Preferred orientation of experimentally deformed_Le Nhan.pdf

8/10/2019 Preferred orientation of experimentally deformed_Le Nhan.pdf

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r e fe r r e d o r i e n t a t io n o f e x p e r i m e n t a l l y d e f o r m e d

p y r i t e m e a s u r e d b y m e a n s o f r i e u t r o n d i f f r a c t i o n

H. SIEMES AND D. ZILLES

Ins t i tu t for Mineralogie und Lagers tf it ten lehre , RW TH Aach en, 5100 Aac hen, G erma ny

S . F . C o x

Research School of Ear th Sc iences , Aust ra l ian Na t iona l Univers i ty , Canb erra A CT 2601, Au st ra l ia

P . ME RZ W. SCHAFER AND G . WILL

Mineralogisches In st i tut , Universitfit B onn, A ur en ste l le Forschungszentrum Ji il ich (K FA ), 5170 JiJl ich,

G e r m a n y

H. SCHAEBEN

La bo ratoir e de M etal lurgie des Ma teriaux Polycrista l lins (LM2P), Un iversi te de M etz, 57045 M etz, France

AND

K . K U N Z E

Brigham Young Univers ity , D ept . of Manufac tur ing Engineer ing , Provo, UT 84602, US A

Abs t r a c t

N e u t r o n d i f f r a c ti o n t e x t u r e g o n i o m e t r y i n d i c a te s t h a t n a t u r a l l y d e f o r m e d p o l y c r y s t a l l in e p y r i t e o r e s

f r o m M t . L y e l l ( T a s m a n i a ) a n d D e g t i a r k a ( U r a l M o u n t a i n s ) h a v e w e a k l a t ti c e p r e f e r r e d o r i e n t a ti o n s .

D u r i n g e x p e r i m e n t a l d e f o r m a t i o n i n v o lv i n g d is l o c at io n f lo w a t e l e v a t e d t e m p e r a t u r e s a n d p r e s s u r e s,

t h e s e i n i ti a l f a b r i cs h a v e b e e n m o d i f i e d to p r o d u c e n e w l a t ti c e p r e f e r r e d o r i e n t a t i o n s .

P o l y c r y st a ll i n e p y r i te f o r m M t . L y e l t ( B - l ) h a s a n i n it ia l < l l l > - f i b r e t e x tu r e p e r p e n d i c u l a r t o a

g r a in - s iz e l a y e ri n g . A f t e r 2 4 s h o r t e n in g p e r p e n d i c u l a r t o t h e < l l l > - f i b r e a x is a t 7 00 ~ a n e w , b u t

w e a k < 1 0 0 > t e x t u re h a s d e v e l o p e d p a r a l le l to t h e s h o r t e n i n g a x is . T h e D e g t i a r k a p y r i t e (P N - 6 )

i n i ti a l ly h a s t w o w e a k f i b r e c o m p o n e n t s . T h e s o m e w h a t s t r o n g e r c o m p o n e n t i s a < 1 0 0 > - f i b r e t e x t u r e ,

s i m i la r t o t h at i n th e e x p e r i m e n t a l l y d e f o r m e d B - 1 p y r it e . T h e o t h e r o n e i s a < l l l > - f i b r e t e x t u r e

s i m i l a r t o t h e i n t it a l B - 1 p r e f e r r e d o r i e n t a t i o n . A f t e r 3 0 s h o r t e n i n g o b l i q u e t o b o t h i n i ti a l f i b r e a x e s a t

6 0 0 ~ w e a k < 1 1 0 > - a n d < 1 11 > - f i b r e t e x t u r e s h a v e d e v e l o p e d . T h e e x p e r i m e n t a l l y p r o d u c e d f a b r i c s

h a v e d e v e l o p e d d u r i n g d e f o r m a t i o n i n v o l v i n g d i s l o c a t i o n f l o w , d y n a m i c r e c r y s t a l li s a t i o n a n d s o m e

m i c r o c r a c k i n g . I n t e r g r a n u l a r s l id i n g m a y a l s o h a v e b e e n i n v o l v e d . D i f f e r e n c e s b e t w e e n l a t t i c e

p r e f e r r e d o r i e n t a t i o n s d e v e l o p e d in t h e 60 0 ~ a n d 7 00 ~ e x p e r i m e n t s a r e i n t e r p r e t e d to in d i c a t e a

c h a n g e i n t h e d o m i n a n t f l o w m e c h a n i s m w i th c h a n g i n g t e m p e r a t u r e .

t n c o m p a r i s o n w i th o t h e r c u b i c m i n e r a l s th a t h a v e b e e n d e f o r m e d e x p e r i m e n t a l l y b y d i s l o c a ti o n f lo w

m e c h a n i s m s , t h e p y r i t e sh o w s a n u n u s u a ll y w e a k p r e f e r r e d o r i e n t a t i o n w h i c h c a n b e d e t e c t e d o n l y b y

m e a n s o f n e u t r o n d i f f r a ct i o n t e x t u r e g o n i o m e t r y .

KEYWORDS p y r i t e, e x p e r i m e n t a l d e f o r m a t i o n , n e u t r o n t e x tu r e g o n i o m e t r y , p r e f e r r e d o r i e n t a ti o n ,

o r i e n t a t i o n d i s t r i b u t i o n f u n c t io n .

I n t r odu c t i on

INVESTIGATIONo f n a t u r a l l y d e f o r m e d p o l y c r y s t a l -

l i n e p y r i t e f r o m d i f f e r e n t l o c a ti o n s b y m e a n s o f X -

r a y t e x t u r e g o n i o m e t r y h a s s h o w n t h a t t h e r e i s

u s u a l l y n o p r e f e r r e d o r i e n t a t i o n r e c o g n i s a b l e ( se e

Mineralogical Magazine March 1993 VoL 57 pp. 29-43

Copyright the Mineralogical Society

r e v i e w b y S i e m e s a n d H e n n i g - M i c h a e l i , 1 9 8 5 ) .

