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Dental Materials > 4. Metals and Alloys > Flashcards

4. Metals and Alloys Flashcards

1
Q

STRUCTURE VRS PROPERTIES

Most metals are ____ with slight differences in tint
____ and ____ are non-white
Properties of elements on periodic table change gradually from metallic to non-metallic with semi-conductors in between (____ and ____)

A 
white
Au
Cu
Si
Ge
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2
Q

Periodic Table of the Elements

Common noble metals: ____, ____ and ____; silver is not a noble metal, but it is a ____ metal (economic term)

Very important category of metals we want to know is the noble metals that are within this box here (in the ductile section, the box containing elements ____ and ____)

A

platinum
gold
paladium
precious

44-47
76-79

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3
Q 
Characteristics of Metals
\_\_\_\_
\_\_\_\_ ring
Strength and \_\_\_\_
Ductility and \_\_\_\_
\_\_\_\_ and \_\_\_\_ conductors
Crystalline solids at RT except \_\_\_\_ and \_\_\_\_
A 
luster
metallic
density
malleability
thermal
electrical
Hg
Ga
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4
Q

METALLIC BONDS

Valence electrons form a ____ electron cloud around ____ charged ions arranged in a space lattice.
Properties determined by ____ and ____

Free electrons act as conductors of ____ and ____

A 
mobile
positively
space lattice
electron gas
heat
electricity
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5
Q

Metallic Bonds

Electron ____
Electron Gas around ____ charges ions

A

sharing

positively

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6
Q

Structure Vrs Properties

Properties vs valence electron configuration

  • –Formation of ____ ions in solution
  • –Leads to ____ and ____
  • –Mobility of electrons responsible for conduction of ____ and ____
A 
positive
luster
malleability
heat
electricity
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7
Q

Solidification of Metals

Pure metals have a ____ melting temperature - ____ temperature
Supercooling may occur before ____ begins
Importance of fusion temperature in ____

A

fixed
fusion
crystallization
casting

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8
Q

Cooling curves

Pure metal fixed temperature

Start with molten metal, and cool until you reach the melting temperature and it remains ____ as it is solidified, then cools again once completely transformed into solid

A

constant

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9
Q

Embryo Formation ____- atoms aggregate
____ - the embryo increases in size
____- tree-like formation
____
Dendrites grow until they contact other dendrites around it.
The completed dendrite is grain or crystal

A

embryo
nucleus
dendrites
grain or crystal

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10
Q

Crystal Growth

 Stages in solidification of a molten metal

 Homogenous vs heterogenous nucleation

____nucleation: pure metal that is cooled, and the nuclei are forming only from the pure metal

____ nucleation: impurities are present within the metal, and the impurities act as nucleating sites for atoms to aggregate around them (____ for this to accomplish rather than homogenous)

A

homogenous
heterogenous
easier

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11
Q

Grains and Grain Boundaries

Gold casting with grains and grain boundaries

Each grain is surrounded by ____

A

grain boundaries

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12
Q

Grain Boundary

Grain boundary
—The ____ between grains or crystals

____ leads to stress resulting in high energy at grain boundaries. This is due to ____ bonds

Unsatisfied bonds present: ____ energy location of the material

A

junction

contact mismatch
unsatisfied

high

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13
Q

Grain Size

____ grains - equal in size in all
dimensions
____ size of grains in microstructure
____ grain size gives better mechanical properties

A

equiaxed
average
small

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14
Q

Controlling Grain Sizes

Can be altered by:
Rapid \_\_\_\_
Degree of \_\_\_\_
\_\_\_\_ design
\_\_\_\_ during solidification
High \_\_\_\_ between mold wall and alloy
Use of \_\_\_\_

Nucleating agents are other metals that have a ____ melting temperature than the metal that you are casting (can thus act as a ____) > fine grain sizes

A 
cooling
supercooling
mold
vibration
thermal differential
nucleating agent

higher
nucleating agent

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15
Q

Control of Grain Size

Practical way of controlling grain size
Use nucleating agents eg: ____, Rubidium, ____
silicide, ____ and iridium

Average grain size of
 Cast pure gold = ____ diameter
 Gold alloy = ____

Finer grain size means you have a ____ material

A

ruthenium
calcium
cobalt

1.0 mm
350 um

stronger

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16
Q

Deformation of Metals

Two types of deformation - ____ and ____
Plastic deformation occurs by ____ of one layer of atoms over another
 Large stresses are needed to cause slip in a ____

A

elastic
plastic
“slip”
perfect lattice

17
Q

Mechanism of Deformation

Elastic deformation is deformation that is ____ when the stress/force is removed.

We have one layer of atoms on top of a second layer of atoms; it’s shown as two planes in this block of material.
Put stress on the top layer of atoms. We can keep increasing the stress on the top layer of atoms, and the atoms will roll until they become exactly ____ right on top of the bottom layer of atoms. (shown in D)
If you remove the stress, the atoms will fall back to their original position, and you get ____ deformation.

On the other hand, if we continue increasing the stress, we eventually displace all of the atoms (one unit) and we get ____ deformation.

