Chuong 2 Bien Dang Deo Va Co Tinh

7/21/2019 Chuong 2 Bien Dang Deo Va Co Tinh

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19

Chng 2

Bin dng do v c tnha s v t li u, c bi t l kim lo i, thng c bn di d ng cc b n thnh

ph m di d ng: d y, thanh, h nh, ng, t m, l , b ng... nh bin d ng d o (cn), ho c c cphi r n kh o s t bin d ng do khng nhng gip hi u bi t c s qu tr nh m cn

gip ra cc bi n php nng cao c t nh, kh c phc nhng khuy t t t.2.1. Bi n dng d o v ph hy2.1. Bi n dng d o v ph hy2.1. Bi n dng d o v ph hy2.1. Bi n dng d o v ph hy2.1.1.2.1.1.2.1.1.2.1.1.Khi nimKhi nimKhi nimKhi nim

Biu t i trng (hay ng sut) vs bi n d ng h nh 2.1. cho th y:

- N u tip tc t ng t i trng n gi tr cao nh t Fb, m u b th t l i t i trng=const (ho c ) nhng /s ph hy im c.

S bi n i v mng tinh th ba trng th i trn tr nh by h nh 2.2.

a) b) c) d)

Khi bin d ng n hi th bi n d ng nh aa, vi a l thngs m ngph hy c c lin k t b hy ho i d n n t ri.Bi n d ng do = c ch trt ( i khi xy ra b ng song tinh), y ch gi i h n kho s tbi n d ng do di h nh thc ny.2.1.2.2.1.2.2.1.2.2.1.2.Trt n tinh thTrt n tinh thTrt n tinh thTrt n tinh th

Trt l s chuyn di tng i gia cc phn ca tinh th theo nhng mt v phng

nht nhgi l mt v phng trt (h nh 2.3.)a. Cc mt v phng trta. Cc mt v phng trta. Cc mt v phng trta. Cc mt v phng trtMt trt l mt(tng tng) phn cch gia hai mt nguy n t dy c nht m theo s trt xy ra.Cc mt v phng trt ca ba kiu mng tinh th thng gp c tr nh b y h nh2.4:- M ng lftm (A1): m t trt {111}, (4 mtx3 phng)=12 h trt ch nh kh c nhau.- M ng lftk (A2): m t trt {110}, (6 m t x 2 phng)= 12 h trt ch nh kh c nhau.- Mng lgxc (A3): m t trt, (1 m t x 3 phng)= 3 h trt ch nh khc nhau.

- Khi F < Fh, gi n d i l t l bc nh t vi t i trngbi n dng n hi. Vi F1bi n d ng O1, b t itrng m u l i tr l i k ch thc ban u.- Khi F > Fh, bin dng t ng nhanh theo t i trng,khi b t i trng bi n d ng vn cn l i mt phn bindng d o. Khi F= Fabi n d ng Oa'', khi F=0 bi ndng Oa' bi n d ng do hay d,

H nh 2.1.Biu ko kim

a a d n di

titrngF

Fb

Fa

Fh

Fl

a

b

c

e

lO

H nh 2.2.S bin i mng tinh thkhi ln lt tng ti trng ban u (a),

bin dng n hi (b), bin dng doc h h d


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20- Ngoi cc mt, phng trt ch nh k tr n cn c kh n ng b trt theo cc m t,phng dy c khc tuy khng ph i l dy c nh t.

H nh 2.3.S biu din s trt: a. ntinh th v mng tinh th trc khi trt,

b. h nh dng n tinh th v mngtinh thsau khi trt.

H nh 2.4.Cc mt v phng trt cbn ca kim loi:

a. lp ph

ng tm khi, b. lp phng tm mt,c. lc gic xp cht,

- Kh nng bi n d ng do ca kim lo i t l thun vi s h trt ch nh: s h trt cngcao kh nng trt c ng ln kim lo i c ng d bi n d ng do- Thc t chng t iu ny: Fe,Al,Ag,Cu...(mng A1) d o v d d t mng hn Zn(A3).So vi lftk (A2) m ng lftm (A1) tuy cng 12 h trt nhng d trt hn t nh do caohnb.b.b.b.ng sut gy ra trtng sut gy ra trtng sut gy ra trtng sut gy ra trt

nh lut Schmid.Khi > th(x c nh i vi tng kim lo i) trt mi x y ra. Gi tr ca =?

=S

Fcos.cos=

OSF

sin.cos.cos

trong F/S0l ng sut ko 0thay v o ta c: = 0,50 sin2 cos. Gi cos.cos l

tha s Schmid. ng su t gy ra trt phthuc vo gc & quatha sSchmid.

Khi = 90o

hay = 90o

= 0, lc F ch lmph hy m khng xy ra bi n d ng do. H nh 2.5.Trt trong n tinh thKhi (+) 90o, max = 0,50khi = = 45o.H trt no c max thun li nht trt xy ratrc cc h t thu n li hn.H nh th i ca trt: h nh 2.2c v 2.3b: c c b c trt, d itrt.

H nh 2.5b. B c trt v ditrt

bc

di

a) b)

a) b)

c)

phngtrtmt

tr

F

F

F


3/14

21c.c.c.c.T nh d trtT nh d trtT nh d trtT nh d trt ---- c ch trtc ch trtc ch trtc ch trt

b n l thuy t: t.h 2G

, r t cao. Thc t c l ch t.h 4310810 .

