BeginnerTopic 6 of 100Materials & Chemical
Crystal defects
Vacancies, dislocations and grain boundaries control strength.
In depth
Defects: point (vacancies, interstitials, substitutional atoms), line (edge and screw dislocations), planar (grain boundaries, stacking faults) and volume (voids, precipitates). Dislocation motion explains plastic deformation; defects control strength, diffusion and conductivity.
Key points
- Burgers vector
- Vacancy concentration rises with temperature
- Grain boundaries block dislocations
ExampleReal metals are far weaker than theory because dislocations glide at low stress.
What is Crystal defects?
Vacancies, dislocations and grain boundaries control strength.
Why is it important to understand crystal defects?
Defects control the strength of real materials, since a perfect crystal would be far stronger than any engineering metal.
What is a dislocation?
A line defect where part of a crystal plane ends, which lets the crystal deform at stresses far lower than a perfect lattice would need.
Why do grain boundaries strengthen metals?
They block dislocation movement, so smaller grains with more boundaries usually give higher yield strength.
How is Crystal defects used in practice?
Typical applications include explaining why cold working increases the strength of a copper wire, improving the yield strength of steel by controlling grain size and understanding why a vacancy speeds up diffusion in an alloy.
What should I learn before Crystal defects?
Study "Packing factor and density" first (topic 5 of 100 in Materials & Chemical). It covers the groundwork this topic builds on.
What are the key points of Crystal defects?
Burgers vector. Vacancy concentration rises with temperature. Grain boundaries block dislocations.
Can you give an example of Crystal defects?
Real metals are far weaker than theory because dislocations glide at low stress.
What comes after Crystal defects?
The next topic is "Diffusion", which builds directly on this one.
How difficult is Crystal defects?
It is classed as Beginner in Materials & Chemical (topic 6 of 100). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.