DISLOCATION VELOCI'l'Y I:'J SINGLE A..c\'D POLYCRYSTALLINE SILICOi\J - IRON·"

D . lV . Moo·a+ aria. T . Vreeland, Jr.

W. M. Keck Laboratory of Engineering Materials California Insti t ute of Technology

Pasadena, California

ABSTRACT

The stress dependence of sere~~~~ disloca"cio~n vcloci L)r i11 single ar1d

polycTystallin.e speciJT1ens of an iTon - 3 . 1490 silicor-1 allo)r T~~Jas m8asu:_--c;d

by observa·tion of slip band growtl-;. An electrolytic etching techniqt.:.8

was used to reveal dislocation intersections with the specimen surfac e ,

and slip bands 1vere obs erved to form from fresh scratc}:.es and from

grain boundari es as a result of pulse loading. Screw dislocation

velocity on the {110} (Ill) system in singl e crystals at room

-::.c:11perature followed the relation v = (T/T0

) n where n = 30 . 1 . A

plot of screw dislocation velocity vs. nominal r esolved shear stress in

individual grains of polycrysta!line specimens s hows considerable

scatter w·h ich is at tributed to t}1e effects of s·:::ress vaTiations due to

elastic anisotropy . Observation of slip band growth in scratched and

unscra'cched grains indicates that ·the stress required to activate g-:..·ain

bounda:;..7 sources is g:ce:::.ter than the st:;..·ess required. to proDa.rrate fresh

dislocations .

·;, This VlOTk i-Jas spo:-~~~ors

2

INTRODUCTION

The mobility of edge dislocations in silicon- iron was first studied

by Stein ~ l

a11u Lo\\I. They stress and temperature

single crys tal specimens .

on tfi .. e r' , ; /, , _.,,, t _j_ _j_ 2 r , _j_ _j_ lJ systen1. Their results show that edge dislocation

1.relocity is a --.. .rery se11sitive fur1ctio·n of s-'cress i:i.1 si li con-iT011 'dhich

7

contains sufficient for tte Dunn and Daniels etching - • J technique

to be effective .

Bo .. ~h dislocation locking by· intei---sti ... cic:l imlJll:cities and disloca~;:ion

d)'11an-1ics have been used to explain ·vai~ious aspects of the yield p11er1omenor1

in BCC materials. The earliest disloc2~-~ion theo:ries of a disti11ct yield

point were based upon the concept of Cot~rell locking of dislocations by

intersticial impurities. The yield point drop was attributed to t he first

break - away of dislocations .

that a yield point drop in single crystals

of dislocation inul tiplication arid rnotion.

c Gilrnan...; and

ca11 result from the

dislocation kinetics theory to the yiel ding of polycrystalline materials.

Neither of these treatments considered t he heterogeneous nature of the

polycTystal line ma"'~e:rial. r~"'l:c Ye Sul ts of the S"t:Lldy Teportecl he~~ei:n. give

info-r-1110.tion or1 \,..rhich a 1110-:rc quaJ:1titat.ive tTeatT11er1t of dislocation dyna111ics

in polycrystalline materials ") ~ ,

n1ay oe oasea..

Conflicting conclusions regarding the source of dislocations in

polycrystalline silicon- iron appear in the literature. Suits and

9 - ' Cha.l1nc::-s conc1 :.~Cled t:J:.at th.2 so:...1rces of !11.cbi.lc clisJ.ocatior1s &TC lace;.:

across gTa:i.n s ·with the s tress rcqui~8ci to produce a suff icicn·cl)r

[1ig:h Gislocatio11 vclocit)'· ~ . •' 10 ' ; h J ~rni -ch OOS8YVCCi ·:.: .... ac

g rain. bounda:r=!._es SO'!.JYC:C of mobi ~e dislo c a t ions in

They also concluded

t hat the stress necess ary to generate dislocations is les s than t~e

stress necessary to move dislocatio~s across grai~s.

