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Explain in detail any two of the following: (i) Age hardening; (ii) The differences between eutectic alloy and partial solubility alloy; (iii) Three crystal point defects; (iv) Intermetallic compound - Leaving Cert Engineering - Question 4 - 2013
Question 4
Explain in detail any two of the following: (i) Age hardening; (ii) The differences between eutectic alloy and partial solubility alloy; (iii) Three crystal point de... show full transcript
Worked Solution & Example Answer:Explain in detail any two of the following: (i) Age hardening; (ii) The differences between eutectic alloy and partial solubility alloy; (iii) Three crystal point defects; (iv) Intermetallic compound - Leaving Cert Engineering - Question 4 - 2013
Step 1
Explain in detail any two of the following: Age hardening
Answer
Age hardening, also known as precipitation hardening, is a heat treatment technique used to increase the yield strength of malleable materials, especially alloys. It involves heating the alloy to a high temperature to dissolve soluble elements, followed by rapid cooling to room temperature. This process results in the formation of fine precipitates within the alloy matrix, which impede dislocation motion, thus increasing hardness and strength. An example is the hardness increase in aluminum alloys when copper is added and aged at high temperature.
Step 2
Explain in detail any two of the following: The differences between eutectic alloy and partial solubility alloy
Answer
Eutectic alloys consist of two or more metals that are completely soluble in the liquid state but show limited solubility in the solid state. For instance, a cadmium-bismuth alloy is a classic example of a eutectic system. In contrast, partial solubility alloys allow for some solubility in both the liquid and solid phases. An example is the lead-tin alloy system where both components have limited solubility in the solid state, creating a range of compositions with varying melting points.
Step 3
Using the graph paper supplied, draw the thermal equilibrium diagram according to the given data.
Answer
To draw the thermal equilibrium diagram, plot the % of metal B in alloy on the x-axis (from 0% to 100%) and the temperature in °C on the y-axis (ranging from about 0°C to 630°C). Mark the start and end of solidification temperatures for each composition as provided in the table and connect these points with smooth curves to illustrate the liquid, solid, and pasty regions as indicated.
Step 4
Label and describe the main features of the diagram.
Answer
Label the diagram to indicate key areas such as the liquid phase, solid phase, and the pasty zone. The liquidus line represents the transition from liquid to solid, while the solidus line marks where the alloy is entirely solid. Indicate the regions where various phases exist and highlight the compositions that correspond to the start and end points of solidification for different alloy percentages.
Step 5
Determine the composition of the phases present at 450 °C for the alloy containing 60% of metal B.
Answer
At 450 °C, 60% of metal B corresponds to a composition where the alloy is in a solid and liquid state. By reviewing the thermal equilibrium diagram, it can be determined that the composition possesses approximately 20% of metal A in the solid phase and 70% of metal A in the liquid phase.
Step 6
Outline the stages of metal solidification from the liquid phase.
Answer
The stages of metal solidification from the liquid phase begin with nucleation, where small crystals form as the temperature drops. These nuclei grow and coalesce into dendrites, creating a tree-like structure. As cooling continues, these dendrites interconnect, forming a solid microstructure. Eventually, as the last of the liquid solidifies, a grain structure is established with distinct grain boundaries.
Step 7
Explain the relationship between cooling curves and the formation of alloy equilibrium diagrams.
Answer
Cooling curves illustrate the temperature changes a substance experiences over time during cooling. For an alloy like the 20% Ni example, the cooling curve shows the onset of solidification as the temperature stabilizes. These curves can be utilized to construct alloy equilibrium diagrams by plotting the temperature against composition, capturing the relationships between different phases as temperature decreases and solidification occurs.