Materials Science Test 1 flashcards ME344

AFM delivers a -dimensional image

3

How can we cast ingots with a fine grain size?

Use grain refiners

Are edge dislocations a permanent or temporary dislocation?

Permanent

How can you use an SEM to view more materials?

Coat the specimen with a small layer of metal

Are larger grains more or less likely to creep?

More

How common are vacancies?

Very

Are smaller grains typically weaker or stronger than larger grains?

Stronger

Can a vacancy change positions?

Yes

How does an AFM work?

Points laser on cantilever beam with a SHARP tip and detects deflections as the tip travels across the specimen

How does an SEM work?

Sends a beam of electrons to surface of material

The displacement distance of the atoms in a dislocation is called…

The Burgers Vector

How does an STM work?

The tip is placed 1 atom diameter from surface and applies a voltage to produce a current

The energy contained in a surface is called the…

Specific Surface Free Energy

The energy released by a liquid when forming a solid is called the…

Volume Free Energy

How does a TEM work?

Shoots a beam of electrons through a (thin) material to scatter electrons

How does homogeneous nucleation occur?

Metal atoms start sticking together to form an embryo, which continues to grow to form a nuclei

How are dendritic growths formed?

Begins solid form, then ejects heat around it (which prevents the solid from forming directly around it)

How is a Substitutional Solid Solution formed?

Solute atoms substitute solvent atoms in a crystal lattice

How are Interstitial Solid Solutions formed?

Solute atoms fit into the spaces between the solvent atoms

How is the nucleus of each grain oriented?

Randomly

How much energy does it take to form a vacancy?

1 eV

Is the Burgers vector parallel or perpendicular to the screw dislocation line?

Parallel

If shown a picture of the grains, how can we find the ASTM grain size number?

Count the number of grains in the box (including partial grains!)

A mixed dislocation can be described as…

A combination of an edge defect and a screw defect

In the graph for homogeneous nucleation, how can you find the critical radius?

Find when the derivative of AG1=0

A negative edge dislocation is indicated by…

an inverted perpendicular symbol

In the graph for homogeneous nucleation, is the line for specific surface free energy positive or negative?

Positive

A positive edge dislocation is indicated by…

an inverted T

In the graph for homogeneous nucleation, is the line for volume free energy positive or negative?

Negative

Roughly how common are vacancies?

1 per 10,000 atoms

In the graph for homogeneous nucleation, what does the horizontal axis represent?

The radius of the nucleus

In the graph for homogeneous nucleation, what does the vertical axis represent?

Free energy change

In the graph for homogeneous nucleation, what is the line created by adding the specific surface energy and the volume free energy?

The total free energy

Roughly what shape are columnar grains?

Columns

Roughly what shape are equimaxed grains?

Spherical

SEM provides a -dimensional image

3

In the single crystal solidification process, what purpose do single-crystal selectors have?

Preventing Creep

TEM delivers a -dimensional image

2

Is the Burgers vector parallel or perpendicular to the edge dislocation line?

perpendicular

True or False

Dislocations are equilibrium defects

dislocations are nonequilibrium defects

True or False

Dislocations store energy in the distorted region of the crystal lattice

What are zero dimensional imperfections in crystals called?

Point Defects

True or False

SEM is unable to conduct X-ray spectrum analysis?

What causes a Frenkel Imperfection to form?

A cation is in the wrong place

True or False

Solute atoms must be much larger than solvent atoms to form an interstitial solid solution

What causes a Schottky imperfection to form?

Two oppositely charged ions are missing from an ionic crystal

True or False

Solvent atoms must be much larger than solute atoms to form an interstitial solid solution

What causes a screw dislocation?

Shear stress

What 2 types of grains are produced when pure metal is cast into a stationary mold without the use of grain refiners?

Equimaxed and Columnar

What causes a stacking fault to form?

When the planes of a crystal aren't in the correct order (ie HCP stacking

What are Columnar grains?

long thin grains in a solidified polycrystalline structure

What causes a vacancy?

an atom missing from a structure

What are Equimaxed grains?

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

What causes different grain structures?

Different processes

What are line defects?

Defects that cause lattice distortion centered around a line

What causes grain boundaries?

Crystals growing into each other

What are one dimensional crystal imperfections called?

Line Defects

What causes Heterogeneous Nucleation?

Adding impurities to act as nucleation agents

What does dendritic growth look like?

A tree

What are the additional steps to finding the ASTM grain size number if the magnification isn't the default?

1- Find n as if magnification was at 100x 2- Multiply answer by (given magnification ÷ 100)^2

What do the letters in the acronym "S.E.M" stand for?

Scanning Electron Microscope

What do the letters in the acronym "T.E.M" stand for?

Transmission Electron Microscope

What do the letters in the acronym "S.T.M." stand for?

Scanning Tunneling Microscope

What do the letters in the acronym "A.F.M." stand for?

Atomic Force Microscope

What equation is needed to find the ASTM grain size number?

N = 2^n-1

What happens if an embryo is too small to form a nuclei?

The embryo re-melts

What does it mean for an element to be undercooled?

Cooled below melting temperature

What is a grain?

A single crystal in a polycrystalline aggregate

What is a grain boundary?

A surface imperfection that separates crystals of different orientation in a polycrystalline aggregate

What is an Edge Dislocation?

A dislocation caused by inserting an extra half plane of atoms

What is an embryo?

A cluster of atoms

What is an example of a 2 dimensional defect?

Stacking faults

grain boundaries

free surfaces

What is an example of a line defect?

Edge dislocation

Screw dislocation

Mixed dislocation

What happens when the Specific Surface Free Energy is greater than the Volume Free Energy?

The element turns into liquid

What happens when the Volume Free Energy is greater than the Specific Surface Free Energy?

The element turns into a solid

What is a 3 dimensional defect?

A crack

What is an Interstitial impurity?

A point imperfection in a crystal lattice where an atom (of the same kind as those of the matrix lattice) is positioned in an interstitial site

What is an Interstitial Solid Solution?

A solid solution formed in which the solute atoms can enter the interstices or holes in the solvent-atom lattice

What is a Solute?

Element that is added and dissolved into the solvent

What is a Solvent?

Element that is able to dissolve other substances

What is single crystal solidification?

Solidification that must take place around a single nucleus so that no other crystals are nucleated and grow

What is a substitutional solid solution?

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

What is the #1 factor for dendritic vs no growth?

Temperature

What is a way additional vacancies can be introduced?

Rapid cooling

Plastic deformation

bombardment with energetic particles

What is the current produced from the specimen an STM is observing proportional to?

The change in gap

What is Homogeneous nucleation?

The metal provides the atoms to form nuclei by itself

What is the energy formation of a vacancy?

1 eV

What is innoculation?

Adding nucleating agents to the liquid metal

What is involved during the solidification of metals?

Nucleation and Growth of Nuclei

What is Nucleation?

Formation of nuclei

What is the term for metallic solid solutions?

Alloys

What kind of defect is a Screw dislocation?

Line defect

What kind of growth is formed when there is very little cooling in the solidification process?

Formation of grain structures