MATERIAL SCIENCE & ENGINEERING AMIE POST BOX NO.77, 2 ND FLOOR, SULTAN TOWERS, ROORKEE – 247667 UTTARANCHAL PH: (01332) 266328 Email : [email protected]1 TOTAL PAGES: 44 AMIE(I) STUDY CIRCLE(REGD.) A Focused Approach Objective Questions IMPORTANT NOTE • Please read this chapter after going through all the theory chapters provided in this course. • This chapters also includes questions asked in previous years. • All the questions are not classified topic wise. Instead these are randomly selected to match examination conditions. Set 1: Crystal Structure 1. Repeatable entity of a crystal structure is known as a) Crystal b) Lattice c) Unit cell d) Miller indices 2. Coordination number for closest packed crystal structure a) 16 b) 12 c) 8 d) 4 3. Atomic packing factor is a) Distance between two adjacent atoms b) Projected area fraction of atoms on a plane c) Volume fraction of atoms in cell d) None 4. Coordination number in simple cubic crystal structure a) 1 b) 6 c) 3
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MATERIAL SCIENCE & ENGINEERING AMIE
POST BOX NO.77, 2 ND FLOOR, SULTAN TOWERS, ROORKEE – 247667 UTTARANCHAL PH: (01332) 266328 Email : [email protected] 1 TOTAL PAGES: 44
AMIE(I) STUDY CIRCLE(REGD.) A Focused Approach
Objective Questions IMPORTANT NOTE
• Please read this chapter after going through all the theory chapters provided in this course.
• This chapters also includes questions asked in previous years.
• All the questions are not classified topic wise. Instead these are randomly selected to match examination conditions.
Set 1: Crystal Structure 1. Repeatable entity of a crystal structure is known as
a) Crystal
b) Lattice
c) Unit cell
d) Miller indices
2. Coordination number for closest packed crystal structure
a) 16
b) 12
c) 8
d) 4
3. Atomic packing factor is
a) Distance between two adjacent atoms
b) Projected area fraction of atoms on a plane
c) Volume fraction of atoms in cell
d) None
4. Coordination number in simple cubic crystal structure
6. The following phenomena are useful in zone-refining process
a) Coring
b) Segregation
c) Both
d) None
7. For the same diffusion time, the depth of diffusion penetration at 500 and 850 degree Celsius is in the ratio of 1:6. The activation energy for diffusion is
a) 57 kJ/mol
b) 37 kJ/mol
c) 114 kJ/mol
d) 74 kJ/mol
8. If D₀ = 0.00004 m²/sec and Q = 100 kJ/mol, to double the depth of penetration, the initial temperature
4. Which elements are to be used for doping silicon to make it a p-type semiconductor?
5. Define drift mobility of electrons in semi conducting materials.
6. What is meant by zone refining ?
7. State Matthiessen’s rule.
8. State Curie law for paramagnetic materials.
9. What are garnets ?
10. What is meant by a 'spinel’ ?
11. Why is cast iron used as a material for machine tool beds ?
12. When does Hook’s law appear to fall ?
13. Define the term `dislocation’.
14. What are the units of surface energy of a grain boundary ?
15. When is grain boundary shear possible in metals ?
16. Give two examples of heat resisting alloys.
17. If a tensile force of 10 N is applied to a specimen of length 100 mm, width 10 mm and thickness 1mm, what is the tensile stress developed in the specimen ?
18. Name the property by virtue of which the material can absorb maximum energy before the fracture takes place.
19. What is compressive strength of a material ?
20. Name the heat treatment process used for duralumin alloy.
21. What is the main objective of normalizing as a heat treatment process ?
22. What is the maximum solubility of carbon in iron ?
23. How are resistivity and conductivity related ?
24. Why does the resistivity of copper increase due to presence of solute atoms ?
25. What is the effect of the use of plasticizer on thermoplastic materials ?
26. What is the permeability of diamagnetic material ?
27. What are the constituents of white metal bearing alloys ?
28. What is 18-4-1 high speed steel.
29. Which alloying element is most important to make steel corrosion resistant ?
30. What is the carbon percentage in high-speed steel (W : Cr : V) ?
55. Name at least two mechanisms of plastic deformation.
56. Which of the two main mechanism of plastic deformation requires greater shear stress to deform.
57. If you wound annealed MS and copper wire around our finger one of the two will not form a smooth circular.
58. Before cold working of AL alloy it is heated to about 5840C and then quenched or it should be heated to lower temperature 100 to 2000C and then air cooled ?
