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materials science engineering

Questions and Answers of Materials Science Engineering

Briefly explain why fine pearlite is harder and stronger than coarse pearlite, which in turn is harder and stronger than spheroidite.
Cite two reasons why marten site is so hard and brittle.
Rank the following iron–carbon alloys and associated microstructures from the highest to the lowest tensile strength:(a) 0.25 wt%C with spheroidite,(b) 0.25 wt%C with coarse pearlite,(c) 0.60 wt%C
Briefly explain why the hardness of tempered martensite diminishes with tempering time (at constant temperature) and with increasing temperature (at constant tempering time).
Briefly describe the simplest heat treatment procedure that would be used in converting a 0.76 wt% C steel from one microstructure to the other, as follows:(a) Spheroidite to tempered martensite(b)
(a) Briefly describe the microstructural difference between spheroidite and tempered martensite.(b) Explain why tempered martensite is much harder and stronger.
Estimate the Rockwell hardnesses for specimens of an iron–carbon alloy of eutectoid composition that have been subjected to the heat treatments described in parts (b), (d), (f), (g), and (h) of
Estimate the Brinell hardnesses for specimens of a 0.45 wt% C iron-carbon alloy that have been subjected to the heat treatments described in parts (a), (d), and (h) of Problem 10.20.(a) Rapidly cool
Determine the approximate tensile strengths for specimens of a eutectoid iron–carbon alloy that have experienced the heat treatments described in parts (a) and (c) of Problem 10.23.(a) 200°C/s,(c)
For a eutectoid steel, describe isothermal heat treatments that would be required to yield specimens having the following Rockwell hardnesses:(a) 93 HRB,(b) 40 HRC, and(c) 27 HRC.
Is it possible to produce an iron-carbon alloy of eutectoid composition that has a minimum hardness of 90 HRB and a minimum ductility of 35%RA? If so, describe the continuous cooling heat treatment
Is it possible to produce an iron-carbon alloy that has a minimum tensile strength of 690MPa (100,000psi) and a minimum ductility of 40%RA? If so, what will be its composition and microstructure
It is desired to produce an iron-carbon alloy that has a minimum hardness of 175 HB and a minimum ductility of 52%RA. Is such an alloy possible? If so, what will be its composition and microstructure
(a) For a 1080 steel that has been water quenched, estimate the tempering time at 425°C (800°F) to achieve a hardness of 50 HRC.(b) What will be the tempering time at 315°C (600°F) necessary to
An alloy steel (4340) is to be used in an application requiring a minimum tensile strength of 1380MPa (200,000psi) and a minimum ductility of 43%RA. Oil quenching followed by tempering is to be used.
Is it possible to produce an oil-quenched and tempered 4340 steel that has a minimum yield strength of 1400MPa (203,000psi) and a ductility of at least 42%RA? If this is possible, describe the
(a) List the four classifications of steels.(b) For each, briefly describe the properties and typical applications.
(a) Cite three reasons why ferrous alloys are used so extensively.(b) Cite three characteristics of ferrous alloys that limit their utilization.
Compute the volume percent of graphite VGr in a 3.5 wt% C cast iron, assuming that all the carbon exists as the graphite phase. Assume densities of 7.9 and 2.3 g/cm3 for ferrite and graphite,
Compare gray and malleable cast irons with respect to(a) Composition and heat treatment,(b) Microstructure, and(c) Mechanical characteristics.
Compare white and nodular cast irons with respect to(a) Composition and heat treatment,(b) Microstructure, and(c) Mechanical characteristics.
Is it possible to produce malleable cast iron in pieces having large cross-sectional dimensions? Why or why not?
What is the principal difference between wrought and cast alloys?
Why must rivets of a 2017 aluminum alloy be refrigerated before they are used?
What is the chief difference between heat-treatable and non-heat-treatable alloys?
Give the distinctive features, limitations, and applications of the following alloy groups: titanium alloys, refractory metals, super alloys, and noble metals.
Cite advantages and disadvantages of hot working and cold working.
(a) Cite advantages of forming metals by extrusion as opposed to rolling. (b) Cite some disadvantages.
List four situations in which casting is the preferred fabrication technique.
Compare sand, die, investment, lost foam, and continuous casting techniques.
If it is assumed that, for steel alloys, the average cooling rate of the heat-affected zone in the vicinity of a weld is 10°C/s, compare the microstructures and associated properties that will
In your own words describe the following heat treatment procedures for steels and, for each, the intended final microstructure: full annealing, normalizing, quenching, and tempering.
Cite three sources of internal residual stresses in metal components. What are two possible adverse consequences of these stresses?
Give the approximate minimum temperature at which it is possible to austenitize each of the following iron–carbon alloys during a normalizing heat treatment:(a) 0.20 wt% C,(b) 0.76 wt% C, and(c)
Give the approximate temperature at which it is desirable to heat each of the following iron–carbon alloys during a full anneal heat treatment:(a) 0.25 wt% C,(b) 0.45 wt% C,(c) 0.85 wt% C, and(d)
What is the purpose of a spheroidizing heat treatment? On what classes of alloys is it normally used?
