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Lab4-PhaseDiagramsF06-1

# Lab4-PhaseDiagramsF06-1 - Laboratory 4 Phase Diagrams...

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MatE 215 Lab 4: Phase Diagrams (Fall 06) Page 1 of 16 Laboratory 4 Phase Diagrams: Tracking Phase Changes with Cooling Curves Goal: To use phase diagrams to predict stable phases, determine melting and freezing points, and identify suitable operating temperatures for alloys in engineering applications. Learning Objectives: 1. Define alloy , solid solution , and phase . 2. Determine the stable phase(s) of a certain alloy from the proper phase diagram given the alloy composition and temperature of interest. 3. Find the melting or freezing temperature of a given alloy system. 4. Make the connection between cooling curves and phase diagrams identifying the stable phases and the phase changes on the cooling curve. 5. List a eutectic reaction; sketch and label the eutectic microstructure. 6. Give practical examples of instances where engineers might choose to use a eutectic alloy system. 7. Sketch and label the phases and phase transformations that occur in a typical eutectic alloy upon solidification from the liquid.

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MatE 215 Lab 4: Phase Diagrams (Fall 06) Page 2 of 16 Why Study Phase Diagrams? Each type of engineer uses graphical tools to communicate information or to perform some calculations. For example, structural engineers use Mohr’s circle to determine the stress on a component in a certain orientation, electronic engineers use timing patterns to help them analyze the digital output of a circuit board, agricultural engineers use a contour map to assist them in designing an irrigation system. Materials engineers – especially metallurgists and ceramists – use phase diagrams to determine which phases are stable at certain combinations of composition and temperature. One of the more important aspects of phase diagrams is that it will let you know at what temperatures your alloy is solid and what temperatures it becomes either partially or completely liquid. Going Through a Phase Imagine a chocolate chip cookie… like the one shown in the graphic at the right. In general, the cookie consists of the “cookie base” and the chocolate chips. In fact, this is a statement of the two phases present in our chocolate chip cookie. The big reason they are separate phases is that you can immediately and easily tell the difference between the two. This is obvious, but it’s important. Consider the chocolate chips: they have a homogeneous composition, a given structure, and they have a real boundary. These are the three attributes of a phase in materials engineering: composition, structure, and boundary. Now consider the cookie base. This is an example of a phase that is made up of several components: flour, sugar, eggs, butter, baking powder, etc. You cannot see these components in the cookie because they form a solution . The cookie base is single phase and multi- component.
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Lab4-PhaseDiagramsF06-1 - Laboratory 4 Phase Diagrams...

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