I n c o m p l e t e u n n o r m a l i s e d p o l e f ig u r e s o f p o l y -

c r y s t a l li n e p y r i t e o r e f r o m t h e B a y e r l a n d m i n e

w e r e i n t e r p r e t e d b y G e h l e n ( 1 9 7 1 ) t o i n d i c a t e a

p r e f e r r e d a l i g n m e n t o f < 1 1 1 > p a r a ll e l t o t h e

n o r m a l o f a m e t a m o r p h i c l a y e r in g .


2/15

30

H . S I E M E S E T A L .

I n t r i a x i a l c o m p r e s s i o n t e s t s , c y l i n d e r s o f p o l y -

c r y s t a l li n e p y r i t e 1 2 m m l o n g a n d 7 m m i n

d i a m e t e r h a v e b e e n s h o r te n e d u p t o 3 0 b y C o x

e t a l . ( 1 98 1 ) . B e c a u s e o p t i c a l a n d T E M m i c r o s -

t r u c t u r a l s t u d i e s i n d i c a t e d t h a t d e f o r m a t i o n h a s

a p p a r e n t l y o c c u r r e d p r e d o m i n a n t l y b y d i s l o ca -

t i o n f l o w m e c h a n i s m s i t s e e m e d w o r t h w h i l e t o

a n a l y se t h e p r e f e r r e d o r i e n t a t i o n t h a t d e v e l o p e d

i n a n u m b e r o f s p e c i m e n s . S u r p r i s i n g ly , Z i ll e s

( 1 9 8 9 ) c o u l d o n l y d e t e c t i n s o m e o f t h e i n c o m -

p l e t e X - r a y p o l e f i g u r e s r a t h e r u n c e r t a i n a n d

i n c o n s i s t e n t i n d i c a t i o n s o f p r e f e r r e d o r i e n t a t i o n .

A s s u m i n g a n a v e r a g e g r a i n d i a m e t e r o f 5 0 ~ t m ,

t h e i r r a d i a t e d s a m p l e a r e a o f a p p r o x i m a t e l y

2 5 m m 2 c o n t a i n s 1 0 4 g r a i n s . I t w a s c o n c l u d e d t h a t

t h e i r r a d i a t e d a r e a a s w e l l a s a s t h e n u m b e r o f

g r a i n s w a s t o o s m a l l f o r a t h o r o u g h t e x t u r e

a n a l y s i s o f a v e r y w e a k p r e f e r r e d o r i e n t a t i o n .

T h e r e f o r e t h e c e n t r a l p a r t s o f t w o e x p e r i m e n t a l l y

u n d e f o r m e d a n d t w o e x p e r i m e n t a l ly d e f o r m e d

s p e c i m e n s w e r e a n a l y s e d b y n e u t r o n d i f f r a c t i o n

t e x t u r e g o n i o m e t r y ( W i l l e t a l . 1 9 8 9 ) . W i t h

n e u t r o n d i f f r a c ti o n , th e t o t a l v o l u m e o f t h e

s p e c i m e n ( 2 4 0 m m 3 w i t h a p p r o x . 2 . 10 6 g r a i n s ) i s

i r r a d i a t e d an d c o n t r i b u t e s t o t h e m e a s u r e d c o m -

p l e t e p o l e f i g u r e s .

e f o r m a t io n m i c ro s t r u ct u r e s a n d m e c h a n i s m s i n

e x p e r i m e n t a l l y d e f o r m e d p y r i t e

S i n g l e c r y s t a l s t r e n g t h d a t a , s t r u c t u r a l c o n -

s i d e r a t i o n s a n d t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y

s t u d i e s s u g g e s t t h a t a b o v e 4 0 0 ~ { 10 0} < 0 0 1 >

a n d p o s s i b l y { 10 0} < 0 1 1 > a r e im p o r t a n t s li p

m o d e s i n p y r i t e t h a t h a s b e e n e x p e r i m e n t a l l y

d e f o r m e d a t s t r a i n r a t e s b e t w e e n 10 4 S 1 a n d

10 5 s i (C o x e t a l . 1981 ; Gra f e t a l . 1981;

L e v a d e e t a l . 1 9 8 2 ) . C o u d e r c e t a l . ( 1 9 8 0 ) h a v e

a l so r e co g n i s e d th e o p e r a t i o n o f { 10 0 ) < 0 0 1 >

g l id e in n a t u r a l l y d e f o r m e d p y r i t e fr o m D e g -

t i ar k a . D u r i n g < 1 0 0 > s h o r t e n in g o f si n gl e

c r y s t a l s , a { 1 1 0 } g l i d e s y s t e m i s a l s o i n f e r r e d t o

h a v e o p e r a t e d , b u t h a s a c r it i ca l r e s o l v e d s h e a r

s t r e s s h i g h e r t h a n f o r { 1 0 0 } g l i d e ( C o x , 1 9 8 7 ) . I n

c o m p a r i s o n t o o t h e r c u b i c m i n e r a l s ( T a b l e 1 )

p y r i t e is q u i t e u n i q u e b e c a u s e o f th e p r e d o m i n a n t

g l i d e m o d e { 1 00 } < 0 0 1 > .

B e t w e e n 4 5 0 ~ a n d 5 5 0 ~ d i s l o c a t i o n f lo w

g i v e r i s e t o a w e a k g r a i n e l o n g a t i o n f o l i a t i o n ,

l a tt ti c e b e n d i n g , a n d d e f o r m a t i o n b a n d d e v e l o p -

m e n t a t s t r a in s u p t o a b o u t 2 0 s h o r t e n i n g .

