Processing

Question 1

Describe how each of the following properties would be beneficial to forging process:
1. Flow stress
2. UTS
3. Coefficient of friction between die and metal
4. Thermal conductivity of Lubricant

Answer 1

1. Low flow stress
2. High UTS
3. Low coefficient of friction
4. Low Thermal conductivity

Question 2

Why would you shot peen Austenitic SS?

Answer 2

To place the surface in compression to increase fatigue resistance (and SCC resistance)

Question 3

How do you calculate Cold work %?

Answer 3

Use the equation in the reference manual

Question 4

Name 3 advantages and 1 disadvantage of plasma nitriding?

Answer 4

Adv: energy consumption, ability to mask off areas not requiring the nitriding, low distortion of components.

Dis: very difficult to harden the surface of deep, blind holes

Question 5

Describe Pack cementation

Answer 5

Components are packed with metal powders and heated. the pack coating metal reacts with a chemical activator on heating to form a gaseous compound (e.g., pure Al with NaF to form AlF). This gas is the transfer medium that carries aluminum to the component surface. The gas decomposes at the substrate surface depositing Al and releasing the halogen activator.

Question 6

What temperature does recrystallization occur at?

Answer 6

1/3 to 1/2 of the absolute melting temperature

Question 7

What sort of microstructure does friction stir welding produce?

Answer 7

thoroughly mixed microstructure of both parent materials, grains are roughly equiaxed and often an order of magnitude smaller than the grains in the parent material

Question 8

Describe the basics of a shaker hearth furnace

Answer 8

Continuous trolley (conveyor belt style) that moves parts through furnace atmosphere and drops them into a quench bath at the other side

Question 9

What is a muffle furnace?

Answer 9

A furnace, in which the heat source does not directly make contact with the material being heat-treated, is described as a muffle furnace. The components are charged in a muffle, and gas firing, or electrical energy can be used to heat the muffle from outside.

Question 10

Describe pit furnace

Answer 10

Furnace that is placed in the floor. Suitable for long parts that need to be kept vertical without distortion. Not feasible to quench parts in pit furnaces

Question 11

What’s the difference between soldering and brazing?

Answer 11

Soldering takes place at a temperature below 840°F (450°C), and brazing occurs at a temperature above 840°F (450°C)

Question 12

How would you increase the strength of a thermoplastic with regard to crystallinity?

What happens if you reduce the chain length?

Answer 12

Increase crystallinity = higher strength.

lower chain length = less crystallinity

Question 13

What is Spinodal decomposition?

Answer 13

a mechanism by which a single thermodynamic phase spontaneously separates into two phases (without nucleation)

Question 14

Define thermite reaction and name the two common base metals for it.

Answer 14

reaction in which a metal (usually aluminum or magnesium) is oxidized by an oxide of another metal

Question 15

What is galvanization? What are the two types and which one is better?

Answer 15

Applying a layer of zinc to steel for corrosion resistance.

1. Electro-galvanization - uses electricity to plate zinc onto steel, very thin coating, shiny (also known as zinc plating)
2. Hot Dip Galvanization - dip steel part into molten zinc bath. 10x thicker coating, dusty grey appearance but much more durable

Question 16

What is the approximate relationship for diffusion rate vs distance?

Answer 16

x = sqrt(2Dt)

x = diffusion distance
D = diffusion rate
t = time

Question 17

Will salt water or tap water quench steel quicker?

Answer 17

Salt water

Question 18

Quenching can enhance the fracture toughness of a material’s surface through which mechanism?

Answer 18

Pre-stressing

Question 19

What is commonly used toughening mechanism for ceramics?

Answer 19

transformation toughening - where a crack that initiates creates a phase transformation which then inhibits crack growth

Question 20

Define crazing and shear banding

Answer 20

a method to improve toughness of brittle polymer by arresting cracks as they form.

Question 21

define crack bridging

Answer 21

addition of a fiber to a polymer composite to arrest crack growth and improve impact toughness

Question 22

Define Normalizing, including what temperature based on phase diagram

Answer 22

Heating above recrystallization temperature to improve ductility and then air cooling (faster cooling than anneal, creates higher hardness)

Normalize - 50C above the phase boundary between austenite and 2 phase region. (higher temp than Anneal)

Question 23

Define Annealing, including what temperature based on phase diagram

Answer 23

Heating above recrystallization temperature to improve ductility and then slow cooling (controlled cooling rate in furnace)

Full Anneal - 50C above the eutectoid temp (lower than normalizing temp)

Question 24

What process is used for braze material to flow?

Answer 24

Capillary action

Question 25

what manufacturing process is used to produce cemented carbides?

Answer 25

Liquid phase sintering (a form of powder metallurgy)

Question 26

What is the cheapest and most common powder processing techniques for press and sinter applications?

Answer 26

water atomization

Question 27

what is melt fracture (with regard to polymer extrusion)?

Answer 27

surface defect on extruded part that can be caused by too high of extrusion rate or lack of lubrication at die

Question 28

Volume and Surface area of a sphere

Answer 28

vol: (4/3)* pi * r^3
SA: 4pir^2

Question 29

How do you calculate average temperature of heat exchanger?

Answer 29

Log Mean Temperature Difference

LMTD = (deltaTa - deltaTb) / ln(deltaTa / deltaTb)

A and B are each end of the heat exchanger (counter or parallel flow doesn’t matter)

Question 30

Equation for generalized Hooke’s law

Answer 30

strain(x) = stress.x / E - (vstress.y / E) - (vstress.z / E)

OR strain(x) = stress.x/E - vstrain(y) - vstrain(z)