Crystal Structures and Slip
FCC, BCC and HCP structures explained through deformation, diffusion and anisotropy.
Why crystals matter
Most engineering metals and many ceramics are crystalline. Their atoms repeat in ordered patterns, and that geometry controls available slip systems, packing, diffusion paths and directional properties.
The three metal structures
Face-centred cubic metals generally possess many easily activated slip systems and therefore good ductility. Body-centred cubic metals also have many potential slip systems, but dislocation motion is more temperature-sensitive. Hexagonal close-packed metals have fewer easy deformation modes at room temperature and often show stronger texture effects.
Planes, directions and texture
A single crystal is anisotropic. A polycrystal may appear nearly isotropic when grain orientations are random. Forming, solidification and additive manufacturing can create preferred orientations—texture—which makes properties direction-dependent.
What to calculate
Know how to identify coordination number, atomic packing, planar density and the relationship between lattice parameter and atomic radius. More importantly, connect these quantities to deformation and diffusion rather than treating them as geometry exercises.
Takeaway
Crystal structure is useful only when linked to a mechanism: slip, phase transformation, diffusion, cleavage or anisotropic response.