A b o v e a b o u t 5 5 0 ~ g r a in b o u n d a r y m i g r a t i o n

a n d d y n a m i c r e c r y s t a l li s a t io n a l s o b e c o m e

i m p o r t a n t , w i t h r e c r y s t a l l i s a t io n o c c u r r in g b y a

c o m b i n a t io n o f g ra i n b o u n d a r y b u l g in g a n d

s u b g r a i n r o t a t i o n m e c h a n i s m s ( C o x e t a l . 1981,

a n d C o x , 1 9 8 7 ) .

P r e f e re d o r i e n t a t i o n i n s h o r t e n i n g t e s ts

B e c a u s e o f t h e a x i a l s y m m e t r y o f t h e e x p e r i -

m e n t a l d e f o r m a t i o n p r o c e s s o n e e x p e c t s th e

d e v e l o p m e n t o f a fi b r e t e x t u r e , t h a t i s a p r e f e r r e d

o r i e n t a t i o n w i t h a r o t a t i o n a x i s o f in f i n it e o r d e r

p a r a l l e l t o t h e a x i s o f c o m p r e s s i o n . T h a t m e a n s

t h a t t h e r e d e v e l o p s a p r e f e r r e d o r i e n t a t i o n w i t h

a n a l i g n m e n t o f o n e ( o r t w o c r y s t a l l o g r a p h i c

d i r e c t i o n ( s ) p a r a l l e l t o t h i s a x is . A l a t t i c e p l a n e

p e r p e n d i c u l a r t o t h i s c r y s t a l lo g r a p h i c d i r e c t i o n

g i v e s r i se t o a c i r c u l a r m a x i m u m i n th e c e n t r e o f

t h e p o l e f i g u r e . A l l o t h e r l a t t i c e p l a n e s h a v e

c o n t i n u o u s p o l e d e n s i t y d i s t r i b u t i o n s o n c i r c l e s

a r o u n d t h e c e n t r e o f t h e p o l e f i g u r e s . I f t h e

u n d e f o r m e d s p e c i m e n s a r e i n h o m o g e n o u s o r

i n t ia l l y h a v e a p r e f e r r e d o r i e n t a t i o n t h e n t h e f in a l

p o l e d e n s i t y o n t h e c i r c l e s d e v i a t e s f r o m p e r f e c t

a x ia l s y m m e t r y . T h e d e n s i ty o f th e m a x i m u m i n

t h e f i b re a x i s ( e x p r e s s e d i n m u l t i p l e s o f u n i f o r m

d e n s i t y , m . u . d . ) i s u s e d a s a m e a s u r e o f p r e f e r r e d

o r i e n t a t i o n . N a t u r a l o r e s c a n h a v e a x i s y m m e t r i c

c o m p o n e n t s o f p r e f e r r e d o r i e n t a t i o n w i t h d i f fe r -

e n t o r i e n t a t e d f i b e r a x e s . T h e s e c a n o r i g i n a t e b y

o r i e n t e d g r a i n g r o w t h o r c o a x i a l d e f o r m a t i o n

p a t h s .

C u b i c m i n e r a l s s u c h a s h a l i te , g a l e n a , f l u o r i t e ,

s p h a l e r i t e , a n d m a g n e t i t e h a v e s l i p m o d e s w i t h

{ 1 0 0 ) , { 11 0} a n d { 1 1 1 ) a s g l i d e p l a n e s a n d

d 0 1 1 > a s g l i d e d i r e c t io n s . I n T a b l e 1 t h e g l i d e

m o d e s a r e o r d e r e d a c c o r d in g t o t h e ir i m p o r t a n c e ,

t h a t i s w i t h i n c r e a s i n g r e l a t i v e c r i t ic a l r e s o l v e d

s h e a r s t r e s s e s ( s e e r e v i e w f o r s u l f i d e a n d o x i d e

m i n e r a l s b y S i e m e s a n d H e n n i g M i c h a e l i , 1 9 8 5 ,

f o r g a l e n a b y F o i t z i k e t a l . 1 99 1, f o r h a l i t e b y

C a r t e r a n d H e a r d , 1 97 0, a n d f o r f lu o r i t e b y P r a t t

e t a l . 1 9 6 6 ). I n a l l t h e s e c r y s t a l s o n e s l i p m o d e o r

a c o m b i n a t i o n o f s e v e r a l o f t h e m y i e l d f iv e

i n d e p e n d e n t s l ip sy s t e m s w h i c h a l l o w a g e n e r a l

d e f o r m a t i o n w i t h o u t v o l u m e c h a n g e ( M i s e s ,

1 92 8; K e l l y a n d G r o v e s , 1 9 70 ) . D u r i n g u n i a x i a l

s h o r t e n i n g , f i b r e t e x t u r e s d e v e l o p s u c h t h a t

< 1 1 0 > i s a l i g n e d w i t h th e a x i s o f c o m p r e s s i o n

( T a b l e 1 ). O n l y h a l i t e e x h i b i ts tw o f i b r e c o m p o -

n e n t s; t h e m o s t p r e d o m i n e n t b e i n g ag a i n < 1 1 0 >

t h e m i n o r c o m p o n e n t b e i n g < 1 0 0 > ( K e r n a n d

B r a u n , 1 97 3) . B o t h c o m p o n e n t s a r e f o u n d i n

n a t u r a l l y d e f o r m e d h a l i t e s ( K ~ i m p f e t a l . 1987;

K e r n a n d R i c h t e r , 1 98 5). C u b i c f a c e - c e n t e r e d

m e t a l s ( A 1, C u , N i ) d e v e l o p p r e d o m i n a n t l y t h e

< l l 0 > - f i b r e w i th a s p r e ad t o < 1 0 0 > a n d < 3 1 1 >

( B a r r e t t a n d L e v e n s o n , 1 9 40 ). A l l t h e s e o r i e n -

t a t io n s a r e s u c h t h a t s e v e r a l s li p s y s te m s h a v e h i g h

r e s o l v e d s h e a r s t r e ss e s w i t h r e f e r e n c e t o t h e

m a x i m u m p r i n c i p a l s t r es s . T h e s l i p m o d e s o f

p y r i t e a r e q u i t e d i f f e r e n t f r o m t h o s e o f o t h e r

c u b i c m i n e r a l s , b e c a u s e t h e m a j o r s l ip m o d e s

y i e l d o n l y 3 i n d e p e n d e n t s l i p s y s t e m s . I n a n


3/15

EXPERIMENTALLY DEFORMED PYRITE

TABLE l. Preferred orientation of polycrystalline cubic crystals in axial symmetric shortening tests

31

Max. exp . Max.

