  The microstructural features and high-temperature oxidation resistance of
hybrid (TiC+TiB) networks reinforced Ti-6Al-4V composites were investigated
after fabricated with reaction hot pressing technique. The inhomogeneous
distribution of hybrid reinforcers resulted in a sort of stress-induced grain
refinement for {\alpha}-Ti matrix phase, which was further facilitated by
heterogeneous nucleation upon additive interfaces. HRTEM analyses revealed the
crystallographic orientation relation between TiB and alpha-Ti phases as
(201)TiB//(-1100)alpha-Ti plus [11-2]//[0001] alpha-Ti, while TiC and
{\alpha}-Ti phases maintained the interrelation of (-200)TiC//(-2110)
{\alpha}-Ti and [001]TiC//[01-10] alpha-Ti. The hybridly reinforced
Ti-6Al-4V/(TiC+TiB) composites displayed superior oxidation resistance to both
the sintered matrix alloy and the two composites reinforced solely with TiC or
TiB addition during the cyclic oxidation at 873, 973 and 1073 K respectively
for 100 h. The hybrid reinforcers volume fraction was a more influential factor
to improve oxidation resistance than the matrix alloy powder size. As
temperature rose from 873 to 1073 K, the oxidation kinetics transferred from
the nearly parabolic type through qusilinear tendency into the finally linear
mode. This corresponded to the morphological transition of oxide scales from a
continuous protective film to a partially damaged layer and ended up with the
complete spallation of alternating alumina and rutile multilayers. A
phenomenological model was proposed to elucidate the growth process of oxides
scales. The release of thermal stress, the suppression of oxygen diffusion and
the fastening of oxide adherence were found as the three major mechanisms to
enhance the oxidation resistance of hybrid reinforced composites.
