Tribo-oxidation of Ti-Al-Fe and Ti-Al-Mn cladding layers obtained by non-vacuum electron beam treatment

The research was devoted to studying unlubricated tribological behaviors of.-TiAl-based coatings in the temperature range 25-400 degrees C. These gamma-TiAl-based intermetallic coatings alloyed with Fe or Mn were formed on CP-Ti workpieces using a non-vacuum electron beam deposition. The microstructure, phase and elemental analyses proved the formation of gamma-TiAl and appearance of the ternary phases (Laves and G-phases). It was shown that friction coefficients obtained for three materials were barely different but their fluctuations were strongly dependent on surface oxidation and the phase composition. It was found that the Ti-45Al-8Mn (at.%) coatings consisting mainly of gamma and alpha(2) phases had lower wear resistance in comparison with the Ti-42Al-7Fe (at.%) and Ti-57Al-13Fe (at.%) coatings. Whereas the Ti-57Al-13Fe (at.%) coating contained. and G phases possessed better wear resistance as compared to that of Ti-42Al-7Fe (at.%) coating with the structure represented by the gamma matrix and a eutectic (alpha(2) + Laves phases). The microprobe analysis, scanning electron and optical microscopy, and XPS measurements revealed the formation of highly oxidized mechanically mixed layers after the sliding tests. The Ti-45Al-8Mn (at.%) coating subsurface consisted of Al2O3, Al, TiO2, and Ti sub-oxides, whereas for both Ti-Al-Fe coatings the formation of an initial oxide film consisted of a titanium dioxide (rutile structure), alumina, and a low amount of iron oxide (hematite structure) was revealed. Thermal softening of the counter body provoked the iron oxide growth in the wear traces of the coatings alloyed with Fe. Tribooxidation behaviors of Ti-Al-Fe coatings may be interpreted as an example of adaptation the as-deposited structure and phases to high-temperature sliding condition and therefore these coatings can be recommended for protection of the titanium alloy components.