alloys Flashcards

1
Q

what are alloys

A

a combination of two or more metals

or a metal with a metalloid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Benefits of alloys

A

improved properties
o EL
o FS
o UTS
o Hardness
o More resistant to corrosion
o Lower melting point than individual metal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

uses of alloys

A

steel
 burs and instruments

gold alloy
 inlays and crowns etc

cobalt chromium
 dentures

nickel titanium
 ortho wires

nickel chromium
 crowns and bridge

amalgam
 restoration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

phase definition

A

Physically distinct homogenous structure
Can have more than one component

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

solution definition

A

Homogenous mixture at an atomic scale

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

pure metal has how many phases

A

1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

an alloy with 2 insoluble metals has how many phases

A

2 phases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

solid solution has how many phases

A

1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

solid solution def

A

2 metals coexisting in a lattice network; both metals in a homogenous mixture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

3 categories of alloys

A
  1. 2 phases (insoluble)
  2. intermetallic compound (partially soluble)
  3. 1 phase (solid solution)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

solid solution has 3 types what r they

A
  1. substitutional random
  2. substitutional ordered
  3. interstitial
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

diff between cooling curve of metal and alloy?

A

pure metal Crystalises at one temperature

alloy Crystallizes over a range of temperatures (between TL and Ts)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

liquidus def

A

line representing the temperature which different alloy composition begin to crystallise

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

solidus def

A

line representing the temperature which different alloy composition have completely crystallised

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

do you want fast or slow cooling

A

fast

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

benefits and disadvantages of fast cool

A

small grains good but coring occurs, can overcome with annealing

16
Q

benefits and disadvantages of slow cool

A

homogenous good but large grains with poor properties

17
Q

what determines the extent of coring?

A

 the larger the difference between the liquidus and solidus line, means that there will be MORE CORING during rapid cooling

18
Q

when does coring occur

A

fast cooling, and a difference between the liquidus and solidus state

19
Q

why is coring bad

A

alloy becomes less resistant to corrosion

20
Q

Benefits of annealing after coring

A
  • makes the grains homogenous
  • allows atoms to diffuse and rearrange
21
Q

Benefits of small grains over large ones

A
  • impede dislocation movement
  • improve mechanical properties
22
Q

why is there less dislocation movement in alloys compared to metals

A
  • because solid solution has metals of different atomic size which means there is a distorted grain structure.
  • distorted grain structure impedes dislocation movement and improves mechanical properties such as (EL UTS FS hardness)

-> defects have to “climb” over each atom and settle in between the metal atoms. it requires a lot of energy to climb over the next atom in the lattice plane. hence it takes more force to move the defect to the grain boundary. greater stress to move any dislocations, harder to distort, more fracture resistant and stronger than metal

23
Q

what sort of alloy is Au-Cu

A

solid solution, completely soluble

24
Q

what sort of alloy is Au-Pt

A

solid solution

25
Q

what is eutectic alloy

A

an alloy with 2 metals that are completely insoluble so the metals exist in seprate grains

DO NOT FORM solid solution, that is for soluble metals

26
Q

what sort of alloy is Ag-Cu

A

partially soluble

27
Q

when does crystallisation occur for eutectic alloys

A

at a single temperature, where the liquidus line meets the solidus line, the grains of each metal form simultaneously

28
Q

function of eutectic alloys

A

soldering alloys tgt since it has the lowest melting point of all alloys

29
Q

properties of eutectic alloys

A

hard
brittle
poor corrosion resistance

30
Q

How do you improve the mechanical properties of a partially soluble alloy

A

precipitation hardening = pushes the metals to the grain boundaries to make the alloy stronger and harder

31
Q

what is the key point of partially soluble alloy graph with the solid solubility limits?

A

solid Solubility limit lines means alloys cannot form grains with the composition between H1 and H2 %

they can only form grains with composition below H1 or above H2

producing alpha or beta grains which are either silver rich or copper rich grains

32
Q
A