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23/12/2013, 00:15
... ặ
1
ẳ1=5boundaryisoneinwhich1in5ofthegrainboundaryatoms
match,asshowninFig.2.8(c).
Twinboundariesmayformwithincrystals.Suchboundarieslieacross
deformationtwinplanes,asshowninFig.2.8(d).Notethattheatomson
eithersideofthetwinplanesaremirrorimages.Stackingfaultsmayalsobe
formedwhentheperfectstackinginthecrystallinestackingsequenceis
disturbed,Figs2.8(e)and2.8(f).Thesemaybethoughtofastheabsence
ofaplaneofatoms(intrinsicstackingfaults)ortheinsertionofrowsof
atomsthatdisturbthearrangementofatoms(extrinsicstackingfaults).
IntrinsicandextrinsicstackingfaultsareillustratedschematicallyinFigs
2.8(e)and2.8(f),respectively.NotehowtheperfectABCABCstackingof
atomsisdisturbedbytheinsertionorabsenceofrowsofatoms.
2.3.4VolumeDefects
Volumedefectsareimperfectionssuchasvoids,bubble/gasentrapments,
porosity,inclusions,precipitates,andcracks.Theymaybeintroducedintoa
solidduringprocessingorfabricationprocesses.Anexampleofvolume
defectsispresentedinFig.2.9.ThisshowsMnSinclusionsinanA707
steel. AnotherexampleofavolumedefectispresentedinFig.1.16(d).
This ... approximately 0.3–0.5
of the melting temperature in degrees Kelvin.
Since the evolution of microstructure is often controlled by diffusion
processes, a brief introduction to elementary aspects of diffusion ... ặ
1
ẳ1=5boundaryisoneinwhich1in5ofthegrainboundaryatoms
match,asshowninFig.2.8(c).
Twinboundariesmayformwithincrystals.Suchboundarieslieacross
deformationtwinplanes,asshowninFig.2.8(d).Notethattheatomson
eithersideofthetwinplanesaremirrorimages.Stackingfaultsmayalsobe
formedwhentheperfectstackinginthecrystallinestackingsequenceis
disturbed,Figs2.8(e)and2.8(f).Thesemaybethoughtofastheabsence
ofaplaneofatoms(intrinsicstackingfaults)ortheinsertionofrowsof
atomsthatdisturbthearrangementofatoms(extrinsicstackingfaults).
IntrinsicandextrinsicstackingfaultsareillustratedschematicallyinFigs
2.8(e)and2.8(f),respectively.NotehowtheperfectABCABCstackingof
atomsisdisturbedbytheinsertionorabsenceofrowsofatoms.
2.3.4VolumeDefects
Volumedefectsareimperfectionssuchasvoids,bubble/gasentrapments,
porosity,inclusions,precipitates,andcracks.Theymaybeintroducedintoa
solidduringprocessingorfabricationprocesses.Anexampleofvolume
defectsispresentedinFig.2.9.ThisshowsMnSinclusionsinanA707
steel. AnotherexampleofavolumedefectispresentedinFig.1.16(d).
This shows evidence of $12 vol % of porosity in...