week 4

Question 1

how are atoms gathered in a solid

Answer 1

atoms are gathered together as an aggregate (collection of atoms)

Question 2

what 2 things can a ‘melt’ turn into when its temperature is lowered to a certain point

Answer 2

turn into a solid. it can become ethier a amorphous or a crystalline

Question 3

what is an amorphous

Answer 3

the solid structure’s atoms and molecules are not organized in a defined lattice pattern

Question 4

what is chain order

Answer 4

this is the order and arrangements of an atom over a long or short distance. (long-chain order/short-chain order)

Question 5

what is an isotropic

Answer 5

this is when the atoms in a structure have similar properties in all directions

Question 6

what is a crystalline lattice

Answer 6

this is when a structure has atoms which are in a regular, repeated pattern

Question 7

what is a Crystalline strcutre

Answer 7

when the atoms are arranged in small groups called unit cell in 3D

Question 8

How many different types crystal structures are there and what are they also known as

Answer 8

14 different types and they are known as Bravis lattices

Question 9

what is the simplest crystalline cell and its atom strucutre

Answer 9

this is the cube, with an atom at each corner

Question 10

are cubic crystals rare or not and why

Answer 10

yes because they are not as closely packed as possbile

Question 11

what does BCC stand for and how is it structured

Answer 11

(Body-Centered-Cubic) this is a cubic unit cell with an extra atom at the centre of the cube

Question 12

what does FCC stand for and how is it structured

Answer 12

(Face-Centered-Cubic) this is a cubic unit cell with an extra atom at the centre of each face of the cube

Question 13

what does HCP stand for and how is it structured

Answer 13

(Hexagonal Close Packed) One atom at each corner of a hexagon, one atom at the centre of each top and bottom face, and 3 atoms in the middle layer

Question 14

what does APF stand for and what is it

Answer 14

atomic packing factor, the fraction of the volume of the cell actually occupied by the hard spheres

Question 15

what is the APF formlua

Answer 15

volume of atoms in unit cell / total unit cell volume

Question 16

what type of movement does close-packed lattice allow and what property does it improve

Answer 16

it allows slip of atoms, improving ductility

Question 17

how packed is a BCC structure and what strength of metal does it form

Answer 17

not closely packed and forms strong metals

Question 18

how strong are FCC structures

Answer 18

they are very ductile and strong

Question 19

how packed are HCP structures and are they more ductile than FCC structures or not

Answer 19

they are closely packed, however not as ductile as FFC structure

Question 20

how many different crystal structures are there

Answer 20

14 different types

Question 21

what is a solid also referred as?

Answer 21

a grain

Question 22

what are the gaps in between the crystals called?

Answer 22

grain boundaries

Question 23

are the crystals perfect?

Answer 23

no all crystals have defects

Question 24

can defects contribute to the mechanical properties of the metal?

Answer 24

yes it can

Question 25

what are the 3 classes of crystal defects

Answer 25

point, linear and planar

Question 26

what is a point defect

Answer 26

this is when an atom is missing or irregularly placed

Question 27

what is a linear defect and what can it also be called

Answer 27

a plane of atoms in an irregular position is a line defect called dislocation

Question 28

what is a planar defect

Answer 28

this is the interfaces between homogeneous regions of the material, the crystal grain boundaries is an example of this

Question 29

what is a lattice vacancies (point defect)

Answer 29

when an atom is missing from the atom patten structure

Question 30

what is a self-interstitial atom (point defect)

Answer 30

when the atom pattern structure has an extra atom

Question 31

what is a substitutional impunity (point defect)

Answer 31

the atom is a different type to others around it

Question 32

what is an interstitial impurity (point defect)

Answer 32

very small atoms found in between the atom pattern structure

Question 33

what is the cause plastic deformation (in terms of atom strucutre)

Answer 33

this is caused by the movement of dislocations

Question 34

how can we move dislocations and strength a crystalline material (3 things)

Answer 34

controlling the grain szie
strain hardening
alloying

Question 35

how can we control the grain size

Answer 35

by heating the material up then by the rate of cooling the material to reform the crystals

Question 36

do bigger or smaller grains make the material stronger

Answer 36

smaller grains make the material stronger

Question 37

what size grains form from rapid solidification

Answer 37

smaller grains

Question 38

what size grains form from slow solidification

Answer 38

larger grains

Question 39

what is work hardening

Answer 39

this is the process of making a metal harder and stronger through plastic deformation

Question 40

what will happen to the material when the loaded stress level is greater than yield stress

Answer 40

it will deform plastically

Question 41

what will hapen to the material if it is loaded then unloaded many times

Answer 41

the material becomes harder

Question 42

what is cold working

Answer 42

this is work/strain hardening at low tempertures

Question 43

what is the benefit of work hardening

Answer 43

because it is at a low temp it will prevent the rearrangement of atoms

Question 44

is there a limit to how much work hardening can be done to a material

Answer 44

yes, a material will get harder however also more brittle and the more its done the more the material losses its functionality