Briefly explain the difference between hardness and hardenability.
What influence does the presence of alloying elements (other than carbon) have on the shape of a hardenability curve? Briefly explain this effect.
How would you expect a decrease in the austenite grain size to affect the hardenability of a steel alloy? Why?
Construct radial hardness profiles for the following:(a) A 50-mm (2-in.) diameter cylindrical specimen of an 8640 steel alloy that has been quenched in moderately agitated oil(b) A 75-mm (3-in.)
Compare the effectiveness of quenching in moderately agitated water and oil by graphing, on a single plot, radial hardness profiles for 65-mm (2½ -in.) diameter cylindrical specimens of an 8630
Compare precipitation hardening (Section 11.9) and the hardening of steel by quenching and tempering (Sections 10.5, 10.6, and 10.8) with regard to(a) The total heat treatment procedure(b) The
Below is a list of metals and alloys: Select from this list the one metal or alloy that is best suited for each of the following applications, and cite at least one reason for your choice: (a) The
A group of new materials are the metallic glasses (or amorphous metals). Write an essay about these materials in which you address the following issues:(a) Compositions of some of the common metallic
Of the following alloys, pick the one(s) that may be strengthened by heat treatment, cold work, or both: R50500 titanium, AZ31B magnesium, 6061 aluminum, C51000 phosphor bronze, lead, 6150 steel, 304
A structural member 100 mm (4 in.) long must be able to support a load of 50,000 N (11,250 lbf) without experiencing any plastic deformation. Given the following data for brass, steel, aluminum, and
Discuss whether it would be advisable to hot work or cold work the following metals and alloys on the basis of melting temperature, oxidation resistance, yield strength, and degree of brittleness:
A cylindrical piece of steel 25 mm (1.0 in.) in diameter is to be quenched in moderately agitated oil. Surface and center hardnesses must be at least 55 and 50 HRC, respectively. Which of the
A cylindrical piece of steel 75 mm (3 in.) in diameter is to be austenitized and quenched such that a minimum hardness of 40 HRC is to be produced throughout the entire piece. Of the alloys 8660,
A cylindrical piece of steel 38 mm (1½in.) in diameter is to be austenitized and quenched such that a microstructure consisting of at least 80% martensite will be produced throughout the entire
A cylindrical piece of steel 90 mm (3½ in.) in diameter is to be quenched in moderately agitated water. Surface and center hardnesses must be at least 55 and 40 HRC, respectively. Which of the
A cylindrical piece of 4140 steel is to be austenitized and quenched in moderately agitated oil. If the microstructure is to consist of at least 50% martensite throughout the entire piece, what is
A cylindrical piece of 8640 steel is to be austenitized and quenched in moderately agitated oil. If the hardness at the surface of the piece must be at least 49 HRC, what is the maximum allowable
Is it possible to temper an oil-quenched 4140 steel cylindrical shaft 100 mm (4 in.) in diameter so as to give a minimum tensile strength of 850 MPa (125,000 psi) and a minimum ductility of 21%EL? If
Is it possible to temper an oil-quenched 4140 steel cylindrical shaft 12.5 mm (0.5 in.) in diameter so as to give a minimum yield strength of 1000 MPa (145,000psi) and a minimum ductility of 16%EL?
Copper-rich copper???beryllium alloys are precipitation hardenable. After consulting the portion of the phase diagram (Figure), do the following: (a) Specify the range of compositions over which
A solution heat-treated 2014 aluminum alloy is to be precipitation hardened to have a minimum tensile strength of 450 MPa (65,250psi) and a ductility of at least 15%EL. Specify a practical
Is it possible to produce a precipitation-hardened 2014 aluminum alloy having a minimum tensile strength of 425 MPa (61,625psi) and a ductility of at least 12%EL? If so, specify the precipitation
For a ceramic compound, what are the two characteristics of the component ions that determine the crystal structure?
Show that the minimum cation-to-anion radius ratio for a coordination number of 4 is 0.225.
Show that the minimum cation-to-anion radius ratio for a coordination number of 6 is 0.414.
Demonstrate that the minimum cation-to-anion radius ratio for a coordination number of 8 is 0.732.
On the basis of ionic charge and ionic radii given in Table 12.3, predict crystal structures for the following materials: (a) CsI, (b) NiO, (c) KI, and (d) NiS. Justify yourselections.
Which of the cations in Table 12.3 would you predict to form iodides having the cesium chloride crystal structure? Justify yourchoices.
Compute the atomic packing factor for the rock salt crystal structure in which rC/rA = 0.414.
The zinc blende crystal structure is one that may be generated from close-packed planes of anions.(a) Will the stacking sequence for this structure be FCC or HCP? Why?(b) Will cations fill
The corundum crystal structure, found for Al2O3, consists of an HCP arrangement of O2- ions; the Al3+ ions occupy octahedral positions.(a) What fraction of the available octahedral positions are
Iron sulfide (FeS) may form a crystal structure that consists of an HCP arrangement of S2- ions.(a) Which type of interstitial site will the Fe2+ ions occupy?(b) What fraction of these available
Magnesium silicate, Mg2SiO4, forms in the olivine crystal structure that consists of an HCP arrangement of O2- ions.(a) Which type of interstitial site will the Mg2+ ions occupy? Why?(b) Which type
Using the Molecule Definition Utility found in both ?Metallic Crystal Structures and Crystallography? and ?Ceramic Crystal Structures? modules of VMSE, located on the book?s web site
Calculate the density of FeO, given that it has the rock salt crystal structure.
