl) was confirmed under the outermost layer. The maximum thickness of TiAl3 during the initial stage increases as the diffusion temperature decreases. In addition, the shape of TiAl3 layer was dependent on the diffusion temperature; the outermost layer without pores was confirmed at the temperature of 700°C. TiAl2 and Al-rich TiAl developed by solid-state diffusion from TiAl3 layer following a parabolic low. The activation energies for growth have been calculated to be 194 kJ/mol for TiAl2 and 292 kJ/mol for Al-rich TiAl.