Page 207 - Fiber Fracture

192 H.U. Kunzi

recrys tal lised I I I
I
0 10 20 30 40 50
Distance from wire axis m] ,-p
Fig. 7. Micro-hardness measured on the section of a 100 rnrn thick Au wire in the as-drawn, a partially and
the completely recrystallized state.

order increases generally with the total deformation. In fcc metals both textures [loo]
and [ 1 1 11 may appear simultaneously and their relative occurrence depends strongly on
the deformation and the initial orientation. Subsequent restoration or annealing often
favor the formation of the (100) texture (Shin et al., 2000). The presence of a second
phase strongly perturbs the development of pronounced textures or even prevents its for-
mation when the second-phase particles are undeformable. Such undeformable particles
force the matrices to flow around them and therefore modify the flow pattern locally.
Textures are usually determined by X-ray diffraction and the obtained results
are conveniently represented by so-called pole figures. These figures give the polar
projection of the angular density distribution of a selected crystal axis with respect to
a given sample orientation. For wires and sheets the vertical axis of the pole figure is
usually chosen as the drawing or rolling direction. Fig. 8 shows the pole figure for the
(100) direction of drawn, restored and annealed Cu wires. Fig. 8a,b shows the presence
of two dominating grain orientations. The round regions at the top and the bottom
belong to grains with one (100) axis almost parallel to the wire axis. The other two (100)
directions of these grains make up the intensity in the central strip (going through the
center). The remaining two regions (between the central strip and the top and bottom,
respectively) belong to grains whose (1 11) axis is parallel to the drawing direction.
Fig. 8b clearly indicates that restoration, which in heavily deformed Cu already sets in at
room temperature, gives rise to significant modifications. The (100) texture component
becomes much sharper and the number of grains with a (1 11) direction parallel to the
wire is reduced. In view of Fig. 6, the term grain should here probably better be replaced
by shear bands. In fact, the orientation remains constant only within a band, whereas
it gradually changes in between two neighboring bands. Subsequent heat treatments
at higher temperatures and for prolonged times strongly reduce the degree of grain
polarization. Similar results have also been observed in Au wires (Busch-Lauper, 1988).