As. Gay et al., INTRAGRANULAR SEGREGATION OF BORON IN FE- 40 AT-PERCENT AL WITH B2 STRUCTURE - INFLUENCE OF THE INTERACTION OF THERMAL VACANCIES AND BORON ATOMS, Journal de physique. IV, 6(C2), 1996, pp. 153-158
Boron segregation to grain boundaries was studied in ordered (B2) FeAl
containing 40 at% Al. It was observed that small additions of boron (
200 at ppm) change the fracture mode from intergranular to mixed (tran
sgranular and intergranular). A low level of boron (few at%) was detec
ted by AES in grain boundaries of this hypostoechiometric alloy. Never
theless, the kinetic of boron segregation is rapid : even a quench fro
m 950 degrees C promotes it. As FeAl alloys are known to retain large
concentrations of thermal vacancies, the possibility of an interaction
between boron atoms and vacancies was investigated in order to unders
tand the mechanism of boron segregation. Dilatometric isothermal exper
iments showed that vacancies eliminate more rapidly in B-doped Fe-40 a
t%Al than in B-free Fe-40 at%Al. Modelisation of the kinetics of vacan
cies elimination predict that complexes boron atoms - vacancies migrat
e more rapidly than free vacancies : the difference between their migr
ation energies is higher than 0,4 eV. This result could justify the as
sumption that at least a part of boron segregation in FeAl is due to a
non-equilibrium mechanism.