Materials Science: Slip Systems in Crystals

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Questions and Answers

What characterizes a slip system in crystalline materials?

A slip direction over multiple planes

A random arrangement of atoms

A combination of a slip direction lying on a slip plane (correct)

Only one slip direction in all planes

In BCC crystals, there is typically a clear choice of slip planes.

False

What is the significance of the Burgers vector in dislocations?

It describes the lattice distortion caused by dislocations in the crystal.

Close packed volumes, areas, and lines tend to remain _____.

close packed Signup and view all the answers

Match the type of crystal structure with its corresponding Burgers vector:

Monoatomic FCC = ½ Monoatomic BCC = ½ NaCl type structure = ½ CsCl type structure = Not specified DC type structure = ½ Signup and view all the answers

Which of the following statements is true regarding slip systems at high temperatures?

More slip systems may become active. Signup and view all the answers

Ductility in polycrystalline materials improves as temperature decreases.

False Signup and view all the answers

What does the term 'close packed' imply in the context of dislocation and slip planes?

It implies a structure with better bonding and increased atomic density. Signup and view all the answers

What is the primary slip plane for FCC crystals?

{111} Signup and view all the answers

BCC crystals have a clear choice of slip plane.

False Signup and view all the answers

What effect does a c/a ratio greater than the ideal value have on HCP metals?

It favors basal slip. Signup and view all the answers

A __________ leaves the dislocation on the slip plane.

kink Signup and view all the answers

Which of the following describes a jog in a dislocation line?

It moves the line out of the current slip plane. Signup and view all the answers

Match the following crystal structures with their slip planes.

FCC = {111} HCP = (0001), (0002) BCC = {110}, {112}, {123} Anisotropic slip = None Signup and view all the answers

What is the significance of the Burgers vector in dislocations?

Determines the slip direction. Signup and view all the answers

Jogs and Kinks are considered to be defects in a dislocation line.

True Signup and view all the answers

What is the primary benefit of separating the extra half-plane in a crystal?

To reduce the strain energy associated with dislocation Signup and view all the answers

Burgers vector of partial dislocations in a Shockley partial dislocation is equal to a full lattice translation vector.

False Signup and view all the answers

What is the effect of the presence of Shockley partial dislocations on the stacking fault in CCP crystals?

They create a stacking fault bounded by the two partial dislocations. Signup and view all the answers

The Burgers vector of Shockley partial dislocations is __________ of the type vector.

1/3rd Signup and view all the answers

Which plane do the Shockley partial dislocations lie on?

{111} slip plane Signup and view all the answers

Match each term with its correct description:

Strain Energy = Energy associated with deformations in the crystal structure Stacking Fault Energy = Energy required to create a stacking fault Burgers Vector = Vector describing the magnitude and direction of lattice distortion Slip Plane = Plane along which dislocations move Signup and view all the answers

Glissile dislocations can easily move within the crystal lattice.

True Signup and view all the answers

What is a stacking fault in the context of CCP crystals?

A defect caused by displacement of atomic planes, typically created by partial dislocations. Signup and view all the answers

Study Notes

Crystal Slip Systems and Behavior

Slip Planes and Directions:
- FCC (Face-Centered Cubic): Slip planes are {111}, with slip direction also along {111}.
- HCP (Hexagonal Close-Packed): Slip planes are (0001), (0002).
- BCC (Body-Centered Cubic): Slip planes include {110}, {112}, and {123}. Lacks a clear slip plane choice, leading to wavy slip lines.
Planar Density:
- Defined as a measure of how tightly packed atoms are in the crystallographic structure.
- Calculated as:
  - For {110}: ( \frac{a^2}{2} )
  - For {112}: ( \frac{2\sqrt{2}}{3}a^2 )
  - For {123}: ( \frac{4\sqrt{3}}{3}a^2 )

Defects in Dislocations

Jogs and Kinks:
- Jog: Moves dislocation out of its original slip plane to a parallel plane.
- Kink: Keeps dislocation within the current slip plane.
- These are considered defects in a dislocation line (defects in a defect).
Burgers Vector:
- A fundamental lattice translational vector on the slip plane.
- Monoatomic FCC: ( \frac{1}{2} )
- Monoatomic BCC: ( \frac{1}{2} )
- Simple Cubic: Value varies based on structure.
- NaCl and CsCl types also have defined Burgers vector values.

Slip Systems and Plastic Deformation

Definition of Slip System:
- A combination of slip direction (b) on a slip plane; crucial for understanding how materials deform.
- Close-packed crystals feature a close-packed direction along a close-packed plane.
Active Slip Systems:
- BCC crystals can exhibit multiple active slip systems due to varying planes with similar density, resulting in non-linear slip lines.
- Temperature effects: More slip systems may activate at high temperatures, allowing brittle materials to become ductile.

Dislocation Types and Characteristics

Perfect Edge Dislocation:
- Includes configurations such as (111) slip plane with defined Burgers vectors ( b_1, b_2, b_3 ).
Shockley Partial Dislocations:
- Arise from the separation of the extra half-plane of atoms, which reduces strain energy.
- Burgers vector of partial dislocations is generally one-third of the full lattice translation vector, residing in the {111} slip plane and capable of movement (glissile).
- The region between two partial dislocations forms a stacking fault in the Crystal Close-Packed (CCP) structure.

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Description

Explore the crucial aspects of slip systems in various crystal structures such as FCC, HCP, and BCC. This quiz covers the types of slip planes and directions unique to these structures and highlights anisotropic behavior in materials. Test your understanding of how crystal structures influence mechanical properties.