Exam 1: Chapters 3 & 4

Question 1

True or false?
Seeding a casting by adding small inert particles promotes homogeneous nucleation throughout the casting and results in smaller grain size than casting without seeding.

Answer 1

False

Question 2

True or false?

Dislocations moving cause plastic deformation, ductility, and the existence of a yield strength.

Answer 2

True

Question 3

True or false?

The center of a casting is generally the first region to freeze.

Answer 3

False

Question 4

True or false?
Heterogeneous nucleation is easier than homogeneous nucleation and is what usually happens in any real materials process where a liquid transforms to a solid.

Answer 4

True

Question 5

FCC materials are more ductile than BCC or HCP materials because?

Answer 5

FCC materials have close packed planes in four directions

Question 6

True or false?
The critical radius for nucleation of a solid phase in a liquid to solid transformation gets larger as the temperature is decreased more and more below the solidification temperature.

Answer 6

False

Question 7

True or false?
An interstitial solid solution generally results when there is little difference in size between the solvent and the solute atoms of the solid solution

Answer 7

False

Question 8

What is the atomic packing factor of a BCC cell?

Answer 8

0.68

Question 9

Substitution solid solution

Answer 9

a solid solution in which solute atoms of one element can replace those of solvent atoms of another element

Question 10

Interstitial solid solution

Answer 10

a solid solution formed in which the solute atoms can enter the voids or holes in the solvent atom lattice

Question 11

Vacancy

Answer 11

a point imperfection in a crystal lattice where an atom is missing from an atomic site

Question 12

Frenkel imperfection

Answer 12

a point imperfection in an ionic crustal in which a positive cation moves into an interstitial site in an ionic crystal, and a cation vacancy is created in the normal ion site

Question 13

Schottky imperfection

Answer 13

A point imperfection in an ionic crystal in which two oppositely charged ions are missing from an ionic crystal creating a cation-anion divacancy.

Question 14

Grain boundry

Answer 14

A 2D planar defect that separates crystals of different orientations in a polycrystalline aggregate.

Question 15

Grain size number

Answer 15

A nominal number of grains per unit area at a particular magnification

Question 16

Atomic packing factor

Answer 16

The volume of atoms per unit cell divided by the volume of the unit cell.

Question 17

Metallic glass

Answer 17

metals with an amorphous atomic structure

Question 18

Nuclei

Answer 18

Small particles of a new phase formed by a phase change that can grow until the phase change is complete.

Question 19

Homogeneous nucleation

Answer 19

The formation of very small regions of a new solid phase in a pure metal that can grow until solidification is complete. The pure metal itself provides the atoms that make up the nuclei.

Question 20

Embryos

Answer 20

Small particles of a new phase formed by a phase change that are not of critical size and that can redissolve.

Question 21

Critical radius

Answer 21

The minimum size that a particle of a new phase formed by nucleation must have to become a stable nucleus.

Question 22

Heterogeneous nucleation

Answer 22

The formation of very small regions of a new solid phase at the interfaces of solid impurities. These impurities lower the critical size at a particular temperature of stable solid nuclei.

Question 23

Grain

Answer 23

a single crystal in a poly-crystalline aggregate

Question 24

Equiaxed grains

Answer 24

Grains that are approximately equal in all directions and have random crystallographic orientations.

Question 25

Columnar grains

Answer 25

Long, thin grains in a solidified polycrystalline structure. These grains are formed in the interior of solidified metal ingots when heat flow is slow and uniaxial during solidification.

Question 26

Poly-crystalline structure

Answer 26

a crystalline structure

Question 27

Alloy

Answer 27

A mixture of two or more metals or a metal (metals) and a nonmetal (nonmetals).

Question 28

Solid Solution

Answer 28

the simplest form of alloy

Question 29

Amorphous

Answer 29

lacking in long range atomic order

Question 30

Allotropy

Answer 30

The phenomenon in which many elements and compounds exist in more than one crystalline form under different conditions of temperature and pressures.

Question 31

Ioninc

Answer 31

Common in ceramic materials

Question 32

Covalent

Answer 32

common in polymers along carbon backbone

Question 33

Metallic

Answer 33

loosely shared electrons