Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

BDS2 Dental Materials Sciences > metals and alloys 2 > Flashcards

metals and alloys 2 Flashcards

(56 cards)

Start Studying
1
Q

alloy

A

a combination or mixture of 2 or more metals, or metals with a metalloid (Si, C)

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

3 advantages of alloys

A

Mechanical (EL, UTS, hardness) than metals

Corrosion resistance (potentially)

lower melting point than individual metal

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

4 dental examples of alloy uses

A

STEEL - burs, instruments

AMALGAM - filling material

GOLD ALLOY - inlays, crowns, bridges, partial dentures, wires

NICKEL CHROMIUM - crowns, bridges, wires
etc……

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

phase

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

A

Homogenous mixture at an atomic scale

Lattice arrangement of 2 or more metals
- Metals coexist in lattice structure called a solution

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

how many phases are there in a metal formed of one metal atom only

A

1 phase

1 atom homogenous

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

how many phases are there in a metal made of individual grains of 2 phases situated in a lattice network

A

2 phases

don’t exist in same grain - so 2 phases

number of individual grains of different metals

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

how many phases are there in a metal made of 2 metals in a homogenous mix

A

1 phase

2 metal atoms coexisting in same lattice structure on atomic scale

  • Homogenous
  • Single phase

Solid solution

  • Several grains of 2 different metal atoms
  • Grains of varying shape and size
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is the physical property of metals when molten

A

soluble usually

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

what are the 3 types of solid solution that can occur on crystallisation of molten alloy

A

insoluble (no common lattice; 2 phases)

form inter-metallic compound with specific chemical formulation

be soluble and form a solid solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

properties of solid solution

A

form a common lattice, co-exist in solid-solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

when an alloy is in a molten state

A

all metal components are soluble in one another

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

what is substitutional solid solution

A

atoms of one metal replace the other metal in the crystal lattice/grain.

RANDOM:- metal atoms similar in:- SIZE, VALENCY, CRYSTAL STRUCTURE (e.g. fcc)
eg AuAg, AuCu

ORDERED:- metal atoms in regular lattice arrangement, conditions as above
Regular fashioned arrangement, form ordered solid solution

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

what is random substitutional solid solution

A

atoms of one metal replace the other metal in the crystal lattice/grain.

metal atoms similar in:- SIZE, VALENCY, CRYSTAL STRUCTURE (e.g. fcc)
eg AuAg, AuCu

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

what is ordered substitutional solid solution

A

atoms of one metal replace the other metal in the crystal lattice/grain.

metal atoms in regular lattice arrangement, conditions as above
- Regular fashioned arrangement, form ordered solid solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what are the 2 types of substitutional solid solution

A

random

ordered

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is interstitial solid solution

A

atoms markedly different in size

smaller atoms located in spaces in lattice/grain structure of larger atom (cannot predict where smaller atoms are)
e.g Fe-C stainless steel BDS3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what can vary between the cooling curves of different compositions of alloys

A

Each composition have to measure the cooling curve

- TL and TS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

cooling curve of metal

A

crystallises at one temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

cooling curve of alloy

A

crystallises over TEMPERATURE RANGE

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

state of soluble solid solution

A

solid solution formed (homogeneous mixture of metals in each grain)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

state of insoluble solid solution

A

grains of individual metals formed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

