5. Alloys and Equilibrium Diagrams Flashcards Preview

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1

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

2

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

3

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

4

- 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

5

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

6

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

7

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

8

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

9

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

10

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

11

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

12

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

13

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

14

Interpretation of Constitution Diagrams

Phases present at ____
____ of phases present at any
temperature
____
____

temperature
composition
coring
homogenization

15

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

16

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

17

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

18

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

19

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

20

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

21

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

22

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

23

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

24

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

25

Ordered Structure Au-Cu system

Ordered Structure of AuCu ____ superlattice

Second ordered structure > AuCu (1:1); copper at ____ and two ____, and gold occupies four ____

Each corner contributes ____, and face atoms contribute a ____; so although there are fewer golds on the lattice, the ratio remains ____

____ region

face centered tetragonal

corners
faces
faces

1/8
1/2
1:1

alpha double prime

26

Solid State Reactions

____ and ____
Alloy formation
____ in the solid state
Grain Size reduction

Terminology
Heat treatment
____, Soften, alter ____, Corrosion Resistance

Quenching

Strain hardening > ____ a metal > hardening it (solid state reaction occurs as you deform metal)
Annealing > heat treat a metal in order to revert the strain harden back to the ____ state (solid state reaction) (____)

strain hardening
annealing
heat treatment

harden
grain size

deform
cast
heat treatment