of dislocation source s within the grai~ and sources at or near the

gYai~ boundaTies) and to th.e l"()lat~ ve irnpol'"'tance of souTce acti ·vatio11

and disl 0cation niobility in tl-Lc forwat:.on of slip baT1ds.;

used in this ~1vestigation. Table I lists tto composition of tte ai1oy, r-

which is from t he same heat as that used by Suits and Chalmers.~

Silicon CaTbon JvI:'..::1ganese Pho s-ohorous Sl1 1 phuT l~i ckel

Co1Jpe :L"" Tin ~..., ., . L.i1YOTI1lUill

Al uni.inuin IT011

Ti\BL:S I

3. ltj. 0 . CO]_ 0.043 0.003 0 .0 18

0.079 C.010

T~·ace

Re:ma~L:_-1dcr

"'. -'._:c; be revea~ed Oy tl1e Dunn a~1d Dan.ie 1s e t cl1i11g -tec1-l11i ql1e . ...,

t h e a s -received strip stock was gas carburized to increase t he carbon

been co l cl Tolled to a 6% rec.-._1c ·tio~n. in. ai""e2. . Re crystallization for ; \ .._ ..L ......

... , -:-Cl. \... (an average of 6.7

A dislocation etch pi~ den3ity

h - 7 - 2 of lOV to 10 cm was observed wi~hin ~~e grains.

Single cryst&l specimens were ~rod~ced by the strain- annc&l sethod

or not GT. C.-1 ·co

:~:isJ..:JC.:::lt:5 .. 011S.

of ~asscd the into

t 1"1e 1'"'..ot zor1e ol. th0 furnace~ Within this small portion of the single

c: ... ;rstal, etc}1ing t~1e ·ooL-:nda~ti es of a

c losely res embling the adjacent polycrystall ine gr&in structure .

bc1:.u:vio'l ....

grain boundary carbon is r eleased so ~~at the carbon content of the

sillgle j_s

oi dislo cations.

to the polycrystalline material, the ~orraer grain boundary carbon nas not

su~f~cient dif~usion ~- -, .... .., ,--:,. l..-..L 1Hv dis t-:i~Jti.-~·.3d

single

and 112nce

specime11s

,rovi~c the correct carbon content for dislocation etching. 7he

6

·1:0 o.ocs weigh~ % carbon was accomp l i shed by he&t in~ for 10 :"'t ,-. ··-c .... l,... r , 1·/rOri (,.j ;.) \_;

Dis lo -

cations in c-r;.rstal.s etched

these trcztments, a~d the dislocation etch pit densi~y was 106 - 10 7 c~ 2

1~e single crys~als were to

and polycrystalline speci~ens by scratching a polishe~ surface o~ the

The specimens were pu se loaded within 5 min o: scratching.

~ise

?ulse loading of t he

lin1itccl ·co 1% of ·i.:}1e

2 1nsec.

r:.

1 7 -'-J

-;:Gi1Sile

' .. .., \.:ens:!_lc stress by these fixtures.

oi .... oac. vs .. ~ iill e was recorded

E=.ec.,.:.:; . .-·oly-~j_ c etci~i.ngv i:rr~·Tled:.a-'ce::. 1 afte-i ... loaa

. ' a.c:t_c.

etcn pit ~ac e i.e .• ~

~ . ,.., . . -- r·- ·· ..:;;.,..:_ . ., , ;,.... .:..::. se on

2. Sl

section were used to

.r::-; ··· ·'-....... ~ ( .'- ~~

- . :.L 2 ·~: e :.:·~·:·, :~_ r:. e

the Mil ler inaices of the slip planes .

be clearly icicntified.

single slip ~race is .r:::,....,_., •.. ,.,, -"- ~,, ;._,j,. _-. ..

s:.rs t . 8~T:S Vl2i.S

. (: ~ ~ _-.;_'_-_.·::.. ~ ~- ..:: -""\ "'c~-- ~J- -..L;_J

The resolved shear stress xar each oE t~es e

eac1: C2.se

st resolved shear stress was cf t\e ., J_lO j· ; i .· -"- - ·"'

The final mo~e cf defcruation

Disloca~ion velocity along the slip trace on ~he

given

_ ) 2 .. 8 A lO -~ CE~/ sec .. "i.'/GTe -i...~.l1Sl.lCC2SS :C·:.1: dL~_;.:_; ·co "2:\·1i·;.'1:.:i:.1g o:: cl.cs.:vage or· ·i:.:l1e

specirnens ~ Tole crac}:s

is COi'".:.SistCT'rt

T~1e i;eJ..cci

plying t~e observed vcloci~y

'. ' ~ .

screw dislocat i on ve loc ity vs. r 2sclvcd s t ear stres s aa~ a fo r ~ n o

s le cryst ~ls follows tho relation

v

-,

i/ 0

T c

2.30 _.,,.. ,;..C~

The dislocat i on configur&ticn

SOlTI 8 slip

~raverse the entire grain.