Crystal structure glide modes temp. ~ strain Fibre a x i s Reference

Halite 200 21 Kern and Braun, 1973

sodium chloride

F m 3 m

{1 1 0) slip

{l 0 0} slip

{l 1 1} slip

Galena 25 36 Siemes, 1970, 1976

sodium chloride

F m 3 m

300 16 Siemes and Hennig-

{1 0 0) slip Michaeli, 1985

{1 1 0) slip

{4 4 1} twinning

Fluorite 25 14 Lang, 1968

fluorite

F m 3 m

{1 0 0} slip

(1 1 0) slip

Sphalerite 25 20 Saynisch, 1970

sphalerite

F 4 3 m

300 10 Kollenberg and

{1 1 1} slip Siemes, 1983

{1 1 1) twinning

Magnetite 300 20 Mfiller and Siemes,

spinel

F d 3 m

1972

{1 1 1) slip

{1 0 0} slip

{ I

0} slip

{1 I 1) twinning

Metal 98 Barrett and Levenson,

cubic face centred F m 3 m with 1940

~1 1 1) slip spread to

,

Pyrite 600 30 Present work

sodium chloride

derivative P a 3 700 24

{1 0 0} slip

{1 0 0} slip

{1 10 }< ? >s lip

orient ation with < 10 0> parallel to the axial stress

the major glide systems have zero shear stresses.

All the glide directions are either parallel or

perpendicular to the stress axis. Therefore addi-

tional mechanisms must be activated, e.g. the

{ 110} slip mode or microcracking or grain boun d-

ary sliding. By analogy one should expect for axial

symmetric deformation of pyrite only fibre

textures with an alignment of and prob-

ably parallel to the shortening axis.

M e a s u r e m e n t a n d a n a l y s is o f p r e f e r r e d

o r i e n t a t i o n

Eight complete pole figures (pole density

functions, PDFs) of the reflections (111), (200),

(210), (220), (222), (211), (311), and (321) were

measured on the pyrite specimens by neutron

diffraction goniometry (Will

e t a l .

1989). The

information which is presented in different pole

figures is combined by means of pole figure

inversion algorithms (e.g. Bunge and Esling,

1985; Matthies, 1991; Pawlik

e t a l .

1991; Schae-

ben and Siemes, 1991; Vadon and Heizmann,

1991) to an orientation distribution function

(ODF). From the me asured pyrite reflections the

(200)-, (220)- and (111)-pole figures were used to

calculate a MENTEX-ODF according to the

inversion method involvingfinite series expansion

and entropy optimisation (Schaeben, 1988;

Schaeben

e t a l .

1990; Schaeben, 1991). Table 2

summarises the results after 22 iterations. The

mean relative errors (Tab le 2) and comparison of

the experimental pole figures with the recalcu-


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32 H. SIEMES

E T A L .

TABLE2. Calculation of the ODFs by means of maximum entropy

t e x t u r e

program MENTEX, 3 pole figures: (111),

(200), (220), 22 interactions

I ODF I (111) PDF I (200 PDF I (220) PDF I

I m.u.d. I m.u.d. I m.u.d. I m.u.d. I

I min. max . ] rain. m a x . RPO I min. m a x . RPO I min. m a x . RPO I

Mt. Lyell, undeformed: B-1

exp.: 0.73 1.24 0.81 1.22 0.78 1.18

calc.: 0.71 1.87 0.83 1.20 3.06 0.80 1.18 2.66 0.88 1.19 3.07

Mt. Lyell, deformed: RUN 053

exp.: 0.84 1.18 0.76 1.28 0.89 1.11

calc.: 0.73 1.94 0.86 1.15 4.65 0.82 1.30 2.49 0.88 1.08 2.34

Degtiarka, undeformed: PN-6

exp.: 0.68 1.31 0.71 1.44 0.85 1.14

calc.: 0.65 1.81 0.72 1.26 3.22 0.71 1.36 3.81 0.89 1.15 1.74

Degtiarka, deformed: RUN 092

exp.: 0.77 1.29 0.64 1.31 0.84 1.22

calc.: 0.60 2.03 0.77 1.27 4.10 0.63 1.30 4.40 0.89 1.23 3.02

ODF: orientation distribution function, PDF: pole density function (= pole figure), m.u.d.: multiples of uniform

density, exp.: experimental data, calc.: calculated data, RPO: mean relative error in percent

lated pole figures prove the MEN TE X- OD F to be

a reasonable approximation. The ODFs are

presented in sigma sections (Matthies e t a l .

1990a). Compa red to the tradit ional plotting of

ODF data in rectangular arrangements (Bunge,

1985), sigma sections provide an easier visulisa-

tion of preferred ori entations. The series of sigma

sections can be int erpreted as a spread (001)-pole

figure. Each section contains the density distribu-

tion for all crystal orientat ions with a constan t 20

= (e~ = y) in dependence on azimuth c~ and pole

distance [3, where ~ (rotatation about the crystal

z-axis) [3 (rot ation about the crystal y-axis) and 7

(rotation about the crystal z-axis) are the Euler

angles of an or ient ation. A n arbit rary poi nt (e~, [3)

within a 2o-section immediately gives the direc-

tion of the (001)-crystal axis of that orientation

with reference to the specimen axes. Orien tations

at the same posit ion (c~, f5) but with di fferent

sections 2ol and 202 only differ in a rotati on about

that common axis through the angle 2 (o~-o2).