Magnesium oxide has the rock salt crystal structure and a density of 3.58 g/cm3. (a) Determine the unit cell edge length. (b) How does this result compare with the edge length as determined from the
Compute the theoretical density of diamond given that the C—C distance and bond angle are 0.154 nm and 109.5°, respectively. How does this value compare with the measured density?
Compute the theoretical density of ZnS given that the Zn—S distance and bond angle are 0.234 nm and 109.5°, respectively. How does this value compare with the measured density?
Cadmium sulfide (CdS) has a cubic unit cell, and from x-ray diffraction data it is known that the cell edge length is 0.582 nm. If the measured density is 4.82 g/cm3, how many Cd2+ and S2- ions are
(a) Using the ionic radii in Table 12.3, compute the theoretical density of CsCl. (b) The measured density is 3.99 g/cm3. How do you explain the slight discrepancy between your calculated value and
From the data in Table 12.3, compute the theoretical density of CaF2, which has the fluoritestructure.
A hypothetical AX type of ceramic material is known to have a density of 2.65 g/cm3 and a unit cell of cubic symmetry with a cell edge length of 0.43 nm. The atomic weights of the A and X elements
The unit cell for MgFe2O4 (MgO-Fe2O3) has cubic symmetry with a unit cell edge length of 0.836 nm. If the density of this material is 4.52 g/cm3, compute its atomic packing factor. For this
The unit cell for Cr2O3 has hexagonal symmetry with lattice parameters a = 0.4961 nm and c = 1.360 nm. If the density of this material is 5.22 g/cm3, calculate its atomic packing factor. For this
Compute the atomic packing factor for the diamond cubic crystal structure (Figure 12.15). Assume that bonding atoms touch one another, that the angle between adjacent bonds is 109.5°, and that each
Compute the atomic packing factor for cesium chloride using the ionic radii in Table 12.3 and assuming that the ions touch along the cubediagonals.
For each of the following crystal structures, represent the indicated plane in the manner of Figures 3.11 and 3.12, showing both anions and cations: (100) plane for the rock salt crystal
In terms of bonding, explain why silicate materials have relatively low densities.
Determine the angle between covalent bonds in an SiO4-4 tetrahedron.
Calculate the fraction of lattice sites that are Schottky defects for sodium chloride at its melting temperature (801°C). Assume an energy for defect formation of 2.3 eV.
Calculate the number of Frenkel defects per cubic meter in zinc oxide at 1000°C. The energy for defect formation is 2.51 eV, while the density for ZnO is 5.55 g/cm3 at (1000°C).
Calculate the number of Frenkel defects per cubic meter in zinc oxide at 1000°C. The energy for defect formation is 2.51 eV, while the density for ZnO is 5.55 g/cm3 at (1000°C). Discuss.
If cupric oxide (CuO) is exposed to reducing atmospheres at elevated temperatures, some of the Cu2+ ions will become Cu+.(a) Under these conditions, name one crystalline defect that you would expect
(a) Suppose that Li2O is added as an impurity to CaO. If the Li+ substitutes for Ca2+, what kind of vacancies would you expect to form? How many of these vacancies are created for every Li+ added?(b)
What point defects are possible for Al2O3 as an impurity in MgO? How many Al3+ ions must be added to form each of these defects?
For the ZrO2?CaO system (Figure), write all eutectic and eutectoid reactions for cooling.
From Figure, the phase diagram for the MgO???Al2O3 system, it may be noted that the spinel solid solution exists over a range of compositions, which means that it is nonstoichiometric at compositions
When kaolinite clay [Al2(Si2O5)(OH)4] is heated to a sufficiently high temperature, chemical water is driven off.(a) Under these circumstances, what is the composition of the remaining product (in
Briefly explain(a) Why there may be significant scatter in the fracture strength for some given ceramic material, and(b) Why fracture strength increases with decreasing specimen size.
The tensile strength of brittle materials may be determined using a variation of Equation 8.1. Compute the critical crack tip radius for an Al2O3 specimen that experiences tensile fracture at an
The fracture strength of glass may be increased by etching away a thin surface layer. It is believed that the etching may alter surface crack geometry (i.e., reduce crack length and increase the tip
The fracture strength of glass may be increased by etching away a thin surface layer. It is believed that the etching may alter surface crack geometry (i.e., reduce crack length and increase the tip
A circular specimen of MgO is loaded using a three-point bending mode. Compute the minimum possible radius of the specimen without fracture, given that the applied load is 425 N (95.5lbf), the
A three-point bending test was performed on an aluminum oxide specimen having a circular cross section of radius 3.5 mm (0.14 in.); the specimen fractured at a load of 950 N (215lbf) when the

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