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Explain any two of the following: (i) Dislocation defect; (ii) Age hardening; (iii) Intermetallic compound; (iv) Eutectoid point - Leaving Cert Engineering - Question 4 - 2010
Question 4
Explain any two of the following: (i) Dislocation defect; (ii) Age hardening; (iii) Intermetallic compound; (iv) Eutectoid point. The lead-tin equilibrium diagram ... show full transcript
Worked Solution & Example Answer:Explain any two of the following: (i) Dislocation defect; (ii) Age hardening; (iii) Intermetallic compound; (iv) Eutectoid point - Leaving Cert Engineering - Question 4 - 2010
Step 1
Explain any two of the following: Dislocation defect;
Answer
A dislocation defect arises from an incomplete layer of atoms in a crystal structure. This defect can weaken the structure, as dislocations allow for the movement of atoms under stress, leading to deformation at lower stress levels. Dislocations play a significant role in the mechanical properties of materials, and their presence can result in early failure of the material.
Step 2
Explain any two of the following: Age hardening;
Answer
Age hardening is a heat treatment process used to strengthen certain alloys, particularly aluminum alloys. During this process, the alloy is heated to high temperatures and then rapidly cooled, creating a supersaturated solid solution. Over time, the material is then held at room temperature, allowing precipitates to form within the matrix. This precipitation hardening can significantly improve the mechanical properties of the alloy, such as its yield strength.
Step 3
Step 4
Describe the main features of the diagram.
Answer
The lead-tin equilibrium diagram illustrates several key aspects of the phase behavior in the lead-tin alloy system:
- Solidus Line: The boundary where the solid phase is fully formed.
- Liquidus Line: The boundary that indicates the melting point; above this line, the alloy is entirely liquid.
- Pasty Region: The area between the solidus and liquidus lines, where both solid and liquid phases coexist.
- Eutectic Point: The specific composition of 38% tin and 62% lead at which the alloy changes from liquid to solid at a temperature of 183°C.
Step 5
Step 6
Describe any two of the following: Solid solution alloy;
Answer
A solid solution alloy is formed when two or more metals are completely soluble in each other both in the liquid and solid state. Examples include metals like copper-nickel, where the solid solution appears as a single phase under a microscope, exhibiting homogeneity.
Step 7
Describe any two of the following: Eutectic alloy;
Answer
A eutectic alloy consists of a mixture of two or more components that solidify at a specific composition and temperature. In the solidified state, these components exhibit a distinct microstructure. The cadmium and bismuth combination serves as a prominent example of a eutectic alloy.
Step 8
Describe any two of the following: Partial solubility alloy;
Answer
In a partial solubility alloy, two metals are only partially soluble in each other in the solid state. The lead-tin alloy exemplifies this behavior, as it demonstrates limited solubility, with specific compositions yielding two distinct phases.