Metal Crystals Flashcards
DMM1: materials Deck 3
describe metallic bonding
Atoms release electrons into a delocalised cloud, giving stable configuration.
Electron cloud held in place around positive ions.
Negative charge of electrons prevents ions repelling
what determines metling point and stiffness of a material?
intermolecular bond strength
what is a lattice?
a regular
repeated arrangement of
atoms
What is a unit cell
Smallest
repeating unit that can be
used to describe a lattice
describe the close pack plane of a metal crystal
metal atoms act as solid spheres which pack to take up the smallest possible space
atoms are touching in three dimensions
Describe a face centered cubic
three close pack planes are stacked offset to each other so none align.
Describe Hexagonal close packed structure
three close packed planes are stacked with the central plane offset and the top and bottom planes are algined
Describe body centered cubic
close packed plane is distored slightlty so only two close pack directions exist. these planes are stacked on top of each other ofsett
What is packing factor? how is it cauculated?
a measurement of how closely packed atoms are
P.F= total volume of atoms / total volume of unit cell
what is the mechanism for elastic deformation of metals?
atoms pull apart extending intermolecular bonds in a reversable manner
What is the mechanism for plastic deformation of metals?
crystal layers slide past each other are realign in a new configuration perminantly atering the shape
What is a slip system?
Directions in which the crystal structure can mosty easily slip. these are along the close pack directions
Where are the slip planes in HCP (hexagonal close packed)
only along a single plane across the three slip directions
Where can a body centered cubic (BCC) crystal slip
slips along the six diagonal planes across the two slip directions
Where can a FCC (face centered cubic) system slip
slips along four difference diagnonal planes each with three slip directions