Tl 3G ~ 1

bands wn1cn general

cation ve l oci~y vs . stress ~est s . Screw dislocation velocity was ob~uined

fro~ the observed ve loci~y along ~te s1

dislocation velocity vs. t~c no2inal resolved snear stress in tic gra1n

i_s - . -f1 __ o~c.~=. c c~ 3 ..

crysta~ 1 1ne S)ec imens raay oe seen in Fig. 3, an a tte data poin~s all l i e

1e c~cystals.

Spt.. c51: --il l\ r_' .

(". 1.. • .1 . ~

Sl O

S9

ETL

SJl

SJ.J

;_::1 1

SlO

Sl2

S2

( "' 1..) .>

( 1 C1 i..J (';

S9

s1:;

R',:;o l\,-cd SLc aJ~ St:[·ess

r -1

" ·; ,, - -· , · 'l J. u J "-'--' ''

io_~ -~~xnc:_~L0.~C._ . l. 4'1

1 r:.· 'i . ... ,t.,.

l. 52

L60

l.60

1. 74

l .f45

l. 0~1;

1. 93

1. 96

1. '/3

1 .88

r J • 7 !: 'l. l.80

r 1. 91 'L 1. 83

TJ\BLE Tl

Results or Single Crystal Tests

l~csoh'l : T\·;i1111i-11 6

s -ucsc; .r] J ? 'i / 1 1 -1 ':-L -,_- ·-J .... _._ .J. J.~

·1 n9 1 i 2 - v c - Y~"j~~t . ~~2l _ cL~ .. - --- --

1. 6:5

1. 57

l .M

1. 52

1 r r. •JU

1. 66

1. / (>

J .86

]. 87

1. 86

l. 88

1. 9'7

l. 93 l • SH

2.03 ] (' ~ - ~ u(.;

Ob __ . (-~T 1 · ~rJ Dis JOU L io:1

S CTC:

U :i. ~; J oca t- ::_ ()'.1 Velocity Veloci t y

cli1.I s ec. cm/;:: ____________ } ____ ~'-·--···- --------·- --~---· --- -·- ---~------r:

7 . 19 )'. J () - \_) 7 / 0 -.- 11)-6 .J • J '-. - -- '-r

J , 0:2 :x JO ·-.) 4 . G S ~~ J 0 - 6 r:

i. 21 x JO .. J 6 ? 7 ] , --6 . ---· x __ () 3 (' ' 1 ( - 5 • j::; } ~ -- 1_) rA y -1n-S 2 0 ,) • 0 J'- , L V

~

1. !J G x 10-.. , -- r:; 9 . ,:0 x lO.

7 -·n --- - r--4 -' . /I; A .I cl

~.-- (! • . - 4-2, ."l o X 10

-· 3 1./: 2 x 10

11 9 , }ff } _ 10 '

-· --;, 6. 01 x 10 '

7.

2 . 7 !! )~ Hi - ,,

2 "(• - 1 ' '1 · -2 • 0,1 x .. l. ' I -· .,

4 .85 x 10

·1 J

F:Ln:'l Behavior

f. 1EL:.~:-~jvc Sl:ip

l"··~~··.3:: j "/0 s J_ -~ }} l\~(~_;3:.~:ivc S1jp

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1- ~ 850

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-- f:-3 "i 61

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-; 79 (~ . '.

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vs .

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A ~c·~·.r ~----

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" " -.::::. - -... ......... __ DC~llC..C .. ::.-:.cs .. c ::..:

c:_ ~ . .S :'._ G 1.::. ~-~ ..

so~ ...... :-::G

(

Ct.c_ l11:.e:"' s 'J

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c .. . ··- -1,...-· ._. ___ ....... :::;i

~:.- .. ' -~ -·-Loi.:. •• ...:.... ...... .:.

