MATSE 259 EXAM 3 REVIEW SESSION

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MATSE 259 EXAM 3 REVIEW SESSION

• Exam Structure Multiple choice (same as
  previous exams) , hours , 25 questions
• Please write your student I.D. on the answer
  sheet (NOT SSN)
• Please mark your answers clearly
• Do not leave a question unanswered there is no
  negative marking
• Hand in both question and answer sheets at the
  end of the exam the questions will be posted on
  the website after the last conflict exam

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TOPICS

• CASE HARDENING
• JOMINY TEST (HARDENABILITY)
• CAST IRONS
• CORROSION
• POLYMERS

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CASE HARDENING

• Steel alloy is exposed to a carbonaceous (usually
  CO) or nitrogenous (usually NH3) atmosphere at
  elevated temperature so that the case becomes
  carbon or nitrogen rich.
• - In nitriding, Fe2N forms which is very hard.
  In carburizing, the alloy is then quenched and
  tempered to get a hard casing.
• In induction hardening, a high frequency AC is
  used to heat the alloy surface past its
  austenitizing temperature and the alloy is then
  quenched and tempered.

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JOMINY TEST

• hardenability ability to form martensite! (not
  hardness)
• specimen is fully austenitized
• max. cooling at the quench end, decreases with
  distance from quenched end.
• hardness is measured as a function of distance
  from quenched end.

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JOMINY TEST

• Cooling rate, severity of quench, is dependent
  on
• quenching medium
• Water --- most severe
• Oil
• Air --- least severe
• specimen size and geometry
• as surface area / mass increases, more rapid
  cooling rates
• are achieved
• (rounded shapes)

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JOMINY TEST
Hardness at the center of a 2 diameter bar
quenched in water with a little agitation for
1040, 3140 and 4340 steels?
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CAST IRONS

• Ferrous alloys with 2.5 lt wt C lt 5.5 and other
  alloying elements.
• For slow cooling rates,
  
• Fe-C (as opposed to Fe-Fe3C) phase diagram

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CAST IRONS

• Types
• Gray cast iron ? graphite flakes in an a or P
  matrix, depending on the cooling rate and Si
• - Weak and brittle in tension, stronger and
  more ductile under compression
• - Effective in damping vibrations
• - High fluidity at casting temperature, low
  casting shrinkage

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CAST IRONS

• Nodular (ductile) cast iron
• - flakes become spheres, with addition of
  small amounts of Mg and/or Ce before casting
• - Several times stronger than gray cast irons
• - High ductility EL up to 40
• White cast iron
• - almost all C is as CM in P matrix
• - Extremely hard wear resistant
• - Very brittle unmachinable
• Heating white cast irons to 850 ?C for 30 hrs
  gives Malleable Cast Irons
• - Graphite clusters in an a or P matrix
• - Mechanical properties Relatively high
  strength and malleability

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CAST IRONS
Gray cast iron
Nodular (ductile) cast iron
White cast iron
Malleable cast iron
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CORROSION

• Requirements
• Anode
• Cathode
• Electrolyte
• Electrical connection

• Anode oxidation ? CORROSION
• Cathode reduction

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CORROSION

• Classes of electro-chemical corrosion
• - Uniform attack - Galvanic
  corrosion
• - Crevice corrosion - Pitting
• - Intergranular corrosion - Selective
  leaching
• - Erosion-corrosion - Stress corrosion

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CORROSION

• MACRO
• Dissimilar metals
• - (Galvanic series) A galvanic series
  determines which metal will act as the anode
  the lower the metal in the series, the more
  anodic it is.
• Same metal in different electrolytes
• - Crevice / pitting corrosion
• Deformation
• - Non-homogeneous residual stress
• non-passivated vs. passivated metal couple

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CORROSION

• MICRO (single material)
• grain boundary anodic wrt bulk (high energy
  regions)
• orientation difference in grains
• presence of different phases
• segregation

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CORROSION

• WELDING

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CORROSION

• Remedies
• Environmental alteration
• Protective coating
• - anodizing (Al coating)
• - galvanizing (Zn coating)
• Material selection (i.e. passivated
  material usage)
• Design (i.e. keep the ratio anode area /
  cathode area large
• Cathodic protection
• -Electrically connect the metal to be
  protected to another metal (sacrificial anode)
  that is more reactive in the particular
  environment. Ex Zn, Mg.
• - Connect the negative terminal of an external
  DC source to the metal to be protected and the
  positive terminal to an inert anode like
  graphite.

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POLYMERS

• Polymers long chains of covalently bonded
  small, successively repeating units called
  monomers.
• Classification of polymers
• - Based on monomer/s homopolymer, copolymer,
  blend.
• 
  O O
• 
  
• -NH-(CH2)6-NH-C-(CH2)4-C-
• Polyethylene Nylon (6,6)
• Copolymers random, alternating, block, graft.
• A A B A B B B A A A
  A A B B B B B B B B A A
  A A A
• A B A B A B A B A A
  A A A A A A A A A A A A A
  A A A
• B B
• B B
• B B

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POLYMERS

• - Based on molecular structure linear polymer,
  branched polymer, crosslinked polymer, network
  polymer.
• CH3 CH3 CH3
• C CH2 CH CH2
  CH CH2
• CH3 CH
• CH2
• CH3 CH3 CH3
• C CH2 CH CH2 CH CH2
  Polyethylene
• C CH2 CH CH2 CH CH2
• CH3 CH3 CH3

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POLYMERS

• - Based on tacticity isotactic, syndiotactic,
  atactic.
• Polypropylene
• - Based on monomer geometry cis-polymer,
  trans-polymer.
• H CH3 H
• CH2 C C CH2 CH2 C C CH2
• CH3
• Polyisoprene
• - Based on properties thermoplasts, thermosets.

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POLYMERS

• The molecular weight of polymers is determined in
  two ways
• - Number-average molecular weight
• - Weight-average molecular weight
• Degree of polymerization