59. For which type of fracture, the direction of crack propagation is very nearly perpendicular to the direction of applied tensile stress ?
60. Brass and Bronze are the alloys of copper. What are the other constituents in these alloys ?
61. Suggest one suitable material for each of the following purpose with justifications:
(i) File cabinet
(ii) Water tap
(iii) Manhole cover
(iv) Garden chair
(v) Glass cutter
62. Atomic radii of two metal atoms are 0.128 nm and 0.133 nm respectively. Find out whether they form an solid solution, and if they form, state what type of solid solution it is.
63. Atomic radii of two metal atoms are 0.1278 nm (Cu) and 0.1431 nm (Al) respectively. Find out whether they form an solid solution, and if they form, state what type of solid solution it is.
64. Write down the slip plane and slip direction (one plane and one direction) of Nickel (only Miller indices). How many slip systems are there in Nickel?
65. Why has ferrite very low solubility of carbon, while austenite has high solubility of carbon?
66. Given an activation energy, Q of 142 kJ/mol, for the dilution of carbon in FCC iron and an initial temperature of 1000 K, find the temperature that will increase the diffusion coefficient by a factor 10. [ R = 8.314 J/(mol.K)]
67. A tension test recorded an engineering strain of 0.0046 against the engineering stress of 345 MPa of a material within its elastic range. Find out the elastic modulus of the material and the type of metallic alloy (like iron base etc.).
68. The final thickness of a hard copper sheet is 1.0 mm. It was produced by cold working with 25% deformation. What was the starting thickness of the metal before cold working?
69. The fracture toughness equation of a material is given by Kfc= σf√(π.a). If the material has a strength of 300 MPa, and a fracture toughness of 4 MPa√m, find out the largest internal crack in microns the material will support without cracking. σf = strength (MPa), a = crack size, m
70. Explain why ceramics are hard.
71. Name two important ceramic insulators with their properties.
72. Write the scientific names of following polymers with one of their typical use: Teflon, ABS
73. State the basic structural units of PMMA and Nylon 6,6 elaborating their properties.
74. What is E-Glass? Where it is commonly used?
75. What is Alnico?
76. Name two soft magnetic materials.
77. Which of the following materials shown in figure.
(a) the most ductile
(b) the most brittle
(c) the strongest
(d) the stiffest
78. Which of the following materials is the most ductile ?
Material Percentage elongation
80 - 20 brass 50
70 - 30 brass 70
60 - 40 brass 40
79. What are the two forms which carbon can take in cast iron and which type of iron does it produce ?
80. State whether low, medium or high carbon steel should be used for the following applications:
92. What is the disadvantage of using pure aluminium structurally?
93. Give the composition of solders having the following uses or applications:
(a) Plumber’s solder
(b) For soldering iron and steel
(c) For soldering tin cans.
94. Which of the following thermoplastics has the highest operating temperature?
(a) PVC
(b) Nylon
(c) PTFE
(d) Polystyrene.
----------Key----------
1. Creep is a slow deformation of an object loaded at a constant stress. It is also called as the time dependent past of the strain of a loaded member.
2. Cold working is the plastic deformation of a metal below its recrystallisation temperature. This increases the hardness and strength of the metal.
3. Burger’s vector is the displacement around a dislocation during plastic deformation. It is parallel to a screw dislocation and perpendicular to an edge dislocation.
4. Boron, Aluminium, Indium and Gallium.
5. Drift mobility is the drift velocity per unit field gradient. Or dimensionally it is given by m.sec-1/V m-1 = m2 V-1 sec.-1.