Finally, the average distribution of all sigma

sections is identical to the recalculated (001)-pole

figure, The preferred orient ations displayed in the

pole figures and ODFs sigma sections were

modelled by mathematical standard distributions

by means of programs which have been deve-

loped at Rossendo rf (Matthies e t a l . 1987, 1988a,

1990b; Matthies

e t a l .

1988b). The models give a

simplified impression of the main features of the

measured pole figures and the calculated orien-

tation distributions, and can be described by a

small number of characteristic parameters

(Table 3).

P y r i t e f r o m M t L y e l l

The polycrystalline material (B -l) from the

Blow orebody of the Mt. Lyell Mining and

Railway Company near Queenstown , Tasmania,

exhibits some compositi onal and grain size layer-

ing with grain sizes between 50 and 70 ~tm. The

specimen cylinders were drilled parallel to the

layering. Fig. la shows the pole figures of the

three reflections (200), (220), and (111). In Fig.

lb the recalculated pole figures and in Fig. 2a the

OD F in sigma sections are presented. Because of

the good correspondence of the experimental and

recalculated pole figures and the small mean

relative errors (Table 2) the ODF provides

reliable information about the preferred orien-

tation. The pole figures and sigma sections are

projected parallel to the cross section of the

specimen and perpendicular to the layering of the

ore. The pole figure shows a (lll)-maximum

perpendicular to the long axis of the specimen and

a (lll)-girdle in the plane of the layering. The

associated fibre axis is orien ted per pendic ular to

the layering and the preferred orie ntati on is very

weak because this maximum has a density of

1.24 m .u.d. (Table 2) that is close to randomness.

Fig. lc shows the modelled pole figures and Fig.

2b the related mathematical ODF- sections which

confirm the in terpret ion as fibre texture.

The de formation of this pyrite at a strain rate of

2 10 4 s- l, a temperatu re of 700 ~ and at a

confin ing pressure of 300 MPa (RU N 053, Cox

e t a l .

1981) occurred at a steady state stress

difference of around 120 MPa up to 30% strain.


5/15

EXPERIMENTALLY DEFORMED PYRITE

FI6.3. Fibre components of textures of the pyrite ores

33

fibre axis position of the mathematical model ODF

fibre axis [ uniform [ Gauss shaped distrib.

[ azimuth [pole angle portion I portion I half-width

Mt. Lyell, undeformed: B-I

< 111 > 302~ 90~ 70% 30% 40.0~

Mr. Lyell, deformed: RUN 053

0~ 0~ 70% 30% 40.0~

Degtiarka, undeformed: PN-6

262~ 35~ 70% 15% 40.0~

0~ 35~ 15% 40.0~

Degtiarka, deformed: RUN 092

262~ 35~ 60% 7.5% 40.0~

0~ 35~ 7.5% 40.0~

195~ 10~ 12.5% 35.0~

0~ 0~ 12.5% 35.0~

ODF: orientation distribution function

Dislocation creep was accompanied by dynamic

recrystallisation and the resulting developme nt of

a population of finer new grains. These are

typically 10-15 ~tm in diameter and concentrated

at the boundaries of original host grains. Fig 3a

shows the pole figures of the (200)-, (220)- and

(lll) -refle ction s which are projected in the same

orien tation as those of the undeformed specimen.

The deformation has induced a new weak fibre

texture with a (100)-maximum (1.28 m.u.d.) in

the centre of the pole figure. There is no

indication of the former preferred orientation.

The recalculated pole figures (Fig. 3b) and the

related sigma sections (Fig. 4a) as well as the

mode lled pole figures (Fig. 3c) and sigma sections

(Fig. 4b) confirm this interp retati on.

Pyrite from egtiarka

The polycrystalline material (PN-6) from Deg-

tiarka, Central Ural Mountains, Russia (Zavar-

itsky, 1948) was provided by P. Natale (see

Natale, 1971). The specimen cylinders were

drilled at random because no layering was detec-

table. The grain fabric is similar to that of the Mt.

Lyell ore with the exception that the grain size is

more than twice the size of the pyrite of Mt. Lyell.

Again the three (200)-, (220)- and (111)-pole

figures were used to calculate a MENTEX-ODF

(see Table 2). Fig. 5a shows the experimental,

Fig. 5b the calcu lated pole figures, and Fig. 6a the

ODF in projections perpendicular to the axis of

an undeformed specimen. The main features of

the pole figures are two fibre components . In the

(100)-pole figure a (100)-maximum is located

approximately 35 ~ away from the specimen axis.

A grea t circle distribution of (100)-poles occurs at

90~ to this maximum. T he maximum in the (111)-

pole figure is also situated approx. 35 ~ away from

the specimen axis, but 45 ~ from the -fibre

axis. The presence of this -fibre axis is

interpreted to give rise to the weak, small circle

dist ribut ion of (100)-poles 55 ~ away from the

-fibre axis. The model pole figures (Fig.

5c) and the related ODF (Fig. 6b) closely

resemble the measured pole figures and confirm

this interpetation.

This pyrite has been experimentally deformed

by axial shorten ing at a strain rate of 2 10 -4 s -1, a

temperatu re of 600 ~ of 300 MPa confin ing

pressure (R UN 092). Aft er yielding at 200 MPa,

continuous work har dening occurred up to a flow

stress of about 450 MPa at 24% strain. The

development of weakly elongate grain fabrics,

lattice bend ing and the progressive strain harden-

ing in this sample indicate that deformation has

involved dislocation flow processes. Fine grained,

dynamically recrystallised grains developed

locally along grain boundaries. Intragranular

microcracking that is clearly related to Hertzian

loading, has also occurred. The localised presence

of diamond grain-shapes and long, planar grain-

boundary segments, indicates that shortening

may also have involved intergranu lar translat ion,

by either frictional or ductile sliding processes.

