Assignment 2 part d Materials Engineering 1M03 answer+question PDF

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View Results Assignment 2 (Ch 4 & 5) Name: AARON MURENBEELD

Attempt: 2 / 3

Out of: 16

Started: February 3, 2007 11:41pm

Finished: February 3, 2007 11:48pm

Time spent: 6 min. 41 sec.

Question 1

(1 point)

Which of the following types of point defect would you expect to be the most mobile, meaning it would be easiest to move around in the structure? Student response:

Correct Response

Student Response

Answer Choices a.

self- interstitial atom

b.

vacancy

c.

substitutional solute

d.

interstitial solute

General feedback: The mobility of a defect depends on its size (smaller is better) and the availability of sites for it to jump to. Sect. 4.3 of the text discusses both of these factors. 1/1

Score: Question 2

(1 point)

True or False: A metal is more likely to dissolve in a host metal that has a lower valency. Student response:

Correct Response

Student Response

Answer Choices a.

True

b.

False

General feedback: Other factors being equal, a metal will have more of a tendency to dissolve another metal of higher valency than one of a lower valency. ~ from page 69 of the text. Score: Question 3

1/1 (1 point)

The number of vacancies present in some metal at 917°C is 3.34 x 1024 m-3. Calculate the number of vacancies at 583°C (in m^-3) given that the energy for vacancy formation is 0.780 eV/atom. Assume that the density of the metal remains constant. Use scientific notation, significant figures in answer: 3 Student response: Not answered Correct answer:

1.72E23 (1.72 * 1023) m^-3

General feedback: See section 4.2 in the text. Score: Question 4

0 / 1 (Question not answered.) (1 point)

For a Cu-Zn alloy that contains 22.15 at% Zn, what is the concentration of Cu (in wt%)? The atomic weights for Zn and Cu are 65.39 and 63.55 g/mol, respectively. Use decimal notation, digits after decimal: 2

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Student response: Not answered 77.35 wt%

Correct answer:

General feedback: For help on composition conversions, please see page 71 of the textbook. An example similar to this question is given on page 73. 0 / 1 (Question not answered.)

Score: Question 5

(1 point)

Niobium forms a substitutional solid solution with vanadium. Calculate the concentration (in wt%) of niobium that must be added to vanadium to yield an alloy that contains 3.08 x 1022 Nb atoms per cubic centimeter. The densities of pure Nb and V are 8.57 and 6.10 g/cm3, respectively. Use decimal notation, digits after decimal: 1 Student response: Not answered Correct answer:

63.6 wt%

General feedback: If you're having trouble deriving the equation for this problem, it is introduced in exercise 4.17 of the text. 0 / 1 (Question not answered.)

Score: Question 6

(1 point)

Two metal specimens, A and B, have ASTM grain size numbers of 3 and 8 respectively. Which specimen has the larger grain size? Student response:

Correct Response

Student Response

Answer Choices a. b.

General feedback: The ASTM grain size number (n) is related to the number of grains per square inch ( N) according to the following equation:

Thus, as n increases, so does the value of N. However, as N increases, the grain size diminishes, so

Score: Question 7

0/1 (1 point)

The concentration of carbon in a carbon-metal alloy is found to be 47.3 kg/m3. It is also known that the concentration of carbon in wt% in the alloy is 1.23. Knowing that the density of carbon is 2.25 g/cm3, determine the density of the metal (in g/cm^3). Use decimal notation, digits after decimal: 2 Student response: Not answered Correct answer:

3.88 g/cm^3

General feedback: For more information on the mass per unit volume composition scheme, see page 71 of the text. Score: Question 8

0 / 1 (Question not answered.) (1 point)

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The phenomenon of material transport by atomic motion is called _______________. Student response:

No. Student response 1.

Not answered

Grade Correct answer (Value) 0%

Answer evaluated by the formula. (100%)

General feedback: Diffusion is the phenomenon of material transport by atomic motion. 0 / 1 (Question not answered.)

Score: Question 9

(1 point)

Diffusion by which mechanism occurs more rapidly in metal alloys? Student response:

Correct Response

Student Response

Answer Choices a.

Vacancy diffusion

b.

Interstitial diffusion

General feedback: In metal alloys, interstitial diffusion takes place more rapidly than vacancy diffusion because the interstitial atoms are smaller and more mobile. Also, there are more vacant adjacent interstitial sites than there are vacancies. For more information, see the section on diffusion mechanisms in the text. Score: Question 10

0/1 (2 points)

Consider a metallic species which diffuses in a host metal. The values of D0 and Qd are 1.39 x 10-5 m2/s and 185 kJ/mol, respectively. If the temperature is 765 °C, calculate the value of the diffusion coefficient (in m^2/s). Use scientific notation, significant figures in answer: 3 Student response: Not answered Correct answer:

6.74E-15 (6.74 * 10-15) m^2/s

General feedback: This problem can be solved using the temperature-dependent formula for diffusion. See the section on factors that influence diffusion in the text for more information. Score: Question 11

0 / 2 (Question not answered.) (2 points)

Carbon is allowed to diffuse through a steel plate 15.5 mm thick. The concentrations of carbon at the two faces are 0.733 and 0.256 kg/m3, and are maintained constant. The preexponential (D0) and the activation energy are 8.89 x 10-6m2/s and 163 kJ/mol, respectively. Calculate the temperature (in K) at which the diffusion flux is 3.18 x 10 -7 kg/(m2-s). Use decimal notation, digits after decimal: 0 Student response: Not answered Correct answer:

2901 K

General feedback: The diffusion flux through the plate is given by Fick's law and is proportional to the concentration gradient between the ends of the plate:

Before you can use this equation, however, you need to determine the diffusion coefficient, D. That can be accomplished using the relationship between diffusion and temperature:

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Remember to watch your signs. More information can be found in the sections of your text which discusses steady-state diffusion and factors that influence diffusion. Score: Question 12

0 / 2 (Question not answered.) (3 points)

A sheet of BCC iron is exposed to a carburizing atmosphere on one side and a decarburizing atmosphere on the other. Diffusion is carried out at 725°C. After it reaches steady state, the iron is quickly cooled to room temperature. The carbon concentrations at the two surfaces are determined to be 0.0152 and 0.0075 wt%. The diffusion flux is found to be 1.8 x 10-8 kg/m2-s and the diffusion coefficient is 8.0 x 10-11 m2/s. Knowing that the densities of carbon and iron are 2.25 and 7.87 g/cm3, respectively, find the thickness of the sheet of iron (in mm). Use decimal notation, digits after decimal: 1 Student response: Not answered Correct answer:

2.7 mm

General feedback: To solve this problem, first convert the concentrations from weight percent to kilograms of carbon per cubic meter of iron using the following equation:

The diffusion flux (in mass diffusing per unit area per unit time) is proportional to the concentration gradient as follows:

Here the high and low concentrations are denoted by subscripts 1 and 2, respectively. Substitute the C1 and C2 concentration expressions from the first equation into the second equation, and solve for x2 (let x1=0mm). For more information, see the section in the text on steady-state diffusion. Score:

0 / 3 (Question not answered.)

Total score:

2 / 16 = 12.5%...