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```							                                                Cabrillo College
ENGR 45 – Engineering Materials

Summary: Chemistry Crystal Structures
_______________________________________________________________________________

Amorphous Matls, Crystalline Materials, Semi Crystalline

Single Crystals/Polycrystalline: nucleation, growth, grain boundaries

Isotropic/ Anisotropic Behavior of amorphous matl, unit cells, single cry, polycrystals

Isotropic/ Anisotropic Behavior from processing: extrusion, injection molding, casting

Properties that are a function of order: strength, stiffness, optical

Def of unit cell; Crystal Systems & Bravais lattice structures

3 reasons why are ceramic crystal structures more complex than metal cry structures

Metals exist as BCC, FCC, HCP

Cubic Structures: SC, BCC, FCC: a vs r; # atoms/uc, coord #, PF, density

Def of polymorphism and examples

Crystallographic Geometry: points, lines, planes

LD equation and calculation of edge, face diag, and body diag lines for SC, BCC, & FCC and
PD equation and calculation of face diag, body diag, and {111} planes for SC, BCC, & FCC

Which are the closest-packed directions and planes for SC, BCC, & FCC

Details of the four types of defects (everything that I covered in class)
 examples of each type and examples of how they are formed
 eq for Nv
 Hume-Rothery Rules for unlimited solubility

Types of diffusion

Def of slip

Be able to sketch a dislocation moving through the lattice structure

How does slip affect a matl’s strength and ductility? Why?
[Strength decreases because not as many bonds need to be broken at once in order to deform the metal….one line
instead of one plane of atoms.]

In the SC, BCC, & FCC, which are the slip planes and the slip directions?

Why does slip occur on the closest-packed plane along the closest-packed direction?
[Less force needed when the planes of atoms are dense….not as much force needed to push atoms up from the spaces
between less dense planes.]

What are slip systems?

How does the presence of defects affect the strength and ductility of metal

Be able to discuss theoretical strength vs. real strength based on the presence of slip and the presence of dislocation
barriers

As the # of defects increase, the conductivity decreases due to scattering.

Plus topics discussed in Hmwks 1B and 1C.

```
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