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    Ment 120 Exam

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    nattydreadfathelah
    This document is an examination for a Material Science course consisting of 5 questions. It covers topics like crystal structures, phase diagrams, and heat treatments as they relate to bonding, properties of materials like steel, and microstructure development. Students are instructed to answer any 4 of the 5 multi-part questions, which involve calculations, explaining differences in properties, sketching microstructures, and specifying phases that would form under different heat treatments.

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    Ment 120 Exam

    Uploaded by

    nattydreadfathelah
    9 views5 pages
    This document is an examination for a Material Science course consisting of 5 questions. It covers topics like crystal structures, phase diagrams, and heat treatments as they relate to bonding, properties of materials like steel, and microstructure development. Students are instructed to answer any 4 of the 5 multi-part questions, which involve calculations, explaining differences in properties, sketching microstructures, and specifying phases that would form under different heat treatments.

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    This document is an examination for a Material Science course consisting of 5 questions. It covers topics like crystal structures, phase diagrams, and heat treatments as they relate to bonding, properties of materials like steel, and microstructure development. Students are instructed to answer any 4 of the 5 multi-part questions, which involve calculations, explaining differences in properties, sketching microstructures, and specifying phases that would form under different heat treatments.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    9 views5 pages

    Ment 120 Exam

    Uploaded by

    nattydreadfathelah
    This document is an examination for a Material Science course consisting of 5 questions. It covers topics like crystal structures, phase diagrams, and heat treatments as they relate to bonding, properties of materials like steel, and microstructure development. Students are instructed to answer any 4 of the 5 multi-part questions, which involve calculations, explaining differences in properties, sketching microstructures, and specifying phases that would form under different heat treatments.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 5

    MENT 120

    EGERTON UNIVERSITY

    UNIVERSITY EXAMINATIONS
    REGULAR - NJORO CAMPUS

    SECOND SEMESTER, 2020/2021 ACADEMIC YEAR

    THIRD YEAR EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE IN


    MECHANICAL & MANUFACTURING ENGINEERING.

    MENT 120: MATERIAL SCIENCE I

    STREAM: BSc. (MENT) TIME: 2 HOURS

    EXAMINATION SESSION : JULY YEAR: 2022

    INSTRUCTIONS

    (i) ANSWER ANY FOUR QUESTIONS.


    (ii) ALL QUESTIONS CARRY EQUAL MARKS
    (iii) ELECTRONIC CALCULATORS ARE NEEDED.

    “Transforming Lives through Quality Education”


    Page 1 of 5
    MENT 120

    QUESTION ONE

    a. Cite two important quantum-mechanical concepts associated with the Bohr model of the
    atom. (2 marks)
    b. Cite two important additional refinements that resulted from the wave-mechanical atomic
    model. (2 marks)
    c. What is the driving force for the formation of primary bonds? (1 marks)
    d. Briefly describe the three primary bonds. (6 marks)
    e. State the Pauli exclusion principle. (2 marks)
    f. List five physical phenomenon that are influenced by secondary bonds. (2.5 marks)
    g. List four applications/products that utilize secondary bonds (2 marks)

    QUESTION TWO

    a. Pure aluminum is a ductile metal with low tensile strength and hardness. Its oxide Al 2O3
    (alumina) is extremely strong, hard, and brittle. Explain this difference from an atomic
    bonding point of view? (2 marks)

    b. Graphite and diamond are both made from carbon atoms.


    i. List some of the physical characteristics of each. (2 marks)
    ii. Give one application for graphite and one for diamond. (1 mark)
    iii. If both materials are made of carbon, why does such a difference in properties exist?
    (2 marks)
    c. Briefly describe the face-centered cubic, body centered cubic, and hexagonal close packed
    crystal structures. Give an example of metals that have each of these crystal structure.
    (7.5 marks)
    d. Show that the atomic packing factor (APF) for an FCC crystal structure is 0.74. (3 marks)

    QUESTION THREE
    a. Tungsten at 20°C is BCC and has an atomic radius of 0.137 nm.
    i. Calculate a value for its lattice constant a in nanometers. (2 marks)
    ii. Calculate its theoretical density. (4 marks)
    Take the atomic weight of Tungsten to be 183.84 g/mol and Avogadro’s constant = 6.022
    x 1023 atoms/mol
    b. Derive the linear density expression for FCC [110] direction in terms of the atomic radius R
    and then compute the linear density value for this same direction for silver (Ag). Take the
    atomic radius of Ag to be 0.144 nm. (5 marks)
    c. Determine the Miller indices for the planes shown (Figure 1) in the following unit cell:
    (6.5 marks)

    “Transforming Lives through Quality Education”


    Page 2 of 5
    MENT 120

    Figure 1

    QUESTION FOUR

    a. In terms of heat treatment and the development of microstructure, what is the limitation of
    the iron–iron carbide phase diagram? (2 marks)
    b. What is the distinction between hypoeutectoid and hypereutectoid steels? (1 mark)
    c. Consider 2.5 kg of austenite containing 0.65 wt% C, cooled to below 727°C.
    i. What is the proeutectoid phase? (1 mark)
    ii. How many kilograms each of total ferrite and cementite form? (3 marks)
    iii. How many kilograms each of pearlite and the proeutectoid phase form? (3 marks)
    iv. Schematically sketch and label the resulting microstructure. (2 marks)

    d. Rank the following iron–carbon alloys and associated microstructures from the highest to
    the lowest tensile strength, Justify this ranking. (4 marks)
    i. 0.25 wt%C with spheroidite.
    i. 0.25 wt%C with coarse pearlite
    ii. 0.60 wt%C with fine pearlite.
    iii. 0.60 wt%C with coarse pearlite.
    e. How would you prove that martensitic transformation is diffusionless? (1.5 marks)

    “Transforming Lives through Quality Education”


    Page 3 of 5
    MENT 120

    QUESTION FIVE

    a. Define surface hardening and state two reasons why steels are surface hardened.
    (3 marks)
    b. Briefly explain the Carburizing and Nitriding surface hardening techniques. (4 marks)
    c. Give two reasons why martensite is hard. (2 marks)
    d. Using the isothermal transformation diagram for an iron–carbon alloy of eutectoid
    composition (Figure 2), specify the nature of the final microstructure (in terms of
    microconstituents present and approximate percentages of each) of a small specimen that
    has been subjected to the following time– temperature treatments. In each case, assume
    that the specimen begins at 760°C and that it has been held at this temperature long
    enough to have achieved a complete and homogeneous austenitic structure. (8.5 marks)
    i. Cool rapidly to 700°C , hold for 104 s, then quench to room temperature.
    ii. Rapidly cool to 600°C , hold for 4 s, rapidly cool to 450°C , hold for 10 s, then
    quench to room temperature.
    iii. Cool rapidly to 400°C , hold for 20 s, then quench to room temperature.
    iv. Rapidly cool to 575°C , hold for 20 s, rapidly cool to 350°C , hold for 100 s.

    “Transforming Lives through Quality Education”


    Page 4 of 5
    MENT 120

    (Please Note: Figure 2 should be on its own separate page. It’ll be submitted for
    marking with the answer sheets)

    Q4 f (i) and (ii) Q4 f (iii) and (iv)

    Figure 2: The complete isothermal transformation diagram for an iron–carbon alloy of eutectoid
    composition: A, austenite; B, bainite; M, martensite; P, pearlite

    **********************************END********************************

    “Transforming Lives through Quality Education”


    Page 5 of 5

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