Post on 26-Jan-2021
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
rI\~r~i fl~ l.j .1."~~~
T1,,r =i .·1
'I\,:;nning
'1'1.-.ri ri !. ! :Lr~
C 1 ~~~1 VC:t[.: '.)
f· - '
0
r-o --l J
TS
T2
s~;TT!EC.~:."'Y c :~~ S~= --"'OS :.; ' / 5 . Di. s ~:_C; c~~ ·~ :;_ C>T1 \T 2 :_ o c i ·c ~,.,- Te..::..-:.~ s on ?olyciys~&lli~e S)ecice~s
1- ~ 850
Ci . 529 3.68
0.175
0.017
..... - ... -~ .; -~ v~- (~ ......... ;. .-.
,., j
8
_u
-· ...... ~-
2
5 •' v
7 s
2
5 6 7
s \rel oc. it: ~/ 2 Cj~C/c~ cs/sac. cm !s s~ .
·- ~.: 5
-i S8 - ... '!'/
/ ~
l ~-~:.
- 3.: ! 5~-
-- f:-3 "i 61
-, c '7 -- ,) .
_._ .-57
- 62 _, 7J - .. 70
-; 79 (~ . '.
- l.) •· .-
l ·,. 8 - 97 - 75
., -S9
- -- ---------·
0 OiJl '7l 0 Q;__;=._ 7-i
u OC233 0 -~ CJ3 L,.?.
0 0 __ 53
. l 0 -i _.,,. ~
J Cl7.3 u (JlS ,_, 0 GJ56 7 l) 01 ::15
0 0267 0 () __ 75
v __ ,__(__;
!"'1 -0 -'- ~-""'
V- ~ 363
~-"-202 0 177
0 -"- 86
\j .. ; u ..L J"-J
('. . t~ ·" -... ~ \ J \JJ,.,1,_,u _
f' r ' - ,-t.J --..~ -- .... -~
() 002::5 0 GOOC-'?S
C OJ76S
0 00020 () u .i.27
0 C77c.-
v GCS4 u i..:;.7 u 06.:.,.!;,
0 OS:>O
_i_ ..... J... ·-
l\0 .
..... : ·~~ ::: (': ~-~ ~:: - ,._ ~' 2
0 . 0l 7 c: . • l O " :J -- :1. " -- ! ~- " ,,, v ,) . - ,.) l ' ') - ,, 0 0 s 7 - ~ .L ._) v "
' 7 0 u J. \J r ) u r I 7 . V' I L!. .., 0 r, ~~ .2 - 0 C: ,.. -- -- I v - ~ ;_,; ,j _, '.) ·; ..... ; 7 Ci
, . G r. 0 - , -- v u .:'._: \~ 0
-· s ' - ~~ C\ ,r 7 I' < --'- u v 0 -- J v _,_ .,'j ! .L 7 ~~ 0 .~ " ? 0 -- .J _, () J - · -, -; ,-. g n / ,~ 7 0 r '" -- -- u vj I,) \ _/
- 7 2 ...-, 0 --·- ,/ ,_ v· --v -~ "' - " -''- (\ " u Lr 0 (', •, --J -- "' v - v -, J _, 2 - -i 7 ~ c [ - G n _, s - v -- - u -'- 0 L'. J l u 2 - .::; C· 0 7 - -- -- -
n 6 ,-, " 3 7 " -, . .) -'- () v "' J _,_ -/ '
r• 0 r 6 6 r-,,
2 ' ? r ,L v v - u v -2 ::;, ''/ !;. ' 2 n u -· - I J _, 0 .L - .:.>
- ---- - ~~ C
o·\.,,: ·.:
r. . , ... , ; ·: .:.:
:_.,.;
- [J -{
2 c~;stal ~nd ~olyc~ys~al~~ne
'fl: is .. .. . .
CC\T .,_;__-:_ ·c. :_o-:!_ is
vs .