Fig. 7a shows the pole figures of the (200)-, (220)-

and ( lll) -reflec tions which are projected in the

same orientation as the pole figures of the

undefo rmed specimen. The pole figures exhibit a

preferred orientation which seems to be very

similar to the undefo rmed material. The two fibre


6/15

220)

111)

200)

200)

200)

220)

220)

Iii)

34 H. SIEMES E T A L

iii)

FiG. 1. Experimentally undeformed pyrite from Mt. Lyell, Tasmania (B-l), pole figures of the (200)-, (220)-, and

(ll l)-reflections, equal area projection perpendicular to the shortening axis, dotted area: below 1.0 m.u.d., contour

interval: 0.2. (a) measured pole figures; (b) recalculated pole fgures (c) model pole figures: 9 = -fibre axis.

components that are present in the undeformed

material are still there, but two new components

have developed (Fig. 7b, c). The first one is also a

fibre component with a (111)-maximum very

close to the specimen axis and the second one is a

-fibre with the m aximum in the specimen

axis. The sigma sections of the calculated ODF

(Fig. 8a) in comparison to the model ODF (Fig.

8b) confirm this interpreti on.

i s c u s s i o n

The interpretation of the measured textures is

complicated firstly by the fact that the unde-

formed samples already have a weak preferred

orientation. Secondly, after 24% shortening (for

B-l) and 30% shortening (for PN-6) the new

textures are still very weak. In deformation

experiments with other cubic minerals under

conditions in which dislocation glide is the domi-

nant deformation mechanism, the newly devel-

oped preferred ori entati ons are much sharper and

often already well recognizable after 5% strain.

After 10 to 20% strain the maxima often have

densities of the order of 2 m.u. d. (see e.g.

Kollenberg and Siemes, 1983; Siemes, 1976).

Lattice preferred orientation of naturally

deformed pyrite

Although the naturally


7/15

2 ( : I = ~

2(:1=45

o

2 ( : 1 = ~

20=15 ~

2 ( : 1 = 1 5

2 ( : 1 = 6 0

7 0 .

4

i

2o= 45* 2( :1=60* 20= 7 5*

2(:1=30

2(:1=7 5

EXPERI MENTAL LY DEFORM ED PYRITE 35

2(:1:1=30 ~

F,o. 2. Experimentally undeformed pyrite from Mt. Lyell, Tasmania (B-l), ODF-sigma-sections, dotted area:

below 1.0 m.u.d. , con tour interval: 0.5. (a) calculated ODF after 22 interations; (b) model ODF.


8/15

iii)

200)

200)

b

220)

1 2 2 0 )

36 H . S I E M E S

E T A L .

iii)

( 2 0 0 )

1 1 1 )

FIG. 3. Exp erim ental ly defo rm ed pyri te from M t. Ly ell , Tasmania (RU N 053), po le figures of the (200)-, (220)-, and

( l l l ) - r e f le c t ion s , equa l a rea pro jec t ion pe rpend icula r to the shor tening axis , dot ted a rea : be low 1 .0 m.u .d . , co ntour

interval : 0.2. (a) me asured po le figures; (b) recalculated pole figures; (c) mo del pole figures, 9 = -f ibre axis.

d e f o r m e d p y r i t e o r e s f ro m M t . L y e l l a n d D e g -

t i a r k a h a v e w e a k p r e f e r r e d o r i e n t a t i o n s , f i b r e

t e x tu r e s a r e c l e ar l y r e c o g n i sa b l e . T h e < I l l > -

f i b re t e x t u r e i n t h e M t . L y e l l p y r i t e i s p e r p e n d i c u -

l a r to t h e g r a i n - s iz e b a n d i n g i n t h e o r e a n d i s

s i m i l a r to t h e t e x t u r e o f p o l y c r y s t a l l i n e p y r i t e

f r o m B a y e r l a n d ( G e h l e n , 1 9 7 1) . T h e m i c r o f a b r i c

o f th e M t . L y e l l p y r i t e h a s d e v e l o p e d d u r i n g

d e f o r m a t i o n a n d r e c r y s t a l l is a t i o n a t l o w m e t a -

m o r p h i c g r a d e s . T h e p y r i t e lo c a l l y h a s a g r a i n

e l o n g a t i o n f a b r i c p a r a l le l t o t h e g r a i n - s i z e b a n d -

i n g . A n e x t r e m e l y l o w d i s l o c a t i o n d e n s i t y i n t h e

B - 1 p y r i t e , t o g e t h e r w i t h t r u n c a t i o n a n d o v e r -

g r o w t h f e a t u r e s o n i n t e r n a l g r o w t h z o n e s i n t h e

e l o n g a t e p y r i t e , in d i c a t e t h a t t h e M t . L y e l l p y r i t e

o r e h a s b e e n d e f o r m e d p r e d o m i n a n t l y b y d i ss o lu -

t i o n - p r e c i p i t a t i o n c r e e p p r o c e s s e s ( C o x , 1 9 87 ).

T h e l a t ti c e p r e f e r r e d o r i e n t a t i o n o f t h e D e g -

t i a r k a p y r i t e d i f f er s f ro m t h a t o f t h e B - 1 p y r i t e i n

t h a t a d i s t in c t < 1 0 0 > - f i b r e t e x t u r e i s p r e s e n t ,

t o g e t h e r w it h a w e a k e r < 1 1 1 > - f i b r e . I n v ie w o f

t h e m i c r o s t r u c t u r a l e v i d e n c e ( N a t a l e , 1 9 7 1 ;

C o u d e r c

e t a l .