G

r t nh

2.1.3.2.1.3.2.1.3.2.1.3.TrTrTrTrt a tinh tht a tinh tht a tinh tht a tinh th Vt li u kim lo i thc t lun lun l VL a tinh th .a.a.a.a.Cc c imCc c imCc c imCc c i m c i m ca trt a tinh th :1) Cc ht b bin dng khng ng thi vi mc khc nhau2)C t nh ng hng: s h t v cng ln3) a tinh th c b n cao hn: C c ht c n tr bin d ng ln nhau, bi n h t c n trt.lc cao hn bn cao hn.4)Ht c ng nh b n v d o c ng cao: h t nh c tng din t ch bi n h t ln hn,

s c n trt m nh hn n n lm t ng bn. Theo Hall - Petch:ch= o++++ dk

,

Khi h t nh i tng daiv t liu kh b ph hy gin r t u vi tb.b.b.b.T chc v t nh cht ca kim loi sau khi bi n dng d oT chc v t nh cht ca kim loi sau khi bi n dng d oT chc v t nh cht ca kim loi sau khi bi n dng d oT chc v t nh cht ca kim loi sau khi bi n dng d o1) Sau khi bi n dng x lch mng t/th .

=0

=(40-50)%=(40-50)% =(70-90)%

H nh 2.7.S thay i t chc sau bin dngTextua bi n dng. V d khi c n: Al m ng A1: - cc mt {110} song song vi mt cn2) Bi n dng do do x lch mng ng su t d, cho c t nh , ng su t n n db m t l m gii h n mi: l n p, phun bi.3) Xu hng thay i c t nh sau khi bi n dng d o (h nh 2.8):. B n (h,0,2), cng , d o . D n in v t nh chng n mn gim

H nh 2.8.nh hng ca bin dng n c t nh ca kim loi ni chung (a) v Cuni ring (b).

tp cht

H nh 2.6.M h nh trt trong mng tinh

th thc t (c lch bin)

tnhch

t

0,2

b

d n

b,02,k

si

0,2

b

dndi,

20

40

60

a) b)
http://../Movies/BDlech.swfhttp://../Movies/BDlech.swfhttp://../Movies/BDlech.swfhttp://../Movies/BDlech.swfhttp://../Movies/BDnguoi.swfhttp://../Movies/BDlech.swf


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222.1.4.2.1.4.2.1.4.2.1.4.Ph hyPh hyPh hyPh hy

ng su t > [b] ph hy do gy, v hoc t (fractography).u ti n xu t hi n v t n t t vi tr n b mt hay su b n trongpht tri n v t n tphhu Tu theo t i trng:a.a.a.a.Ti trng t nhTi trng t nhTi trng t nhTi trng t nh

Ti trng t nh: Ph hy gin v ph hyd o- Ph hy do km theo bin d ng do- Ph hy gin khng k m theo bin d ng- Ph hu gin xy ra t ngt (d), ph hud o xy ra t t (a) ch m (b), nhanh (c)- Cng cho ph hu d o ln hn- Ph hu do hay gin do:+ bn ch t VL: thp, Al, Cu ph hu do,gang gin.ceramic, polyme nhit r n ph hu gin

a) b) c) d)H nh 2.9. Cc dng mt gy khi ph hy

+ Toph hu gin, t i trng t v o nhanh, t ngt ph hu gin-+ K t cu g y tp trung ng su t (h bc t ngt, r nh, kh a, nt,..) d gy ph huginC ch pC ch pC ch pC ch ph hyh hyh hyh hyPh hy theo 4 giai o n sau:

1) h nh thnh v t nt (t vi),2) v t nt t vi pht trin di t i hn, ti h n3) v t nt ti hn pht trin nhanh,4) nt ch m dt v gy r i,

trong cc giai o n 1,2 v 3 c coi l quan trng nht, ng nh t.Tp trung ng sutTp trung ng sutTp trung ng sutTp trung ng sutTheo A.A Griffith: max:

tmax

a

2 = (2.1)

Gi

= maxIK l h s cng ng su t,

xc nh bng cng thc:aYKI = (2.2)

i vi v t li u gin, ng su t ti h n ghc n thi t ph t tri n v t nt l :

a

E2gh

= (2.3)

3 kiu ph t trin vt nt thng g p (h nh 2.13):

H nh 2.11. S h nh th nh v t nt

ngun l c Frank-Read

cn tr c/

a) b)

o

t

xx

2axx

a

o xx

max

m t c t dc theo

nt

H nh 2.12. S vt rng (a) v s phn bng sut trn tit din ct ngang qua vt rng
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23

H nh 2.13.Ba kiu ti trng v lan chuyn vt nt:

Ki u I l ki u thng g p hn c v c a v o t nh to n.Do t p trung ng sut gh(cng thc 2.3) vt nt g y ph hu gin v t liu. Gitrhscng ng sut tng ng ti c gi l dai ph huca vt liu,k hiu l KIC, c trng cho mi loi vt liu

aYK ghIC = , [N.m-3/2] hay [MPa.m1/2], xc nh bng thc nghi m

i vi v t li u do (phn ln kim lo i v v t li u polyme), u c bin d ng do trckhi ph hy, i u lm cho nh nt t (cn, bt s c nhn) i, bn k nh cong tng ln,nh lm t ng ghv KIC.Bng 2.1.Gii hn chy v dai ph hy bin dng phng ca mt s loi vt liu

