Chapter 2, Lesson 1

Question 1

Compare the bond in molten state and solid state

Answer 1

Molten State: bonds are weak and not arranged in fixed patterns

Solid state: The atoms will be compacted and arranged in regular shape

Question 2

Crystalline Structure/ Lattice Structure

Answer 2

• The atoms are arranged in regular and geometric patterns
• The structure refers to how the atoms are arranged orderly and regularly

Question 3

What are the 3 types of crystal structure of metals?

Answer 3

1. Body-Centred Cubic
2. Face- Centred Cubic
3. Hexagonal Close- packed

Question 4

Describe the structure of the Body-Centred Cubic and the materials that exist in that structure

Answer 4

• Every corner of the Cubic have 1 molecule, with an additional 1 in the middle

• Materials are Chromium, Alpha iron, Tungsten

Question 5

Describe the structure of Face-Centred Cubic and the materials exist in that structure

Answer 5

• All corner occupies one molecules, with additional molecules at EVERY FACE’S centre

•materials are: Aluminium, Copper, Nickel, Gold, Sliver

Question 6

Describe the structure of hexagonal Close- packed and the materials exist in that structure

Answer 6

• one at each corner of the hexagon, additionally with one line drawn straight down (with 1 each on the ends), and an addition triangle in the middle

•Materials are: Magnesium, Zinc, Titanium at low temperature only

Question 7

In a solidification cooling curve what happens?

Answer 7

1. Small nuclei act as centers of crystal growth
2. From nuclei small dendrites are form
3. dendrites will continue to grow until the spaces between is filled in
4. Upon solidification, little evidence of the dendrite structure remains

Question 8

Describe the relationship between the structures and properties

Answer 8

Structures will affect property of the material while property will affect the performance of the material

Question 9

What does cooling rates affect?

Answer 9

Cooling rates affects the formation of crystal grains, then affecting the size and property directly

Question 10

How does a typical solidification process happen?

Answer 10

1. Chill crystals will form on the outmost layers first. They cool down rapidly upon contact with a cold mold wall which also means an increase in nucleation rate and formation of small crystals
2. Columnar grains form in the middle layer , as the temperature tends to decrease which is why the crystals are larger in size, forming in the direction of the heat flow
3. Large equiaxed grains form on the innermost layer as cooling rates is the slowest here, grains will have roughly equal dimensions

Question 11

How does the grain structure affect the property of the material?

Answer 11

Fine grain means better strength, toughness with reasonable ductility

Question 12

What are the effects of cold working?

Answer 12

The plastic deformation of metals will happen below it’s recrystallization temperature

Question 13

Describe the process where structure of grain changes from equiaxed

Answer 13

Initially the grains are equiaxed, after pulling it the grains are distorted and elongated.

The Elongation will increase the chance of deformation to happen

This process causes the material to turn from ductile to brittle and increases the hardness too