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engineering
the science and engineering of materials

Questions and Answers of The Science And Engineering Of Materials

Examine Figure 12-10 and state the phases that will be present in each stage if this process path is followed: (500°C, 20 wt% Mg) to (500°C, 80 wt% Mg) to (200°C, 80 wt% Mg). 600 °C
Draw the eutectoid portion of the Fe- Fe3C phase diagram. Be sure to indicate all of the compositions and temperatures and write the relevant reaction.
If an FCC sample has an observed incubation time of 10 seconds and is fully transformed at 3.5 x 104 s, what are its c and n values in Equation 12-2? f=1 - exp(-ct") (12-2)
Explain clearly the two different ways in which intermetallic compounds can be used.
Consider a Pb-15% Sn alloy. During solidification, determine(a) The composition of the first solid to form;(b) The liquidus temperature, solidus temperature, solvus temperature, and freezing range of
1. What are the effects of thermal cycling on NiTi shape-memory alloys (SMA)?2. Some precipitation-hardened iron super alloys are used for high-temperature service. Describe heat treatment procedures
How is the equation for nucleation of a phase in the solid state different from that for a liquid-to-solid transformation?
For cold-worked copper, construct a plot for the time to 50% recrystallization as a function of annealing temperature.
Most solid-state phase transformations follow the Avrami equation. True or false? Discuss briefly.
What step controls the rate of recrystallization of a cold-worked metal?
What are the different ways by which a second phase can be made to precipitate in a two-phase microstructure?
Explain why the second phase in Al-4% Cu alloys nucleates and grows along the grain boundaries when cooled slowly. Is this usually desirable?
45.7 kg of aluminum comprise 35 wt% of a Cu-Al alloy. The temperature is halfway between the upper and lower bounds of the L + h phase region at this composition. How much more aluminum must be added
What do the terms “coherent” and “incoherent” precipitates mean?
What properties of the precipitate phase are needed for precipitation hardening? Why?
Electromigration (diffusion of atoms/ ions due to momentum transfer from high energy electrons) leads to voids in aluminum interconnects used in many semiconductor metallization processes and thus is
For what dihedral angle will the interfacial energy of the matrix-precipitate boundary and the grain boundary energy of the matrix be equal?
What is the relationship between the interfacial surface energies of the matrix-precipitate boundary and grain boundary when the precipitate forms a tetrahedron?
What is the principle of precipitation hardening?
What is the difference between precipitation hardening and dispersion strengthening?
What is a supersaturated solution? How do we obtain supersaturated solutions during precipitation hardening? Why is the formation of a supersaturated solution necessary?
Why do the precipitates formed during precipitation hardening form throughout the microstructure and not just at grain boundaries?
On aging for longer times, why do the second-phase precipitates grow? What is the driving force? Compare this with driving forces for grain growth and solid-state sintering.
Why is precipitation hardening an attractive mechanism of strengthening for aircraft materials?
Why are most precipitation-hardened alloys suitable only for low-temperature applications?
Examine the Mg-Pb phase diagram. Is an Mg-20 wt% Pb alloy suitable for age hardening? Explain. Temperature (°C) 800 600 400 200 A a 20 L 0 40 60 Weight percent B 80 В B
Why are some alloy systems that exhibit decreasing solid solubility and are agehardening candidates, not used commercially?
Explain the three basic steps encountered during precipitation hardening.
Explain how hot shortness can occur in precipitation-hardened alloys.
In precipitation hardening, does the phase that provides strengthening form directly from the supersaturated matrix phase? Explain.
What is aging? Why is this step needed in precipitation hardening?
What is overaging?
What do the terms natural aging and artificial aging mean?
In the plane flown by the Wright brothers, how was the alloy precipitation strengthened?
Why did the work of Dr. Gayle and coworkers reveal two sets of precipitates in the alloy that was used to make the Wright brothers’ plane?
Speculate as to why a longer time is required to reach the maximum hardness at lower aging temperatures.
Speculate as to why the maximum hardness is higher for lower aging temperatures compared to higher temperatures.
What analytical techniques would you use to characterize the nanoscale precipitates in an alloy?
Why do we have to keep some aluminum alloys at low temperatures until they are ready for forming steps?
Can all alloy compositions be strengthened using precipitation hardening? Can we use this mechanism for the strengthening of ceramics, glasses, or polymers?
A conductive copper wire is to be made. Would you choose precipitation hardening as a way of strengthening this wire? Explain.
What is the major limitation of the use for precipitation-hardened alloys?
Why is it that certain aluminum (not nickel-based) alloys strengthened using age hardening can lose their strength on welding?
Would you choose a precipitationhardened alloy to make an aluminum alloy baseball bat?
What type of dispersion-strengthened alloys can retain their strength up to ,1000°C?
Write down the eutectoid reaction in the Fe-Fe3C system.
Sketch the microstructure of pearlite formed by the slow cooling of a steel with the eutectoid composition.
Compare and contrast eutectic and eutectoid reactions.
Draw the peritectic portion of the Fe- Fe3C phase diagram. Be sure to indicate all of the compositions and temperatures and write the relevant reaction.
What are the solubilities of carbon in the a, d, and g forms of iron?
Define the following terms: ferrite, austenite, pearlite, and cementite.
The pearlite microstructure is similar to a ceramic-metal nanocomposite. True or false. Comment.
