The key difference between annealing twins and deformation twins is that annealing twins form as a result of a change in the crystal system during cooling, whereas deformation twins form as a result of the stress on the crystal after the crystal has formed.
Crystal twinning is the sharing of some of the same crystal lattice points in a symmetric manner between two separate crystals. This twinning process results in an intergrowth of two separate crystals, forming a variety of configurations. We describe a composition surface of the twin plane as a twin surface (where the lattice points are shared between two separate crystals). According to crystallographers, the twining process can be classified into several groups depending on the twin laws. Typically, twin laws are specific to the crystal system. Annealing twins and deformation twins are two such types.
CONTENTS
1. Overview and Key Difference
2. What are Annealing Twins
3. What are Deformation Twins
4. Annealing Twins and Deformation Twins in Tabular Form
5. Summary – Annealing Twins vs Deformation Twins
What are Annealing Twins?
Annealing twins are also known as transformation twins and are a result of a change in the crystal system during cooling. During cooling, one crystal form becomes unstable, and the crystal structure tends to reorganize or transform into some other stable form. Therefore, annealing twins form as a consequence of growth accidents during the recrystallization of metals (specifically the deformed cubic-close packed metals), including alpha brass, copper, nickel, and austenitic iron.
According to history, we can find annealing twinning in gold as early as 1897. But this is a rare phenomenon, and there is much empirical evidence to suggest that there are some important factors that determine the frequency with which this type of gold occurs. Some of these factors include grain size, temperature and time of annealing, grain boundary velocity, crystallographic texture, presence of inclusions, etc.
What are Deformation Twins?
Deformation twins are wedge-shaped or tabular twins. These twins can propagate using the movement of the twin tip or the movement of the twin boundary into an untwinned material having a straight twin boundary. We can distinguish these twins easily from other types of twins by their shape.
Figure 01: Twinned Crystals of Albite
Deformation twinning occurs as a common result of regional metamorphism. We can find this type of twinning as a significant defect structure in most face-centred cubic metals having a low stacking fault energy. Moreover, minerals can deform through deformation twinning or flame-shaped other than a dislocation. There are three major steps of the formation of a deformation twin: nucleation, propagation, and growth stages.
What is the Difference Between Annealing Twins and Deformation Twins?
According to crystallographers, the twining process can be classified into several groups depending on the twin laws. Annealing twins and deformation twins are two such types. The key difference between annealing twins and deformation twins is that annealing twins form as a result of a change in the crystal system during cooling, whereas deformation twins form as a result of the stress on the crystal after the crystal has formed.
The following infographic lists the differences between annealing twins and deformation twins in tabular form for side by side comparison
Summary – Annealing Twins vs Deformation Twins
Crystal twinning refers to the sharing of some same crystal lattice points in a symmetric manner between two separate crystals. According to crystallographers, the twining process can be classified into several groups depending on the twin laws. Annealing twins and deformation twins are two such types. The key difference between annealing twins and deformation twins is that annealing twins form as a result of a change in the crystal system during cooling, whereas deformation twins form as a result of the stress on the crystal after the crystal has formed.
Reference:
1. “Metals and Alloys.” Phase Transformations and Complex Properties Research Group.
Image Courtesy:
1. “Twinned crystals of Albite” By 大英百科全书 – 1911大英百科全书 (Public Domain) via Commons Wikimedia