BeginnerTopic 3 of 100Materials & Chemical
Crystal structures
FCC, BCC and HCP lattices describe atomic arrangements in metals.
In depth
Crystalline solids have atoms in repeating lattices. Common metal structures: BCC (Fe at room temperature, Cr, W: 8 atoms neighbours), FCC (Al, Cu, Au, γ-Fe: ductile, 12 neighbours) and HCP (Zn, Mg, Ti: limited slip systems). Structure influences ductility and strength.
Key points
- Unit cell and lattice parameter
- Coordination number
- Allotropy
ExampleIron changes from BCC to FCC at 912 °C, which allows carbon to dissolve in steel heat treatment.
What is Crystal structures?
FCC, BCC and HCP lattices describe atomic arrangements in metals.
Why is it important to understand crystal structures?
Crystal structure sets the number of slip systems and therefore how a metal deforms, so it controls ductility and strength.
What are FCC, BCC and HCP?
Face-centred cubic, body-centred cubic and hexagonal close-packed, which are the three most common metallic crystal structures.
Why are FCC metals often ductile?
They have many slip systems that let dislocations move easily, so they deform without cracking.
How is Crystal structures used in practice?
Typical applications include explaining why aluminium is ductile while zinc is brittle at room temperature, selecting a metal for cold forming based on its lattice and predicting how strength changes with grain structure in an alloy.
What should I learn before Crystal structures?
Study "Atomic structure and bonding" first (topic 2 of 100 in Materials & Chemical). It covers the groundwork this topic builds on.
What are the key points of Crystal structures?
Unit cell and lattice parameter. Coordination number. Allotropy.
Can you give an example of Crystal structures?
Iron changes from BCC to FCC at 912 °C, which allows carbon to dissolve in steel heat treatment.
What comes after Crystal structures?
The next topic is "Miller indices", which builds directly on this one.
How difficult is Crystal structures?
It is classed as Beginner in Materials & Chemical (topic 3 of 100). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.