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C9
Alloys
83
Science
Undergraduate 3
05/31/2011

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Cards

Term
what is the order of products based on cooling rate starting with austenite
Definition
austenite, ferrite, pearlite, widmanstaaten, bainite, martensite
Term
what qualifies as a grey cast iron
Definition
high carbon/silicon percentage
upon slow cooling will achieve graphite flakes, eutectoid, then C is rejected to form proeutectoid and finally peralite grows
Term
what are the properties of grey cast irons and an application
Definition
there is volume expansion so they are good for casting
brittle due to interconnected flakes
used as car cylinder heads
Term
what qualifies as a spheroidal cast iron
Definition
a type of grey cast iron
Mg or Ce is added which stops growth of graphite flaks so that spheres are made instead increasing toughness
Term
what are the properties of spheroidal cast irons and an application
Definition
increased fracture toughness
manhole covers
Term
what qualifies as a white cast iron
Definition
low C/Si content
Upon fast cool, cementite growths, once carbon is rejected more cementite grows and finally peralite is produced
Term
what are the properties of white cast irons and an application
Definition
they are hard and wear resistant
rolls for crushing mills
Term
what are some steel alpha/ferrite stabilizers
Definition
Cr
Si
Term
what are some steel gamma, austenite stabilizers
Definition
C
Ni
Mn
Term
what makes magnesium ideal
Definition
lightest engineering material*, forms a protective oxide, tough, conductive (thermally and electrically), high coefficient of thermal expansion, machinable*, hcp lattice parameters make it compatible with many other elements
Term
what are some applications of Mg based alloys
Definition
cast is more popular than wrought (because it tends to have a low proof stress)
automobiles (strength/weight ratio)
sacrifical anode for bridges/ships
Term
disadvantages of Mg alloys
Definition
highly susceptible to impurities
stress corrosion cracking/H-embrittling (Zr alloys are less prone)
its oxide speeds up
wrought must be heavily processed (hot worked with alternite tension and compression to form twins)
casting exhibits much porosity though cools faster and has less wear
instability at low pH
Term
Nomenclature for Mg Alloys
Definition
alloying elements are identified by single letters
tempering modelled the same as Al
Term
Zr free Mg Alloys
Definition
subject to stress corrosion cracking
Term
What is the importance of adding Zr to Mg
Definition
most effective grain refiner therefore increases tensile properties however* not compatible with Si, Al, Mn, Fe therefore bad in steel crucibles
Term
Rare Earths in Mg Alloys
Definition
greatly improve properties but are very expensive, increase castability, decrease porosity, increase tensile creep, increase corrosion, these are also solid-solution/precipitation hardeners
Term
Al in Mg Alloys
Definition
improves catability, leads to microporosity, is a precipitation and solid-solution hardener
Term
Mn in Mg Alloys
Definition
increases creep resistance, controls Fe presence by forming new compounds, increases corrosion effects due to iron
Term
small* amounts of Zn in Mg alloys
Definition
increases metal flow and hence castability
Term
Si in Mg Alloys
Definition
formation of Mg2Si at grain boundaries greatly hurts the overall properties of the material
Term
What is the Young's Modulus of steel
Definition
210Gpa
Term
What is the Young's modulus of Aluminium
Definition
70GPa
Term
why are titanium alloys ideal
Definition
chemically and thermally stable (high Tm, low coefficient of thermal expansion)
able to make many stable solid solutions
low density
Term
applications of titanium alloys
Definition
aerospace
biomaterials
Term
what is the most desired titanium alloy
Definition
6-4
Ti-6% Al-4% V
Term
What is the stipulation on e/a ratios for Ti alpha and beta stabilizers
Definition
alpha: e/a<4
beat: otherwise
Term
Features of Ti alpha alloys and some of the stabilizers
Definition
Stabilizers: Al, O, N, C (tend to be interstitial)
low T, hcp, strong, anisotropic
Term
Features of beta isormorphous Ti alloys and some stabilizers
Definition
high T, bcc, easy to form, heat treatable
Stabilizers: V, Nb, Mo, Si
Term
Al in Ti Alloys
Definition
increases ductility
Term
Si in Ti alloys
Definition
reduces creep
Term
Ti beta eutectic stabilizers
Definition
Fe, Mn, Cr
Term
Ti neutral stabilizers
Definition
generally these have good hardenability
Sn, Zr
Term
Properties of fully alpha Ti alloys
Definition
resistant to plastic flow
low ductility/brittle/tough
high creep/corrosion resistance
low diffusion rates
subject to stress corrosion cracking (H)
tends to have equiaxed grains
Term
properties of near alpha Ti alloys
Definition
higher operating tempeartures
higher creep resistance
some beta grains
may be bimodal or lamellar structure
Term
properties of fully beta Ti alloys and an application
Definition
it may contain an omega phase which embrittles the material overall
allows for cold deformability
used for landing gear
Term
properties of alpha + beta ti alloys and an application
Definition
hard to break (basket weave structure)
increased temperature stability
shows superplasticity

