Questions and Answers
What characterizes a slip system in crystalline materials?
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 _____.
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Match the type of crystal structure with its corresponding Burgers vector:
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Which of the following statements is true regarding slip systems at high temperatures?
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Ductility in polycrystalline materials improves as temperature decreases.
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What does the term 'close packed' imply in the context of dislocation and slip planes?
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What is the primary slip plane for FCC crystals?
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BCC crystals have a clear choice of slip plane.
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What effect does a c/a ratio greater than the ideal value have on HCP metals?
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A __________ leaves the dislocation on the slip plane.
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Which of the following describes a jog in a dislocation line?
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Match the following crystal structures with their slip planes.
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What is the significance of the Burgers vector in dislocations?
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Jogs and Kinks are considered to be defects in a dislocation line.
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What is the primary benefit of separating the extra half-plane in a crystal?
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Burgers vector of partial dislocations in a Shockley partial dislocation is equal to a full lattice translation vector.
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What is the effect of the presence of Shockley partial dislocations on the stacking fault in CCP crystals?
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The Burgers vector of Shockley partial dislocations is __________ of the type vector.
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Which plane do the Shockley partial dislocations lie on?
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Match each term with its correct description:
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Glissile dislocations can easily move within the crystal lattice.
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What is a stacking fault in the context of CCP crystals?
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Study Notes
Crystal Slip Systems and Behavior
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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.
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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
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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).
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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
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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.
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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
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Perfect Edge Dislocation:
- Includes configurations such as (111) slip plane with defined Burgers vectors ( b_1, b_2, b_3 ).
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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.
