EA = −Ar,EB =
Brn,EN = −
Ar+Brn, r0 = (
AnB)1/(1−n)
%IC = (1− exp(−0.25)(XA − XB )2 )*100,
ρ =nAVcNA
,ρmetal > ρceramics >polymers
u = 13(2u' − v' ),v = 1
3(2v' −u' ), t = −(u+ v),w = w'
i = −(h+ k)
0D:Vaccumcis,Intrstituals,Impritice 3D:Pore or crack
1D:Screw or edge dislocation 2D:Grain boundaries
NV = N exp−QV
kTD = D0 exp(−
Qd
RT) ∂C∂t
= D ∂2C∂x2
σ =FA0
= Eε,ε = Δll0,%EL = (
l f − l0l0
)*100,Toughness :σ T = KεnT
%RA = (A0 − Af
A0)*100,Re silience :Ur =
12σ yεy (y→ yield)
Grain_ size_ reduction :σ yield =σ 0 + kyd−1/2
Solid _ Solution :σ y ~ C1/2 (C = concentration)
%CW =πr20 −πr
2d
πr20*100
)%2.91()%8()%9.71(:,:
:)%2.91()%8()%9.71(:
),()()(C:_
,)exp(:
_,_,_,)(1,
__,__,__mod:,]2[:
3
02
2max
max
2/1
AgwtAgwtAgwtLEgLPeritectic
CFeEutectoidAgwtAgwtAgwtLEg
CCLreactionEutectictll
tRTQ
KsCreep
SamplitudestressrangestressstressmeanYK
aaYK
crackoflengthaenergysurfacespecificelasticityofulusEaE
Crack
EEE
s
Cn
armdesign
CCdesign
ss
C
βα
γδ
αγ
βα
βα
εσ
σσσσππ
σ
γπγ
σ
βα
ε
+⎯→←
⎯→←+
+⎯→←
+⎯→←
+⎯→←
Δ
Δ
=Δ
Δ=−=
====<<
===
•
BCC FCC
2 4
a=4R/(√3) a=2R√2
0.68 0.74
8 12
Cubic a=b=c α=β=ϒ=90°
Hexagonal a=b≠c α=β=90°, ϒ=120°
Tetragonal a=b≠c α=β=ϒ=90°
Trigonal a=b=c α=β=ϒ≠90°
Orthorhombic a≠b≠c α=β=ϒ=90°
Monoclinic a≠b≠c α=ϒ=90°≠β
Triclinc a≠b≠c α≠β≠ϒ≠90°
Eutectic:Liquid-‐>two solid phases Eutectoid:One solid phase-‐>two other solid phase Peritectic:Liquid&one solid phase-‐>a second solid In Fe-‐C diagram: wt%C <0.76: Hypoeutectoid steel,ferrite-‐soft most 0.76<wt%C<2.1 : Hypereutectoid steel, Fe3C most Polymer: Saturated hydrocarbons:1 C-‐ 4 other atoms Methane:CH4, Ethane:C2H6, Propane:C3H8, Butane:C4H10, Pentane:C5H12, Hexane:C6H14 Doubel bond:1 C-‐3 other atoms; Triple bond...
Isomerism: Same chemical formula, different structure. Condensation: Process is conducted in presence of a catalyst. Water,CO2 are commonly condensed out.
R(cation)/R(anion): less than 0.155,
linear; 0.155-‐0.225, triangular; 0.225-‐0.414, TD; 0.414-‐0.732, OH; 0.732-‐1.0, Cubic; Zinc Blende: TD site AX(include rock-‐salt),AX2,ABX3. FCC:4OH sites, 8TD sites Linear: Repeating Units: single chains, Van der waals force, very flexible, example: Nylon. Branched: Side chains, lowers density due to chain packing, example:LDPE Cross-‐Linked: Covalent bonding, stronger, can be caused by a non-‐reversible reaction. Some rubber: adding in additional additives (Vulcanization). Network: Multifunctional (3 or more activate covalent bond). Example: epoxy – good mechanical strength and thermal properties. Conformation:Molecular orientation can be changed without break bonds. Configurations – to change must break bonds Stereoisomerism: mirror plane; Tacticity: isotactic: all R groups on same side; syndiotactic: all R groups alternate side; atactic: random R groups. Cis isomerism: bulky(CH2) groups on same side. Trans isomerism: bulky group on opposite side. Copolymers: random;alternating(ABAB);block(AAAABBBB);graft(branch). Drawing increase in %Crystallinity, increase in TS and E, decrease in ductility. Annealing reverses effects of drawing. Thermoplastics: Little cross-‐linking; ductile; soften with heat. Eg: PE,PS. Thermosets: Cross-‐liking(15-‐50%);brittle;don’t soften with heat,Eg:Epoxy. Improve mechanical properties: Fillers: Improve TS and toughness, reduce cost; Plasticizers: Reduce Tg, less brittle. Processing: Thermoplastic: can be reversibly cooled & reheated; heat till soft, shape as desired, then cool. Thermoset:when heated forms a network, degrades when heated, mold the prepolymer then allow further reaction. Polymer types: Elastomers(rubber);Fibers;Coatings;Adhesives;Films;Foams. Ceramics: Applications: Die blanks; die surface; tools(Singal crystal or add polycrystalline diamond); sensors. Fabrication: Glass forming(Pressing, blowing, fiber drawing, sheet forming), Particulate forming(Slip casting, hydroplastic forming, drying, firing, sintering,uniaxial compression, hot pressing), Cementation. Application: Heat engine; ceramic armor. Heat treating Glass: Annealing: remove internal stress caused by uneven cooling; Tempering: put surface part into compression to suppresses growth of crack from surface scratches. For glass: viscosity decrease with T increase while specific volume increase with T; impurities lower deformation temperature. Defect: Frenkel Defect: a cation is out of place.Shottky Defect: a paired set of cation and anion vacancies. Substitutional cation impurity: cation vacancy; Substitutional anion impurity: anion vacancy. Metal Ferrous alloy with >2.1 wt% C, low melting. Cementite decomposes to ferrite + graphite. Limitations of ferrous alloy: relatively high density, low conductivity, poor corrosion resistance. Cu Alloy: Brass;Bronze;Cn-‐Be Alloy: density=2.7g/cm3;Mg Alloy: density =1.7g/cm3,ez ignite;Refractory metal: Hight melt T,eg:Nb,Mo; Noble metal: oscide corrosion resistance; Ti alloy: density=4.5g/cm3,reactive at high T. Strengthen and Failure %EL<5% -- Brittle(Ceramic) %EL>5% Not Brittle (Metal)
Resilience: Capacity to absorb energy when deformed elastically and then upon loading, to have this energy recovered.
Toughness: Ability to absorb energy up to fracture. Hardness: Resistance to permanently indenting the surface.
Moch Hardness; Rockweel Hardness; Brinell Hardness; K&V Microindetantion
Youngs’Modulus: Metal≈Ceramics>Polymers; Yield Strength Metal> Polymers Tensile strength:
Metal≈Ceramics≈Polymers
If dislocation does not occur,neiter does deformation. Smaller grain/crystal size more likely to slip. Larger crystal yield at first.
Strengthening 1: Reduce grain size. Grain boundaries are barriers to slip and strength increases with misorientation. Before
rolling: isotropic; uniformity in all direction. After: anisotropic, direction dependence Strengthening 2: Solid solutions. Impurity atoms distort the lattice and generate stress oppose dislocation direction. Strengthening 3: Precipitation Strengthening. Hard
precipitates are difficult to shear. Strengthening 4: Cold working: Forging, Drawing, Rolling, Extrusion. Room temperature,
reversible.
Recovery: No change in strength & ductility
Recrystallization: New crystals are formed
Grain growth: Grain boundary area increase => energy is reduced.
Ductile fracture: occurs with plastic deformation, warning before failure
Brittle fracture: occurs with little or no plastic deformation, no warning
Brittle failure: Many pieces, little deformation
Ductile failure: One piece, large deformation
Intergranular: between grains; Intragranular: within grains. Three non-destructively ways to detect: 1)X-ray 2)Ultrasonic
inspection 3)Surface inspection(Dye penetration) Ts(Engineering material)<Ts(Ideal or perfect material)
Longer sample, smaller load for failure. Flaws cause premature failure, larger samples contain more flaws.
Increased loading rate increases . .y sand Tσ ,decreases %EL.
Improving fracture toughness: a)add monoclinic grain to crack b).Microcracks. Fatigue = failure under cyclic stress.
Fatigue can cause part failure below critical stress. Improving fatigue lifeL impose a compressive surface stress; remove stress
concentrators. Water and some chemicals can accelerate crack growth and shorten life performance(Break network).
Metal fabrication methods: Forming(Forging, rolling, drawing, extrusion),Casting(die,sand,investment),Joining(Powder metallurgy, welding) How working: recrystallization. Cold working: no recrystallization. Annealing: Stress relief: reduce stress by plastic deformation; not uniformed cooling. Spherodize: for steel, make steel soft and ductile, longer time. Full anneal: make a material softer. Normalize: Steel;deform steel to grow large grain. Process Anneal: Notify the effect of cold work. Hardenability: 4in heigh, 1in in diameter. Diffusion: Interdiffusion; self diffusion; vacancy diffusion; interstitial diffusion
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