Improvement of oxidation resistance of TiAl6V4 alloy by siliconizing from liquid phase using melts with high silicon content

This work deals with a study of properties of layers prepared by a simple, cheap, and efficient method of siliconizing from liquid phase. They were prepared using the melts AlSi20 and AlSi28 (wt.%); their high silicon content provides for almost a twofold rate of the layers formation. Main component of the layers formed by siliconizing is τ2 − phase [Ti(AlxSi1−x), where x = 0.15–0.3]. This phase is also formed in aluminium melts containing 5 and 10 wt.% of silicon, as documented in [1], [2], [3] and [4]. The growth rate of silicide–aluminide layers is a parabolic function; the rate constant for melts AlSi20 and AlSi28 expressed in m2/s was determined as:kAlSi20=22.344   exp −227,412.8RT   and   kAlSi28=7,936,635   exp −329,741RT.This equation is valid under experimental conditions. The protective layers with a high silicon content are particularly suitable for high-temperature applications as they contain thermodynamically stable phases, such as TiSi2, SiO2 and Al2O3 creating an efficient barrier against diffusion of oxygen and nitrogen. The protective effect of these layers was studied by cyclic oxidation at temperatures 1123 and 1223 K. These layers rich in silicide–aluminide phase have been proved to provide, in spite of their inhomogeneity, for excellent protection of the titanium alloy against high-temperature oxidation.

► Method “Liquid phase siliconizing” excels in simplicity.
► In a short reaction time there is a massive layer of τ2 phase rich in silicon.
► Content of silicon in Al–Si melt has a significant influence on the layer growth.
► Layers have excellent oxidation resistance at high temperature even at 1223 K.