Peritectic reaction

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Peritectic reaction

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Eutectoid reaction

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Terminal and intermediate solutions

Terminal solid Terminal solid

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Terminal and intermediate solutions

Terminal solidTerminal solid

Intermediate solids

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Congruent-Incongruent phase transformation

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Polymorphism or Allotropy• Some metals, as well as nonmetals, may have more than one crystal

structure, a phenomenon known as polymorphism

• When found in elemental solids, the condition is often termedallotropy

• One familiar example is found in carbon: graphite is the stablepolymorph at ambient conditions, whereas diamond is formed atextremely high pressures.

• Also, pure iron has a BCC crystal structure at room temperature,which changes to FCC iron at 912 ˚ C

• Modification of the density and other physical propertiesaccompanies a polymorphic transformation

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HAND OUT EXERCISES

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Ans1

• Draw vertical projection from 76wt% Ag and 92wt% Ag

• Check If both are inline between beta+liquid region

• If yes check the temperature by taking horizontal projection on Temperature axis

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Ans2

• Draw vertical projection from 4 wt% Ag

• Draw horizontal projection from intersection of left solvus line and vertical projection drawn in first step

• Draw vertical projection from intersection of right solvus line and horizontal projection drawn in step 2

• Check composition

• If yes check temperature

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Ans3

• Fix the point, draw tie line

• Take vertical projections from intersection of solvusline and tie line

• Note composition

• Use equation for finding amount of phase

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Ans4

• Draw tie line at given temperature

• Note composition of alpha

• Use equation for finding amount of primary alpha

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Ans5

• Draw tie line

• Find compositions of alpha and beta

• Find amount using equations

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• What is pre-eutectic alpha/beta?

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In a eutectic structure, amount of eutectic alpha is 67%. What is the amount of eutectic beta?

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Eutectic alphaEutectic beta

• In a structure on eutectic phase diagram amount of pre-eutectic alpha is 31% and amount of total alpha is 70%, what is the amount of eutectic alpha?

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Pre-Eutectic alpha

• What is binary alloy?

• What is solvus line?

• What is isomorphous system?

• What is eutectic reaction?

• What is Peritectic reaction?

• What is eutectoid reaction?

• What is stable phase diagram?

• Why pre eutectic exists?

• Which rule is used for phase amount calculation?

• What is tie line?

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R.D.Makwana,IT,NU

Construct the hypothetical phase diagram for metals A and B between room

temperature

20˚C and 700˚C and given the following information:

• The melting temperature of metal A is 480 ˚C

• The maximum solubility of B in A is 4 wt%B, which occurs at 420 ˚C.

• The solubility of B in A at room temperature is 0 wt% B.

• One eutectic occurs at 420 ˚C and 18 wt% B–82 wt% A.

• A second eutectic occurs at 475 ˚ C and 42 wt% B–58 wt% A.

• The intermetallic compound AB exists at a composition of 30 wt% B–70 wt% A,

and melts congruently at 525 ˚C.

• The melting temperature of metal B is 600 ˚C

• The maximum solubility of A in B is 13 wt% A, which occurs at 475 ˚C.• The solubility of A in B at room temperature is 3 wt% A.

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• Iron-Iron carbide diagramR.D.Makwana,IT,NU

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Phase transformation

• Phase equilibrium

• Structural equilibrium never achieved

• Kinetics of transformation

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Solid solution

• Substitution solid solution

• Interstitial solid solution

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Hume-Rothery theorem Substitutional Solid solution1. The atomic diameter of the solute and solvent atoms must differ by no more than 15%:

2. The crystal structures of solute and solvent must match.

3. Complete solubility occurs when the solvent and solute have the same valency.

metal of lower valence dissolves more amount of higher valence metal than vice versa.

Nickel is lower in valence than Aluminum

Solid Nickel dissolves 5 % of solid Aluminum

4. The solute and solvent should have similar electronegativity.

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Hume-Rothery theorem

• Interstitial solid solution

1. Solute atoms must be smaller than the interstitial sites in the solvent lattice.

2. The solute and solvent should have similar electronegativity

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BCC FCC

% empty space 32 25

Largest interstitial sphere

0.36X10-8 cm3 0.52X10-8 cm3

Max. % Solulibilityof iron

0.0025 2

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