5. Alloys and Equilibrium Diagrams Flashcards
Introduction
Alloy
A mixture of two or more metals that are mutually ____ in the molten condition; or a mixture of a ____ and a ____
Why mix metals
To improve ____
Making an alloy improves the ____ of the metal
soluble
metal
non-metal
physical properties
strength
Description of Alloys
____; a mixture of two or more metals in all possible combinations.
Describe an alloy
List ____
Amount of each
—____ or ____
An alloy system describes the whole possible ____ of two metals
____ is more important for determining properties
alloy system
elements
atomic percent
weight percent
range/combination
atomic percent
Classification of Alloys
General
- –____
- –No of ____
Dental Alloys
- –Use – ____, Crowns, ____, Implants
- –Major Elements – ____, Pd, ____ etc
- –Nobility – Noble, Base Metals
If predominant metal is gold in an alloy: ____ alloys, etc
Noble: ____, platinum, ____
Base: ____, chromium, ____
solubility
components
inlays
dentures
Au
Ti
gold-based
gold
palladium
cobalt
titanium
- Solid solution
A solid mixture of two or more metals that are mutually soluble in the ____ condition and in the ____ state
Intermediate phases
- –____ Systems
- –____ systems
- –____
If solubility solution is not met > formation of ____
Most alloys that are used, most are ____ solutions
One alloy that is eutectic that is used in ____
molten
solidified
eutectic
peritectic
order-disorder
intermediate phases
solid
dentistry
Number of Components
Binary alloy
Ternary alloy Quartenary alloy
Binary: ____ components
Ternary: ____ components
Quat: ____ components
As components increase the alloy becomes more and more ____ in its behavior
two
three
four
complex
Definitions/Characteristics
Phase
A physically distinct, ____, and mechanically separable portion of a system eg. Mixture of ____ and ____
Alloys solidify over a ____ of temperatures
Two phases exist- ____ and ____ cf: single temperature for ____.
homogenous
water
ice
range
solid
liquid
pure metal
Phases in Solids
Microstructure of steel with different ____
When you have a solid you can have different compositions of ____ (not ____ through its compositions of crystals/grains)
phases
crystals
uniform
Solid Solutions and Solid Solution Systems
Types of Solid Solutions
____
____
Solid Solution Systems in dentistry
____
____
Substituitional > two different atoms of same ____; occupy any random position in unit; atoms that constituent majority are the ____, and the ____ is the one with lower number of atoms present (substituting atom positions of parent metal)
Interstitial > solute atoms are much ____ > carbon ion > ____
____ > gold and silver, and silver and palladium
substitutional
interstitial
gold and silver
silver and palladium
size
solvent
solute
smaller
steel
substitutional
Conditions for Complete Substitutional Solid Solubility
- Atomic size
- Valence
- Chemical affinity
- Lattice type
First Point - atomic size difference should NOT be more than ____
Second Point - they should have the SAME ____ - if they have different valencies, they are not likely able to form ____
There should be NO ____ between the atoms and they should also have the SAME ____
We have said previously that most of the metal we use in dentistry are face centered cubic, so if you have two different ____ metals, they have a better chance of forming a solid solution or a substitutional solid
solution
15%
valencies
solid solutions
chemical affinity
lattice type
face centered cubic
Physical Properties of Solid Solution
Solute atoms distort lattice and makes \_\_\_\_ difficult Increased \_\_\_\_ Increased \_\_\_\_ Increased \_\_\_\_ Decreased \_\_\_\_
When compared to a pure metal
dislocation movement strength hardness proportional limit ductility
Cooling curves for pure metal vs alloy
Pure metal: ____
Alloy ____
Tm > mixture of ____ where the temp remains constant
Alloy > gradual decrease until melting temp of first component, then a little ____ (range of temperature over which we have mixture of ____), then liquefied
Refers to phase diagrams
fixed temperature
range of temperatures
solid/liquid
curve
solid/liquid
Determination of a Phase Diagram
Cooling curves for determining solidus and Liquidus lines of phase diagram
Pure metal = A; take point and measure on temperature composition axis (the melting point is plotted); do the same for pure metal B; using a ____ and projecting onto a ____
20%A/80%B > two melting temperatures and project onto phase diagram
And so on…
Above the line on the temperature-composition curve it’s always a liquid (____); once you cross the line it is a ____, and once below it is a complete solid (____)
temperature-time curve
temperature-composition curve
liquidus line
mixture
solidus line
Equilibrium Diagram for Solid Solution System
Liquidus curve Solidus curve Melting points for pure metals Specific alloy compositions phases vs. temperature and freezing ranges
Casting > aware of ____ of where melting begins and where it is liquid metal
range of temperature
Interpretation of Constitution Diagrams