Vt liu 0,2,MPaKIC,MPa m Vt li u 0,2,MPa KIC,MPa m Kim lo i Ceramic v polyme

Hp kim nhm 2024-T351

325 36

Hp kim nhm 7075-T651

505 29

oxit nhm - 3-5,3Thu tinh - 0,7-0,8B tng - 0,2-1,4

Thp 4340,ti +ram260oC Th p 4340,ti+ram 425oC

16401420

5087,4

Polyme ,PMMAPolystyren, PS

--

1,00,8-1,1

b.b.b.b.Trong i u kin ti trng thay i theo chu kTrong i u kin ti trng thay i theo chu kTrong i u kin ti trng thay i theo chu kTrong i u kin ti trng thay i theo chu kCu, trc, bnh r ng,.. ch u t i trng khng ln ( 105106chu k) ph hy mi.C ch : t v t nt u tin, thng n m tr n b m t l ni ch u ng su t k o ln nh t,i u ki n thun l i ph t tri n vt nt.Vt nt t vi tr n b mt: r co, bt kh , t p ch t, xc, li lm tng bng b m tV t nt c th sinh ra di tc dng ca t i trng thay i theo chu k (h nh 2.15a).

H nh 2.15a. S h nh th nh v t ntmi

H nh 2.15b. S mt g y khi ph hu mi

Mt g y ch ph hy mi (h nh 2.15b).2.2.2.2.2.2.2.2.Cc c trng c t nh thng thng v ngh aCc c trng c t nh thng thng v ngh aCc c trng c t nh thng thng v ngh aCc c trng c t nh thng thng v ngh a

mt

vt ntngun l chFrank-Readkk

vng 1, stb mt l

vt nt u

vng 3,ph

bi n d ngng su t

chiu d y

daiph

KIC

H nh 2.14. nh hng ca chiudy

Bth

Ki u I=k o Kiu Kiu III=x


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24C t nh cho bi t kh nng ch u t i ca v t liu trong cc iu kin tng ng, l c sca c c t nh to n sc b n, kh nng s dng v o mt mc ch nh t nh. C c ctrng c t nh c xc nh tr n c c m u chun.Thng gp nh t l bn, do, cng, dai va p, dai ph hy.2.2.1.2.2.1.2.2.1.2.2.1. b n (t nh) b n (t nh) b n (t nh) bn (t nh)Ty theo c i m ca t i trng ngi ta ph n bi t bn k o, nn, un, xo n...B n v d o khi k o l thng dng hn c n n khng c n ph i ghi ch, trng hp cn l i uphi ghi ch (nn, un hay xon...).a.a.a.a.Cc ch ti uCc ch ti uCc ch ti uCc ch ti u c trng cho bn t nh:h, C, b: kG/mm

2,MPa, psi, ksi (Anh & Hoa k),. Quan hgia cc n v thng gp nhsau:1kG/mm210MPa, 1kG/mm21,45 ksi, 1ksi = 103psiGii hn n hih, kh x c nh ch p nhn 0,01 hay 0,05theo cng thc:

0

dh

dhS

F= MPa,

0

01,0

01,0S

F= MPa, hay

0

05,0

05,0S

F= MPa,

Gii hn chy vt l ch,

GGGGii hn chy quy c 0,2 , [MPa]Gii hn b n b:

0

bbS

F= , [MPa], trong :

b.b.b.b.Cc y u t nh hngCc y u t nh hngCc y u t nh hngCc y u t nh hngCc phng ph p n ng cao bn:gimgimgimgimho c tng mt l chtng mt l chtng mt l chtng mt l ch.

. Gim: Si Fe l 13000MPa, Fe armco 250MPa

. Tng: bi n dng ngui, hp kim ho , nhi t luy n,...c.c.c.c. CCCCc bi n php ha b n vt liuc bin php ha b n vt liuc bin php ha b n vt liuc bin php ha bn vt li uBi n d ng do: tng m t l ch tng bn:

dp, g, un, gp, ko, cn ngui bin cng, tngb n

H nh 2.16. Thay i bn theom t l ch

Hp kim ha: a nguyn t l vo tng x lch m ng v mt l ch tng bn,To c c pha cng ph n t n hay ha b n ti t pha:Nhi t luyn ti + ram: t i v sau l ram - to n n s qu bo ha tng bn, cngHa - nhi t luyn: th m C, N... t ng bn, cng, ch u m i mn, n ng cao bn miLm- nh h t: lm h t nh ny duy nh t l m t ng t t c cc ch ti u b n, do, dai.2.2.2. d o2.2.2. d o2.2.2. d o2.2.2. d o do l d o l do l d o l kh nng bi n dng ca vt liukh nng bi n dng ca vt liukh nng bi n dng ca vt liukh nng bi n dng ca vt liu di ti trngdi ti trngdi ti trngdi ti trng

a.a.a.a.2222 ch ti uch ti uch ti uch ti u : %100lll

0

01= , %100SSS

0

10=

b.b.b.b.T nh si u d oT nh si u d oT nh si u d oT nh si u d o/n:/n:/n:/n:V t liu c ti tr n 100% (100 1000%), c gi l si u do,Cng dng:Cng dng:Cng dng:Cng dng: ch to cc s n phm rng, d i vi ti t di n khng ng u: chai, l, ng,..Ch to:Ch to:Ch to:Ch to:to t nh si u d o b ng cch:

- t o t chc h t r t nh, (c h t kho ng 10m), ng trc, ng u v n nh khi bindng, y l yu t quan trng nh t,- bin d ng nhi t cao, c (0,6 0,85) TCo,- tc bin d ng r t chm, c 10-410-3 s-1(tc 0,01 0,1%/s).

mt lch,108 1010 1012

b

n


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25

Trt khi siu d o x y ra ch y u theo bin h t2.2.3.2.2.3.2.2.3.2.2.3. dai va p dai va p dai va p dai va p:::: H nh 2.17: cng ph huS th va p (h nh 2.18).

-

H nh 2.17. Cng ph hu v t li u H nh 2.18. S th dai va p

2 loi m2 loi m2 loi m2 loi mu th dai va pu th dai va pu th dai va pu th dai va p::::10x10mmd i 55mm(mu Charpy) v 75mm(Izod) vi rnhkh a h nh ch U hay ch V: ( tp trung ng su t) rngxs u ( 2x2mm). TCVN ch quy nh th theo mu Charpy v k hi u dai va p b ng aK: nh ngh a: nh ngh a: nh ngh a: nh ngh a: dai va p l cng ph hy t nh cho mt .v. tiy di n c t ngang m u:

Cng thc t nh:S

Aa KK= , [j/cm

2]hay [kJ/m2]

trong : AKl cng ph hy, J; S ti t din m u t i ch r nh kh a (0,8cm2)

n vn vn vn v : [j/cm2], : [kj/m2], : [kgm/cm2]1kGm/cm2 10J/cm2; 1kJ/m20,01kGm/cm2; 1kGm/cm2100kJ/m2

Phm vi p dng:Phm vi p dng:Phm vi p dng:Phm vi p dng:

Chi ti t ch u va p aK min = 200kJ/m2 (2kGm/cm2), va p cao phi c aK 1000kJ/m2. Bi n php tng aBi n php tng aBi n php tng aBi n php tng aKKKK::::

N u coi aKt l vi t ch (0,2x ) aKt ng thi 0,2& do :-Lm cho ht nh m nl phng php tt nh t aK.- Ha b n b mt: ti b mt, ha - nhi t luy n va bn, cng, t nh chng mi mnm vn cho aKcao, chng va p tt.- T o ht trn, a cnh c dai cao hn khi h t c d ng t m, h nh kim.- Gi m s lng, k ch thc, t o h t c ng trn, phn b u ca cc pha rn aK.2.2.4.2.2.4.2.2.4.2.2.4. dai ph hy bin dng phng dai ph hy bin dng phng dai ph hy bin dng phng dai ph hy bin dng phng (plane - strain fracture toughness), KIC

Mu th:h nh 2.19 l dng mu n gin nh t, v t nt mi:

- ph i cng chi u vi r nh kh a v ch y d i trn sut chiu d y ca m u B = W/2,- trn c hai b m t ngo i, c 2 b n v t nt mi ph i n s u v o t nh t l 1,3- chiu di a (b ng r nh ban u + nt mi) ph i ~ B hay 0,450,55W.Quy tr nh th:- t ngm trc v o hai l, t c dng lc k o rnh kh a v nt mi c m rng ra(nt pht tri n theo ki u I).- X y dng bi u t i trng ko - m ca r nhnhh nh 2.20.

titrng

bin

vtliu

vtliu


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H nh 2.19.M u th dai ph hu bi ndng phng

H nh 2.20. Biu ko khi th dai phhu

Hshnh hc Y v KI phthuc vo hnh dng v ti trng (shape factor):

/im ca titrng v vt nt

Hscngng sut, KI

c im ca titrng v vt nt

Hscngng sut

KI = a (a


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27

Tnh gi tr A= 2,5(KQ/o,2), nu A B(a) KQ= KIC,ngh a ca Kngh a ca Kngh a ca Kngh a ca KICICICIC::::

L ch ti u c t nh quan trng nh t nh gi kh nng chng ph hy gin.

- Bit KIC v a ng su t thi t k ph i tho mn:aY

KIC

hay KI< KIC

- Bit KIC

v

kch thc vt nt a:2

IC

Y

K.1

a

(2.5)

2.2.5.2.2.5.2.2.5.2.2.5. cng cng cng cnga. c i ma. c i ma. c i ma. c i mXc nh n gin nh t, nhanh chng nh t,/n:/n:/n:/n: cng l kh nng chng li bi n dng d o cc b ca vt li u thng qua mi m.c imc i mc i mc im::::kh n ng chng mi mn, t o m u nh v n gi n, th t i ch, nhanh,..Cc lCc lCc lCc loi:oi:oi:oi:th i v t vi, thng dng cng th i. S ca c c phng php th

cng (h nh 2.21).

a) b) c)H nh 2.21.S tc dng ti trng ca cc phng php o cng:

a. Brinen, b. Rcvel, c. Vicke.b.b.b.b. cng Brinen HB cng Brinen HB cng Brinen HB cng Brinen HB: HB=F/S, F l ti trng, kg hay N, S din tch hnh chm cu.Quan h gia bn v cng:

- Thp c n (tr khng g , b n nng) b 0,34 HB,- Thp c b(0,3 0,4) HB,- Gang xm b(HB - 60) / 6,- ng, latng, brng trng th i bi n cng b0,40HB,- ng, latng, brng trng th i b0,55HB,- ura b0,35HB.

