Processing Flashcards
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
- Low flow stress
- High UTS
- Low coefficient of friction
- Low Thermal conductivity
Why would you shot peen Austenitic SS?
To place the surface in compression to increase fatigue resistance (and SCC resistance)
How do you calculate Cold work %?
Use the equation in the reference manual
Name 3 advantages and 1 disadvantage of plasma nitriding?
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
Describe Pack cementation
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.
What temperature does recrystallization occur at?
1/3 to 1/2 of the absolute melting temperature
What sort of microstructure does friction stir welding produce?
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
Describe the basics of a shaker hearth furnace
Continuous trolley (conveyor belt style) that moves parts through furnace atmosphere and drops them into a quench bath at the other side
What is a muffle furnace?
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.
Describe pit furnace
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
What’s the difference between soldering and brazing?
Soldering takes place at a temperature below 840°F (450°C), and brazing occurs at a temperature above 840°F (450°C)
How would you increase the strength of a thermoplastic with regard to crystallinity?
What happens if you reduce the chain length?
Increase crystallinity = higher strength.
lower chain length = less crystallinity
What is Spinodal decomposition?
a mechanism by which a single thermodynamic phase spontaneously separates into two phases (without nucleation)
Define thermite reaction and name the two common base metals for it.
reaction in which a metal (usually aluminum or magnesium) is oxidized by an oxide of another metal
What is galvanization? What are the two types and which one is better?
Applying a layer of zinc to steel for corrosion resistance.
- Electro-galvanization - uses electricity to plate zinc onto steel, very thin coating, shiny (also known as zinc plating)
- Hot Dip Galvanization - dip steel part into molten zinc bath. 10x thicker coating, dusty grey appearance but much more durable
What is the approximate relationship for diffusion rate vs distance?
x = sqrt(2Dt)
x = diffusion distance
D = diffusion rate
t = time
Will salt water or tap water quench steel quicker?
Salt water
Quenching can enhance the fracture toughness of a material’s surface through which mechanism?
Pre-stressing
What is commonly used toughening mechanism for ceramics?
transformation toughening - where a crack that initiates creates a phase transformation which then inhibits crack growth
Define crazing and shear banding
a method to improve toughness of brittle polymer by arresting cracks as they form.
define crack bridging
addition of a fiber to a polymer composite to arrest crack growth and improve impact toughness
Define Normalizing, including what temperature based on phase diagram
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)
Define Annealing, including what temperature based on phase diagram
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)
What process is used for braze material to flow?
Capillary action
what manufacturing process is used to produce cemented carbides?
Liquid phase sintering (a form of powder metallurgy)
What is the cheapest and most common powder processing techniques for press and sinter applications?
water atomization
what is melt fracture (with regard to polymer extrusion)?
surface defect on extruded part that can be caused by too high of extrusion rate or lack of lubrication at die
Volume and Surface area of a sphere
vol: (4/3)* pi * r^3
SA: 4pir^2
How do you calculate average temperature of heat exchanger?
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)
Equation for generalized Hooke’s law
strain(x) = stress.x / E - (vstress.y / E) - (vstress.z / E)
OR strain(x) = stress.x/E - vstrain(y) - vstrain(z)