1 9 80 ) , t h e d e v e l o p m e n t o f t h e

l a t t i c e p r e f e r r e d o r i e n t a t i o n i n t h e D e g t i a r k a

p y r i t e i s i n t e r p r e t e d t o h a v e i n v o l v e d d i s l o c a t i o n

f lo w p r o c e s s e s . H o w e v e r , t h e c o m p l e x i t y o f th e

f a b r i c i n d i c a t e s th a t t h e s t r a i n h i s t o r y m a y h a v e

i n v o l v e d a n o n - c o a x i a l d e f o r m a t i o n p a t h .


9/15

2 0 = 0 ~

2 o = 1 5 "

2 0 = 6 0 o

2 o =

0 ~

20=30 ~

I

2 o = 1 5 o

2 o = 6 0

2 0 = 7 5 *

: 2 0 = 3 0 ~

2 0 = 7 5

EXPERI MENTALL Y DEFORM ED PYRITE 37

2 0 = 4 5 *

2 o = 4 5 o

9 ~

Fl6. 4. Experimentally deformed pyrite from Mt. Lyell, Tasmania (RUN 053), ODF-sigma-sections, dotted area:

below 1.0 m.u.d .; contour interval; 0.5. (a) calculated ODF after 22 iterations; (b) model ODF.


10/15

38 H. SIEME S

E T A L

200) 220) IIi)

2001 1220) ii11

b

200)

I

c

220)

iii)

|

FIG. 5. Experimentally undeformed pyrite from Degtiarka, Ural (PN-6), pole figures of the (200)-, (220)-, and

(111)-reflections, equal area projection perpendicular to the shortening axis, dotted area: below 1.0 m.u.d., contour

interval: 0.2. (a) measured pole figures; (b) recalculated pole figures; (c) model pole figures; 9 = < 111>-fibre axis,

9 =

-fibre axis.

L a t t i c e p r e f e r r e d o r i e n t a t i o n s i n e x p e r i m e n t a l l y

d e f o r m e d p y r i t e

The interpretation of the

measured lattice preferred orientations in the

experimentally deformed pyrite polycrystals is

complicated by several factors. Firstly, the fabrics

in the experimentally deformed materials are

quite weak, even after 24% shortening (for B-l)

and 30% shortening (for PN-6). Add itionally, the

starting materials have distinct initial lattice

preferred orientations. As the initial fabrics have

only been investigated in two small specimens,

the variability of the fabrics in the B-1 and Pn-6

pyrite has not been evaluated. Accordingly,

direct comparisons between the measured initial

fabrics and the fabrics of the deformed specimens

are subject to some uncert ainty. Clearly, in future

work on such weak lattice preferred orientat ions,

it would be desirable to use the neutron diffrac-

tion technique to measure the lattice preferred

orientation of the total specimen volume both

before and after deformation.

The two specimens have been deformed at

different temperatures whereas the other con-

ditions were approximately the same. The Deg-

tiarka ore had been deformed at 600 ~ just above

the temperature at which dynamic recrystallisa-


11/15

E X P E R I M E N T A L L Y D E F O R M E D P Y R I T E 39

2 = 0 ~ 2 o = 1 5 ~ 2 = 3 ~

~ .~ , ' . . i . .. ' i - ~ 9

2 0 = 4 5 0 2 a = 6 0 o

: ~

: ' d : : i :

\

2 0 = 0 ~ 2 o = 1 5 ~ 2 o = 3 0 ~

2 o = 7 5 o

2 o = 4 5 ~

2 = 6 ~ 2 = 7 5 ~

F 1 c. 6. E x p e r i m en t a l l y u n d e fo rm ed p y r i te f ro m D eg t i a rk a , U ra l (P N -6 ) . O D F -s i g m a-s ec t io n s , d o t t ed a r ea : b e l o w

1.0 m.u .d . , con tou r in terva l : 0 .5 . (a ) ca lcu la ted OD F af te r 22 in tera t ions ; (b ) model OD F.


12/15

200)

40

200)

H. SIEMES

ETAL

220) III)

i

220) 111)

200) 220) iii)

9

FIG. 7. Experimentally deformed pyrite from Degtiarka, Ural (RUN 092), pole figures of the (200)-, (220)-, and

(ll l)-reflections, equal area projection perpendicular to the shortening axis, dotted area: below 1.0 m. u.d., contour

interval: 0.2. (a) measured pole figures; (b) recalculated pole figures; (c) model pole figures; ~ and 9 = -

fibre axes, 9 = -fibre axis, 9 = < ll0>-fibre axis.

tion processes begin. However, the stress strain

curve shows strong strain hardening. The devel-

opment of a -f ib re texture in the experi-

mentally deformed Degtiarka pyrite is similar to

the response of many other cubic minerals.

However the development of the -fibre

component has never been observed in other

cubic minerals. Additional experiments are

necessary to establish whether this com pone nt of

the fabric is inherited from the starting material,

or is purely a response to the dislocation glide

systems operat ive in pyrite at 600 ~ The Mt.

Lyell ore has been defor med at 700 ~ without

strain hardening under conditions where dynamic

recrystallisation has been impo rtan t during dislo-

cation creep. The newly developed -fibre

might therefore be characteristic for these con-

ditions. It is certainly remarka ble that this fibre is

a component in the natural Degtiarka ore.

on c l u s i o n s

Neutron diffracion techniques have been used

successfully to detect weak lattice preferred

orientations in naturally and experimentally

deformed polycrystalline pyrite ores.


