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A range of crystal defects is shown in the lattice below - Leaving Cert Engineering - Question 4 - 2018
Question 4
A range of crystal defects is shown in the lattice below.  (i) Name and describe three crystal point defects in the lattice. (i... show full transcript
Worked Solution & Example Answer:A range of crystal defects is shown in the lattice below - Leaving Cert Engineering - Question 4 - 2018
Step 1
Name and describe three crystal point defects in the lattice.
Answer
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Substitutional Defect: Atoms from another material replace atoms of the base metal. This can lead to changes in the properties due to different atomic sizes and bonding characteristics.
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Interstitial Defect: An additional atom embeds itself within the metal structure, causing distortion. This results in local strain and can alter the mechanical properties.
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Vacancy Defect: This occurs when an atom is missing from the lattice, which reduces the density of the material and can weaken the metal's overall structure.
Step 2
Outline, with the aid of a diagram, the impact of a line defect.
Answer
Line defects, such as dislocations, represent rows of atoms that are spaced irregularly within a crystal lattice. As a result, these defects can either strengthen or weaken the material, depending on the context.
- Diagram:
- As dislocations move through the lattice, they can cause planes of atoms to shift. This movement can enhance ductility by allowing deformation to occur more easily, or it can lead to work hardening, where the material becomes stronger due to dislocation intersections.
Step 3
Step 4
Label the liquidus line, the solidus line and the eutectic point.
Answer
- Liquidus Line: The line separating the liquid phase from the solid + liquid phase.
- Solidus Line: The line below which the material is entirely solid.
- Eutectic Point: The specific composition and temperature at which the alloy can solidify into two distinct solid phases simultaneous.
Step 5
For the alloy with 60% Zinc, determine from the diagram the ratio of the phases at 300 °C.
Answer
At 300 °C for an alloy containing 60% Zinc, we can read off the diagram to determine the ratio of phases. Assuming the phases are labeled as A and B:
- Let A = solid phase percentage.
- Let B = liquid phase percentage.
- The ratio A:B = 34:66 based on the read from the diagram.
Step 6
Explain the difference between partial solubility alloy and solid solution alloy.
Answer
A Partial Solubility Alloy allows for only a certain percentage of one metal to dissolve into another, leading to distinct phases. In contrast, a Solid Solution Alloy occurs when two metals can fully dissolve in each other in both liquid and solid states, appearing homogeneous under a microscope.
Step 7
Explain the difference between work hardening and age hardening.
Answer
Work Hardening is the process of strengthening a material through plastic deformation, such as hammering or drilling. Meanwhile, Age Hardening refers to the process of enhancing strength by aging a material at elevated temperatures, promoting the growth of fine precipitates that impede dislocation movement.
Step 8
Explain the difference between ductility in BCC structures and ductility in FCC structures.
Answer
Ductility in BCC (Body-Centered Cubic) structures is generally lower because the movement of dislocations in these structures is less favorable due to fewer slip planes. In contrast, FCC (Face-Centered Cubic) structures possess more slip planes, allowing for greater atomic mobility and thus higher ductility.