The influence of microstructure of the two-phase alloy Ti-46Al-1Cr-0.2Si on
the oxidation behavior in air between 600 and 900 degrees C was studied. T
he oxidation rate, type of scale, and scale spallation resistance were stro
ngly affected by the type of microstructure, i.e., lamellar in as-cast mate
rial and duplex after extrusion at 1300 degrees C. The oxidation rate was a
ffected by the size and distribution of the alpha(2)-Ti3Al. The type of oxi
de scale determines the spalling resistance. Cast material developed a unif
orm scale that spalled off after short exposure times at 800 and 900 degree
s C when a critical thickness was reached. The extruded material presented
a heterogeneous scale with predominant thick regions formed on gamma-TiAl-a
lpha(2)-Ti3Al grains and thin scale regions formed on gamma-TiAl grains. Th
is type of scale could permit an easier relaxation in the matrix of stresse
s generated by both thermal-expansion mismatch between scale and alloy and
oxide growth, resulting in a higher spallation resistance.