This document discusses texture formation processes in metals and alloys, including deformation, annealing, and transformation textures. It focuses on deformation textures and the mechanisms of slip and twinning. The key factors that determine the dominant deformation mechanism are crystal structure and stacking fault energy. Materials with high stacking fault energy deform primarily through slip, while those with low stacking fault energy experience more twinning. The document also examines differences in slip systems for BCC, FCC, and HCP crystals and how deformation leads to the development of crystallographic texture through grain rotation.

1. Texture in metals and alloys
Basic processes of texture formation in metals and alloys:
processes directly involving dislocations
processes involving dislocation accumulation
Deformation textures
processes involving dislocation annihilation
Annealing textures
processes not directly involving dislocation
Transformation textures

2. Deformation textures

3. Deformation: Microstructural aspects
• In crystalline materials, the deformation proceeds
through the following mechanisms
1) Slip
2) Twinning
3) Grain boundary sliding
4) Diffusion creep
• Out of these mechanisms, only slip and twining are
responsible for the evolution of crystallographic texture
• Grain boundary sliding, has sometimes been found to be
associated with weakening of the overall texture, the
nature of the process is such that it does not lead to
grain rotation, and hence the evolution of texture.

4. The deformed state
 Grain changes their shape and there is surprising large
increase in the total grain boundary area
 The new grain boundary area has to be created during
deformation by incorporation of dislocations being
continuously generated during deformation
 Appearance of internal structure within the grains
 Stored energy = sum of energy of all the dislocations and
new interfaces

5.  During deformation, the orientation of single crystals
and of individual grains of a polycrystalline metal changes
relative to the directions of the applied stresses
 These changes are not random and involve rotations
which are directly applied to the crystallography of
deformation
These rotations lead to the acquisition of preferred
orientation, or texture
Texture becomes stronger as the deformation proceeds

6. Metal/ Alloy Al Ni Cu Au Ag 304 SS 70:30
Bs
Co
(fcc)
91:9
Cu-Si
SFE (mJ m-2) 166 128 78 45 22 21 20 15 5
•Depending on the availability of slip systems, the major
deformation mechanism operated would be either of two
or both mentioned above.
•In materials with FCC crystal structure, the choice of
deformation mechanism is largely controlled by stacking
fault energy. Materials with high to medium stacking
fault energy deform by slip while in materials with low
stacking fault energy, twinning plays an important role in
the deformation.
SFE of some the FCC materials
Slip deformation Twinning assisted deformation

7. •During deformation, slip occurs on the close pack planes
and along the closest packed directon.
•For FCC metals, the slip system is {111}<110>
• At higher temperature, other slip systems do operate,
particularly in metals with high SFE values, for example on
{100}, {110}, {112} and {122} planes.
• More recently, it has been reported that even at low
temperature, slip occurs on {111}, {110} and {122}.

8.  Wavy nature of slip lines generally observed on prepolished
sample of the deformed sample
 At temperatures lower than Tm/4, {112}<111> slip systems
operate, while at temperatures higher than Tm/2, {123}<111>
slip systems is preferred.
 As mentioned at room temperature slip
occurs in the close packed direction
<111>. This direction is contained by
many of the planes like {110}, {112}
and {123} planes
 All planes containing <111> are
potential slip systems thus form pensile
glide
Deformation behaviour of BCC materials
[001]
[100]
[010]
[11 1]
[110]

9. Slip systems in various crystals at room temperature
Crystal Plane Direction
FCC {111} <110>
BCC {110},{112},{123} <111>
Hexagonal {0001}, {10ˉ11}, {10ˉ10} <11ˉ20>
Orthorhombic {010} <100>

10. HCP FCC
BCC

11. 1. What are the differences between slip and twining in a crystal?
2. Why during deformation of BCC materials wavy nature of slip
observed?
3. Explain stacking fault energy (SFE) and its affect on deformation of a
materials.
4. How many slip system/systems is/are required to deform a single
crystal?
5. Near grain boundaries the number of slip lines observed are more
than grain interior. Why?
6. Determine the required tensile load along [1-10] of a FCC crystal to
cause slip on (1-1-1)[01-1] if the critical resolved shear stress is 10
MPa
Question