Cap4(Imperfections in the Atomic Arrangement).ppt

7/21/2019 Cap4(Imperfections in the Atomic Arrangement).ppt

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The Science and Engineering

of Materials, 4thedDonald R. Askeland Pradeep P. Phule

!hapter 4 "#perfections in theAto#ic and "onic Arrange#ents


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Figure 4.1 Point defects: (a) vacancy, (b) interstitial atom,(c) small substitutional atom, (d) large substitutional atom,(e) Frenkel defect, (f) Schottky defect. ll of these defects

disru!t the !erfect arrangement of thesurrounding atoms.


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Figure 4." (a) #he location of the $, %, & interstitial site in 'metals, shoing the arrangement of the normal atoms and theinterstitial atom (b) %, &, & site in F metals, (for *+am!le 4-). (c) *dge centers and cube centers are some of the interstitial

sites in the F structure (*+am!le 4-).


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Figure 4.- hen a divalent cation re!laces a monovalentcation, a second monovalent cation must also be removed,creating a vacancy.


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Figure 4.4 the !erfect crystal (a) is cut and sheared one atoms!acing, (b) and (c). #he line along hich shearing occurs is ascre dislocation. 'urgers vector bis re/uired to close a loo!of e/ual atom s!acings around the scre dislocation.


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Figure 4.1& (a) 'urgers vector for F co!!er. (b) #he atomlocations on a (11&) !lane in a ' unit cell (for e+am!le 40and 4, res!ectively)


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Figure 4.11 sketch illustrating dislocations, sli! !lanes,and etch !it locations. (Source: Adapted from PhysicalMetallurgy Principles, Third Edition, by R.E. Reed-ill andR. Abbaschian, p. !", #igs. $-% and $-&. 'opyright (c)*!!" +roos'ole Thomson earning. Adapted by

permission.)


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Figure 4.1- *lectron !hotomicrogra!hs of dislocations inTi/Al: (a) 2islocation !ileu!s (+"3,&&). (b) 5icrogra!h at +

1&& shoing sli! lines and grain boundaries in6. (c) Schematic of sli! bands develo!ment.

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(c)2003 Brooks/Cole, a division of Thomson Learning, nc! Thomson Learning"is a #rademark used herein under license!


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Figure 4.14 (a) resolved shear stress is !roduced on a sli!system. (7ote: (8 9 ) does not have to be &;.) (b)5ovement of dislocations on the sli! system deforms thematerial. (c)


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Figure 14.1 hen the sli!!lane is !er!endicular to the

a!!lied stress , the angle is90and no shear stress is

resolved.


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Figure 4.1= #he effect of grain si>e on the yieldstrength of steel at room tem!erature.


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Figure 4.1 #he small anglegrain boundary is !roduced byan array of dislocations,

causing an angular mismatch 0beteen lattices on either sideof the boundary.


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Figure 4."& !!lication of a stress to the !erfect crystal (a)may cause a dis!lacement of the atoms, (b) causing th4eformation of a tin. 7ote that the crystal has deformed as aresult of tinning.


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Figure 4."& (c) microgra!h of tins ithin a grain ofbrass (+"&).


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Figure 4."" 6f the dislocation at !ointAmoves to theleft, it is blocked by the !oint defect. 6f the dislocationmoves to the right, it interacts ith the disturbed latticenear the second dislocation at !oint +. 6f the dislocationmoves farther to the right, it is blocked by a grainboundary.

Cap4(Imperfections in the Atomic Arrangement).ppt

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