A

recovered
oriented
elastic
plastic

18
Q

Lattice Imperfections Point defects (Now we’re talking about plastic deformation)

Point Defects

____ in a crystal lattice are not ideal
Some lattice positions are left ____
Others are overcrowded with atoms positioned out of line with lattice planes ____

A

atomic rearrangements
vacant (vacancies)
interstitials

19
Q

Point Defects

Vacancy: A missing \_\_\_\_ in
the lattice
Divancy: \_\_\_\_ atoms missing and
\_\_\_\_ atom replacing
them, creating a defect
in the metal
Interstitial atom: \_\_\_\_ located
within the lattice
A

atom
two
one
foreign atom

20
Q

Dislocations

Instead of a perfect array of atomic planes, one plane of atoms may be discontinuous, forming a ____
The atomic arrangement next to a dislocation line is ____ ie. of ____

A

dislocation line

high energy

21
Q

Line Defects - Edge Dislocation

Instead of having a perfect arrangement of atoms, we can have one plane of atoms that ____ in the middle of the material. This is referred to as a dislocation.

The atomic arrangement next to a dislocation line is ____ and it has high energy.

What happens when you put force on a metal going up and also force going to the right?

o Instead of all of the planes breaking to create a deformation, you can have just ____ break and then the dislocation line keeps moving towards the direction of the ____.

If we continue pushing, the line will keep moving by breaking one plane at a time until it gets to the end of the material; we’ve achieved ____ deformation of the material without having to break all of the planes at
the same time.

A

shearend
strained

one plane
force

plastic

22
Q

Dislocation Movement

This is what we have after the atomic planes are broken down one at a time to get to the end of the material; we have a unit step of ____. We call this a dislocation line because it’s a line that goes through the
material; this line is moving; it’s also called ____.

Dislocation moves until it causes a unit step of ____ at the end of the material. This is how plastic deformation occurs in metal.

Why should we appreciate this?

o If you have a foreign atom, as in if you have an alloy (so, not all of the atoms are the same), the presence of the second type of atom is going to make it more ____ for the dislocations to move.

o Whenever you have a situation where dislocations don’t move easily, you have a ____ material.

A

slip
slip
slip/permanent deformation

difficult
stronger

23
Q

Dislocation Movement

Plastic deformation involves a movement of the edge dislocation along a ____ (____ plane at a time) until the dislocation reaches the ____ of the crystal.

A

slip plane
one
edge

24
Q

Slip bands on a metal surface

Cold worked gold with ____

This is showing a piece of gold that has been
deformed to show ____ (bands that are
due to ____ deformation on the surface).

A

slip bands
slip bands
plastic

25
Q

Strain Hardening

____ deformation hardens and strengthens a metal
 (Defects in a metal interact and inhibit further ____ movement)

Work hardening or strain hardening eg. Bending of a ____, compaction of ____, drawing of ____ wire

Once dislocation line moves through a material, the material becomes ____

A 
plastic
dislocation
clasp arm
gold foil
orthodontic
stronger
26
Q

Strain Hardening

Effects of strain hardening

  • – Increase in ____
  • –____
  • –____ limit
  • –____ in ductility and corrosion resistance

•No change in ____

A 
hardness
strength
proportional
decrease
modulus of elasticity
27
Q

Properties of Cast Vrs Wrought Metals

Wrought:
T/S: ____
Ductility: ____
Corrosion resistance: ____

Cast:
T/S: ____
Ductility: ____
Corrosion resistance: ____

Already been ____ deformed > lost some of its ductility (wrought metal)

A

high
low
low

low
high
high

plastically

28
Q

Annealing

The effects of cold work can be reversed by heating the metal to \_\_\_\_ its fusion temperature - annealing
Three stages of annealing:
\_\_\_\_
\_\_\_\_
\_\_\_\_

Can ____ the work hardening of a metal

A 
half
recovery
recrystallization
grain growth
reverse
29
Q

Annealing

Stages of annealing for a coldworked metal

This shows what is happening during the heating process to recover the properties of the work hardened metal.

The internal stresses are gradually ____ .
Remember: this graph is various properties vs. time.
We are heating the metal at a ____ .
After work hardening, the ____ and ____ are higher, but the ductility is ____ .
As we gradually heat it over time, the strength of the wrought metal ____ to that of the cast metal, the hardness ____ to that of the cast metal, and the
ductility increases ____ to that of the cast metal.

This is what is happening in the grains of the metal. This (recovery) shows elongated grains that have deformed in tensile formation. As we continue to heat it, we begin
to cause ____ (new crystals are formed from the elongated grains to become more ____ ). We have grain growth to the point where the properties of the metal become ____ to what they were when they were first cast.

We go from a stronger metal after plastic deformation to a weaker metal, high hardness to low hardness, and low ductility to high ductility.

A 
decreased
fixed temp
hardness
strength
lower
decreases
decreased
gradually

recrystallization
equiaxed
identical

30
Q

Annealing

____ grains disappear and new ____ grains are formed
Wrought structure is converted to a ____ structure

Practical significance: Bending of ____ or ____ lead to cold work

A

strained
strain-free
cast

orthodontic wires
partial denture clasp arms

31
Q

Annealing of Metals

____ changes during annealing

A

microstructure

32
Q

Annealing

____ or ____ of orthodontic wires
If wires are overheated, the ____ changes
____ strength of appliance

A

soldering
welding
microstructure
reduced

Dental Materials (7 decks)

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