Phase Reaction and Diffusion Behavior between AuTi and CoTi Intermetallic Compounds

Abstract

The phase reaction and diffusion behavior of stoichiometric AuTi and CoTi intermetallic compounds were clarified using diffusion couple technique. It was found by scanning electron microscopy equipped with energy dispersive X-ray spectroscope that two intermetallic compounds of (Au,Co)Ti₃ and (Au,Co)₂Ti were produced near interface between the AuTi and CoTi when heat-treated at 1173 K and 1273 K, and that only (Au,Co)Ti₃ was formed when heat-treated at 1373 K. The presence of these intermetallic compounds was explained by the concentration dependent diffusivity in the diffusion couple. With increasing the heat-treatment temperature from 1173 K to 1373 K, the thickness of the diffusion layer increased from 78 µm to 200 µm. The apparent activation energy for the layer growth was estimated as 127 kJ/mol. Furthermore, the diffusion path in the isothermal section at 1173 K–1373 K in the Au–Ti–Co system was also discussed.