CAPÍTULO 4. LA MANUFACTURA DE LA LÍTICA DE MOLIENDA
4.1 Cadena conductual de los instrumentos de molienda
It has b itn show** previously th a t c was not produced by transform ation iro n a on cooling froia the ogeing Cenporature. thus c vnn both nucleated end grown a t tem peratures for which cs was the
equilibrium phone end i t vas not possib le th a t the p re c ip ita te de\fe.loped frors, h ,e .p . n-udei produced as a thornodynasdcaliy sta b le component during quenching.
3*4*3. The. fowtttlpn of c t o . thc^ c ry s ta l loftrspliic r e l a t i onship, l^ tv re e n ^ rc c ip ita tc and m atrix
It was possible th a t the c p re c ip ita te was nucleated and grown due to a itorc favourable l a ttic e correspondence, between eand the
m atrix, on c e rta in cryr»tallographic planes, chan evicted with equilibrium a; i .e . the surface energy was lower i f the p re c ip ita te was c than i f i t y a s a. In th is case & could be described as a tra n s itio n phase analogous
to the coherent or nerd-coherent m etactable p re c ip ita te s found in various *P,e hardening allo y s, (e .g . huraluid.ii),
a. Determination of the cry stallo g rap h fc re la tio n sh ip
To evaluate the above hypothesis i t was f i r s t necessary Co determine the o rie n ta tio n re la tio n sh ip between e and £*
The h’alco llo y alloys arc extremely b r it t l e end attfrspSff to prepare th in f o ils , iron which the p re c ip ita te o rie n ta tio n could have bean determined by electro n d iffra c tio n , were unsuccessful. The grain o I e c of the m ateriel was s u ffic ie n tly larg e (1-2 van diam eter) fo r Laue back re fle c tio n photographs to be obtained fron sin g le grains in aged samples. The do photographs, although revealing d e a r p attern s
representing the £ m atrix, contained no rcflectio n o a risin g from the c p re c ip ita te and thus gave no in d icatio n o f the re la tio n sh ip between the two phases. It was concluded th a t the c p a rtic le s v?crc o rien ted a t a v ariety of ’angles to the in cid en t boarr, and a number of d iffe re n t Laue p attern s should, th erefo re, have been produced but presumably these m ultiple re fle c tio n s were too weak to be recorded. This view vas su b stan tiated when the o rie n ta tio n re la tio n sh ip war, success fu lly
IB -* CsQtUercdc liuul4 eud Chill Asfttu&ly
Steel chill ~ ~ 7 ~ 7 r
I pfoparation isp w ith kupuT*mK pxviz o m a w tio a A ca»C o f c o m c rc ic l p u rity , w ith an analysed composition of 27* 7£ At, wee poured in to a mould and c h ill csfffirMy an shown in Figure 18. The- could* prepared by the CQn£> technique* consisted of the £ollevin;
■
m ixture of tu to r ia ls end reacted er.othern.lca lly upon ig n itio n .
70 wt X (silica scud
IS rdunitiium powder 7*5 ,! sodium n itr a te
. 2*5 ° sodiurc oi 11 co-fluoride 5 . ‘! sodium s ilic a te
A fter ig n itio n was complete Che molten olloy wen poured in to tho ti^uld mid allowed to s o lid ify . The mould tem perature im r.cdlately p rio r to casting was estim ated to be in excess of 15C<0°C. There was thus l i t t l e tendency fo r heat ex tractio n except in the d ire c tio n of. Urn c h ill and the re s u lt was a columnar c ry sta l stru c tu re with the long usees of the c ry sta ls perpendicular to the c h ill face* This technique of CKothcn&ic castin g is used commercially in the preparation of c ry s ta l o rien ted permanent magnets«
. A sample (1 cvs x I cm x 2 ets) from th is c a st van so lu tio n tre a te d a t 13&?WC and water quenched to re ta in fs. It vms then sectioned porpendi-culer to the columnar axis and etched to roveel cro«© sections through about 50 cryetisla. The o rie nta tio n s of 1.0 c ry sta ls near the centre of the section were determined by Laue back re fle ctio n (see Figure Sc) to show thou in evary cose <U>0> mac w ithin 2° of the normal
* o
to the sectio n . The anemic van next eyed a t SCO C for 15 hours to induce p re c ip ita tio n of c. A fter ageing *U mas 1280 Oc (the i&ap.neiic
^ 0
I I Bytg ra ltiction o r le i^ s tie a
she o rie n ta tio n re la tio n sh ip cotsnanly observed between ft*c«p» & H
cad b ,c« c* stru c tu re s, che burger# 'relatio n sh ip % is for cue c lo se st packed pl&mQ and d ire c tio n s in each s tru c tu re to be p a r a lle l; i . e . -.{0001} h .c .p . p a ra lle l to {110} O.C*C« €!i *. »>» h.O.Jp* piit-iilid. Co <Hl*^ 0*0.0.
