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Identify and describe the crystal point imperfections shown at both A and B - Leaving Cert Engineering - Question 4 - 2015
Question 4
Identify and describe the crystal point imperfections shown at both A and B. The given table shows the solidification temperatures for various alloys of metal A and... show full transcript
Worked Solution & Example Answer:Identify and describe the crystal point imperfections shown at both A and B - Leaving Cert Engineering - Question 4 - 2015
Step 1
Identify and describe the crystal point imperfections shown at both A and B
Answer
The crystal point imperfections shown in diagrams A and B can be identified as follows:
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Diagram A illustrates Substitutional Imperfection: This occurs when an atom of a different element replaces an atom in the crystal lattice. For example, in a copper-nickel alloy, a nickel atom substitutes a copper atom, which can affect properties such as strength and ductility.
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Diagram B represents Interstitial Imperfection: This happens when an atom from another element occupies the spaces between the atoms of the parent metal's lattice. This can lead to compression of surrounding atoms and can strengthen the material, enhancing its resilience to deformation.
Step 2
Draw the equilibrium diagram according to the given data
Answer
The equilibrium diagram can be plotted using the solidification temperatures for the alloys of metals A and B. The x-axis will represent the percentage of metal B in the alloy, ranging from 0% to 100%. The y-axis will depict the temperature in °C, ranging from 1080°C to 1600°C. The liquidus line indicates the temperature above which the alloy is completely liquid, while the solidus line shows the temperature where it is completely solid. The area between these lines represents the pasty region during the solidification process.
Step 3
Label the diagram and describe the main features
Answer
The key features of the equilibrium diagram should include:
- Liquid Region: Above the liquidus line where all components are liquid.
- Solid Region: Below the solidus line where all components are solid.
- Pasty Region: Between the liquidus and solidus lines where both liquid and solid phases coexist.
- A-B lines: Indicate the temperatures for solidification start and completion for varying percentages of metal B in the alloy.
It is crucial to label each region accurately to visualize the solidification behavior of the alloy.
Step 4
Determine from the diagram, the ratio of the phases at 1250 °C for the alloy with 50% B
Answer
At 1250 °C for the alloy with 50% metal B, refer to the diagram to find the intersection of the horizontal line at 1250 °C with the solidus and liquidus lines. From the intersection, estimate the percentage of solid and liquid present. For example:
- Mass of Solid: 24% (from observation)
- Mass of Liquid: 16% (from observation)
Thus, the ratio of solid to liquid at this temperature can be calculated as:
Step 5
Step 6
Explain why structure X is most associated with brittleness in metals
Answer
Structure X, or Body-Centered Cubic (BCC), is associated with brittleness due to its atomic arrangement. The atoms in a BCC structure are not closely packed, leading to fewer slip systems for dislocation movement. This limits the deformation ability of the material, making it more prone to fracture under stress compared to more ductile structures like FCC.
Step 7