PY3090PY3090 PreparationPreparation ofof MaterialsMaterials LectureLecture 55
ColmColm StephensStephens SchoolSchool ofof PhysicsPhysics
PY3090 – 5 MicrostructuresMicrostructures inin EutecticEutectic Systems:Systems: II
L: C wt% Sn • Co < 2 wt% Sn T(°C) o 400 • Result: L --at extreme ends α 300 L --polycrystal of α grains i.e., only one solid phase. L+ α α 200 (Pb-Sn α: C wt% Sn TE o System)
100 α+β
0 10 20 30 Co C , wt% Sn 2 o (room T solubility limit) MicrostructuresMicrostructures inin EutecticEutectic Systems:Systems: IIII
L: Co wt% Sn •2 wt% Sn< Co < 18.3 wt% Sn T(°C) 400 • Result: L Initially liquid + α L then α alone 300 α L + α finally two phases α: Co wt% Sn α ¾ α polycrystal 200 TE ¾ fine β-phase inclusions α β 100 α+ β Pb-Sn system
0 10 20 30 C 2 o Co , wt% Sn (sol. limit at Troom) 18.3 (sol. limit at TE) MicrostructuresMicrostructures inin EutecticEutectic Systems:Systems: IIIIII • Co = CE • Result: Eutectic microstructure (lamellar structure) --alternating layers (lamellae) of α and β crystals. Micrograph of Pb-Sn T(°C) eutectic L: Co wt% Sn microstructure 300 L Pb-Sn L+α system α 200 183°C L + β β TE
100 160μm β: 97.8 wt% Sn α + β Adapted from Fig. 9.14, Callister 7e. α: 18.3 wt%Sn
0 20 40 60 80 100 97.8 18.3 CE 61.9 C, wt% Sn MicrostructuresMicrostructures inin EutecticEutectic Systems:Systems: IVIV
• 18.3 wt% Sn < Co < 61.9 wt% Sn • Result: α crystals and a eutectic microstructure
• Just above TE : T(°C) L: Co wt% Sn α L C = 18.3 wt% Sn L α α C = 61.9 wt% Sn 300 L L Pb-Sn S L+α Wα= = 50 wt% system R + S α 200 R S L+β β WL = (1- Wα) = 50 wt% TE R S • Just below TE : 100 α+β Cα = 18.3 wt% Sn primary α Cβ = 97.8 wt% Sn eutectic α S eutectic β Wα= = 73 wt% 0 20 40 60 80 100 R + S 18.3 61.9 97.8 Wβ = 27 wt% Co, wt% Sn HypoeutecticHypoeutectic && HypereutecticHypereutectic
300 L T(°C) α L+α 200 L+β β (Pb-Sn TE α + β System) 100
0 20 40 60 80 100 Co, wt% Sn eutectic hypoeutectic: Co = 50 wt% Sn 61.9 hypereutectic: (illustration only)
eutectic: C =61.9wt% Sn α o β α β α α β β α β α β 175 μm 160 μm eutectic micro-constituent IntermetallicIntermetallic CompoundsCompounds
Mg2Pb
Note: intermetallic compound forms a line - not an area - because stoichiometry (i.e. composition) is exact. EutecticEutectic
EutecticEutectic -- liquidliquid inin equilibriumequilibrium withwith twotwo solidssolids
cool LL heat αα ++ ββ EutectoidEutectoid && PeritecticPeritectic
EutectoidEutectoid -- solidsolid phasephase inin equilibriumequilibrium withwith twotwo solidsolid phasesphases SS SS ++SS 2 1 3 intermetallic compound - cementite γγ cool αα ++ FeFe CC (727(727ººC)C) heat 3
PeritecticPeritectic -- liquidliquid ++ solidsolid 11 ÆÆ solidsolid 22
SS1 ++ LL SS2 cool δδ ++ LL heat γγ (1493(1493ººC)C) Example:Example: EutectoidEutectoid && PeritecticPeritectic Peritectic transition γ + L δ Cu-Zn Phase diagram
Eutectoid transition δγ+ ε IronIron--CarbonCarbon PhasePhase DiagramDiagram ExtractExtract • 2 important T(°C) 1600 points δ -Eutectic (A): 1400 L L ⇒γ+ Fe C 3 γ γ+L 1200 A L+Fe C -Eutectoid (B): (austenite) 1148°C 3 R S γ⇒α+Fe3C 1000 γ γ γ+Fe3C α γ γ + 800α γ B 727°C = Teutectoid
R S C (cementite) 3 600 α+Fe C
