Slip (materials science)

In

Slip in

Given the permutations of the slip plane types and direction types, fcc crystals have 12 slip systems.[3] In the fcc lattice, the norm of the Burgers vector, b, can be calculated using the following equation:^[4]

${\displaystyle |b|={\frac {a}{2}}|\langle 110\rangle |={\frac {a{\sqrt {2}}}{2}}}$^[4]

Where a is the lattice constant of the unit cell.

Body centered cubic crystals

Slip in

Some bcc materials (e.g. α-Fe) can contain up to 48 slip systems. There are six slip planes of type {110}, each with two <111> directions (12 systems). There are 24 {123} and 12 {112} planes each with one <111> direction (36 systems, for a total of 48). Although the number of possible slip systems is much higher in bcc crystals than fcc crystals, the ductility is not necessarily higher due to increased lattice friction stresses.^[3] While the {123} and {112} planes are not exactly identical in activation energy to {110}, they are so close in energy that for all intents and purposes they can be treated as identical. In the diagram on the right the specific slip plane and direction are (110) and [111], respectively.^[4]

${\displaystyle |b|={\frac {a}{2}}|\langle 111\rangle |={\frac {{\sqrt {3}}a}{2}}}$^[4]

Hexagonal close packed crystals

Cadmium, zinc, magnesium, titanium, and beryllium have a slip plane at {0001} and a slip direction of <1120>. This creates a total of three slip systems, depending on orientation. Other combinations are also possible.^[7]

There are two types of dislocations in crystals that can induce slip - edge dislocations and screw dislocations. Edge dislocations have the direction of the Burgers vector perpendicular to the dislocation line, while screw dislocations have the direction of the Burgers vector parallel to the dislocation line. The type of dislocations generated largely depends on the direction of the applied stress, temperature, and other factors. Screw dislocations can easily

Formation of slip bands indicates a concentrated unidirectional slip on certain planes causing a stress concentration. Typically, slip bands induce surface steps (i.e. roughness due

The main methods to identify the active slip system involve either slip trace analysis of single crystals^[13][14] or polycrystals,^[15][8] using diffraction techniques such as neutron diffraction^[16] and high angular resolution electron backscatter diffraction elastic strain analysis,^[17] or Transmission electron microscopy diffraction imaging of dislocations.^[18]

In slip trace analysis, only the slip plane is measured, and the slip direction is inferred. In zirconium, for example, this enables the identification of slip activity on a basal, prism, or 1st/2nd order pyramidal plane. In the case of a 1st-order pyramidal plane trace, the slip could be in either 〈𝑎〉 or 〈𝑐 + 𝑎〉 directions; slip trace analysis cannot discriminate between these.^[5]

Diffraction methods cannot generally resolve the slip plane of a residual dislocation. For example, in Zr, the screw components of 〈𝑎〉 dislocations could slip on prismatic, basal, or 1st-order pyramidal planes. Similarly, 〈𝑐 + 𝑎〉 screw dislocations could slip on either 1st or 2nd order pyramidal planes.[5]

See also

• Miller indices
• Persistent slip bands

References