in this video i have discussed about Material science related questions for Mechanical Engineering Competitive Exams 2021

2. Crystal structure
In crystalline Material atoms are
arranged in repetitive or periodic
array over large atomic distances.
Bravais Lattice is 14 different
atomic arrangement.
( cubic, Tetragonal,
Orthorhombic, Rhombohedral,
Hexagonal, Monoclinic, Triclinic)
Packing Factor =
Volume occupied by the atoms in
the cell/ volume of unit cell

3. Crystal Imperfection
1. Point Defect ( Vacancy, Interstitial, Schottky, Frenkel)
2. Line Defect ( Edge, Screw)
3. Interfacial Defect ( surface) ( Grain, Twin Boundaries, Stacking Faults)
4. Volume Imperfection

4. Phase Diagram
a) Eutectic Reaction
( Liquid = Solid1 + solid2)
b) Eutectoid Reaction
( solid= solid1+ Solid 2)
c) Peritectic Reaction
( Liquid + Solid1 = Solid
2)
d) Peritectoid Reaction
(solid 1 + solid 2 = solid3 )

5. Types of cast iron
Grey cast iron has damper vibration or self lubricating property.
Pure form of iron is wrought iron. It is never cast.
Blast Furnace ( Pig iron ), Cupola Furnace ( Cast Iron ),
Puddling Furnace ( Wrought Iron ), Bessemer Converter ( Steel)

6. Types of steel
1. Plain Carbon Steel ( Malleable)
2. Dead Mild Steel ( C- 0.05 to
0.15 % )
( steel wire, sheets , rivets, Screws)
3. Medium Carbon Steel (0.3 to 0.7
%)
( Railway coach axles, cushion rings
, gear shaft, Valve spring)
4. High Carbon Steel ( 0.7- 1.5%)
( clutch discs, leaf spring, machines
chisels, music wires)

7. Heat treatment process
Process Metal Hardened Element
added
Characteristic Applications
Carburizing Low Carbon
Steel
Carbon Some
distortion are
present
Hardness 55-
65 HRC
Gears, Cars,
Shaft Bearing,
Piston, Pins,
Clutch
Nitriding Alloys : Steel,
HSS, Stainless
steel
Nitrogen 65 HRC, Gears, Shafts,
Cutters, Boring
Cyaniding Low Carbon
Steel
Carbon &
Nitrogen
65 HRC Bolts, Nuts,
Screws, Small
gears
Flame
Hardening
Medium Carbon
Steel
none 50-60 HRC Lathe Beds,
Gears, Axels
Induction
Hardening
Medium carbon
steel
None 50-60 HRC Lathe Beds,
Piston Roads

8. Ceramics
• It is composition of
metals and nonmetals
oxides, Nitrides,
carbides.
• It is known as Rock or
Clay Mineral
Materials.
• MgO, SO2, BaTio3,
Glasses.

9. Question Session
1. Body Centered cubic (BCC) space lattice is Found in
a) Zinc, Magnesium, Cobalt, Cadmium, Antimony, Bismuth
b) Gamma Iron, Aluminum, Copper, Lead, Silver, Nickel
c) Alpha Iron, Tungsten, Chromium, Molybdenum
d) None of the above ( c )
2. Which of the following defect arises due to dislocation in material?
a) Volumetric defect
b) Line defect
c) Plane defect
d) Point defect ( b )

10. 3. a reversible change in the atomic structure of steel with corresponding
change in the properties is known as
a) Molecular change
b) Physical change
c) Allotropic change
d) Solidus change ( c )
4. The most effective inhibitor of grain growth, when added in small quantities
is
a) Carbon b) Vanadium c) Manganese d) Cobalt ( b )
5. a B.C.C material has 0.6 nm Radius for each atom, then the side of unit cell
is
a) 1.2nm b) 0.689 nm c) 0,98nm d) 1.385nm ( d )

11. 6. Blast furnace produces which of the following materials?
a) Pig Iron b) Wrought Iron c) cast Iron d) Malleable Iron ( a )
7. Which one of the following is an acid factory
a) MgO b) CaO c) silica d) None of the above ( c )
8. The hardness of lathe bed material should be measured by
a) Rockwell Tester b) Brinell Hardness tester
c) Shore Scleroscope d) Vickers hardness Tester ( c )
9. What are the materials which show direction dependent properties, called?
a) Homogeneous Material
b) Viscoelastic Material
c) Isotropic Materials
d) Anisotropic Material ( d )

12. 10. Elastic Limit of Cast Iron as compared to its ultimate breaking strength is
a) Half b) Double c) approximately same d) none ( c )
11. Austempering is employed to obtained
a) 100% martensitic structure
b) 100% Bainitic Structure
c) 50 %Martensite and 50% Bainitic structure
d) 100% pearlite structure (b )
12. The eutectoid of carbon in iron, above lower critical temperature, when cooled ,
results in
a) Ferrite and austenite
b) Ferrite and Cementite
c) Cementite and austenite
d) Ferrite, Cementite and austenite ( b )

13. 13. A constitutional diagram shows relationship among which of the
following combination in a particular alloy system
a) Temperature and composition
b) Temperature and phase present
c) Temperature, composition and Phases Present
d) Temperature and pressure ( c )
14. Which of the following phase of steel is not present in Iron- Carbon phase
diagram?
a) Ferrite
b) Cementite
c) Austenite
d) Martensite ( d )

15. 15. At room temperature, alpha iron contains negligible amount of carbon,
cementite contains 6.67% c and pearlite contains 0.8% C. Pearlite contains
how much cementite?
a) 8% b) 12% c) 10% d) 14% ( b )
Amount of cementite * 6.67 = 0.8
Cementite = 12%
16. Which one of the following elements is a ferritic stabilizer?
a) Nickel b) Manganese c) Copper d) Chromium ( d )
17. Which one of the following materials can be subjects to an age hardening
process?
a) HSS b) Aluminum c) Pure Iron d) Stellite ( b )
The metals and alloys need to be maintained at high temperatures for many
hours for the precipitation to occur; hence this process is called age hardening.

16. 18. Iron-Carbon equilibrium diagram
a) Correlates the microstructure and properties of steel and cast iron
b) Indicates the phase changes occurring during heating and cooling
c) Is made by plotting carbon percentage along x-axis and temperature along
y-axis
d) All of the above ( d )
19. Which one of the following is correct?
When “devitrification” of inorganic glasses done
a) Glass transform from crystalline to non-crystalline
b) Glass transform into a fully transparent material
c) Glass transforms from mono-crystalline state to poly-crystalline state
d) Glass is relieved of internal stresses ( c )
20. Which one of the following materials is not a composite?
a) Wood b) Concrete c) Plywood d) Sialon ( d )