3 Fe 400 0 1234566.7 (Fe) 0.76 4.30 Co, wt% C Fe3C (cementite-hard) α (ferrite-soft) eutectoid C PearlitePearlite
Fe3C (cementite-hard)
α (ferrite-soft)
120 μm Result: Pearlite = alternating layers of
α and Fe3C phases HypoeutectoidHypoeutectoid SteelSteel T(°C) 1600 δ 1400 L (Fe-C γ γ γ γ+L γ γ 1200 1148°C L+Fe C System) (austenite) 3 γ γ 1000 γ γ γ +Fe3C α 800 αγ γ rs 727°C α
γ γ C (cementite)
α 3 wα =s/(r+s) 600 α+Fe C wγ =(1- wα) 3 Fe 400 0 1234566.7 (Fe) C C , wt% C α 0 o 0.76 pearlite wpearlite = wγ wα =S/(R+S) w =(1-w ) Fe3C α HypoeutectoidHypoeutectoid SteelSteel
α pearlite wpearlite = wγ 100 μm wα =S/(R+S) w =(1-w ) Fe3C α
pearlite Proeutectoid ferrite HypereutectoidHypereutectoid SteelSteel
T(°C) 1600 δ (Fe-C System) 1400 L γ γ γ γ+L 1200 1148°C L+Fe C γ γ (austenite) 3 γ γ 1000 γ γ γ +Fe3C Fe C 3 s γ γ 800 r
γ γ C (cementite) α R S 3 600 wFe C =r/(r+s) α +Fe C 3 C 3 Fe wγ =(1-w Fe C) o 3 400 0 1234566.7 (Fe) C , wt%C
pearlite 0.76 o w pearlite = wγ wα =S/(R+S) w =(1-w ) Fe3C α HypereutectoidHypereutectoid SteelSteel
pearlite w pearlite = wγ wα =S/(R+S) w =(1-w ) Fe3C α
60 μm
proeutectoid Fe C pearlite 3 ExampleExample ForFor aa 99.699.6 wt%wt% FeFe--0.400.40 wt%wt% CC atat aa temperaturetemperature justjust belowbelow thethe eutectoid,eutectoid, determinedetermine thethe followingfollowing a)a) thethe amountamount ofof pearlitepearlite andand proeutectoidproeutectoid ferriteferrite ((αα)) perper 100100 gg ofof steelsteel b)b) compositioncomposition ofof FeFe3CC andand ferriteferrite ((αα)) c)c) thethe amountamount ofof carbidecarbide (cementite)(cementite) inin gramsgrams thatthat formsforms perper 100100 gg ofof steelsteel SolutionSolution a. the amount of pearlite and proeutectoid ferrite (α)
note: amount of pearlite = amount of γ just above TE
Co = 0.40 wt% C Cα = 0.022 wt% C C = C = 0.76 wt% C 1600 pearlite γ δ 1400 L T(°C) γ Co −Cα γ γ+L = x 100 = 51.2 g 1200 1148°C L+Fe C γ+α C −C (austenite) 3 γ α 1000 γ +Fe3C
800 727°C
R S C (cementite) 3 pearlite = 51.2 g 600 α +Fe C
3 Fe proeutectoid α = 48.8 g 400 0 1234566.7 Cα Cγ CO Co, wt% C SolutionSolution
b) composition of Fe3C and ferrite (α)
c) the amount of carbide CO = 0.40 wt% C (cementite) in grams that Cα = 0.022 wt% C C = 6.70 wt% C forms per 100 g of steel Fe3C 1600 δ Fe3C Co −Cα 1400 L = x100 T(°C) Fe C + α C −C γ+L 3 Fe3C α 1200 γ L+Fe C (austenite) 1148°C 3 0.4 − 0.022 = x 100 = 5.7g 1000 6.7 − 0.022 γ +Fe3C 800 727°C
R S C (cementite) Fe C = 5.7 g 3 3 600 α +Fe C
3 Fe α = 94.3 g 400 0 1234566.7 C C Cα O Co, wt% C Fe3C AlloyingAlloying SteelSteel withwith MoreMore ElementsElements
• Teutectoid changes: • Ceutectoid changes:
Ti Si Mo W Ni (°C) Cr (wt%C) Cr Si Mn Mn W Eutectoid Ti Mo
T Ni eutectoid C
wt. % of alloying elements wt. % of alloying elements TaxonomyTaxonomy ofof MetalsMetals Metal Alloys
Ferrous Nonferrous
Steels Cast Irons Cu Al Mg Ti <1.4 wt% C 3-4.5 wt%C
T(°C) microstructure: 1600 ferrite, graphite δ cementite 1400 L γ+L 1200 γ 1148°C L+Fe3C austenite Eutectic: 1000 4.30
α + γ+Fe3C α800 γ 727°C Fe3C ferrite Eutectoid: cementite 600 0.76 α+Fe3C
400 0 1234566.7 (Fe) Co , wt% C SteelsSteels
increasing strength, cost, decreasing ductility