Recrystallization textures in metals and alloys

Uniaxial deformation

Aluminium wire

FCC wires retain deformation texture ([111]+[100]) upon

recrystallisation

Composition / Purity plays an important role:

CP Aluminium (99.95%) with ([111] + [100]) deformation

texture

• when recrystallised at 350-550 C, it leads to

(i) sometimes random texture, or

(ii)major component [103] to [113]+minor component [111]

• when recrystallised at 600 C, pure aluminium leads to secondary

recrystallisation texture - [103] to [113]

F.C.C. Metals and alloys

Copper • when recrystallised below 400 C – [100], [112] • when recrystallised above 400 C – may be random • when recrystallised above 950 C – [112] / [111] – mixed or random,

depending on deformation texture

Aluminium after compression • deformation texture is retained on recrystallisation, as a whole but the

individual grains will alter their orientation. • secondary recrystallisation leads to [111] texture in aluminium, [110]

texture in silver

Annealing of F.C.C. sheet materials can produce the following textures:

The cube texture

A texture approximately same as the rolling texture

One or more new types of texture Approximate randomness

Sheet texture

Rolled aluminium partially retains its rolling texture on recrystallisation, in addition to developing a cube texture

Retained component is due to recrystallisation insitu in some grains (without orientation change)

Rolled silver, Cu-33Zn, Cu-5Sn, Ag-1Zn, Ag-30Au (with {110}<112> rolling texture) changes to

a new texture {113}<211> or {225}<734> at low temperature

upon long annealing at 433 to 533 C by secondary grains having the orientation of deformation texture

becomes random texture with annealing above 800 C.

Recrystallisation texture of Brass, Cu-Ge, Cu-Sn gradually change with composition

Most remarkable recrystallisation texture

Extremely sharp texture when fully developed

Resembles a single crystal with subgrains – may contain a minor amount of material with different orientation

The cube texture

Arrangement of Crystallites in cube texture (111) Pole figure

100

1000

4000

RD

TD

(001) ND (Sheet Normal Direction)

[100] RD (Sheet Rolling Direction)

Conditions for Cube texture

Percentage of cube oriented grains vary with

(a) processing variables, and

(b) composition

For example, for a well developed cube texture

– well developed deformation texture is required

– 85-90% cold reduction is necessary

percentage of cube orientation in copper increases with:

(a) annealing temperature

(b) annealing time

(c) high reduction prior to final anneal

(d) a small penultimate grain size

(e) small thickness of cold rolled grains prior to

final anneal

Mechanism of formation of Cube nuclei

Orientation Size of subgrains (m) Stored energy (mJcm-3)

Brass 12 12.2

S 6.3 13.3

Copper 4.3 12.9

Cube 4 7.6

• A large driving pressure provided by higher stored energy* of

adjacent S component.

• A large subgrain size

•cube subgrains tend to be larger than other orientations

•have a larger size spread which results in the presence of some

exceptionally large cube subgrains

•initiation of Strain Induced Boundary Migration of the cube bands

Theory of Cube textures in FCC metals

* Stored energy within a grain is due to the accumulation of

dislocation and other defects during deformation

• A higher mobility of a 40o <111> Cube/S boundary would

promote the early stages of growth- having boundaries that are

curved to favour continued growth at the expense of the others.

•A lower energy of a special boundary such as 40o <111> would

reduce the retarding pressure due to boundary curvature

Pc = 2b/R

Theory of Cube textures in FCC metals (continued)

How to minimise a cube texture? (a) Intermediate anneal and small reduction (b) Large penultimate grain size (c) Low final annealing temperature (d) Addition of alloying elements, particularly the ones which change the deformation texture from copper type to brass type e.g. In copper, following elements minimise or suppress cube

texture 5 wt % Zn 1 wt % Sn

4 wt % Al 0.5 wt% Be /Cd 0.0025 at% P 0.3 at% Sb 1.5 at% Mg 4.2 at% Ni 0.18 at% Cd 0.047 at% As

Size effect strong solid solution hardening

• In Aluminium, conditions for optimising cube texture are different: • Increasing rolling reduction suppresses cube texture; retains rolling texture • Ratio of Fe to Si in Al is critical for cube texture • Recovery is easier in Al. Recrystallisation is replaced by recovery (a) on annealing at high reductions, and (b) with high iron contents

B.C.C. Metals and alloys

Uniaxial deformation

BCC wires retain deformation texture [110] upon recrystallisation

- grains of other orientations are formed on secondary recrystallisation

Composition plays an important role:

Tungten has [320], [321], [531], or [421]

- as secondary recrystallisation texture

Fe, Steels, Vanadium recrystallise with retention of [110]

Iron after compression

– deformation texture [111] is retained on recrystallisation as a major component,

- the minor component [100] is lost on recrystallisation at 580 and 850 C

Sheet texture

Rolled Iron and steel on recrystallisation at 540 and 840 C show three principal texture components:

1. {111}[211]

2. {001}[uvw], where [uvw] is 15 from [110]

3. {112}[uvw], where [uvw] is 15 from [110] – relatively weaker

Recrystallisation texture of V, Fe-Si, Zr-Nb has been found similar to Fe

Mo retains its deformation texture with somewhat spread ~5

Ta has recrystallisation texture {111}[211] (~2400 C)

W recrystallises (~1800 C) to {001}[uvw], where [uvw] is 15 from [110]

H.C.P. Metals and alloys

Uniaxial deformation

Be wires retain deformation texture [1010] upon

recrystallisation

- Ti & Zr change to [1120]

Sheet textures

In Zn, Mg, Ti (annealed below 500 C ), Be (annealed at

700 C )

– deformation texture is retained on

recrystallisation.

- Zr recrystallised between 400-600 C has

orientation with orientations having [1120] rotated to

the position near rolling direction.

Questions

1. The texture component seen dominantly during FCC recrystallization is (a) {110} <001>; (b) 100} <001>; (c) {123} <634>; (d) {100} <013>

2. Which of the following is true. (a) High cube is due to the lowest stored energy (b) Cube formation is independent of amount of deformation and temperature (c) Fraction of cube increases with alloying additions (d) High cube can be attributed to its high boundary migration

3. Which of the following is true regarding nucleation. (a) Surface energy should be larger than strain energy (b) Strain energy should be larger than surface energy (c) Both surface and strain energies should be equal. (d) Surface and strain energies are independent.

4. Recrystallization, in general, is characterized by (a) High hardness and increased HAGB* (b) Low hardness and increased HAGB (c) High hardness and decreased HAGB (d) Low hardness and decreased HAGB

5. Can reducing the SFE of a material by alloying additions suppresses cube texture. Yes/No *HAGB – High angle grain boundary