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Materials Engineering – Day 9 Phases and Phase Diagram

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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  1. 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

  2. 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.

  3. 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.

  4. 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.)

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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!

  10. 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.

  11. The Lead Tin System Let’s work on this one together, using the handout.

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