Free Practice Quiz Question List

03 Defects, Diffusion, and Microstructure Online Quiz Questions

Use this free practice quiz with 20 questions to review 03 Defects, Diffusion, and Microstructure, test your knowledge, and prepare for your next test or exam.

20 questions

True or false

1 point

True or false: Vacancies can occur in a crystal at finite temperature, and their concentration generally increases as temperature rises.

A
True
B
False

Choose one

1 point

Which mechanism allows a small interstitial atom to diffuse through a crystal?

A
They move only by replacing host atoms at lattice sites.
B
They can move between interstitial sites.
C
They move only along grain boundaries.
D
They must move together with a dislocation.

Fill in the blank

1 point

When more particles leave a high-concentration region than enter it, the net transport is toward the region of .

Written response

1 point

What is the name of the ionic point defect formed when an ion is displaced from its lattice site to an interstitial site?

Choose one

1 point

In Fick’s first law, what does the negative sign indicate about the direction of atomic flux?

A
Flux is always directed toward increasing concentration.
B
Flux is independent of the concentration gradient.
C
Flux is directed down the concentration gradient.
D
Flux must be zero whenever concentration varies with position.

Choose all

1 point

Select all the routes identified as short-circuit diffusion paths that are generally faster than diffusion through the crystal lattice.

A
Surfaces
B
Dislocations
C
The regular crystal lattice
D
Grain boundaries

Fill in the blank

1 point

Compared with a coarse-grained material, a fine-grained material has more grain-boundary area per unit volume, making the contribution of grain-boundary diffusion .

True or false

1 point

True or false: A pore can reduce a material’s effective load-bearing area and act as a stress concentrator that may initiate fracture.

A
True
B
False

Choose all

1 point

Select all the features that can hinder dislocation motion and thereby increase the stress required for plastic flow.

A
Solute atoms
B
Precipitates
C
Other dislocations
D
Grain boundaries

Choose one

1 point

For a metal following the Hall–Petch trend over an ordinary grain-size range, what is the expected effect of decreasing average grain diameter in $\sigma_y=\sigma_0+k_y d^{-1/2}$ ?

A
The yield strength usually decreases.
B
The yield strength usually increases.
C
The yield strength remains unchanged.
D
The material must become brittle.

Written response

1 point

Estimate the diffusion distance using $\sqrt{Dt}$ for $D=4\times10^{-10}\,\text{m}^2/\text{s}$ and $t=25\,\text{s}$ . Enter the value in metres.

Open ended

1 point

A metal is cold worked and then heated. Explain why cold working typically strengthens it and how subsequent heating can change its stored deformation and grain structure.

Choose one

1 point

For fixed material parameters in $D=D_0\exp\left(-\frac{Q}{RT}\right)$ , what generally happens to the diffusion coefficient as absolute temperature increases?

A
The diffusion coefficient generally increases.
B
The diffusion coefficient must become zero.
C
The diffusion coefficient is independent of temperature.
D
The diffusion coefficient generally decreases.

Choose one

1 point

A ceramic component contains pores and is subjected to mechanical loading. Which effect is most likely to make the component weaker?

A
It increases the load-bearing area and spreads stress more evenly.
B
It reduces the load-bearing area and can concentrate stress.
C
It prevents all dislocation motion throughout the component.
D
It necessarily increases the material’s diffusion coefficient.

Written response

1 point

In an ionic crystal, an ion leaves its lattice site and occupies an interstitial site. What is this defect called?

True or false

1 point

True or false: The concentration of vacancies in a crystal generally increases as temperature rises.

A
True
B
False

Choose one

1 point

A crystal contains an extra half-plane of atoms that ends inside the crystal. Which defect does this describe?

A
A pore within the crystal.
B
A grain boundary between differently oriented crystals.
C
An extra half-plane of atoms that terminates within the crystal.
D
An atom occupying a normally unoccupied interstitial space.

Choose one

1 point

For a metal within the ordinary grain-size range where the Hall–Petch trend applies, what is the likely effect of reducing its average grain diameter?

A
The yield strength will often increase.
B
The yield strength will always decrease.
C
The yield strength must remain unchanged.
D
The material will no longer contain grain boundaries.

Choose one

1 point

A material is refined from coarse grains to fine grains. What change can this cause in the contribution of grain-boundary diffusion?

A
They have less grain-boundary area per unit volume, so lattice diffusion stops.
B
They eliminate thermally activated atomic motion.
C
They make diffusion through every path equally fast.
D
They have more grain-boundary area per unit volume, increasing the potential contribution of fast boundary diffusion.

Written response

1 point

Estimate the distance over which diffusion has an appreciable effect using $\sqrt{Dt}$ . For $D=9\times10^{-10}\,\mathrm{m^2/s}$ and $t=4\,\mathrm{s}$ , what is the distance in metres?