Metal Grains & Sizes & Properties Flashcards
1
Q
what are metals and alloys made up of, smply?
A
Grains
2
Q
What is important to know about each grain that makes up metals and alloys?
A
Each grain is a distinct crystal which has its own (random) orientation.
3
Q
How are grains formed?
A
By dendritic growth
4
Q
Where grains meet is called what?
A
A grain boundary
5
Q
Give an example of grain sizes?
A
Steels may have hundreds of grains per square millimetre, but you can see grains with the naked eye on zinc and aluminium.
6
Q
Are smaller grains strong?
A
yes, but they are less ductile.
7
Q
How does the size of a grain affect the metal’s properties?
A
Smaller grains are stronger and less ductile while larger grains are the opposite.
8
Q
Why are smaller grains stronger and less ductile? (3)
A
- This is because grain boundaries act as barriers to slip and fractures, because the crystal structures are not lined up.
- It takes more force to cause a slip or fracture to cross or change direction along a grain boundary.
- even if a slap or crack crosses or moves along a grain boundary, with many grains, it won’t be long before it meets another grain boundary barrier.