6. Zone refining is the process of separating impurities from a solid (crystals). It is done by first melting it and then solidifying at a controlled temperature. The solid phase separating in the beginning is purer than the liquid and the subsequent by solidifying portions. The purer phase is separated and the process is repeated to further remove the impurities. In case of silicon and germanium, after zone refining only one impurity atom can be left per 1010 atom of the solvent.
7. According to this rule the resistivity r of a conductor is given by r = rt + rr
Where, rt is the thermal part of the resistivity and rr is the residual resistivity due to solute atoms and other imperfections in the crystal.
8. This law states that the magnetic susceptibility is inversely proportional to the absolute temperature (T). It is expressed as C/T . Where the constant C is called curie constant.
9. garnets are non metallic soft magnetic material. These are usually prepared by powder compacting (sintering) process.
10. Spinels are compounds with two different cat ion A++ and B+++ and oxygen as the anion. A typical group of such materials are ferrites. These are ferromagnetic in nature.
11. Cast iron has good machinability, stable dimensions and has got the property of damping vibrations in machines tools.
12. Hooke’s law states that within elastic limit, for an elastic deformation, stress is proportional to strain. This does not hold in case of elastomers like rubber whose stress-strain behaviour is not linear in their elastic range.
13. It is a type of line imperfection in crystal in which positions of planes of atoms are missing or misaligned. These may be edge type or screw type.
14. Ergs/cm2 or dynes/cm.
15. Grain boundary shear is possible only at temperatures above 0.5 Tm where Tm is the melting point of the metal expressed in absolute scale.
16. (a) Thoria dispersed nickel.
(b) Jet alloy 1570 (0.22 %C, 20% Cr, 28% Ni and Rest Co.)
17. 1 N/mm2
18. The maximum energy absorbed before fracture is known as toughness.
19. The maximum compressive stress which can be developed in material under compressive load.
20. Duralumin is annealed.
21. In normalizing there is complete phase re-crystallization and fine grain structure is obtained.
22. Maximum solubility of carbon in iron is 2 %.
23. Conductivity of reciprocal of resistivity and has units ohm-1 m-1.
24. The solute atoms cause lattice distortion, these imperfections, cause irregularities in electric fields within the metal and decrease mean free path thus reducing mobility of electrons, thereby increasing resistivity of metal.
25. The plastisizer prevent crystallization producing non-crystalline solid. These provide flexibility, impart toughness, improve flow of material and act as internal lubricant.
26. The permeability of diamagnetic material is less than one.
27. The white metal bearing consists of Antimony, Copper, tin and lead typical examples are
52. The percentage carbon in low carbon steel is 0.05 to 0.3.
53. Carburizing is diffusion or impregnation of carbon in the surface.
54. It is wrought alloy.
55. Slip and Twinning
56. Slip
57. Mild steel
58. They are heated to 5840C and the quenched.
59. Brittle type of fracture
60. Brass has other constituents; Zinc, Nickel and Lead Bronze has other constituents; Tin Phosphorous a nd Aluminium.
61. (i) Steel, board (ii) brass (iii) cast iron (iv) Wrough iron, concrete, bamboo, timber (v) Low alloy steel
62. They will form substitutional solid solution because size of atoms are nearly same.
63. Only 20% of copper atoms can be replaced by aluminium because there is a substantial difference in size.
64.
65. Ferrites has a lower packing factor. Each of the many interstitial sites is too small to accommodate even a small carbon atom. Only one carbon atom can be dissolved per 500 unit of cells of � ferrite. On the other hand, austenite accepts carbon atom interstitially. Since the carbon atom is small, the interstices in austenite can accommodate upto 10 a/o carbon. These small atoms reside in 1/2, 1/2, 1/2 sites.
66. Hint: D = D0 e-Q/RT
where D is diffusion coefficient, D0 is proportionality constant, Q is activation energy, T is temperature.
where A0 and Af are original and final areas respectively.
69. Hint: 4MPa.√m = 300√(π.a.m)
70. Positive metallic ions (atoms that have lost electrons) and negative nonmetallic ions (atoms that have gained electrons) develop strong attractions for each other. Each cation (positive) surrounds itself with anions (negative). Considerable force is usually required to separate the two. Ceramic materials tend to be hard.
Ceramic materials are usually ionic or covalent bonded materials, and can be crystalline or amorphous. A material held together by either type of bond will tend to fracture before any plastic deformation takes place, which results in poor toughness in these materials. Additionally, because these materials tend to be porous, the pores and other microscopic imperfections act as stress concentrators, decreasing the toughness further, and reducing the tensile strength. These combine to give catastrophic failures, as opposed to the normally much more gentle failure modes of metals.
71. Alumina (Al2 O3 ): It is used in electrical insulator. It is used in spark plug. It is also used in computer circuits. It has high dielectric constant.
72. Teflon: PTFE (polytetrafluoroethylene)
ABS: Acrylonitrile - Butadiene - Styrene
Teflon-PTFE is a Polytetrafluoroethylene used in GoreTex and nonstick cookware, and also as a high-frequency, high temperature dielectric/insulator for electrical wires and coaxial cables.
ABS is an ideal material wherever superlative surface quality, colorfastness and luster are required. ABS is a two phase polymer blend. A continuous phase of styrene-acrylonitrile copolymer (SAN) gives the materials rigidity, hardness and heat resistance. The toughness of ABS is the result of submicroscopically fine polybutadiene rubber particles uniformly distributed in the SAN matrix.
73. PMMA: Polymethyl methacrylate
where 1 stands for H, 2 stands for H, 3 stands for CH3 and 4 stands for
Nylon 6/6: The polar C=O groups bond to the next chain through hydrogen bridges. This bonding favours a matching of adjacent molecules and leads to more complete crystallinity, than in polyethylene. Within crystals, the molecules are not kinked and coiled.
74. E-glass is fibre reinforced glasses, designed originally for electrical applications. They are most commonly calcium alumino borosilicate glasses that contain no Na+ ions.
75. Alnico Magnet: This permanent magnet, which contains aluminium, nickel and cobalt in an iron base alloy is magnetized as a single phase, then is heat treated to provide, very fine grained, two phase microstructure.
76. Pure iron, Silicon ferrite, Peralloy (Ni-fe), Superpermalloy (Ni-Fe-Mo)
Soft magnetic materials are those materials that are easily magnetised and demagnetised.
77. (a) Material C
(b) Material B
(c) Material A
(d) Material A.
78. The most ductile material is the one with the largest percentage elongation, i.e. the 70 - 30.
79. Cementite - producing ‘white’ iron
Graphite - producing ‘grey’ iron.
80. (a) Medium
(b) Low
(c) High
(d) Medium or low.
81. High carbon steels contain more carbon and are therefore harder both initially and after heat treatment. In most instances the cutting tool must be harder than the material being cut.
84. The only difference between annealing and normalising treatments is the way in which they are cooled. Material which is being annealed is cooled in the furnace whilst for normalising cooling is done in still air.
85. Case-hardening is a method of hardening a ferrous alloy so that the outer portion, or case is made substantial harder than the inner portion or core. Its purpose is to produce a material which can resist abrasion and wear due to the hard surface and resist shock loading due to the softer core.
86. The main reason for preferring normalizing to annealing a ferrous material is when improved machinability is desired. A material in its softest state is not necessarily in its most machinable state. To facilitate machining the material must allow chip cracks to propagate and not spread on the too; point. Annealing a ferrous material produces a soft material which may not machine as easily as a normalized steel.
87. Typical application include: domestic water tanks, rubbing for central heating, ornamental canopies above fires, jugs, vases.
88. The addition of zinc to produce brass, together with other elements and impurities, drastically reduces the conductivity of the material.
89. Both are alloys of copper. Brass is mainly a combination of copper and zinc, whereas bronze is an alloy of copper and tin. Each can contain other elements in smaller quantities.