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........ ...:;: _ .. __ ,__ \~ __ -, ~-· -:1 -~·· . s

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acco:_---di::g -~ 0

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-- ... - .. _, .. ,., ·_J.:... ___ ,, ..,. ___ .I

- . -· . c. ::.. s -~- oc~:·c ic.:::s

,,->_ - , . \. ... _ ... _

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i, . ,.. , .... -- ., .- •. _ ... ---....,, _,.._. .._, ____ ...... ~

., . - . c..:..~ .t. C, 2 8.. . .:2..0i"'..S

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-·- -· - ,.... ..... -~ ... :c

-~·1·• ,., - --~ .._, .,, .,_;

~ .. . - ,..... •. ,.,~.~ .~ ... . -.. \.,...' .l. ~ I.'..· \....4.

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--" .. ~ -·-:... .i. •. 1·.- ·--

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G

1- - r -1.:. C.1 • ..:J 8.

L. " : . . J

-- -..... 1 ... 0.-:. ~

...... -.~ r

(..,,..:. ;. \~-

-r~ -, ., ·~ -,,.., ,:: ·-'- '-· 1._...·_...· '-- ·~ ..;_ ~r

~ '•-. ."

act CLS

l'l

s _ .... ~·

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;_; .

0 is

,, .:; .

7

0. r, _-.. "

' .... .

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. ; -· -. ".:· · ·"- C '·-· ._,_,_ -·

-- . ' i'·~:-_; .:.. J. CJ: i. ~:s ·,: =:... -.=. ::L·:.. 8

--- ... _-:,..,,.~ ::, ·f- .. - , -c. ~- , __ ;..._) ;... >,.,.: .:..~

) -..- ,,.- -- ... ; !.J..J.. ...__;. ...

T"-

., 0 .,

~ .. ·_:fo;:.'d:;

_i._ _ _,,__, ..

. -.,. - -'-'-•

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- ('' ...: - ' _ :._J .._I_._) J _ _i'. "i .

. ' 727 -· .". ,.: "' :.... .,,_ J ·..__, ~-- -··

,.... .. ,

c-·. ,.... .. U L.Ci.'-.-

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7

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352

,. .. ,~, ~::. -, ---- - ~,..)

., --. r'

...... ,;. .:. "--'" ~

.... ,J i.;. ...... •._,

-- :.._)._:. :..._.

I~

· ; ··- '-~ ·- · - , _,,

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- ('1_::--:-,.., ...:.. -..>...J~..J

r, .~j

1.: : . !1 .... . --·. ~:, ,_·.

--··----·---------------·------- --·-·------------·---·-------···- --- --- --------·

Figure l. Unit stereographic triangle showing location of the tensile

axis for the single crystal specimens .

,. -,,

····· -~ -:~·;::: .. ;<

"· -.

,·.'•

• • •• 4.

•:.-·

-----.--.. --·- ------ ---------------- - -·- ··- ····--------··- --- - - -....... -... _---~-- ·--------·~------·- -

J:'j_2urc 2. Dislocation conf i gurat ion after a pulse load in single

crystal spcciwcn S9 .

·!("\:-: ~ ,..,_ ~

"l ' ~ ( .... ~· »:· ~ ~--: · .. ,,,/

...

1 ,•:

: ... , ... ..• ·"'

''-- ~··''

·~ • .......

/ ,-.. '•·' j

. " .. t

..... t ,.w·'--~.~: -' ·~. ,,.

--- .. ::: .. (""'· ,P"'"•

• ·~- • ·- --·· 'i, ~,;"

··- -----------------~- -~ ------- ·-----

_ .... ; ,. ~) • ... :

, .. ,

. , .

r:) 0 c~,~

r,r-~ - ......

() ()

(~~~ () ·C

oc~c/J o ()

0

l

t ~ .:-. -· .. -. .; ...

,. _,-, r · · " p

i !

r

J

~I

, .. : ··., . .,. . ..., ; : .. ~ ·,, •. ~ .

Figure 3. Stress dependence of screw dislocation velocity in single

and polycrystalline specimens. Edge disloca tion ve . ocity

l £1:of!1. the d :1t a o[ Ste i n and Lm·1" :1.s ~~hown 0.s a ch.she d l:Lnc .

Figur e 4.

F :Lgurc 5 .

Typical dislocation configuration in a scratched and aged

specimen ..

· ·~:

" ' ;_ { / ·'

' .. ·:,.:-~ .. ,., · .. -;>· ::'~>:.-:~-.4"-.. .:_;< ~->.

·:· / ... ( ,.· -....- -'- ·

,..,,,, .. .,. ,_

-:~ .

Typical disloca tion configuration in s cratched, pulse loaded