Materials engineering day 9 phases and phase diagram
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Materials Engineering – Day 9 Phases and Phase Diagram. Preliminary Discussion Concept of the Phase Phase Diagram – start with Copper Nickel. What phase or phases are present? What is the chemical composition of each phase present? How much (relative amounts) of each phase is present?

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Materials Engineering – Day 9 Phases and Phase Diagram

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Materials engineering day 9 phases and phase diagram

Materials Engineering – Day 9Phases and Phase Diagram

  • Preliminary Discussion

  • Concept of the Phase

  • Phase Diagram – start with Copper Nickel.

  • What phase or phases are present?

  • What is the chemical composition of each phase present?

  • How much (relative amounts) of each phase is present?

  • More practice with the Lead Tin system


You should be able to

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

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

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

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

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

  • Ice in water

  • Sugar and water

  • Cu-Ni system, as a follow on to above.


Concept of equilibrium

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

Phase Diagram – A Map of the Phase or Phases Present as we change Temp and Composition

Axes:

X-Composition.

Y-Temperature

The symbol a stands for a solid consisting of Ni dissolved in Cu or visca-versa.

Web:http://www.doitpoms.ac.uk/miclib/pds.swf?targetFrame=Cu-Ni


Answering the basic questions at b

Answering the basic Questions- AT B

  • 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

The Lever Rule – Finding Relative Amounts

Once we know how to answer the three major questions, let’s move on to a more complicated binary system.


The lead tin system

The Lead Tin System

Let’s work on this one together, using the handout.


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