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Describe, with the aid of diagrams, the various stages of dendritic growth during the process of metal solidification - Leaving Cert Engineering - Question 4 - 2016
Question 4
Describe, with the aid of diagrams, the various stages of dendritic growth during the process of metal solidification. The table shows the solidification temperatu... show full transcript
Worked Solution & Example Answer:Describe, with the aid of diagrams, the various stages of dendritic growth during the process of metal solidification - Leaving Cert Engineering - Question 4 - 2016
Step 1
Describe, with the aid of diagrams, the various stages of dendritic growth during the process of metal solidification.
Answer
Dendritic growth during metal solidification is a process characterized by the formation of intricate crystal structures. Below are the stages depicted in diagrams:
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Nucleation: As the metal begins to cool, small particles form nuclei at random locations. This initial stage is crucial for crystal growth.
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Growth: After nucleation, these tiny crystals start growing. The first visible crystals form as particles aggregate together, leading to a branched structure known as dendrites.
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Interconnection: As more atoms solidify, the dendritic structures continue to grow and interconnect, filling the space and forming a solid mass.
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Completion of Solidification: Ultimately, upon reaching a specific temperature, the metal solidifies completely, resulting in a solidified microstructure with characteristic dendritic features.
Step 2
Using the graph paper supplied: (i) Draw the equilibrium diagram according to the given data.
Answer
The equilibrium diagram should display the relationship between temperature and the percentage of metal B in the alloy. Ensure you accurately plot the start and end solidification temperatures to identify the liquidus and solidus lines.
- Liquidus Line: The line above which the metal is entirely liquid.
- Solidus Line: The line below which the metal is completely solid.
Mark the eutectic point where the phase change occurs and label the axes accordingly. This diagram effectively illustrates how the composition of the alloy affects its solidification temperature.
Step 3
Using the graph paper supplied: (ii) Label the diagram and describe its main features.
Answer
The key features of the diagram include:
- Liquid Zone: Above the liquidus line, the alloy is completely liquid.
- Solid Zone: Below the solidus line, the alloy is completely solid.
- Pasty Zone: The area between the solidus and liquidus lines where both liquid and solid phases coexist.
- Eutectic Point: A special point where the alloy transitions directly from liquid to solid without passing through the pasty stage. This understanding is crucial for controlling the mechanical properties of alloys during manufacturing.
Step 4
Using the graph paper supplied: (iii) For the alloy with 30% metal B, determine from the diagram the ratio of the phases at 250 °C.
Answer
At 250 °C for the alloy containing 30% metal B, based on the equilibrium diagram:
- Mass of Solid: The mass of the solid phase in the alloy can be found using the sections of the solidus line.
- Mass of Liquid: Correspondingly, calculate the mass of the liquid phase from the liquidus line. Typically, the ratio can be derived from:
With provided data, this can be determined to yield a ratio of 30:23.
Step 5
Identify point X and point Y labelled on the diagram.
Answer
Point X corresponds to the Start of Solidification and marks the temperature at which the first solid phase begins to form in the cooling curve.
Point Y denotes the End of Solidification, which indicates the point at which the entire metal has transitioned into a solid state.
Step 6
Identify two possible defects which may occur during the solidification process.
Answer
Defects during the solidification process can include:
- Vacancy Defect: Missing atoms in the crystal lattice that can affect the material's properties.
- Dislocation Defect: Irregularities within the crystal structure that can lead to weakness in the alloy. These defects should be minimised for optimal mechanical performance.