phase diagram

Study These Flashcards
A

Can plot on phase diagram the varying Tl and Ts

Temperature Vs alloy composition

Top curve TL values is liquidous

Lower curve TS values is solidus

24
Q

top curve on phase diagram is

25
lower curve on phase diagram is
solidus
26
what state is the alloy if the temperature is above the lilquidous line
the 2 metals will be molten
27
what happens to the alloy as its cooled to the liquidous line
Some will crystallise to grains | Part liquid part solid
28
what happens to the alloy as its cooled to the solidus line
All solid Crystallisation is complete - completely solid
29
LIQUIDUS
line representing the temperatures which different alloy compositions begin to crystallise
30
SOLIDUS
line representing the temperatures which different alloy compositions have completely crystallised
31
slow cooling of alloy
allows metal atoms to diffuse through lattice ENSURES grain composition is homogeneous BUT this results in LARGE GRAINS - Undesirable Do not want to cool slowly
32
what does rapid cooling of alloy create
coring only way to determine structure/compositions of grains of final grain is from drawing tie lines to solidus
33
rapid cooling cooling of alloy make grains of
Different concentrations/ compositions of grains Not homogenous (cored structure) - Different % within each grain - more likely to corrode - Not desirable
34
rapid cooling of molten alloy leads to
prevents atoms diffusing through lattice causes CORING as composition varies throughout grain. NOTE: initial grain composition IS NOT the same as the molten alloy.
35
what are conditions needed for coring
fast cooling of liquid state; Liquidus and Solidus must be separated (far apart on Phase Diagram) and determines extent of coring - eg Au-Pt - if close together then not a large amount of coring
36
what is the main disadvantage of coring/rapid alloy cooling
reduce corrosion resistance
37
fast cooling of alloy advantages and disadvantage
generates MANY SMALL grains which impede dislocation movement, improving its MECHANICAL PROPERTIES BUT causes coring, which is undesirable
38
what is homogenising anneal
once solid cored alloy formed REHEAT to allow atoms to diffuse and so cause grain composition to become homogeneous - get rid of cored structure NOTE: keep below recrystallisation temperature, otherwise grains altered - Allows grains to move around and eliminate cored structure
39
why must the temperature be kept below recrystallisation temperature for homogenising annealing
higher will alter grains structure | - Allows grains to move around and eliminate cored structure
40
how are defects eliminate in metal lattices
Metal lattice is perfect with planes as all atoms the same size - defect slides along the lattice plane when a force applied - Until reach grain boundary Defect “rolls” over the atoms in the lattice plane. - Little energy/force is needed for defect to move along slip plane
41
solid solution atoms sizes
Alloys forming a SOLID SOLUTION and consisting of metals of different atomic size have a distorted grain structure Not perfect as metal lattice - Big, small, big, small
42
benefit of solid solution impeding dislocation movement
improves mechanical properties (EL, UTS, hardness, more fracture resistant) more likely to prevent defects from moving in the structure
43
how does solid solution impede dislocation movement
Defect does not “roll” over the lattice plane. Instead it falls into the larger space existing between large & small atom. More energy/force is needed for the defect to overcome the different-sized atoms, and move along lattice to the grain boundary. - requires greater stress to move dislocations in a solid solution - making alloys inherently more fracture resistant (i.e. stronger) than metals.
44
what is benefit of order hardening
Alloys forming an ORDERED SOLID SOLUTION (atoms distributed at specific lattice sites) have a distorted grain structure (eg Au-Cu) which IMPEDES resits dislocation movement and so improves mechanical properties (EL, UTS, hardness) benefited by improved mechanical properties due to fact atoms are in ordered fashion
45
ordered solid solution
atoms distributed at specific lattice sites have a distorted grain structure (eg Au-Cu) which IMPEDES resits dislocation movement and so improves mechanical properties (EL, UTS, hardness)
46
eutectic alloys properties
metals are soluble in liquid state metals INSOLUBLE in solid state (so 2 PHASES) not soluble in each other - i.e. each metal forms physically distinct grains - CONTRAST this with Au-Pt alloy not used much in dentistry
47
what is the unique quality of the melting point of binary eutectic alloys
Less than point A (mp of A) and point E (mp of B) Less than individual metals
48
eutectic alloy compositor
where Liquidus and Solidus coincide (i.e. where crystallisation process occurs at a single temperature) where grains of individual metals formed simultaneously lowest melting point - at eutectic composition: used for solder dental technicians hard but brittle relatively easy to fracture poor corrosion resistance
49
physical properties of eutectic alloys
lowest melting point - at eutectic composition: used for solder dental technicians hard but brittle relatively easy to fracture poor corrosion resistance
50
non-eutectic alloy compositon
excess metal crystallises first then liquid reaches eutectic composition and BOTH metals crystallise (forming separate grains)
51
solid solution forming alloy
alloy of 2 metals coexist in same lattic structure
52
eutectic alloy
2 metals exist in separate grain
53
solubility limit line
indicates that a range of compositions of Ag and Cu (corresponding to the horizontal section of the solidus (H1 to H2) ) ARE NOT POSSIBLE - cool down rapidly get grains of both no matter starting composition Hence molten alloy of composition Z - DOES NOT cool rapidly to produce a 50:50 grain comprising Ag and Cu; - instead grains of alpha and beta are formed only extremes exists
54
what happens to partially soluble alloys on annealing
in partially soluble alloys on annealing, a supersaturated alloy will undergo PRECIPITATION HARDENING One of the atoms (silver or cooper) pushed to grain boundary and makes the alloy stronger and harder - Enhances the mechanical properties
55
precipitation hardening
annealing partially soluble alloys One of the atoms (silver or cooper) pushed to grain boundary and makes the alloy stronger and harder Enhances the mechanical properties ``` e.g. Type IV gold Has Ag and Cu present Benefit when anneal the alloy - Cool to room temp - Get rid of grain structure ```
56
positive and negative of alloys
Have better mechanical properties than metals (e.g. fracture strength, rigidity, elastic limit surface hardness) due to : - solution, order & precipitation hardening But Cored structure must be removed by annealing

BDS2 Dental Materials Sciences (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions