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GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering PDF Download

Q1: The phases present in pearlite are  [GATE ME 2024]
(a) austenite and ferrite
(b) cementite and austenite
(c) ferrite and cementite
(d) martensite and ferrite
Ans:
(c)
Coarse pearlite →α Ferrite +Fe3C→ Alternating layers of a ferrite and Fe3C that are relatively thick.
Fine pearlite →α Ferrite +Fe3C→ Alternating layers of a ferrite and Fe3C that are relatively thin.

Q1: A steel sample with 1.5 wt. % carbon (no other alloying elements present) is slowly cooled from 1100ºC to just below the eutectoid temperature (723ºC). A part of the iron-cementite phase diagram is shown in the figure. The ratio of the pro-eutectoid cementite content to the total cementite content in the microstructure that develops just below the eutectoid temperature is ________.
(Rounded off to two decimal places)  [GATE ME 2023]
Ans: 
0.53 to 0.55
GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical EngineeringMass friction of proeutectoid cementite GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering

Mass fraction of total cementite

GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering
So, GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering

Q2: The atomic radius of a hypothetical face-centered cubic (FCC) metal is (√2/10) nm. The atomic weight of the metal is 24.092 g/mol. Taking Avogadros number to be 6.023 × 1023 atoms/mol, the density of the metal is _______  kg/m3. (Answer in integer) [GATE ME 2023]
Ans: 2490 to 2510
Data given:
r = √2/10 nm
M = 24.092 kg/mol
A = 6.023 x 1013
For FCC structure GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering
So, volume of unit cell GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering
Ne = 4 for FCC
GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering
= 2500 kg/m3

Q1: Fluidity of a molten alloy during sand casting depends on its solidification range. The phase diagram of a hypothetical binary alloy of components A and B is shown in the figure with its eutectic composition and temperature. All the lines in this phase diagram, including the solidus and liquidus lines, are straight lines. If this binary alloy with 15 weight % of B is poured into a mould at a pouring temperature of 800ºC, then the solidification range is  [GATE ME 2022 SET-2]

GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering

(a) 400ºC
(b) 250ºC
(c) 800ºC
(d) 150ºC
Ans:
(d)
GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical EngineeringSolidification range = A′B 
△ABC and △MB′C is similar
GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering
GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering
700 - TA = (1/2) x 300
TA = 550ºC
Solidification range = TA − TB = 550 − 400 = 150ºC 

Q2: In Fe − Fe3C phase diagram, the eutectoid composition is 0.8 weight % of carbon at 725°C. The maximum solubility of carbon in α-ferrite phase is 0.025 weight % of carbon. A steel sample, having no other alloying element except 0.5 weight % of carbon, is slowly cooled from 1000°C to room temperature. The fraction of pro-eutectoid α-ferrite in the above steel sample at room temperature is [GATE ME 2022 SET-1]
(a) 0.387
(b) 0.864
(c) 0.475
(d) 0.775
Ans
: (a)
GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical EngineeringFraction of pro eutectoid α− Ferrite
GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering

Q3: Which of the following methods can improve the fatigue strength of a circular mild steel (MS) shaft?  [GATE ME 2022 SET-1]
(a) Enhancing surface finish
(b) Shot peening of the shaft
(c) Increasing relative humidity
(d) Reducing relative humidity
Ans: (a, b, d)
Surface Treatments:
During machining operations,small scratches and grooves are invariably introduced into the workpiece surface by cutting tool action. These surface markings can limit the fatigue life. It has been observed that improving the surface finish by polishing will enhance fatigue life significantly.
One of the most effective methods of increasing fatigue performance is by imposing residual compressive stresses within a thin outer surface layer. Thus, a surface tensile stress of external origin will be partially nullified and reduced in magnitude by the residual compressive stress. The net effect is that the likelihood of crack formation and therefore of fatigue failure is reduced.
Residual compressive stresses are commonly introduced into ductile metals mechanically by localized plastic deformation within the outer surface region. Commercially, this is often accomplished by a process termed shot peening. Small, hard particles (shot) having diameters within the range of 0.1 to 1.0 mm are projected at high velocities onto the surface to be treated. The resulting deformation induces compressive stresses to a depth of between one-quarter and one-half of the shot diameter.

Q4: Which of the following heat treatment processes is/ are used for surface hardening of steels?  [GATE ME 2022 SET-1]
(a) Carburizing
(b) Cyaniding
(c) Annealing
(d) Carbonitriding
Ans: (a, b, d)
Case-hardening, also referred to as surfacehardening, commonly involves one of four different methods: carburizing, nitriding, cyaniding, or carbonitriding. Case- hardening is used on parts such as gear teeth, cutting wheels, and tools. These case-hardened pieces represent a compromise between the hard, wear-resistant brittleness of high-carbon steel and the softer, more ductile, less wear-resistant low-carbon steels.

Q1: The Cast Iron which possesses all the carbon in the combined form as cementite is known as  [GATE ME 2021 SET-2]
(a) Grey Cast Iron
(b) Spheroidal Cast Iron
(c) Malleable Cast Iron
(d) White Cast Iron
Ans: (d) 
On the basis of nature of carbon present in cast iron, it may be divided into white cast iron and gray cast iron.
In the gray cast iron, carbon is present in free form as graphite. Under very slow rate of cooling during solidification, carbon atoms get sufficient time to separate out in pure form as graphite. In addition, certain elements promote decomposition of cementite. Silicon and nickel are two commonly used graphitizing elements.
In white cast iron, carbon is present in the form of combined form as cementite. In normal conditions, carbon has a tendency to combine with iron to form cementite.

Q1: Which one of the following statements about a phase diagram is INCORRECT?  [GATE ME 2020 SET-2]
(a) It indicates the temperature at which different phases start to melt
(b) Relative amount of different phases can be found under given equilibrium conditions
(c) It gives information on transformation rates
(d) Solid solubility limits are depicted by it
Ans: (c)
Phase diagram - Useful information:
Important information, useful in materials development and selection, obtainable from a phase diagram:
It shows phases present at different compositions and temperatures under slow cooling (equilibrium) conditions.
It indicates equilibrium solid solubility of one element/compound in another.
It suggests temperature at which an alloy starts to solidify and the range of solidifcation.
It signals the temperature at which different phases start to melt.
Amount of each phase in a two-phase mixture can be obtained.

Q2: Match The Following  [GATE ME 2020 SET-1]
GATE Past Year Questions: Structure & Properties of Engineering Materials | Engineering Materials - Mechanical Engineering(a) P-2, Q-3, R-4, S-1
(b) P-1, Q-1, R-3, S-2
(c) P-3, Q-3, R-1, S-3
(d) P-4, Q-3, R-2, S-1
Ans:
(a)
Tempering is a process of heat treating, which is used to increase the toughness of iron-based alloys.
Quench hardening is a mechanical process in which steel and cast iron alloys are strengthened and hardened.
Annealing is a process involving heating and cooling, usually applied to produce softening of the metal to facilitate machining or forming operations.
Normalising is used to improve the mechanical properties of, mainly, unalloyed and low-alloy structural steel and cast steel.

Q2: The crystal structure of γ iron (austenite phase) is  [GATE ME 2020 SET-1]
(a) BCC
(b) FCC
(c) HCP
(d) BCT
Ans: 
(b)
Austenite has a cubic-close packed crystal structure, also referred to as a face-centred cubic structure with an atom at each corner and in the centre of each face of the unit cell.

Question for GATE Past Year Questions: Structure & Properties of Engineering Materials
Try yourself:The number of atoms per unit cell and the number of slip systems, respectively, for a facecentered cubic (FCC) crystal are

[ME 2018, Set-1]

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Question for GATE Past Year Questions: Structure & Properties of Engineering Materials
Try yourself:The crystal structure of aluminium is

[ME 2017, Set-2]

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Question for GATE Past Year Questions: Structure & Properties of Engineering Materials
Try yourself:The material property which depends only on the basic crystal structure is

[ME 2010]

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Question for GATE Past Year Questions: Structure & Properties of Engineering Materials
Try yourself:Which of the following is the correct data structure for solid models?

[ME 2009]

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Question for GATE Past Year Questions: Structure & Properties of Engineering Materials
Try yourself:The effective number of lattice points in the  unit cell of simple cubic, body centered cubic, and face centered cubic space lattices, respectively, are

[ME 2009]

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Question for GATE Past Year Questions: Structure & Properties of Engineering Materials
Try yourself:The most widely used reinforcement in modern day FRP tennis racket is

[PI 1992]

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FAQs on GATE Past Year Questions: Structure & Properties of Engineering Materials - Engineering Materials - Mechanical Engineering

1. What are the key properties of engineering materials that are important for mechanical engineering?
Ans. The key properties of engineering materials include mechanical properties (such as strength, ductility, toughness, and hardness), thermal properties (like thermal conductivity and thermal expansion), electrical properties (conductivity and resistivity), and corrosion resistance. Understanding these properties helps in selecting appropriate materials for specific applications in mechanical engineering.
2. How does the microstructure of materials affect their properties?
Ans. The microstructure of materials, which includes the arrangement of grains, phases, and defects, significantly influences their properties. For example, finer grain sizes typically enhance strength through the Hall-Petch relationship, while the presence of certain phases can improve toughness or corrosion resistance. Thus, controlling the microstructure through processes like heat treatment is crucial in material design.
3. What is the significance of phase diagrams in material selection?
Ans. Phase diagrams are essential tools in material selection as they illustrate the stability of different phases at various temperatures and compositions. They help engineers predict phase transformations, solubility limits, and the conditions under which certain materials will perform best, aiding in the development of alloys and composites tailored for specific engineering applications.
4. How can mechanical properties of materials be tested in the laboratory?
Ans. Mechanical properties can be tested using various standardized methods such as tensile testing (to measure strength and ductility), hardness testing (using Rockwell, Brinell, or Vickers scales), impact testing (to assess toughness), and fatigue testing (to evaluate durability under cyclic loading). These tests provide quantitative data necessary for material characterization and selection.
5. What role does temperature play in the properties of engineering materials?
Ans. Temperature significantly affects the properties of engineering materials. For instance, as temperature increases, many materials exhibit decreased strength and increased ductility, while others may become brittle. Additionally, thermal expansion can lead to dimensional changes, which must be considered in design. Understanding these temperature effects is important for ensuring material performance in various operating conditions.
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