. - , .. s::._1cv~~~ - :.T·c~'"'... :-.. ~~:y
Sil) -;; C .s 2:: .. :vccl
A ~c·~·.r ~----
-: ~ ~ V/.!.;_:.,_.._:r: . . ::...J...C. .• l. v ,_
" " -.::::. - -... ......... __ DC~llC..C .. ::.-:.cs .. c ::..:
c:_ ~ . .S :'._ G 1.::. ~-~ ..
so~ ...... :-::G
(
Ct.c_ l11:.e:"' s 'J
Sr:~=!_-;:il~-- -..;
c .. . ··- -1,...-· ._. ___ ....... :::;i
~:.- .. ' -~ -·-Loi.:. •• ...:.... ...... .:.
.i.. ,_ '· ~ -- .\
........ ...:;: _ .. __ ,__ \~ __ -, ~-· -:1 -~·· . s
J_~-... c:::r·casss ..
acco:_---di::g -~ 0
- ., ' •• •• , ""l
:. c.- ,.--- 1!. ~: -.J·~ :.:clc.. a~ ... --::. 8 s
-- ... - .. _, .. ,., ·_J.:... ___ ,, ..,. ___ .I
- . -· . c. ::.. s -~- oc~:·c ic.:::s
,,->_ - , . \. ... _ ... _
.. '-"--·
i, . ,.. , .... -- ., .- •. _ ... ---....,, _,.._. .._, ____ ...... ~
., . - . c..:..~ .t. C, 2 8.. . .:2..0i"'..S
-r_ ·- ·- - -· . .1 u ~-- ·-~
' ' -t.O:.;:.c. ~ ,....,. _ ,-..
,J.. . h;;
·.: sst s of
cc _._-:_......, ;,.. ; ... ~;;
-·- -· - ,.... ..... -~ ... :c
-~·1·• ,., - --~ .._, .,, .,_;
~ .. . - ,..... •. ,.,~.~ .~ ... . -.. \.,...' .l. ~ I.'..· \....4.
, .., ' ' .. · 1 r · · • •· - • • ,..., ·~ \ • : :.; ,_, ••• '.' .: • • 1~ -'- ·d' ..• )
--" .. ~ -·-:... .i. •. 1·.- ·--
J:b
.. .., -:.=..c·;._,1~-l ~.c.r:..-:: s
G
1- - r -1.:. C.1 • ..:J 8.
L. " : . . J
-- -..... 1 ... 0.-:. ~
...... -.~ r
(..,,..:. ;. \~-
-r~ -, ., ·~ -,,.., ,:: ·-'- '-· 1._...·_...· '-- ·~ ..;_ ~r
~ '•-. ."
act CLS
l'l
s _ .... ~·
-. --. ..L-' --
;_; .
0 is
,, .:; .
7
0. r, _-.. "
' .... .
-U ..
....:... ~:-.
_;_ ')'. ::J.
- (J ..
, .. u"
u .
.'-' .
:n-::
0. . ' -. ~ .. 1
~-,,
..._ _.' ·- • ;._,1, - ..;; . ... .i. \...... L'' ~
. ; -· -. ".:· · ·"- C '·-· ._,_,_ -·
-- . ' i'·~:-_; .:.. J. CJ: i. ~:s ·,: =:... -.=. ::L·:.. 8
--- ... _-:,..,,.~ ::, ·f- .. - , -c. ~- , __ ;..._) ;... >,.,.: .:..~
) -..- ,,.- -- ... ; !.J..J.. ...__;. ...
T"-
., 0 .,
~ .. ·_:fo;:.'d:;
_i._ _ _,,__, ..
. -.,. - -'-'-•
2 ~. ~ · : .
- ('' ...: - ' _ :._J .._I_._) J _ _i'. "i .
. ' 727 -· .". ,.: "' :.... .,,_ J ·..__, ~-- -··
,.... .. ,
c-·. ,.... .. U L.Ci.'-.-
·"\ LJ •
7
/' - ..- , -·· .-_ ... • .... . :.. ::.,. ~ •~)
352
,. .. ,~, ~::. -, ---- - ~,..)
., --. r'
...... ,;. .:. "--'" ~
.... ,J i.;. ...... •._,
-- :.._)._:. :..._.
I~
· ; ··- '-~ ·- · - , _,,
' f ':: ,· : , ...... J ·, ,) . .Lj
- ('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