Effect of scandium and chromium on the structure and heat resistance of alloys based on gamma-TiAl

It is established that microalloying of gamma -titanium aluminides with sca ndium provides an increase in heat resistance, structure refinement and mod ification, and formation of a dispersion-strengthened structure with a cohe rent bond between the strengthening and matrix phases. Proceeding from this an improvement might be expected in strength characteristics over a wide t emperature range. The effect in scandium consists in changing the ratio of Al:Ti thermodynamic activities in the direction of forming aluminum oxide a t the alloy surface during oxidation as a result of the deoxidizing effect of scandium and the formation of fine oxide inclusions. As a result of this aluminum does not form oxides within the alloy. The distribution of elemen ts within the microstructure of gamma -Ti - Al with 5% Cr after oxidation a t 900 degreesC for 300 h is studied. It is established that the surface sca le layer that forms sometimes contains Cr in addition to Al and O. A diffus ion mechanism is suggested for realizing the Cr-effect according to which c hromium and aluminum ions participate in place of titanium ions in forming Al2O3 - Cr2O3 scale at the metal - air atmosphere interface.