matse 259 exam 3 review session 1. exam structure: multiple choice (same as previous exams), hours,...
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MATSE 259 EXAM 3 REVIEW SESSION
1. Exam Structure: Multiple choice (same as previous exams) , hours , 25 questions
2. Please write your student I.D. on the answer sheet (NOT SSN)
3. Please mark your answers clearly
4. Do not leave a question unanswered – there is no negative marking
5. 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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TOPICSCASE 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 TESTCooling 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 TESTHardness 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 < % wt C < 5.5 and
other alloying elements. For slow cooling rates,
Fe-C (as opposed to Fe-Fe3C) phase diagram:
1153
740 + GRAPHITE
+ GRAPHITE
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CAST IRONS
Types:» Gray cast iron graphite flakes in an
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 or P matrix - Mechanical properties: Relatively high strength and malleability
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CAST IRONSGray 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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CORROSIONMACRO~ 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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CORROSIONMICRO (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
CH2 CH2
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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
CH CH2
CH3
CH CH2
CH3
CH CH2
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.
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
CH CH2
CH3
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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: