V.Z.Bengus, E.D.Tabachnikova, P.Duhaj*
Received March 24, 1999
Concentration dependences of the critical stress sigmafp
for the catastrophic plastic shear under a uniaxial tension of the
Fe100-xBx (x = 14, 16, 17, 20) and
Fe85-xCoxB15 (x = 15, 17,
19, 21, 25, 30, 40, 50, 64) metallic glass ribbons are measured experimentally.
Minima of the sigmafp are discovered at compositions corresponding
to the eutectic (x = 17) in the Fe-B metallic glasses
and at x = 21 and 40 at.% Co, which are close to
the rational ratios 3:1 and 1:1 of atomic concentrations of Fe
and Co in the Fe-Co-B metallic glasses (these compositions
are regarded as "stoichiometric" for the formation of nanoclusters
with a high average binding energy per atom). This is explained in
the framework of polycluster model of amorphous solids by small values
of critical stresses for local plastic shear along intrecluster boundaries
in the stoichiometric metallic glasses due to the large concentration
of non-coinciding atomic sites (analogs of grain boundary glide dislocations)
at these boundaries in comparison with those in metallic glasses of
nearby compositions.