Tuy nhin cng HB cng c nhng nhc im sau:+ khng th o cc v t li u c cng cao hn 450 HB, mu ph i phng, to, d y+ khng cho php o tr n c c lo i trc (v c m t cong), o tng i chmCh nh v vy trong sn su t thng dng c ch o Rcvel hn.

d.d.d.d. cng Rcvel HR (HRC, HRA, HRB) cng Rcvel HR (HRC, HRA, HRB) cng Rcvel HR (HRC, HRA, HRB) cng Rcvel HR (HRC, HRA, HRB)o cng Rcvel HR (h nh 2.21b) ti n li hn do nhanh, k t qu o cho ngay

tr n m y v o c cc v t liu t tng i m m n cng, o t i ch, o c lp b

mt.Kh c vi HB, HR l lo i cng quy c (khng c th nguyn):- cng Rcvel theo cc thang C, A k hi u l HRC, HRA c o bng mi h nh nnb ng kim cng o th p ti, lp ha - nhi t luyn...- cng Rcvel theo thang B k hi u l HRB c o bng mi bi bng thp ti oth p , thng ha, gang c...d. cng Vicke HVd. cng Vicke HVd. cng Vicke HVd. cng Vicke HVL lo i cng c phng php o tng t nhBrinen, HV= F / S [kG/mm2] hay [MPa ]song vi nhng khc bi t sau:

D

F

d h d

Ff

F


10/14

28- mi m kim cng h nh th p bn mt u vi gc nh gia hai m t i din l136o- Vicke c dng o cng cho mi vt liu t rt mm n rt cng cho c ccmu mng (0,3 0,5mm), c coi l cng chu n trong nghi n cu khoa hc.e.e.e.e.Chuyn i gia cc thaChuy n i gia cc thaChuyn i gia cc thaChuy n i gia cc thang cngng cngng cngng cng

Dng bng tra (trong t i li u th nghim).2.3.2.3.2.3.2.3.Nung kim loi qua bin dng doNung kim loi qua bin dng doNung kim loi qua bin dng doNung kim loi qua bin dng do ---- Thi b nThi b nThi b nThi b n ---- Bi n dng nngBin dng nngBin dng nngBin dng nng2.3.1.2.3.1.2.3.1.2.3.1.Trng thi kim loi qua bi n dng doTrng thi kim loi qua bi n dng doTrng thi kim loi qua bi n dng doTrng thi kim loi qua bi n dng do

Sau bin dngvt liu trng thi khng n nh nung nng thi b n.Tc dng:khi phc li trng thi ban u: do v mm: bin dng do, gia cng ct,kh b ng su t b n trong trnh ph h y gin.2.3.2.2.3.2.2.3.2.2.3.2.Cc giai on chuy n bi n khi nung nngCc giai on chuy n bi n khi nung nngCc giai on chuy n bi n khi nung nngCc giai on chuy n bi n khi nung nnga.a.a.a.Hi phcHi phcHi phcHi phc

nhi t thp (< 0,1 0,2TC)Tc dng:gim sai lch mng (im:gim nt trng), gi m m t lch v ng su t b ntrong..., trong khi t chc t vi cha thay i, gi m in tr cht t, c t nh cha thayi.b.b.b.b.Kt tinh liKt tinh liKt tinh liKt tinh li (kt tinh l i l n th nh t)Bn cht kt tinh liBn cht kt tinh liBn cht kt tinh liBn cht kt tinh li::::qu tr nh h nh th nh cc h t mi khng c c c sai l ch do bi ndng do g y ra theo c ch to m m v ph t tri n m m nhk t tinh gi l kt tinh li:---- To mTo mTo mTo mmmmm:::: nhng vng b x l ch mnh nh t, bi n d ng do c ng mnh, c ng nhiumm- S pht tri n mmti p theo l qu tr nh t nhin.Sau khi k t tinh liSau khi kt tinh liSau khi k t tinh liSau khi k t tinh li::::thi bn: d o t ng ln v bn, cng gim i mt cch tngt.Nhit kt tinh li::::T=aTC(K), > 40 50%, thi gian gi nhi t =1h, kim lo i tinh khi t

th a 0,2 0,3, kim lo i nguy n ch t k thu t th a 0,4, dung d ch r n a 0,5 0,8. bi n d ng c ng ln, thi gian c ng d i h s a c ng nh.V d cc kim loi nguyn cht kthut:

Fe (TC= 1539oC) - 450oC, Cu (TC= 1083

oC) - 270oC,Al (TC= 660

oC) - 100oC, Pb, Zn, Sn (TCtr n di 300oC) < 25oC.

