Nucleation, Solidification and Phase Transformations - Thermodynamics, Kinetics and Phase Transformations - Engineering Sciences Previous Year Questions

1

2007 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2007

Melting point of a metal is 1000 K and its enthalpy of melting is 2.0x10⁹ J.m^-3. If the solid-liquid interface energy is 0.5 J.m^-2, the radius of critical nucleus during solidification at 900 K would be

A

10.0 nm

B

5.0 nm

C

5.0 μm

D

2.5 nm

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2

2008 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2008

What is the driving force for grain growth (stored grain boundary energy) just after recrystallization at 450°C in the given specimen?

A

375 mJ

B

750 mJ

C

1.5 J

D

3.0 J

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3

2010 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2010

A plain carbon steel sample is water- quenched from 900°C to room temperature. Its microstructure will consist of

A

Pearlite

B

Bainite

C

Martensite

D

Ferrite and pearlite

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4

2019 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2019

Which one of the following conditions will NOT favour the separation of impurities in zone refining process?

A

Increase in the gap between solidus and liquidus lines

B

Increase in the solubility of impurities in solid as compared to that in liquid phase

C

Agitation of melt

D

Low cooling rate of melt

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5

2020 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2020

During homogeneous solidification of a liquid metal, the radius of critical nucleus (in nanometer, nm) at a temperature \(T_s\) which is below the melting point (\(T_m\)), is _________ nm (round-off to one decimal place). Given that \(\gamma_{sl}\) (solid | liquid interfacial energy) is 0.18 J.m\(^{-2}\) and \(\Delta G_v\) (change in volume free energy upon transformation from liquid to solid) at \(T_s\) is \(0.18 \times 10^9\) J.m\(^{-3}\).

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6

2021 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2021

A metal has a melting point of 600 °C. By rapid cooling, liquid metal can be made to solidify either at 500 °C or 400 °C or 300 °C. Critical size of the solid nuclei is

A

same for solidification at 400 °C and 500 °C

B

smaller for solidification at 400 °C as compared to solidification at 500 °C

C

larger for solidification at 400 °C as compared to solidification at 500 °C

D

the smallest for solidification at 300 °C

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7

2021 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2021

Match the different transformations/reactions in Column I with the most suitable information in Column II.

Column I
(P) Eutectoid reaction
(Q) Martensitic transformation
(R) Precipitation reaction

Column II
(1) involves no diffusion
(2) one solid phase transforms into two solid phases
(3) occurs in supersaturated solutions

A

P-2; Q-3; R-1

B

P-1; Q-2; R-3

C

P-2; Q-1; R-3

D

P-3; Q-2; R-1

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8

2022 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2022

During the ageing of a homogenized Al-Cu alloy (1 to 4 wt.% Cu) below the GP zone solvus, hardness of the alloy:

A

increases monotonically

B

decreases monotonically

C

first increases and then decreases

D

first decreases and then increases

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9

2022 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2022

For a diffusional transformation (i.e., growth of β precipitates in an α matrix), which of the following is/are true with increasing degree of undercooling?

A

Rate of transformation first increases and then decreases

B

Rate of transformation first decreases and then increases

C

Thermodynamic driving force increases monotonically

D

Mobility of atoms in α matrix remains unchanged

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10

2022 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2022

A spherical β particle nucleates from the α matrix on a non-deformable substrate δ, forming a contact angle of θ as shown in the schematic.
The value of \(\frac{\Delta G_{het}^*}{\Delta G_{hom}^*}\) is __________. (Round off to three decimal places)

\(\Delta G_{hom}^*\) = Gibbs free energy change at the critical radius for homogeneous nucleation
\(\Delta G_{het}^*\) = Gibbs free energy change at the critical radius for heterogeneous nucleation
α-β interfacial energy = 0.4 J/m²
α-δ interfacial energy = 0.3 J/m²
β-δ interfacial energy = 0.02 J/m²

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11

2023 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2023

In age-hardening of an aluminium alloy, the purpose of solution treatment followed by quenching is to

A

form martensitic structure

B

increase the size of the precipitates

C

form supersaturated solid solution

D

form precipitates at the grain boundaries

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12

2025 · Engineering Sciences · Thermodynamics, Kinetics and Phase Transformations · Nucleation, Solidification and Phase Transformations

Engineering Sciences (XE) 2025

For Al – 4.5 wt% Cu alloy, the correct sequence of precipitation during age hardening at room temperature is

A

GP zone → θ'' → θ' → θ

B

GP zone → θ' → θ'' → θ

C

GP zone → θ'' → θ → θ'

D

GP zone → θ → θ' → θ''

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