Asctsaios th a t the Burgers re la tio n sh ip a a lsto d between the tu e .p . p re c ip ita te sad b .c .c . tnntri*; in &$lcolloy i t was passible* using the
ieaw caris cfe&ara and the columnar specisroa of known tu&tris o rien tatio n * to e s ta b lis h conditions fo r d iffra c tio n , from a p a rtic u la r p lan t its cue? t p a r tic le s , such th a t i f Cite assumption was valid* d iffra c tio n from the selected plane only would bo recorded ou cue film*
Vhc cus^ra vao set up so th a t the norms! to Clio columnar
apecinau crosc sectio n ( i .e . <001 >fj) , the in cid en t beam o f mouocbrormatic chromium he ra u ia tio u and a c y lin d ric a l film strip * veto in the ease plane, which ecu he described ss the plane of the ceasara. lha c plane selected
for study in the f i r s t instance? «*«& {101l}c, fig u re 19 shove the a n tic ip a te d re la tio n sh ip between {00i}b (the spccimcu s e c tio n ), (O ll}£, {0301}c, and
those {loll}?: pole* asso c ia te d *1tuiOOOlIt p a ra lle l to (011)b* Since {Oil} planes contain two < lll> d ire ctio n s there o ra, in each { 0 ll)p i»X&ne» fc»o posslble o rie n ta tio n s fo r <112i»e and, th erefo re, w » possible p o sitio n s in the etaraographic p ro je ctio n for each {loXl}c pole. ¥herc arc thus 24 possible p o sitio n s fo r {lO llje polos asso ciated w ith each (0001}t pole,
(only 12 ere shown in the X‘i&u?e, a fu rth e r 12 are on the reverse aide of the. projected sphere) * *hc broken lin e in the Figure rep resents the plane of the camera and i t can he eeer. th a t i f the specimen ro ta te s about JtKjljd
( l u i l k poles rove through tuiu plane*
Using Cr he ra d iati cn the brag*; angle 0 lo r ( lo ll }c is 07u . The
£ .
two possible positions of (I 101} t: poles in figure 19 ere a t Id to Cue pole of the specimen sectio n ( i . e . (001) &)« liut re lo re , i f t.»o in cid en t
beam stakes an angle of 19° ( i . e . 37° - 10°) to the specimen sectio n ( i . e . 71° to the (001)h pole iu the F igure), and i f the asauuaid o rie n ta tio n re la tio n -
Fig. 19 - (001)b pro jectio n with {0001 }c and {lGlX}s poles superimposed according to the burgers re la tio n sh ip (only taose (1011}c poles associated v itk {OOOljs p a ra lle l to (Oil)is are shown)
The broken lin o rep resents the plane o f the canera, as defined in, the te s t, cad the point oarked X is the p o sitio n of the
&~roy
bean incident on (001)b a t 19°* Tae c irc le s ehow the moveasot of {iOiiJfc poles on rota tio n aboutJo0fj3
110 AjDOOl i o n ^010 00! -0— iToi oooi 110 oooi 01111
& 0 ~ \ (031)r< p ro jectio n v i t a <OOOI}c and { iik v jc p o le s ’ &ni^viuimn&4
a ccording to tne Barkers Rctlatioseiiip (only th o se' i l l £ 0}e • poles m m c in te d with- {£031}& per& llel to (IQi)ih are j&owa)
liie broken iic e rep resents the 52 lane ©f the cszEorss as defined i n the tent* the p o in t eiarked h is the X-ray bees in c id e n t'©a (ooi)h et Sl*°. ta n c irc le s shew the sspveseat of the poles’ on ro ta tio n of the epeci&en
r.s the a a m al to ehi t plcae ro ta te s in to the plane of the ca®era. The d iffra cte d beam Trill also he in the p le a t of the caeera «ad v £ ll he recorded ou the file * *h&re ere twelve p o ssib le o rie n ta tio n s o f {0001}c pi cues; i# e . p a ra lle l to (O lllf (only e ig ht shoun in the Figure, four being on the reverse eide of the p ro jected sphere)* ha rotation* four o f these eovn in to p o sitio n s'su ch th a t d iffra c tio n , in the plane of the cm -ora, ir o n tiro of the associated { io il)c planes w ill occur* Assuaia# th a t e l l the possible o rie n ta tio n s described by the Burgers relatio n sh ip &m p resen t, conditions fo r d lffro c c io a frog* {I0 ll}c are thus esta b lish ed eig h t tin es during ro ta tio n through 36i> - • th orn {lO lD c pianos asso ciated with the (C'OSlIc pianos whonc p o le s'a re on the reverse of the projected sphere, cad those associated w ith {c&Glle plaxen which are «u 90 to (001)h itmhc angles w ith the in cid en t bean* which do not approach the Bragg eagle in or near the plane of the CST32m)«
A d iffra ctio n p attern wee, th erefo re, obtained w ith the Incident Ucan a t a c e n tte a t angle of 19’ to the 6pacittfc& sectio n cad w ith the
spocie&ft ro ta tin g about dm columnar nadls In order to obtain d iffra c tio n iro n ( I0l l } c , gotatioo- was ec c e n tric w ith resp ect to the p oint of
in c id e n c e with the £**roy bc&sa so th a t n number of grains wore irra d ia te d . the area c&enin&d vs& n e a r.th e centre of the sectio n and contained those
groins f the e&trlsr: o rie n ta tio n of vfcicu had been determined ss described e a rlie r* '-Uy one lin e fro* the d iffra c tio n p a tte rn of c appeared on
o the filr?, the a n ticip ated U c iljc re fle c tio n r.t a d value of l*Sln*
’Xhe eagle bcCuaeu the incident bem;; end the specicon sectio n
o «
was then adjusted to 39 in order to catch lia h coudicions fo r d if f r a c t ton
fr o c {llZ O jc, (0 ** dff.3 ) , as cbowa in F igu re du. Ih e r e s u lt in g
d iffra c tio n p a tte rn contained a sin g le lin e which was the a n ticip ated ( il2 ‘d}c rcflcdion*
I I I ticcu sclo a of the jte ^ o ^ u o
experiments is co n sisten t with the existence of tie Burners relatio n sh ip# It could kn argued, however, th a t chose re fle c tio n s wight conceivably occur even I f cors other o rie n ta tio n re la tio n sh ip existed* I f the p re c ip ita te was o rien ted in <sor& nmiKpec tc d manner the in cid en t beass would be in cid en t on pieae® iu the p re c ip ita te a t & v ariety of eagles end conditions fo r d iffra c tio n iro n so«s» e planes* including, .those