T chc t vi v htT chc t vi v htT chc t vi v htT chc t vi v htHt mi a cnh, ng trc, ht phthuc:-Mc bi n dng: bin dng nh 2 8%ht to thnh rt ln, gi l bin dngti hn,thng ph i trnh.- Nhit : c ng cao h t to ln.- Thi gian gi nhi t: cng di ht cngln.Thc t thng bi n d ng (40 50%), nhit cao (tu tng kim loi), thigian 1h(ti a khng qu 2h) h t nh.

c.c.c.c.Kt tinh li ln th haiKt tinh li ln th haiKt tinh li ln th haiKt tinh li ln th hai

H nh 2.22.T chc v c t nh ca kimloi sau khi kt tinh li

b,0,2

,k,

tktl1 tktl2 to

b

0,2

hiphc kt tinh li

ln 1 ln 2 d o d n


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29

Nhi t cao, thi gian gi nhi t d i: s t nhp ca c c h t "nut" h t b lm h t to l nth m c gi l k t tinh l i l n th hai. Xu ctnh phi trnh2.3.3.2.3.3.2.3.3.2.3.3.Bi n dng nngBi n dng nngBi n dng nngBi n dng nnga.a.a.a.Khi ni mKhi ni mKhi ni mKhi ni mBin dng nng l bin dng do nhit cao hn nhit kt tinh li ca n , cn thp hn l bin dng ngui. Fe 400oC bin dng ngui (Tktl=450oC)ch (Pb), thi c

(Sn), km (Zn) bin dng ( nhit thng)bindng nng v nhi t k t tinh l ica chng thp hn 0oC. Thng bin d ng nng nhi t (0,7 0,75)TC.b.b.b.b.Cc qu tr nh xyCc qu tr nh xyCc qu tr nh xyCc qu tr nh xy rarararaHai qu tr nh i l p nhau x y ra ng thi:- bin d ng do l m x lch mng to n n ha b n,bin cng,- k t tinh l i l m m t x lch mng gy ra thi b n, gim cng.

Nu : hi u ng th i b n > ho bn hoc kt thc bin d ng nhit mmNgc l i: k t tinh l i ti p theo = cch vi v o c t hay vi bt.

c. Cc c imc. Cc c imc. Cc c imc. Cc c i mV u i m

- Kim lo i xt cht, do cao hn, t khib nt, n ng su t cao, gia cng c cc phi ln,tit kim nng l ng.V nhc i m

+ kh ng u, t chc v c t nh, kmch nh x c h nh d ng, k ch thc,oxyho,

+ ch t lng b mt khng cao: vy xyt, thot cacbon.

a) b)2.2.2.2.4.4.4.4. n mn v bo v kim loi:n mn v bo v kim loi:n mn v b o v kim loi:n mn v bo v kim loi:

/n: n mn l s ph hu kim lo i di tc ng ca mi trng. Thi t hi do n mnh ng n m chim kho ng 4% GDP ca mi quc gia.2.4.2.4.2.4.2.4.1. Phn loi:1. Phn loi:1. Phn loi:1. Phn loi:Theo c ch xy ra n mn :a. n mn i n ho : n mn trong nc (ngt v nc bin), t, kh quyn m, trongdung d ch ho ch t (axit, ki m),b. n mn ho hc ( n mn trong mi trng kh ): cc ch t x m thc nhO

2, S

2, Cl

2...

2.4.2. C chC chC chC chca qu tr nh n mn kim loi:ca qu tr nh n mn kim loi:ca qu tr nh n mn kim loi:ca qu tr nh n mn kim loi:2 c ch n mn thng gp nht l: cch i n ho, ch yu i vi kim lo i v c ch n mn ho hc, i vi t t c cc lo iv t liu.aaaa.... C chC chC chC chi n ha ca qu tr nh n mn kim loii n ha ca qu tr nh n mn kim loii n ha ca qu tr nh n mn kim loii n ha ca qu tr nh n mn kim loia. in th i n cc v kh nng xy ra n mn:

i n th i n cc kim loi:i n th i n cc kim loi:i n th i n cc kim loi:i n th i n cc kim loi: nh lu t Nernst: Meo

KL ClnnFRT

EE += ,

Eoca mt s kim lo i:K/lo i : Mg Al Zn Cr Fe Ni Sn Pb H Cu AgEo, vol:-2,37 -1,67 -0,76 -0,74 -0,44 -0,25 -0,14 -0,13 0 +0,34 +0,80

H nh 2.23. T chc th ca trckhuu theo cc phng php

ch to khc nhau: a. to phibng dp nng (tt), b. ct tmt thi thp nguyn (xu)


12/14

30i n th i n cc mi trng:i n th i n cc mi trng:i n th i n cc mi trng:i n th i n cc mi trng:

Mi trng axit khng ho tan oxyEMT= - 0,059 pH - 0,030 lgPH2, EMT= - 0,059 pH khi p sut ring ph n ca hydro PH2= 1 at.Mi trng axit, kim v mi trng nc (ngt v nc bi n) c ho tan oxy

