Although some knowledges about the fatigue deformation mechanisms of fcc alloy
single crystals containing precipitates have been obtained in the past several
decades, few relevant research findings have been reported on precipitates
containing bcc alloy single crystals. In the present work, a single--slip--oriented
bcc Fe-35%Cr alloy (mass fraction) single crystal containing Cr--rich precipitates
was prepared as the target material, and its fatigue deformation features were
investigated under constant plastic strain amplitude control. Experimental results
and analyses demonstrate that, when the plastic strain amplitude
ε_pl≧2.5×10^-3, the Cr--rich precipitates can be
readily sheared by the moving dislocations during deformation, leading to an
obvious stress softening phenomenon observed at the tensile loading stage of the
first cycle, and subsequently to a slight cyclic softening phenomenon at a very
early stage of cycling. In addition, the tension--compression stress asymmetry was
found during cyclic deformation of the crystals, and this enhanced stress asymmetry
should be related to the deformation instability of Cr--rich precipitates. The slip
deformation features were mainly manifested by the formation of coarse slip bands
comprising a quantity of fine slip lines and also by the formation of the kink band
at high ε_pl(e.g., 5.0×10^-3). The primary crack
develops roughly along the primary slip plane (101) and the crystal
finally cracks along this plane, accompanied with some secondary cracks having
various morphologies being formed on the crystal surface. Microstructural
observations indicate that persistent slip band (PSB) ladder--like structures
can be found at a low ε_pl of 5.0×10^-4, and the
volume fraction of them increases with increasing ε_pl.
As ε_pl is raised to 5.0×10^-3, the microstructural
features are primarily characterized by the formation of dislocation cells.