JNTU
JNTU B.Tech II METALLURGY AND MATERIALS SCIENCE Previous Question Paper (March - 2022 - R15)
Answer any five questions. All questions carry equal marks.
Main
Find the Miller indices of a plane that makes an intercept of '1' on the X-axis, '2' on the Y-axis and is parallel to the Z-axis.
Answer
To determine the Miller indices (hkl) of a plane, follow these steps:
- Identify the intercepts on the crystallographic axes: 1, 2, and infinity (since the plane is parallel to the Z-axis).
- Take the reciprocals of these intercepts: 1/1, 1/2, 1/∞, which results in 1, 0.5, and 0.
- Reduce these to the smallest set of whole numbers by multiplying by the least common multiple (2): 2, 1, 0.
The Miller indices of the plane are (210).
Explain the effect of grain size on mechanical properties of materials.
Answer
Grain size significantly influences the mechanical properties of polycrystalline materials, primarily described by the Hall-Petch relationship. The relationship states that the yield strength of a material increases as the grain size decreases.
Key effects include:
- Strength and Hardness: Finer grains provide a greater total grain boundary area. Grain boundaries act as barriers to dislocation motion; therefore, smaller grains require higher stress to initiate plastic deformation, increasing yield strength and hardness.
- Ductility and Toughness: Unlike strength, reducing grain size often simultaneously improves ductility and impact toughness. This is because finer grains allow for more uniform strain distribution and inhibit crack propagation along cleavage planes.
- Creep Resistance: At high temperatures, the effect is reversed. Larger grains are preferred for creep resistance because grain boundary sliding, which facilitates deformation at elevated temperatures, is minimized when there are fewer grain boundaries.
In this formula, σ_y is the yield stress, d is the average grain diameter, and σ_0 and k_y are material-specific constants.
Determine the Miller indices of a plane that make an intercept of 2 Å and 4 Å on the coordinate axes of an orthorhombic crystal with a:b:c = 4:3:2.
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Classify solid solutions? Explain with necessary sketches.
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What are different methods of construction of phase diagrams? Explain the construction of isomorphous phase diagram by using cooling curves.
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What is eutectoid transformation? Draw a neat sketch of Eutectoid phase diagram. Explain its features.
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The phase diagram of a binary system of A and B has a three phase equilibrium at 250°C, with the composition of α, liquid and β phases equal to 10%, 55% and 95% B. Just below 250°C, find the compositions at which the proeutectic phase is 1 ½ times the eutectic mixture.
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Derive Lever rule and explain its importance.
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What is hardening? Why hardening is done? What are different quenchents used in hardening? Explain the effect of cooling rate on hardening of steels.
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Differentiate between Annealing and Normalizing.
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What is allotropy? What are different allotropic forms of iron? Show the allotropic temperatures on Fe-Fe3C system?
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How are tool steels different from plain carbon steels? Explain.
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Differentiate between steels and cast irons.
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What are the important properties of aluminium? Give the important applications of aluminium and its alloys.
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Drive an equation to determine the modulus of a fibre reinforced composite when the fibres are aligned in transverse direction.
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Give the properties and applications of polymers.
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