EMT= 1,23 - 0,059 pH + 0,015 lgPO2, EMT= 1,23 - 0,059 pH khi PO2= 1 atKh nng xy ra n mn:Kh nng xy ra n mn:Kh nng xy ra n mn:Kh nng xy ra n mn: Kim lo i ch b n mn khi EKL< EMT,Trong mi trng axit khng ho tan oxy (EoH=0) do cc kim loi c E

o< 0 s b nmn l : Mg, Al, Pb, cc kim lo i khng b n mn l Cu v AgKhi axit c ho tan oxy th EoH(O)=1,23V do t t c cc kim lo i trn u b n mn.Trong mi trng nc Eo khong 0,4V tr Ag cn hu h t c c kim lo i u b n mn.Khi kim lo i b n mn th xy ra ph nng: Me Men++ neaxit khng c oxy: 2H+ + 2e H2,axit c oxy: O2+ 4H

+ + 4e 2H2ONc c oxy: O2+ 2H2O + 4e 4OH-Xem s h nh 5.15. Cc electron dichuynt ant sang catt, H+ v O2 chuyn ncatt

H nh 5.15. S n mn i n ho kim lo i

RU

I m/a = ), trong U l hi u i n th gia catt v ant, U=EMT-EKL, R tng i n tr

n mn galvanic: latng 2 pha: gi u Cu v giu Zn khi ngm trong nc pha s b nmn thnh cc l, ta gi l n mn tho t Zn.bbbb. C ch n mn ho hc kim loi. C ch n mn ho hc kim loi. C ch n mn ho hc kim loi. C ch n mn ho hc kim loi

n mn ho hc kim lo i Me c m t bng ph n ng sau:xMe + y/2G2= MexGy

trong G2l ch t kh g y n mn : O2, Cl2,

Nng lng t do ca ph n ng n mn cn b ng bi u th bng:

G = G o+ RT ln2

1yGP

= 0, do : ln PG = yRTGo2

biu din trn th : (h.5.16):

H nh 5.16. Gi n pha ngng t2.42.42.42.4.3.3.3.3.Tc .Tc .Tc .Tc n mnn mnn mnn mnthng c bi u th di 3 dng:---- Mt dng n mn:Mt dng n mn:Mt dng n mn:Mt dng n mn:ia/m=Ia/m/S, c th nguy n l : [A/cm

2], [A/dm2],

ant

H+, O2

e-

kim lo i

catt

Men+ O2,OH-

. Khi PP1, Me1 b n mn (vng n nh MexGy). T=TC: n u P>PCc 2 kim loi b n mn(PC>P1). 2 kim lo i Me1 v Me2:T>TC (tri im TC), Me1 b n n mn hn Me2T


13/14

31

---- Tc n mn khi lng:Tc n mn khi lng:Tc n mn khi lng:Tc n mn khi lng:Pkl=m/St, th nguy n: [g/cm2.ngy].---- Tc thm nhp:Tc thm nhp:Tc thm nhp:Tc thm nhp:Ptn=Pkl/, th nguyn: [mm/n m], (- khi lng ri ng ca kim lo i).Da v o tc thm nhp ca mi trng, ngi ta chia kim lo i thnh ba nhm:. Ptn< 0,125 mm/n m c coi l rt bn n mn, . (0,125 < Ptn< 1,25) mm/nm l trungb nh. Ptn> 1,25 mm / n m c coi l khng bn n mn. Tng ng, ngi ta cng chia tc n mn thnh cc lo i: chm, trung b nh v nhanh.Theo ASTM, bn n mn ca v t li u gm 5 c p A,B,C,D,E theo th t gim dn.2.4.4.2.4.4.2.4.4.2.4.4. Cc yuCc yuCc yuCc y u t nh hng n tc n mnt nh hng n tc n mnt nh hng n tc n mnt nh hng n tc n mn

a.a.a.a. nh hng ca bn cht kim loinh hng ca bn cht kim loinh hng ca bn cht kim loinh hng ca bn cht kim loi---- i n th n mn:i n th n mn:i n th n mn:i n th n mn:Mi kim loi trong mi trng c th c mt gi tr i n th n mnx c nh. Gi tr ny c ng nh th kh nng x y ra n mn cng ln.---- S th ngS th ngS th ngS th ng n mnn mnn mnn mn::::Cc kim loi Fe, Cr, Ni c kh nng th ng n mn tc l tc n mn gim nhanh theo thi gian, tuy nhi n mc kh c nhau: Cr th ng nhanhnht thp khng g c >12%Cr. Fe (th p cacbon) c th ng nhng ch m, ttln.b. nh hng ca mi trngnh hng ca mi trngnh hng ca mi trngnh hng ca mi trng

---- in tr ca mi trng:i n tr ca mi trng:in tr ca mi trng:i n tr ca mi trng:ch c mi trng dn in mi c n mn in ho, intr cng ln th tc n mn cng nh.---- nh hng ca pH v oxy n in th i n cc ca mi trng:nh hng ca pH v oxy n in th i n cc ca mi trng:nh hng ca pH v oxy n in th i n cc ca mi trng:nh hng ca pH v oxy n in th i n cc ca mi trng:Gi m pH (mi trng axit), tng nng oxy th tc n mn t ng

---- nh hng ca nhit :nh hng ca nhit :nh hng ca nhit :nh hng ca nhit :khi t ng nhi t tc n mn t ng.

c. nh hng ca cu trc v t nhnh hng ca cu trc v t nhnh hng ca cu trc v t nhnh hng ca cu trc v t nh cht ca hp kim:cht ca hp kim:cht ca hp kim:cht ca hp kim:

