ME 250

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  1. Tie line
    • line constructed when calculating phase
    • compositions
  2. Eutectic Reaction
    involves one liquid and two solids
  3. Eutectoid Reaction
    involves a single phase and two phase solid
  4. Austenite
    (ϒ) FCC
  5. Ferrite
    (α) BCC
  6. Cementite
    (Fe3C) Metal carbide, ceramic
  7. Martensite
  8. Pearlite
    (α+Fe3C) lamellar structure
  9. Bainite
    (α+Fe3C) carbide plates
  10. Widmanstatten Ferrite
    • α needles with C buildup in
    • ϒ
  11. Spheroidization
    When left at elevated temperatures for extended amounts of time the lamellar pearlite begins to form globs, and as time continues, the particles will get larger
  12. Metallic Bonding
    sharing of valence electrons across the entire molecule
  13. Covalent Bonding
    sharing of valence electrons in a localized region
  14. Abrasive Wear
    Loss of material from a surface by the gouging-out of channels by hard particles lying etween the two surfaces being sheared past one another
  15. Adhesive Wear
    Closely related to the primary cause of friction; invloves the transfer of material from one surface to another when the surfaces are being sheared past one another while a force is being applied normal to the interface. It is caused by cold welding across the touching asperities on the respective surfaces. The normal force acts to flatten the asperities and to increase the contact area over which cold welding can occur.
  16. Boundary Lubrication
    This occurs when a solid or semi-solid material lies in an interface and reduces the resistance to shear between the interfaces.
  17. Hydrodynamic Lubrication
    Same as boundary lubrication but at high velocities that gives it a much lower coefficient of friction.
  18. Hardenibility
    The capacity of a steel to be transformed to martensite, instead of the diffusion-controlled transformed products, ferrite and cementite.
  19. Case Hardening
    The hardening of the outside surfaces of a steel component by introducing extra amounts of carbon and/or nitrogen by diffusion at an elevated temperature, either to cause high-carbon martensite to form upon quenching, or to form a fine dispersion of alloy nitrides, and thereby to make the surface harder and more resistant to wear.
  20. Carburization
    This is a surface hardening, or case hardening, treatment carried out by heating a steel in an atmosphere of H2/CH4 or CO/CO2, that deposits carbon on the surface. Inward diffusion of carbon raises the carbon content of the surface regions so that high-carbon martensite is formed when the steel is quenched.
  21. Annealing
    Heating a cold-worked metal to remove the effects of strain hardening. It comprises the processes of recovery, recrystallization, and grain growth.
  22. Tempering
    The heat treatment of steel that has been austenitized and quenched to form martensite. It involves heating in the ferrite + carbide region of the phase diagram (below the eutectoid temperature) to promote the decomposition of the metastable martensite. Done to improve toughness at the sacrifice of hardness.
  23. Toughness
    Measure of the resistance of a material to the propagation of a crack when stress is applied
  24. Hardness
    Usually means the resistance of a material to plastic deformation
  25. Precipitation hardening
    A mechanism of hardening that involves the formation of a finely dispersed array of very small particles of a second phase that act as a strong barrier to dislocation motion. The alloy is solution treated and quenched, then aged at a temperature in the two-phase region.
  26. Homogeneous nucleation
    The nucleation of a second phase in a supersaturated parent phase at random locations throughout the parent phase, without regard for the presence of any structural defects that could enhance the nucleation rate.
  27. Heterogeneous nucleation
    The nucleation of a second phase in a supersaturated parent phase not randomly, but on structural defects that act to lower the energy barrier for this nucleation, often by providing an existing interphace on which the new phase can form. Much less undercooling is required.
  28. Entropy
    The amount of disorder in a system.
  29. Enthalpy
    H, the sum of the internal energy, E, and the energy due to the pressure times the volume.
  30. Activation Energy
    the energy that must be supplied to a system in metastable equilibrium to allow it to pass to a state of lower energy.
  31. Ductility
    the ability of a material to deform plastically without fracturing
  32. Strength
    the maximum nominal stress a material can sustain.
  33. Octahedral site
    In a Bcc, the site that produces the minimum overall strain energy in the lattice.
  34. Fatigue
    failure due to a dynamic and fluctuating stress in a structure.
  35. Fatigue limit
    A value of stress below which a material will not fail due to fatigue and where, theoretically, a material can endure infinite cycles.
  36. Component
    participating elements
  37. Solvent
    Majority element
  38. Solute
    minority element
  39. Phase
    physically and chemically distinct region of material
  40. Solution
    solid solution, single phase (syrup)
  41. Mixtures
    more than one phase (syrup + sugar)
  42. Solubility Limit
    Max concentration for which only a single phase solution occurs
  43. Brazing
    A technique of joining two solid pieces by melting a filler metal and letting it flow into the crevice between the two pieces. Can occur at temperatures above 450 C.
  44. Soldering
    A technique of joining two solid pieces by melting a filler metal and letting it flow into the crevice between the two pieces. Can occur at temperatures below 450 C.
  45. Contact Angle
    The measure of a liquid on a solid surface to determine how well a liquid "wets" a surface. Depends on the energies of the interactions of the phases.
  46. Casting
    A process that involves the melting of a metal or alloy and pouring the molten metal into a mold in which it solidifies, taking the shape of the mold.
Card Set
ME 250
terms for exam 2 for ME 250
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