13/15

2 = 0 ~

.

o = 4 5 o

2 a =

0 ~

2 0 = 4 5 ~

2 o = 1 5 ~

2 o = 1 5 o

2 0 = 6 0 ~

~ ~

~ 0

2 0 = 7 5 ~

2 0 = 3 0 ~

E X P E R I M E N T A L L Y D E F O R M E D P Y R I T E 41

2 0 = 3 0 ~

2 0 = 6 0 o 2 a = 7 5 o

I

i i

F IG . 8 . E x p e r i m e a t a ll y d e f o r m e d p y r i t e f r o m D e g t i a r k a , U r a l R U N 0 9 2 ) , O D F - s i g m a - s e c t i o n s , d o t t e d a r e a : b e lo w

1 . 0 m . u . d . , c o n t o u r i n te r v a l : 0 . 5. a ) c al c u l a te d O D F i n s i g m a - s e c ti o n s ; b ) m o d e l O D F .


14/15

42

H . S I E M E S

E T A L .

T h e d e v e l o p m e n t o f l a tt i ce p r e f e r r e d o r i e n -

t a t io n s d u r in g t h e e x p e r i m e n t a l d e f o r m a t i o n o f

t w o p o l y c r y s t a l l i n e p y r i t e o r e s s u p p o r t s e a r l i e r

m i c r o s t r u c t u r a l a n d m e c h a n i c a l e v i d e n c e ( C o u -

d e r c

e t a l ,

1 9 8 0 ; C o x

e t a l . ,

1 9 8 1 ; G r a f

e t a l . ,

1981 ;

L e v a d e

e t a l . ,

1 9 8 2 ; C o x , 1 9 8 7 ) t h a t d i s l o c a t i o n

f lo w p r o c e ss e s o p e r a t e i n p y ri t e a t e l e v a t e d

t e m p e r a t u r e s a n d p r e s s u re s . H o w e v e r , a f te r 2 4

a n d 3 0 s h o r t e n i n g o f t h e s a m p l e s , th e l a tt i ce

p r e f e r r e d o r i e n t a t i o n s a r e u n u s u a l l y w e a k i n

c o m p a r i s o n w i t h th o s e d e v e l o p e d i n o t h e r e x p e r i -

m e n t a l l y d e f o r m e d c u b i c m i n e r a ls . T h e s e f a b r ic s

h a v e o n l y b e e n d e t e c t e d b y m e a n s o f n e u t r o n

d i f f ra c t i o n t e x t u r e g o n i o m e t r y .

T h e w e a k n e s s o f th e f a b r ic s is i n t e r p r e t e d t o

h a v e b e e n i n f l u e n c e d b y a n u m b e r o f f a c t o rs

i n c l u d in g m i c r o c r a c k i n g a n d i n t e r g r a n u l a r s li d in g

b e c a u s e o f t h e a p p a r e n t l y l o w n u m b e r o f i n d e -

p e n d e n t s li p s y s te m s d u r i n g s p e c i m e n s h o r t e n i n g .

T h e d e v e lo p m e n t o f < 1 1 0 > - a n d < l l l > - f i b r e

t e x t u r e s i n t h e 6 0 0 ~ e x p e r i m e n t c o n t r a s t s w i t h

t h e d e v e l o p m e n t o f a < 1 0 0 > - f i b r e t e x t u r e i n t h e

7 0 0 ~ e x p e r i m e n t , a n d m a y i n d i c a te a c h a n g e i n

t h e d o m i n a n t f l o w m e c h a n i s m w i t h c h a n g i n g

t e m p e r a t u r e .

A d d i t i o n a l e x p e r i m e n t s a r e n e c e s s a r y t o a ss e ss

m o r e c l e a r l y t h e d e v e l o p m e n t o f la t ti c e p r e f e r r e d

o r i e n t a t i o n s d u r i n g t h e h i g h - t e m p e r a t u r e d e f o r -

m a t i o n o f p o l y c r y s t a l l i n e p y r i t e , a n d e s p e c i a l l y t o

e x a m i n e t h e p o s s i b i l i t y t h a t f a b r i c t r a n s i t i o n s

o c c u r i n r e s p o n s e t o c h a n g e s i n d o m i n a n t s li p

s y s te m s w i t h c h a n g in g t e m p e r a t u r e . I n v i e w o f

t h e w e a k n e s s o f th e f a b r i c s in p y r i t e , t h e u s e o f

n e u t r o n d i f f ra c t i o n t e c h n i q u e s h a s a n u m b e r o f

a d v a n t a g e s r e l a t i v e t o X - r a y d i f f r a c t i o n t e c h -

n i q u e s f o r f a b r i c a n a l y s is . I n p a r t i c u l a r , t h e

a p p l i c a t i o n o f n e u t r o n d i f f r a c t i o n t e c h n i q u e s w i ll

a l l ow t h e m e a s u r e m e n t o f t h e l a tt i ce p r e f e r r e d

o r i e n t a t i o n o f t h e t o ta l s a m p l e v o l u m e b o t h

b e f o r e a n d a f t e r d e f o r m a t i o n .

cknowlegements

S F C ack n o w l ed g es t h e s u p p o r t o f a C S IR O P o s t d o c -

t o ra l F e l l o w s h i p w h en t h e d e fo rm a t i o n ex p e r i m en t s

w ere o rg i n a l l y p e r fo rm ed i n t h e D ep a r t m en t o f E a r t h

Sciences a t Monash U nivers i ty . The Deg t iar ka pyr i te

was supp l ied by P . Nata le . C omp ut ing was done wi th an

IB M 3 0 9 0 a t t h e co m p u t e r c en t r e o f t h e A ach en

T ech n i ca l U n i v e r s i t y (R W T H ) . T h e c r i t i c a l co m m en t s

of the referees especia l ly o f G . E . L loyd con t r ibu ted to

t h e i m p ro v e m en t o f t h is p u b l i ca ti o n .

References

B ar re t t , C . S . an d L ev en s o n , L . H . (19 40 ) T ran s . A I M E

137 (1940) 112-127, ci ted in Mecking, H. (1985)

Tex tu res o f Meta l s . In Pre f e rred Or i en ta t i on i n

D e f o r m e d M e t a l s a n d R o c k s : A n I n t r o d u c t i o n t o

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