What do the terms hypoeutectoid and hypereutectoid steels mean?
Determine the eutectoid temperature, the composition of each phase in the eutectoid reaction, and the amount of each phase present in the eutectoid microconstituent for the following systems. For the
What is the difference between a microconstituent and a phase?
Austenite and Fe3C are in equilibrium at 1000°C and 3 wt% C. What is the weight percent of iron carbide in the two-phase alloy?
For an Fe-1.15% C alloy, determine(a) The temperature at which austenite first begins to transform on cooling;(b) The primary microconstitutent that forms;(c) The composition and amount of each phase
A steel contains 8% cementite and 92% ferrite at room temperature. Estimate the carbon content of the steel. Is the steel hypoeutectoid or hypereutectoid?
A steel contains 18% cementite and 82% ferrite at room temperature. Estimate the carbon content of the steel. Is the steel hypoeutectoid or hypereutectoid?
Plot the yield and tensile strengths of the ratio of coarse to fine pearlite as a function of carbon composition according to Table 12-1. Table 12-1 The effect of carbon on the strength of
A steel contains 18% pearlite and 82% primary ferrite at room temperature. Estimate the carbon content of the steel. Is the steel hypoeutectoid or hypereutectoid?
A steel contains 94% pearlite and 6% primary cementite at room temperature. Estimate the carbon content of the steel. Is the steel hypoeutectoid or hypereutectoid?
A steel contains 55% a and 45% γ at 750°C. Estimate the carbon content of the steel.
Why are the distances between lamellae formed in a eutectoid reaction typically separated by distances smaller than those formed in eutectic reactions?
Why is it that a eutectoid steel exhibits different yield strengths and % elongations, depending upon if it was cooled slowly or relatively fast?
What is a TTT diagram?
Sketch and clearly label the different parts of a TTT diagram for a plain carbon steel with 0.77% carbon.
On the TTT diagram, what is the difference between the γ and γu phases?
How is it that bainite and pearlite do not appear in the Fe-Fe3C phase diagram? Are these phases or microconstituents?
Why is it that we cannot make use of TTT diagrams for describing heat treatment profiles in which samples are cooled over a period of time (i.e., why are TTT diagrams suitable only for isothermal
What is bainite? Why do steels containing bainite exhibit higher levels of toughness?
Describe the hardness and microstructure in a eutectoid steel that has been heated to 800°C for 1 h, quenched to 350°C and held for 750 s, and finally quenched to room temperature.
Describe the hardness and microstructure in a eutectoid steel that has been heated to 800°C, quenched to 650°C, held for 500 s, and finally quenched to room temperature.
Describe the hardness and microstructure in a eutectoid steel that has been heated to 800°C, quenched to 300°C and held for 10 s, and finally quenched to room temperature.
Describe the hardness and microstructure in a eutectoid steel that has been heated to 800°C, quenched to 300°C and held for 10 s, quenched to room temperature, and then reheated to 400°C before
A 1080 steel was austenitized at 775°C for one hour and quenched to 550°C until it isothermally transformed at 550°C. How long must the austenite be held at 550°C to complete the transformation?
What is the primary source of hardening (strengthening) during heat-treating for steels?
What are the similarities and/or differences between the processes for agehardened alloys and steel?
What is the difference between solidstate phase transformations such as the eutectoid reaction and the martensitic phase transformation?
What is the difference between isothermal and athermal transformations?
A steel microstructure contains 92% martensite and 8% Fe3C; the composition of the martensite is 1.10% C. Using Figure 12-35, determine(a) The temperature from which the steel was quenched and(b) The
What step controls the rate of martensitic phase transformations?
Why does martensite not appear on the Fe-Fe3C phase diagram?
Does martensite in steels have a fixed composition? What do the properties of martensite depend upon?
Can martensitic phase transformations occur in other alloys and ceramics?
Compare the mechanical properties of martensite, pearlite, and bainite formed from the eutectoid steel composition.
Describe the complete heat treatment required to produce a quenched and tempered eutectoid steel having a tensile strength of at least 125,000 psi. Include appropriate temperatures.
Describe the complete heat treatment required to produce a quenched and tempered eutectoid steel having an HRC hardness of less than 50. Include appropriate temperatures.
What is the tempering of steels? Why is tempering necessary?
What phases are formed by the decomposition of martensite?
What is tempered martensite?
If tempering results in the decomposition of martensite, why should we form martensite in the first place?
Describe the changes in properties that occur upon the tempering of a eutectoid steel.
What is the principle by which shapememory alloys display a memory effect?
Design a process to produce a polypropylene polymer with a structure that is 75% crystalline. Figure 12-30 will provide appropriate data. Fraction transformed (f) 1.0 0.5- 0 1 /130°C 10 9.0 min 55.0
Give examples of materials that display a shape-memory effect.
What are some of the applications of shape-memory alloys?
You wish to attach aluminum sheets to the frame of the twenty-fourth floor of a skyscraper. You plan to use rivets made from an age-hardenable aluminum, but the rivets must be soft and ductile in
An age-hardened, Al-Cu bracket is used to hold a heavy electrical-sensing device on the outside of a steel-making furnace. Temperatures may exceed 200°C. Is this a good design? Explain. If it is
You use an arc-welding process to join a eutectoid steel. Cooling rates may be very high following the joining process. Describe what happens in the heataffected area of the weld and discuss the

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