MATERIALS ENGINEERING – DAY 9
PHASES AND PHASE DIAGRAM
Preliminary Discussion
 Concept of the Phase
 Phase Diagram – start with Copper Nickel.
1. What phase or phases are present?
2. What is the chemical composition of each phase
present?
3. How much (relative amounts) of each phase is
present?
 More practice with the Lead Tin system

YOU SHOULD BE ABLE TO:
Define a phase is and explain how the amount,
nature, size, shape, distribution, and orientation
of the phases affects the material properties.
 Given an equilibrium phase diagram,

identify the liquidus, solidus, or solvus lines, and
state what they represent.
 identify the eutectic or eutectoid point, composition,
or temperature, and state what they represent.
 find the number of phases present, name those
phases, find their chemical compositions (phase
analyses), and find in what proportions (amounts) the
phases occur.
 predict whether age hardening is possible for a given
alloy.

LET’S LOOK AT SOME METALLOGRAPHS

An alloy of Cu in Aluminum
Al, surrounded by a
mixture of Al and CuAl2.
Al and CuAl2 mixture.
ANOTHER – A CLOSEUP OF A STEEL.
The darker area is Fe
with small amount of
interstitial carbon.
The lighter standout
areas are the
compound cementite,
Fe3C. (Iron carbide.)
WHAT HAVE WE SEEN?
Multiphase materials, or alloys. Phases are
separate, they are clearly different materials.
But they are mixed together, at times very finely.
 We do not always have multiphase alloys. There
are many useful single phase alloys. BUT
 The presence of the second phase is very
important to…

BLOCK DISLOCATIONS! INCREASE STRENGTH.
CONCEPT OF THE PHASE
Phase: “A distinct state of matter in a system;
matter that is identical in chemical composition
and physical state and separated.” (Google)
 Examples
1. Ice in water
2. Sugar and water
3. Cu-Ni system, as a follow on to above.

CONCEPT OF EQUILIBRIUM
What phases do we get as we cool off a molten
metal?
 This depends very much on the rate of cooling. If
we can cool slowly enough, we get phases that are
close to what thermodynamicists would call
“equilibrium.”
 This is the basic phase balance that we get if we
have enough time and temperature for diffusion
to do its work.
 Diffusion of key species is essential to being able
to get equilibrium.

PHASE DIAGRAM – A MAP OF THE PHASE OR
PHASES PRESENT AS WE CHANGE TEMP AND
COMPOSITION
Axes:
X-Composition.
Y-Temperature
Web:http
://www.do
itpoms.ac
.uk/micli
b/pds.swf
?targetFr
ame=CuNi
The symbol a
stands for a
solid consisting
of Ni dissolved
in Cu or viscaversa.
ANSWERING THE BASIC QUESTIONS- AT B
1.
2.
3.
What Phase or Phases are present?
What is the composition of each phase?
What is the relative amount of each phase
1. Liquid and a
2. CL = 32% Ni and
Ca = 43% Ni
3. Use the
Lever Rule!
THE LEVER RULE – FINDING RELATIVE
AMOUNTS
Ca  Co
WL 
100% 
Ca  C L
43  35
100%  73%
43  32
Wa  100%  WL  27%
Once we know how to answer the three major questions,
let’s move on to a more complicated binary system.
THE LEAD TIN SYSTEM
Let’s work on this one together, using the handout.