phase diagrams 1

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Information about phase diagrams 1

Published on January 3, 2008

Author: Megane


Slide1:  Phase Diagrams Slide2:  Why do cocktail ice served in expensive restaurants are clear whereas the ice formed in your refrigerator is cloudy? What is a solder alloy? What is the best composition for solder? How is ultrpure Si for computer chips produced? Slide3:  Melting point of an alloy Cu Ni Wt% Ni 1085ºC 1453ºC Liquid, L Solid solution,  Liquidus solidus L +  Slide4:  A diagram in the space of relevant thermodynamic variables (e.g., T and x) indicating phases in equilibrium is called a phase diagram. Equilibrium phase diagram or Equilibrium diagram or Phase diagram Slide5:  The independent chemical species (element or compound) in terms of which the composition of the system is described are called components. H2O Water +ice liquid solution  + Fe3C components Water liquid H2O Liquid+solid nimbu, chini and pani shikanji Fe + C Mild steel phases System Components Slide6:  A single component phase diagram: Unary diagram A two-component phase diagram: Binary diagram A three-component phase diagram: Ternary diagram Slide7:  Cu-Ni binary phase diagram Callister, Fig. 9.2 Any given point (x,T) on the phase diagram represents an alloy of composition x held at equilibrium at temperature T Point A: 60 wt% Ni at 1100ºC Point B: 35 wt% Ni at 1250ºC Slide8:  Phase Diagrams For any given point (x,T) the phase diagram can answer the following: What phases are present? What are the phase compositions? What are the relative amounts of the phases (phase proportions or phase fractions)? Slide9:  Point A: 60 wt% Ni at 1100ºC Q: Phase present? Ans:  Q: Phase composition ? Ans: 60 wt%Ni Q: Phase amount ? Ans: 100% Slide10:  Point B: 35 wt% Ni at 1250ºC Q: Phases present? Ans:  + L Q: Phase compositions ? Tie Line Rule Q: Phase amounts ? Lever Rule Slide11:  Composition of phases in the two-phase region Tie Line CL= 31.5 wt% Ni C= 42.5 wt% Ni Tie Line Rule Slide12:  Amount of phases in the two-phase region Tie Lever Rule Tie-Line: A lever Alloy composition C0: Fulcrum fL: weight at liquidus point f: weight at solidus point The lever is balanced Slide13:  The Lever Rule: A Mass balance Proof Prob. 7.6 f + fL = 1 Wt of Ni in alloy = W C0/100 Wt of Ni in  = fWC/100 Wt of Ni in L = fL WCL/100 C f + CL fL = C0 Wt of alloy = W Wt of  in alloy = fW Wt of L in alloy = fLW Wt of Ni in alloy = Wt of Ni in  + Wt of Ni in L Slide14:  Development of Microstructure during solidification Slide15:  Solder alloy? An alloy of Pb and Sn What is best composition of the solder alloy? Requirements: 1. should melt easily 2. should give a strong joint Slide16:  L    Pb Sn Solder alloy Wt % Sn 327 232 183 L L 1-2-1 rule Eutectic horizontal Eutectic diagram Liquidus Liquidus solidus solidus solvus solvus Slide17:  : Pb rich substitutional solid solution of Pb and Sn crystal structure: monatomic FCC : Sn rich substitutional solid solution of Pb and Sn crystal structure: monatomic BCT Pb: monatomic fcc Sn: monatomic bct Slide18:  Woods metal tea party Bi 50.0 wt% Pb 25.0 wt% Cd 12.5 wt% Sn 12.5 wt% An eutectic alloy with m.p. of 70ºC 100 g US$ 181 Anti-Fire Sprinklers Slide19:  Eutectic reaction Invariant reaction Callister Figs. 9.11, 12 Slide20:  Microstructure of hypoeutectic alloy Slide21:  Amount of total  and total  at a temperature just below 183ºC Tie line just below 183ºC (red) Eutectc mixture  Proeutectic or Primary  Slide22:  Amount of proeutectic  at a temperature just below 183ºC Tie line just above 183ºC (green) Eutectc mixture  Proeutectic or Primary  = Amount of  at a temperature just above 183ºC Slide23:  Let the fraction of proeutectic  in micrograph fpro = 0.25 Tie line just above 183ºC (green) Eutectc mixture  Proeutectic or Primary  Let the composition (wt% Sn) of the alloy be C0 EXPERIMENT 5 Slide24:  Optimum composition for solders For electronic application Eutectic solder 62 wt% Sn For general application Minimum heating Hypoeutectic solder Cheaper Allows adjustment of joint during solidification in the L range Slide25:  Modern Trend Lead-free solders Phase diagrams can help in identification of such solders Sn-Ag-Cu Slide26:  Please collect your Minor I answer books from Lab in the afternoon Those who can, do. Those who can’t teach G.B. Shaw Slide27:  Gibbs Phase Rule Thermodynamic variables: P, T, Phase Compositions (overall composition is not considered) If there are C components then C-1 compositions have to be specified for each phase Therefore total number of composition variables: P (C-1) With Pressure and Temperature, total number of variables = P (C-1) + 2 Slide28:  Degrees of Freedom F: No. of thermodynamic variables that can be specified independently Gibbs phase rule states that one cannot specify all of the above P (C-1) + 2 variables independently in a system at equilibrium Slide29:  Gibbs Phase Rule F = C – P + 2 F = Degrees of freedom C = No. of components in the system P = No. of phases in equlibrium If pressure and temp both are variables F = C – P + 1 If pressure is held constant Slide30:  F = C – P + 1 F =2 F =1 C=2 F=3-P At eutectic reaction P=3 (L, , ) F=0 Invariant reaction Slide31:  steel Cast iron The Iron-carbon system Mild steel 0-0.3 wt% C Bicycle frame Ship hull Car body Medium C steel 0.4-0.7 wt% C Rail wheel rail axle rails High C steel 0.8-1.4 wt% C Razor blades scissors, knives Slide32:  Phases in Fe-C system Phase Symbol Description Liquid L Liquid solution of Fe and C -Ferrite  Interstitial solid solution of C in -Fe (high temperature bcc phase) Austenite  Interstitial solid solution of C in -Fe (FCC phase of Fe) Ferrite  Interstitial solid solution of C in -Fe (room temperature bcc phase) Soft and Ductile Cementite Fe3C Intermetallic compound of Fe and C (orthorhombic system) Hard and Brittle Slide33:  Ferrite Austenite Slide34:  Invariant Reactions in Fe-C system Peritectic Reaction A horizontal line always indicates an invariant reaction in binary phase diagrams Eutectic Reaction Eutectoid Reaction Slide35:  Eutectoid Reaction Pearlite Slide36:  Ammount of Fe3C in Pearlite Red Tie Line below eutectoid temp Slide37:  Development of Microstructure in a hypoeutectoid steel Slide38:  Proeutectoid Ferrite Pearlite Microsructure of a hypoeutectoid steel, 0.38 wt% C EXPERIMENT 5 Slide39:  fpearlite below TE = faustenite above TE Tie-Line above the eutectoid temperature TE Slide40:  Development of Microstructure in a hypereutectoid steel Slide41:  Microsructure of a hypereutectoid steel, 1.4 wt% C Proeutectoid cementite on prior austenite grain boundaries Pearlite Slide42:  Fproeutectoid cementite=fcementite above TE Slide43:  Phase vs. microconstituents A phase or a mixture of phases which has a distinct identity in a microstructure is called a microconstituent Pearlite is not a phase. It is microconstituent which is a mixture of two phases  and Fe3C. Slide44:  Eutectoid steel +Fe3C Pearlite Hypoutectoid steel +Fe3C Pearlite + proeutectoid ferrite Hypereutectoid steel +Fe3C Pearlite + proeutectoid cementite Slide45:  A Wt % B C0 T TmA L  +L C CL C < CL Principle of Zone Refining T Slide46:  SemiconductorTransistor was invented by Bardeen, Brattain and Shockley At AT&T Bell Labs One needs ultrapure Si (impurity level few ppm) Zone Refining was invented by Pfann at Bell Labs as a process to obtain ultrapure Si Basis for modern Si technology

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