- Nhng hp kim a k m b n n mn hn hp kim mt pha,- Hp kim ho vi cc nguyn t c Eocao s lm tng EKLgim nhy cm vi n mnhn.- Hp kim ho vi cc nguy n t c kh nng th ng n mn th cng tng kh nng

th ng n mn ca hp kim. Tc n mn thng li n quan n b n ch t ca m ngoxit h nh th nh tr n b m t : axit (Cr, Si), baz (Fe,Ni,Cu), lng t nh (Al) ho c tr (Pt).d. nh hng ca cc cng ngh vt li uhng ca cc cng ngh vt li uhng ca cc cng ngh vt li uhng ca cc cng ngh vt li u

. Ti nh n c t chc mt pha ng nh t s bn n mn hn.

. Thp cacbon trung b nh sau khi ti th t nhy c m vi n mn hn nhng sau khi ram l itr nn nhy c m vi n mn. Tc n mn ln nh t khi ram 400-500oC.. Khi hn ho c nhi t luy n c s ti t pha: n mn galvanic.2.2.2.2.4.4.4.4.5.5.5.5. Chng n mn kim loiChng n mn kim loiChng n mn kim loiChng n mn kim loiThi t k k t cu hp l, m bo cc nguy n tc sau:Thi t k k t cu hp l, m bo cc nguyn tc sau:Thi t k k t cu hp l, m bo cc nguy n tc sau:Thi t k k t cu hp l, m bo cc nguyn tc sau:- Chi ti t quan trng: v t li u b n n mn hn, ng su t n n, nh v khng thay i

- Thay cc mi ghp inh tn b ng hn, v t li u l m inh tn, l m bulng c EKLcao hn- C c thng, cc b cha, cc ng ng d n: d lm s ch, chy h t, khng g p khc- D bo dng thay th cc b ph n d b n mn: cnh bm axit, c nh khuy,..- K t c u ph i hp l va m b o y u c u k thu t, va d chng n mn.La chn vt liu th ch hp:La chn vt liu th ch hp:La chn vt liu th ch hp:La chn vt li u th ch hp:

3 quy tc chung chn v t li u kim lo i :1. Trong mi trng kh ho c oxy ho yu: Ni ho c hp kim Cu2. Trong mi trng oxy ho: cc hp kim cha Cr3. Trong mi trng oxy ho cc m nh: Ti v hp kim TiX l b mt chng n mn:X l b mt chng n mn:X l b mt chng n mn:X l b mt chng n mn:


14/14

32Cr : Ch u m i mn, xi mn v ch u n mn r t tt, h s ma st nh, phn x lnCu: D n i n, dn nhi t t t, dng l m lp n chn cho cc lp m kh cNi: B n n mn trong nhi u mi trng, m a lp vi Cu+CrSn: B n n mn trong thc ph m, b, sa, d hn, l catt so vi thp (ch c t c dng cheph)Zn: B n n mn, l ant so vi thp, c t c dng b o v cattLp sn chng n mn cho cc lo i cng tr nh kh c nhau c p dng nhsau:

-Mi trng kh quyn thng thng, dng sn tng hp alkyd cho nh , xe c, c u,..-Kh quy n bin, dng lp sn acrylic, phenol, vinyl, vinyl-alkyd-Mi trng ng p trong nc, dng sn Phenolic, Vinyl cho v t u, nc tu-Hi ho ch t, dng Epoxy, caosu clorinat, vinyl, urethan, cho thi t b ho ch t, v t dngkhc-Cng tr nh ni c m cao, dng sn amino alkyd, cho t l nh, m y gi t- Nhi t cao, dng sn Alkyd, cho ng c ch u ti 100 oC, sn aminoalkyd bin t nhcho thi t b sy nhi t t i 100 oC, sn Silicon bi n t nh cho l s y, l nng ti 200 oC,sn silicon c thm ph gia Al cho l sy, l nng t i 290 oC n 650 oC.X l mi trng:X l mi trng:X l mi trng:X l mi trng:

1. H thp nhit th tc n mn gim.2. Gim tc chuyn ng tng i gia mi trng v kim loi th tc n mngim

3. Kh oxy v cc ion thc y n mn (Cl) ho tan trong mi trng4. Dng ch t c ch n mn, to c c hp ch t l m chm n mnBo v i n ho:Bo v in ho:Bo v i n ho:Bo v in ho:2 phng php bo v i n ho : b o v catt v bo v ant---- Bo v catt bng ngun in:Bo v catt bng ngun in:Bo v catt bng ngun in:Bo v catt bng ngun in:h nh 5.17a. EBV=E

a/m- 0,2V, ng th p ng m trong t:Ea/m~ -0,6V EBV=-0,8V, m t dng b o v IBV=(10-30)mA/m2, trong nc ngt

H nh 5.17a. Bo v catt bng dng i n 1chiu

H nh 5.17b. S b o v catt b ngprotector

---- Bo v catt bng protector:Bo v catt bng protector:Bo v catt bng protector:Bo v catt bng protector: p dng cho cc cng tr nh ng m trong nc bi n: ni kimlo i c n b o v vi protector: Zn- (0,2-0,7)%Al+

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