Phases present at \_\_\_\_ \_\_\_\_ of phases present at any temperature \_\_\_\_ \_\_\_\_
temperature
composition
coring
homogenization
The Ag-Pd phase diagram
Determination of composition of phases
A is silver, C is palladium’s melting point
65% palladium at point P > solid solution that is molten, cool and once you get to top of solidus line it has started ____ > composition of liquid by projecting across and projecting down onto the ____ axis
Cool metal to S; ____ you determine composition of liquid, ____ you determine composition of solid; because of this composition is not uniform: ____
(the ____ remains the same; going straight down to the x-axis)
solidifying
composition axis
left
right
coring
average composition
Cored structures
CORING
____ alloy compositions because of ____ cooling rates
Occurs during ____ of alloys
—Developing dendrite has a higher concentration of one
____ than the other at the ____ of the grain
Consequence: ____ can occur between dissimilar atoms
____ is not the same throughout the entire material (coring)
Corrosion can occur within same material, but in different portions of the same material
inhomogeneous
non-equilibrium
solidification
element
center
corrosion
composition
Cored Structure of Ag-Cu Alloy
As cast vs after homogenization
Heat alloy at temperature lower than ____ > diffusion of atoms in order to even out composition of alloy (____) (fixes ____)
liquidus line
homogenization
coring
Eutectic Systems
If the components of an alloy are completely ____ in the liquid state, but have a ____ in the solid state a eutectic alloy forms
- Examples in dentistry: ____ alloy system
Silver/tin alloy system present in ____
soluble
limited solubility
silver/tin
dental amalgams
Ag-Cu System
Ag-Cu phase diagram showing eutectic point
Phase diagram of a eutectic alloy system
Liquidus line broken down to E and increases to D; and solidus goes from D to G to B to A
____ > solution of low concentration of copper in silver (left is silver, right copper)
____ > the opposite
Alloy composition that freezes at T lower than either component: ____ (____, at letter E); when cool here, you go from straight liquid going to a solid but two ____ (alpha/beta) (behaves similarly to a ____ at this temperature and composition)
alpha
beta
eutectic temperature
eutectic composition
solid phases
pure metal
Properties of alloys in eutectic systems
____ - Inhibition of slip
High ____ and ____
Poor ____ and ____
Clinical Applications
____ in Dental Amalgam-Ag-Cu Dental ____
Different phases, can have ____ between the two alloy compositions
Dental solder > making a long span bridge (5 unit) > cast off 5 units at once you may not get a good fit, so we make it in 2/3/single units and then join them together > cannot join together with same metal that you cast with, so you use a eutectic alloy (____ temperature than the bridge), you can get it to melt without melting the ____
brittle hardness strength tarnish corrosion resistance
dispersant
solders
corrosion
lower
parent metals
The Au-Cu System
Au-Cu system showing ordered (superlattice) regions
Right is melting temp of pure gold; left is pure copper
As composition changes; eutectic temperature ____ than either consitituent
Gold and copper are not perfect for each other > there’s some attraction, as you cool at certain temperature they show a ____ > at 50%/50%, if you cool below liquidus (380) > formation of a new phase > instead of cooling as solid solution > ____ phase (if comp is between 65-55 = ____ prime) > ____ structures, formation of a ____
Above liquidus line > liquid; then mixture of liquid and solid, and then all solid, until cooled down enough at specific temperatures > formation of a ____ (reactions)
____ (rapidly cooling and initially makes them softer) metal that just solidifed at 400 centigrade, throw into water and quickly cools, you freeze the solid solution state at that selected composition; the solid solution is relatively ____ and ____, you can heat in this position in order to form the ____ structures and making the metal even stronger (____ treatment treatment of an alloy)
lower
reaction
alpha prime
alpha double prime
ordered
super lattices
super lattice
quenching weak malleable ordered hardening
Equilibrium Diagram for Gold Copper Alloy System
____ substitutional solid solutions 880oC.
Ordering of compositions between ____ and ____%
gold below about 425oC.
Comparison of disordered and ordered AuCu structures
Relationships between ____ or ____ treatment and ____ of ordering
disordered
40
90
cooling schedule
heat
extent
Order-Disorder Reactions and Gold-Copper Alloy System
If the different atoms in a solid solution have an affinity for each other, an ____ of atoms results by diffusion of atoms in the ____ state.
ordered arrangement
solid
Ordered Structure Au-Cu system
- ____ arrangement of atoms in solid solution
- Ordered structure of ____
Left: solid solution where both occupy any space on lattice without ____
Right: you get ordering > gold at ____, and copper on ____ > AuCu3 (3 coppers for each gold)
____ region
random AuCu3 discrimination corners faces
alpha prime