tanks for missles
airplane rotors
Term
what controls microstructure in Ti alloys
Definition
alloy class/type
temperature/time
amount of deformation
cooling rate
Term
grain size in Ti alloys is controlled by...
Definition
recrystallization temperature
recrystallization time
annealing
deformation
Term
What are some high temperature alloys
Definition
Ni, Co, v, cr, Nb, M, Ta, W, Graphite
Term
What are properties of high temperature alloys
Definition
high Tm
reasonable strength at T of service
ability to be formed/manufactured
sufficient ductility at room Temrpature
resistance to oxidation (inherent or with coatings)
Term
Nickel superalloys
Definition
ideal because of their high Tm and FCC-stable structure
Applications: turbine blades
Major solutes: Al, Ti
Term
Phases of Ni superalloys
Definition
gamma - FCC
gamma' - cubic P with the solute at corners
the gamma/gamma' interfacial energy is low therefore the system is stable
Term
What is the significance of recrystallization
Definition
T-controls ggrain size and fraction of species
leads to equiaxed grains
determines amount and size of species
cooling rate determines lamellae size
Term
What is the importance of quench rate
Definition
supersaturates system with vacancies which shorten/annihilate dislocations
decrease in QR increases ductility
high QR leads to increased strength and lamellar structure
Term
effects of deformation on alloys
Definition
if rolled too much, recrystallization will not happen
rolling and solidfication lead to banding
deformation leads to texture
Term
conditions for superplasticity
Definition
dislocations originate and annihilate at the same rate
Term
secondary hardening
Definition
formation of stable carbides (Cr, Mo, W, Nb, V) increases wear resistance
applications: cutting tools, creep resistance
Term
normalizing
Definition
heat to gamma, air cool for coarse structure
Term
annealing
Definition
heat to gamma, slow cool for cloarse pearlite leading to good machinability
Term
age hardening
Definition
solution treat at high termpatures, quench, age to make a dispersion of precipiates in a matrix
Term
superalloy
Definition

 one that can be used at very high temperatures >0.7Tm

creep and oxidation resistance are desired

Term
hardening mechanisms
Definition

precipitates (fine and uniform) to prevent dislocation mobility

if there are 2+ phases 1 should be fine to increase strength and 1 platelike to resist strain

 

Term
homogenization
Definition
reduces partitioning, removes eutectic, and controlls the precipiation of the elements
Term
importance of light metals
Definition

a.     High tensile strength, high modulus, high compressive yield strength, low density
b.     Recyclable and long years of supply (though there tends to be expensive intial production and often alloying elements can not be removed)
c.     Corrosoin resistance, electrical/thermal conductivity, machinability
d.     Al, Mg and Ti are all in abundance (ocean, crust, etc.)
e.     Growth mainly a result of transportation and aerospace industries

 

Term
What are TTT diagrams used for
Definition
to illustrate the kinetics of phase formation
Term
Why do alloying elements change the properties of materials
Definition

different T at which phases first nucleate

the rates of nucleation and growth change due to relative diffusion coefficients

relative stabilities of phases present are different

Term

Upper bainite v. Lower bainite

features and applications

Definition
Upper:
Term
what is tempering and how does it effect the properties of materials
Definition

heating the material of interest to a temperature just below the eutectic temperature

allows for control of yield strength, ductility, and toughness (makes a material more usable)

Term

martensite properties

effects of adding carbon

Definition

tends to be hard and brittle because of the high internal strain energy

with increased carbon content, these values continue to increase because there is an increase in the c/a ratio

fine twins

Term
stainless steel
Definition
steel with the additon of Cr to increase corrosion resistance
Term
steel ferrite stabilizers
Definition
Cr and Si allow ferrite to exist at higher temperatures
Term
Steel austenite stabilizers
Definition
C, Ni, Mn
Term
Steel alloying elements that promote secondary hardening
Definition

Cr, Mo, W, Nb, V

these form stable carbides in the steel

Term
features of Al alloys
Definition

strength is based on precipitates

toughness is based on constituents

few alloying elements have significant solid solubility

cooling rate and grain refiners are very important

Term
microalloying
Definition

the addition of VERY small amounts of an alloying element that still manage to drastically change properties

 

Term
Si in Al alloys
Definition
leads to low density and reduces porosity
Term
importance of precipitate size in increasing strength
Definition

if they are too fine dislocations can 'cut' them (underaged)

if they are too coarse, dislocations can 'bow' around them (overaged)

Term
Al- Li alloys
Definition

low density

high specific modulus

weldable

good fatigue and cryogenic toughness properties

Term
Al 1XXX 2XXX 6XXX alloys
Definition

1xxx-pure Al

2xxx-Al-Cu

6xxx-Mg, Si

Term
hall-petch equation
Definition

relates grain size to yield strength

 

σy0+kd-1/2

Term

why is pearlite lamellar

significance of the interfaces

Definition
  • partitioning is ideal but there is a competition between the number of interfaces and the distance carbon has to travel to reach cementite phases
  • the interfaces control toughness
Term
Mn in steel
Definition
increases hardness
Term
Ni in steel
Definition
effects the ductile/brittle transition
Term
Cr in steels
Definition
increases corrosion resistance
Term
Mo in Steel
Definition
aids with hardening
Term
properties of ferrite steel
Definition
formable
Term
properties of austenite steels
Definition
strong
Term
why is the TTT diagram C shaped
Definition

high T, hard to nucleate

low T, hard to diffusive

Term
what methods can be used to measure transformations
Definition
microstructural evolution, volume change, XRD
Term
what is the effect of adding alloying elements to TTT diagrams
Definition
tends to shift TTT curves right because it takes longer for these atoms to diffusive
Term
why is pure aluminium not ideal
Definition

low yield strength requires solid solution hardening

Mg is the most effective strengthener on a weight basis

Term
what are inclusions
Definition

intermetallic and stable (sulifdides, phosphates, etc.)

hard to get rid of and responsible for onset of cracks due to microstructural changes

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