REVIEW MATERIALS SCIENCE

Chap. 3UNIT CELL

CRYSTAL STRUCTURES

A sites

B sites

A sites

SC (SIMPLE CUBIC)FCC (FACE – CENTERED CUBIC)

BCC (BODY – CENTERED CUBIC) HCP (HEXAGONAL CLOSE PACKED)

DIFFERENT POSSIBLE COMBINATIONS OF LATTICE PARAMETERS

CRISTALOGRAPHIC DIRECTIONS

CRISTALOGRAPHIC PLANES

EXERCICE 3.31 y 3.41

Here are unit cells for two hypothetical metals:

a) What are the indices for the directions indicated by the vectors in the sketch (A, B)?

b) What are the indices for the two planes drawn in sketch ?

CRYSTALLINE MATERIALS

SINGLE CRYSTALS

POLYCRYSTALLINE MATERIALS

• Vacancies:-vacant atomic sites in a structure.

Vacancydistortion of planes

• Self-Interstitials:-"extra" atoms positioned between atomic sites.

self-interstitialdistortion

of planes

POINT DEFECTS

CHAP. 4 IMPERFECTIONS IN SOLIDS

Two outcomes if impurity (B) added to host (A):• Solid solution of B in A (i.e., random dist. of point defects)

• Solid solution of B in A plus particles of a new phase (usually for a larger amount of B)

OR

Substitutional alloy(e.g., Cu in Ni)

Interstitial alloy

(e.g., C in Fe)

Second phase particle--different composition--often different structure.

POINT DEFECTS IN ALLOYS

• Dislocations slip planes incrementally...• The dislocation line (the moving red dot)... ...separates slipped material on the left from unslipped material on the right.

INCREMENTAL SLIP

LINE DEFECTS

Atomic view of edgedislocation motion fromleft to right as a crystalis sheared.

Grain boundaries: • are boundaries between crystals. • are produced by the solidification process, for example. • have a change in crystal orientation across them. • impede dislocation motion.

grain boundaries

Schematic

heat flow

~ 8cmMetal Ingot

AREA DEFECTS: GRAIN BOUNDARIES

Fe-Cr alloy

microscope

grain boundarysurface groove

polished surface

Grain boundaries...• are imperfections,• are more susceptible to etching,• may be revealed as dark lines,• change direction in a polycrystal.

ASTM grain size number

N = 2n-1

no. grains/in2 at 100x magnification

OPTICAL MICROSCOPY