Abstract
The microstructure of the secondary deformation zone (SDZ) near the cutting surface in
metal chips of Ti-6Al-4V formed during machining was investigated using focused ion beam
(FIB) specimen preparation and transmission electron microscopy (TEM) imaging. Use of
the FIB allowed precise extraction of the specimen across this region to reveal its
inhomogeneous microstructure resulting from the non-uniform distribution of strain, strain
rate, and temperature generated during the cutting process. Initial imaging from conventional
TEM foil preparation revealed microstructures ranging from heavily textured to regions of
fine grains. Using FIB preparation, the transverse microstructure could be interpreted as fine
grains near the cutting surface which transitioned to coarse grains toward the free surface. At
the cutting surface a 10 nm thick recrystallized layer was observed capping a 20 nm thick
amorphous layer.
