Solid Solution StrengtheningSolid Solution Strengthening

Line Defects - DislocationsLine Defects - Dislocations

• Line Imperfections in the lattice of a crystalline material.

• Movement of dislocations => material deformation

• Interference with movement of dislocations => material strengthened

• Types:– Edge– Screw– Mixed

Edge Dislocation Screw Dislocation

““Preventing” Dislocation MovementPreventing” Dislocation Movement

• Slip Impeded by Lattice Slip Impeded by Lattice Imperfections:Imperfections:

– Point DefectsPoint Defects

• VacanciesVacancies

• InterstitialsInterstitials

• SubstitutionalSubstitutional

• EtcEtc

– Line type: another Line type: another dislocationdislocation

– Surface type: Surface type:

• Crystal grain boundary Crystal grain boundary

• Material surfaceMaterial surface

Some Ways to Strengthen a Metal By Some Ways to Strengthen a Metal By Disrupting the Crystal LatticeDisrupting the Crystal Lattice

• Alloy: Alloy:

– Solid Solution StrengtheningSolid Solution Strengthening

– Dispersion StrengtheningDispersion Strengthening

– Precipitation Hardening Precipitation Hardening

• Heat Treatment:Heat Treatment:

– Controlled heating and cooling of metals for purpose of altering Controlled heating and cooling of metals for purpose of altering propertiesproperties

• Strain Harden or Cold WorkStrain Harden or Cold Work

Three Basic Three Basic Types of Lattice Types of Lattice ImperfectionsImperfections

• Point DefectsPoint Defects

• Line Defects Line Defects (Dislocations)(Dislocations)

• Surface DefectsSurface Defects

Edge Dislocation

Screw Dislocation

Dispersion StrengtheningDispersion Strengthening–Two Phase, Non-CoherentTwo Phase, Non-Coherent–Point and Surface DefectPoint and Surface Defect–Medium Strengthening EffectMedium Strengthening Effect

Defects and Strengthening Defects and Strengthening MechanismsMechanisms

Solid Solution StrengtheningSolid Solution Strengthening–Single PhaseSingle Phase–Point DefectsPoint Defects–Low Strengthening EffectLow Strengthening Effect

Precipitation HardeningPrecipitation Hardening–Two Phase, CoherentTwo Phase, Coherent–Point and Surface Defects +Point and Surface Defects +–High Strengthening EffectHigh Strengthening Effect

Strain HardeningStrain Hardening–Introduces Line DefectsIntroduces Line Defects–Varied StrengthsVaried Strengths

Grain Size RefiningGrain Size Refining–Surface DefectsSurface Defects–Varied StrengthsVaried Strengths

Exceed Solubility LimitExceed Solubility Limit

Solid Solution StrengtheningSolid Solution Strengthening

• Single PhaseSingle Phase

• Point DefectsPoint Defects

• Strengthening Effect Strengthening Effect Depends on:Depends on:– Difference in size Difference in size

between solute and between solute and solvent atomssolvent atoms

– Amount of solute Amount of solute addedadded

Effect of Solid Solution Effect of Solid Solution Strengthening on PropertiesStrengthening on Properties

• StrengthStrength• HardnessHardness• DuctilityDuctility

• Electrical ConductivityElectrical Conductivity• Creep ResistanceCreep Resistance

Formation of a Solid SolutionFormation of a Solid Solution

Dispersion StrengtheningDispersion Strengthening–Two Phase, Non-CoherentTwo Phase, Non-Coherent–Point and Surface DefectPoint and Surface Defect–Medium Strengthening EffectMedium Strengthening Effect

Defects and Strengthening Defects and Strengthening MechanismsMechanisms

Solid Solution StrengtheningSolid Solution Strengthening–Single PhaseSingle Phase–Point DefectsPoint Defects–Low Strengthening EffectLow Strengthening Effect

Precipitation HardeningPrecipitation Hardening–Two Phase, CoherentTwo Phase, Coherent–Point and Surface Defects +Point and Surface Defects +–High Strengthening EffectHigh Strengthening Effect

Strain HardeningStrain Hardening–Introduces Line DefectsIntroduces Line Defects–Varied StrengthsVaried Strengths

Grain Size RefiningGrain Size Refining–Surface DefectsSurface Defects–Varied StrengthsVaried Strengths

Exceed Solubility LimitExceed Solubility Limit

Dispersion StrengtheningDispersion Strengthening• Exceeds solubility limit => two solid phasesExceeds solubility limit => two solid phases

– MatrixMatrix

• continuouscontinuous

• soft and ductilesoft and ductile

– PrecipitatePrecipitate

• discontinuousdiscontinuous

• strongstrong

• roundround

• numerousnumerous

Dispersion Strengthening => Non-Coherent Dispersion Strengthening => Non-Coherent PrecipitatesPrecipitates

• Non-CoherentNon-Coherent– DiscontinuousDiscontinuous

– Only blocks slip if precipitate lies directly in path of dislocationOnly blocks slip if precipitate lies directly in path of dislocation

– Does not disrupt surrounding crystal structureDoes not disrupt surrounding crystal structure

One solid phase

Another solid phase

Phase boundary = surface defectBlocks slip!

Group Work – Turn in!

• Label two phase regions• What are the solid solutions and what are intermetallics?• Three phase reactions• Formation of microstructure of 1% Mg upon cooling• Formation of microstructure of 5% Mg upon cooling• Where do you have solid solution strengthening only?• Where do you have dispersion strengthening?• Generate a plot of strength as a function of composition from 0% Mg to 10% Mg at 300 C and explain this

graph in terms of crystalline defects and slip.• What is the amount and composition of phases present at 200 C for 2 % Mg, 4 % Mg, 6% Mg

• Solid solutions are , intermetallics are • Three phase reactions, eutectic L => L => • Where do you have solid solution strengthening only? In single phase regions.• Where do you have dispersion strengthening? In two phase regions.• At 0% Mg we have pure material – no defects to block slip, with increasing amounts of Mg we have solid

solution strengthening = point defects to block slip at 5% Mg we exceed the solubility limit and now we have two phases, so we have phase boundaries which are surface defects as well as point defects from the solid solution to block slip, the amount of second phase will increase with increasing Mg so the number of surface defects will also increase = more opportunities to block slip (more obstacles in Goldie’s path!!!!!

L L

L

Eutectic

Formation of Microstructures1% Mg:All L at 700 C starts to form at ~ 650 C+L at ~640 CAll at ~625 – 0 C (blue line doesnot really cross solvus line)5% Mg:All L at 700 C starts to form at ~ 640 C+L at ~620 CAll at ~580 C starts to form at ~ 240 C +L at ~240 – 0 CAmount and composition2% Mg: C = 2% Mg and 100% 4% Mg: C = 3% Mg; C = 36% MgAmount = 36-4/36-3 * 100 = 97%Amount = 4-3/36-3 * 100 = 3%6% Mg: C = 3% Mg; C = 36% MgAmount = 36-6/36-3 * 100 = 91%Amount = 6-3/36-3 * 100 = 9%**what do you notice about the compositions?****what do you notice about the amounts?**

(psi)