Lecture 9- control of strength in metals

Question 1

What are the 5 ways to control the strength of metals?

Answer 1

grain size control
solid solution strengthening
phase balance control
precipetate strengthening
work hardening

Question 2

What is the relationship between grain size and strength?

Answer 2

the smaller the grain size, the stronger a material is

Question 3

How is grain size altered?

Answer 3

control during processing. eg casting, rolling, extrusion, heat treatment

Question 4

Why does reducing the grain size make a metal stronger?

Answer 4

smaller grain size means there are more grain boundaries in the metal, which makes it difficult for dislocations to move and deform the metal

Question 5

what is solid solution strengthening

Answer 5

replacing an atom in in an electron with another atom, eg replacing an aluminium atom with a magnesium atom in an aluminium structure

Question 6

how does solid solution strengthening increase strength of a material?

Answer 6

it strains the material, making it harder for dislocations to move

Question 7

what are the 2 types of solid solution strengthening ? explain them

Answer 7

substitutional: replacing atoms with other atoms

interstitual: adding atoms into vacancies

Question 8

What is a phase?

Answer 8

a portion of a material that has uniform properties and chemical characteristics

Question 9

how many phases are in a pure metal vs an alloy?

Answer 9

pure metals have one phase
alloys can have more than one phase

Question 10

how does controlling phases change strength?

Answer 10

different phases have different properties so by changing the phase balance, we can increase strength

Question 11

what is precipitate strengthening?

Answer 11

some elements do not mix into another atom by atom; instead, they go into groups of atoms, forming a precipitate.

siliar to solid solution strengthening but instead of one atom, its groups

Question 12

how does precipitate strengthening make metals stronger?

Answer 12

the large number of fine precipitates prevents dislocations from moving past them

Applying stress must push dislocation through precipitate, which are pinning the dislocation

Question 13

what is work hardening?

Answer 13

plastically deforming a material to make it stronger

Question 14

how does work hardening make metals stronger?

Answer 14

by deforming the material, we get more dislocations, increasing dilocation densities, This means theyre closer together so they bunch up, making it harder for them to move

Question 15

which type of metal work hardens more?

Answer 15

FCC, more than BCC and HCP

Question 16

What is the relationship between work hardening and ductility?

Answer 16

the more work hardening done, the more brittle a material becomes and less ductile