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Evidence for plastic deformation in the natural polycrystalline diamond, framesite
Mat. Res. Bull. Vol. 8, pp. 733-742, 1973. in the United States.
Pergamon Press, Inc. Printed
EVIDENCE FOR PLASTIC DEFORMATION IN THE NATURAL POLYCRYSTALLINEDIAMOND, FRAMESlTE R. C. DeVries General Electric Corporate Research and Development Schenectady, New York 12301
(Received April 27, 1973; Communicated by R. C. DeVries)
ABSTRACT Relief-polished s t r i a t i o n s have been found within grains in polished sections of framesite, a naturally occurring polycrystall i n e diamond. Because the narrow zones represented by these surface s t r i a t i o n s are harder than any orientation of the matrix (as revealed by abrasion resistance) and because they etch p r e f e r e n t i a l l y , they have been interpreted as representing oriented deformation bands within the grains. I t is concluded that the microstructure of framesite is the result of plastic deformation of diamond grains probably under conditions such that b r i t t l e fracture was inhibited.
Introduction Framesite is a form of polycrystalline diamond which is described as "a coarse, g r i t t y , rather f r i a b l e , black, non-gem quality of diamond found primarily in the Premier Mine, South Africa"(1). named a f t e r P. Ross Frames of Johannesburg. being very d i f f i c u l t
This bort type of material is
Framesite has the reputation of
to cut (2) or to grind (3) in spite of the fact that i t is
c l e a r l y not as well-bonded as some other b o r t - l i k e materials.
Within
individual grains in polished sections of this material are some structural features which are remarkably l i k e deformation structures in other inorganic non-metallic materials (eg. MgO, LiF).
In the context of the i n t e r e s t in
plastic deformation of diamond (5-18) and in the b e l i e f that there might be a d i r e c t relationship of the "toughness" of framesite to this unique microstructure, a more detailed study and interpretation was undertaken.
I t is
concluded that the microstructure of framesite is the result of plastic 733
734
FRAMESITE
Vol. 8, No. 6
deformation of diamond grains under conditions that inhibited b r i t t l e fracture and that the strain-hardened regions are responsible for the resistance to wear. Experimental Description of the Sample The specimen studied was an i r r e g u l a r l y shaped, coarse-grained block (about 4x5x7 mm) with some cracks--one of which could be traced around the entire piece.
The bulk sample was dark gra~but when observed with polarized
transmitted l i g h t at 360X in a refractive index o i l , colorless, transparent diamond grains are seen.
Many individual grains show strain birefringence in
patterns markedly similar to multiple parallel twinning bands in an anisotropic transparent solid.
A black, opaque, b r i t t l e second phase (perhaps 2% of the
total volume) was present as a coating on some of the diamond grains and often seems to be concentrated in cracks.
When suspended in an index oil and
observed in transmitted l i g h t , this phase can be seen responding readily to a magnet brought near the sample.
Perhaps this implies a genetic relationship
of framesite to the magnetic bort, stewartite (I).
The magnetic phase appears
to contribute to the bonding of the sample. Although not enough of this phase could be concentrated for i d e n t i f i c a t i o n by X-ray methods, there are some indications i t could be magnetite.
When the
sample was etched in molten KN03 for 3 minutes, the framesite changed from dark gray to white with some red particles v i s i b l e along the cracks.
In
transmitted l i g h t , the red particles were transparent and birefringent. were s t i l l
A few
s l i g h t l y magnetic, but they were c l e a r l y less magnetic than the
original dark gray phase.
I t is suggested that the dark gray phase was pre-
dominantly magnetite, which converts to the red ~-Fe203 in the oxidizing etchant. A f t e r
etching, the sample is more f r i a b l e than the original and the
grain boundaries are deeply etched. Polishin 9 Technique The sample was mounted with a metal'epoxy composite in a dop on a pivoted tang which was cam operated to constantly swing the sample back and forth in an arc over the rotating cast iron scaife. vertical axis by a motor drive. mesh) were used on the scaife.
The dop was also rotated about i t s
Man,Made T diamonds (General Electric RVG-325 This abrasive grain has the property of pro-
viding both a grinding and a polishing function--the former during the i n i t i a l stages and the l a t t e r as the g r i t becomes worn down. could be achieved in about 1 hour.
A satisfactory surface
Vol. 8, No. 6
FRAMESITE
735
The method provides a constantly changing grinding direction, and the best polished sections were produced this way.
I t was established that the
structure also could be revealed by unidirectional polishing, but not as well. Polishing was also done by hand on a frosted glass lap with 30u and 1.5u diamond compound followed by final polishing on cloth or paper with coarse A1203 polishing powder (4). The results were equivalent to polishing on the scaife, but i t took longer.
The reproducibility of the structure has been
established, and i t was concluded that among borts and carbonados, the framesite microstructure is unique and not the result of the polishing procedure. Framesite Microstructure The microstructure of framesite as seen in polished sections is shown in Figures l through 6.
Two prominent characteristics are described in some
detail.
FIG. l Framesite microstructure striations revealed by relief-polishing. (As polished, 150X)
Grains and Grain Boundaries The highly irregular grain boundaries and rather open structure (Fig. I) are definitely not characteristic of the "equilibrium" grain boundary configuration seen in well-sintered materials.
There are many cracks and the
736
FRAMES1TE
Vol. 8, No. 6
FIG. 2 Framesite microstructure. More detailed view of 2 intersecting sets of striations, some of which show curvature. (As polished, 500X)
FIG. 3
Three sets of traces in a diamond grai,n of approximately { I l l } orientation. (As polished, 500X)
poor bonding mentioned earlier is confirmed by the polished section, There has been obvious removal of grain boundary material during polishing.
Vol. 8, No. 6
FRAMESITE
1
/
/
1 FIG. 4
Four sets of traces in diamond grain of approximately {315} orientation on basis of { I I I } traces. (As polished, 500X)
FIG. 5 Comparison of relief-polished microstructure.
a.
As polished, 150X
b.
Etched 3 minutes in molten KN03. 150X
737
738
FRAMESITE
Vol. 8, No. 6
FIG. 6 Interference and bright field photomicrograph of polished surface of framesite.
a.
TC~ = 5350.5~
385X
b.
Bright field
385X
Striation Within the Grains In many grains, sets of parallel striations or narrow bands can be seen as a result of r e l i e f polishing (Fig. I-4, 5a, 6b). Using light interference techniques, these striations (about l~ wide) have been found always to be higher in elevation than the polished surface of the grains in which they are found, and several different grain orientations are represented as seen from the different arrangements of the striations.
As measured with a Leitz
interference microscope, these ridges are about 400-600A high (Fig. 6a).
In
other words, their abrasion resistance is greater than that of the matrix grain.
The striations are variable in length--ranging from short spikes
ending within the grain to those completely crossing a large grain.
The
frequency of appearance of different directions or sets of traces per grain decreases in the order I>2>3>4. Four sets are rare (Fig. 4), and no examples of greater than four were found. Using a stereographic analysis (assuming all four traces were from the same family of Planes), the orientation of the
Vol. 8, No. 6
FRAMESITE
739
traces is consistent with { I I I }
planes in agreement with previously reported
s l i p planes for diamond (5-18).
This j u s t i f i c a t i o n
for the { I I I }
orientation
of the deformation lamellae is admittedly not completely satisfying.
All
attempts to obtain d i r e c t experimental confirmation via Laue photographs either of ( I ) a grain in a polished section, or (2) by removal of a polished grain were unsuccessful.
In the former, the small grain size coupled with the
depth of penetration of X-rays in diamond precluded unequivocal results. Because of the small grain size, removal of a single grain that also contained an adequate polished section revealing more than one set of traces was never achieved.
Attempts to polish two surfaces on the same grain so trace analysis
could be performed simultaneously on them were unsuccessful because of the difficulty
of polishing a sharp edge in this hard material with i t s r e l a t i v e l y
weak intergranular bonding and small grain size.
Etching has not been a useful
technique for determining orientation in framesite because the material f a l l s apart before etch p i t t i n g occurs.
In spite of the ambiguity, the p r o b a b i l i t y
of the traces being on planes other than { I I I }
is considered to be very low.
I t is quite common to see s t r i a t i o n s which show curvature (Fig. 2)--as i f a s t r i a t i o n cross-slipped to avoid another s t r i a t i o n from a nearby parallel plane.
Unequivocal
evidence of f a u l t i n g of one set of traces by an i n t e r -
secting set has not been found. Besides cleaning the sample and converting the dark gray, magnetic second phase to a red non-magnetic phase, the etching procedure described e a r l i e r also p r e f e r e n t i a l l y etches the s t r i a t i o n s .
Several examples of a one-to-one cor-
respondence between the r e l i e f - p o l i s h e d structure and the etched structure were easily found (Fig. 5).
However, the etching process also reveals
s t r i a t i o n s in grains that did not show any r e l i e f - p o l i s h e d microstructure. This may be due to an o r i e n t a t i o n e f f e c t , e.g., i f the planes responsible for the traces are nearly parallel
to the polished surface.
The etching rate of
the deformed regions was extremely rapid, and i t was not possible to etch long enough to develop etch pits related to dislocations before total disappearance of the sample.
This r e s u l t emphasizes the high degree of strain associated
with the deformation structures. Electron microprobe scanning of the polished surfaces showed no chemical differences between s t r i a t i o n s and the matrix. Discussion The above observations on the s t r i a t i o n s seen in polished sections of framesite are all consistent with localized strain along d e f i n i t e c r y s t a l l o -
740
FRAMESITE
Vol. 8, No. 6
graphic planes. The greater abrasion hardness of the striations, their preferential etching behavior, and the zoned strain birefringence seen in single grains are all compatible with such an interpretation.
In common with many
other examples in physical metallurgy, i t is d i f f i c u l t to distinguish between slip and deformation twinning.
Fromconsiderations of the diamond structure
and from the experimental studies of the deformation of diamond and related materials at one atmosphere,(14) both types of plastic deformation would be expected to take place predominantly on the { I l l } planes. From studies of natural diamond crystals, i t seems likely that the deformation mode would be similar at high pressures and temperatures also (5,15). By analogy with previous work, there is a marked resemblance of the structures described here to some of those seen by Phaal (lO) in a diamond deformed with an indenter at high temperatures at one atmosphere and to structures identified as slip lines in a p~per by Varma (18). In Phaal's study, the surface traces of planes were attributed
to both slip and deformation twinning--the latter being the only
structure remaining after repolishing the sample. One set of slip lines was consistent with { I l l } while another appeared to correspond with {123} (lO). Varma used the criterion of whether or not the sets of traces cross each other to distinguish slip from deformation twinning in diamond (18). Sets of slip traces can cross while deformation twins tend to end at another intersecting twin. Growth twinning occurs on { I l l } in diamond and is recognizable by r e l i e f polishing in framesite and in other polycrystalline diamonds as a single line or a wide band extending completely across a grain.
These are much more gross
features than the fine striation structure emphasized here. Although they were not a prominent feature in framesite, occasional growth twins were seen as a single straight line--a relief-polished step resulting from the orientation dependent hardness difference on either side of the boundary. A set of striations from the deformation structure has been seen to intersect a growth twin boundary. Although { I l l } twinning can exist on a fine scale in diamondtype structures, intersecting sets of growth twins on the fine scale seen here are considered highly unlikely.
I t would be expected also that i f the s t r i -
ations were due to fine scale growth twinning, for some orientations the striations would be lower than the matrix rather than higher as found by r e l i e f polishing.
I f the phenomenon is due to a twinning or faulting mechan-
ism, i t is more likely by deformation twinning than by growth twinning. Because there are no apparent chemical differences between the matrix and the striations, a precipitation mechanism for their origin seems remote. The
Vol. 8, No. 6
741
FRAMESITE
nitrogen precipitate found in Type la diamond is an extremely fine scale feature which lies along {lO0} planes (19) and is certainly not revealed by r e l i e f polishing. Oriented graphite has been reported in a framesite sample studied by X-ray techniques (2). No evidence for graphite was seen in the specimens studied here. However, the relationship of graphite formation to the structures seen should not be discounted completely without further study.
I t has been noted
that diamond is highly strained near graphitized regions (8,9). I t would be interesting to know the structure of a slip plane in diamond and its possible relationship to graphite-related structures.
Although a layer of graphite on
edge might be expected to be harder than diamond from a simple C-C bond length argument, i t seems an unlikely explanation for the properties of l~ thick deformation structures reported here. In conclusion, i t seems clear that framesite was subjected to stress probably while hot and some of the individual crystals in a polycrystalline aggregate recorded that event by deforming plastically under conditions in which b r i t t l e fracture was inhibited.
Following Frank (21~ i t can also be
stated that not much annealing took place after that event. Within the grains, the deformation process--either slip or deformation twinning--produced oriented lamellae which are harder in an abrasion test than any orientation of the matrix diamond grain.
These strain-hardened zones are probably the reason for
the observations that framesite is d i f f i c u l t to cut and grind much in the same manner that a "knot" is a problem in polishing gem diamonds. Acknowledgments Several people have become involved in this work. their various contributions:
I thank all of them for
M. Houle (who, indeed, may have been the f i r s t
person to reveal the fine structure of framesite), E. Raviola, C. Robb, E. Lifshin and Carol Kirk, E. Koch and A. Ritzer for metallography and microscopy; L.Osika and S. F. Bartram, for X-ray characterization; K. Darrow, for much teaching and encouragement in revealing and observing the microstructure, for providing samples of framesite and for making polishing equipment available; W. Roth, for helpful discussions; W. G. Johnston and J. Westbrook for their interest and helpful discussions on interpretation of deformation structures; Rod Hanneman and P. D. S. St. Pierre for critical reading of the manuscript.
742
FRAMESITE
Vol. 8, No. 6
References I.
L . L . Copeland, et al., The GIA Diamond Dictionary, Gemological Institute of America, Los Angeles (1960).
2.
A.F. Williams, The Genesis of the Diamond. E. Benn Ltd., London (1932).
3.
E. Hull and K. A. Darrow, unpublished research, Feb. 1965.
4.
M. Houle, unpublished (1959).
5.
S. Tolansky and M. Omar, Phil. Mag. 44, 513 (1953).
6.
M. Seal and J. W. Menter, Phil. Mag. 44 1408 (1953).
7.
M. Seal, Proc. 34d International Congress for Electron Microscopy, London (1954), pp. 513-517.
8.
M. Seal, Nature 182, 1264 (1958).
9.
T. Evans and P. F. James, Proc. Roy. Soc. A277, 260 (1964).
lO.
C. Phaal, Phil. Mag. 8th Series
II.
T. Evans and R. K. Wild, Phil. Mag. 12, 479 (1965).
12.
T. Evans and R. K. Wild, Phil. Mag. 13, 209 (1966).
13.
R. K. Wild, T. Evans and A. R. Lang, Phil. Mag. 15, 267 (1967).
14.
H. Alexander and P. Haasen, Solid State Physics 22, 27 (1968). Academic Press, New York.
15.
C. K. R. Varma, J. Phys. Chem. Solids
16.
C. K. R. Varma, Acta Met. 18, I l l 3 (1970).
17.
C. K. R. Varma, Scripta Met. 6_, 383 (1972).
18.
C. K. R. Varma, Scripta Met. 6 799 (1972).
19.
T. Evans and C. Phaal, Proc. Roy. Soc. A270, 538 (1962).
20.
K. Lonsdale and H. J. Milledge, in Chap. 2, Physical Properties of Diamond, edited by R. Berman. Clarendon Press, Oxford (1965), pp. 53-54.
21.
F. C. Frank, in Science and Technology of Industrial Diamonds. Proc. of Intern. Ind. Diamond Conference, Oxford, 1966, ed. John Burls. Industrial Diamond Information Bureau, London (1967).
lO, 887 (1964).
3_]_I,890 (1970).
This paper was pr e s e nt e d at the Annual Meeting of the A m e r i c a n C e r a m i c Society, 1972.
Pergamon Press, Inc. Printed
EVIDENCE FOR PLASTIC DEFORMATION IN THE NATURAL POLYCRYSTALLINEDIAMOND, FRAMESlTE R. C. DeVries General Electric Corporate Research and Development Schenectady, New York 12301
(Received April 27, 1973; Communicated by R. C. DeVries)
ABSTRACT Relief-polished s t r i a t i o n s have been found within grains in polished sections of framesite, a naturally occurring polycrystall i n e diamond. Because the narrow zones represented by these surface s t r i a t i o n s are harder than any orientation of the matrix (as revealed by abrasion resistance) and because they etch p r e f e r e n t i a l l y , they have been interpreted as representing oriented deformation bands within the grains. I t is concluded that the microstructure of framesite is the result of plastic deformation of diamond grains probably under conditions such that b r i t t l e fracture was inhibited.
Introduction Framesite is a form of polycrystalline diamond which is described as "a coarse, g r i t t y , rather f r i a b l e , black, non-gem quality of diamond found primarily in the Premier Mine, South Africa"(1). named a f t e r P. Ross Frames of Johannesburg. being very d i f f i c u l t
This bort type of material is
Framesite has the reputation of
to cut (2) or to grind (3) in spite of the fact that i t is
c l e a r l y not as well-bonded as some other b o r t - l i k e materials.
Within
individual grains in polished sections of this material are some structural features which are remarkably l i k e deformation structures in other inorganic non-metallic materials (eg. MgO, LiF).
In the context of the i n t e r e s t in
plastic deformation of diamond (5-18) and in the b e l i e f that there might be a d i r e c t relationship of the "toughness" of framesite to this unique microstructure, a more detailed study and interpretation was undertaken.
I t is
concluded that the microstructure of framesite is the result of plastic 733
734
FRAMESITE
Vol. 8, No. 6
deformation of diamond grains under conditions that inhibited b r i t t l e fracture and that the strain-hardened regions are responsible for the resistance to wear. Experimental Description of the Sample The specimen studied was an i r r e g u l a r l y shaped, coarse-grained block (about 4x5x7 mm) with some cracks--one of which could be traced around the entire piece.
The bulk sample was dark gra~but when observed with polarized
transmitted l i g h t at 360X in a refractive index o i l , colorless, transparent diamond grains are seen.
Many individual grains show strain birefringence in
patterns markedly similar to multiple parallel twinning bands in an anisotropic transparent solid.
A black, opaque, b r i t t l e second phase (perhaps 2% of the
total volume) was present as a coating on some of the diamond grains and often seems to be concentrated in cracks.
When suspended in an index oil and
observed in transmitted l i g h t , this phase can be seen responding readily to a magnet brought near the sample.
Perhaps this implies a genetic relationship
of framesite to the magnetic bort, stewartite (I).
The magnetic phase appears
to contribute to the bonding of the sample. Although not enough of this phase could be concentrated for i d e n t i f i c a t i o n by X-ray methods, there are some indications i t could be magnetite.
When the
sample was etched in molten KN03 for 3 minutes, the framesite changed from dark gray to white with some red particles v i s i b l e along the cracks.
In
transmitted l i g h t , the red particles were transparent and birefringent. were s t i l l
A few
s l i g h t l y magnetic, but they were c l e a r l y less magnetic than the
original dark gray phase.
I t is suggested that the dark gray phase was pre-
dominantly magnetite, which converts to the red ~-Fe203 in the oxidizing etchant. A f t e r
etching, the sample is more f r i a b l e than the original and the
grain boundaries are deeply etched. Polishin 9 Technique The sample was mounted with a metal'epoxy composite in a dop on a pivoted tang which was cam operated to constantly swing the sample back and forth in an arc over the rotating cast iron scaife. vertical axis by a motor drive. mesh) were used on the scaife.
The dop was also rotated about i t s
Man,Made T diamonds (General Electric RVG-325 This abrasive grain has the property of pro-
viding both a grinding and a polishing function--the former during the i n i t i a l stages and the l a t t e r as the g r i t becomes worn down. could be achieved in about 1 hour.
A satisfactory surface
Vol. 8, No. 6
FRAMESITE
735
The method provides a constantly changing grinding direction, and the best polished sections were produced this way.
I t was established that the
structure also could be revealed by unidirectional polishing, but not as well. Polishing was also done by hand on a frosted glass lap with 30u and 1.5u diamond compound followed by final polishing on cloth or paper with coarse A1203 polishing powder (4). The results were equivalent to polishing on the scaife, but i t took longer.
The reproducibility of the structure has been
established, and i t was concluded that among borts and carbonados, the framesite microstructure is unique and not the result of the polishing procedure. Framesite Microstructure The microstructure of framesite as seen in polished sections is shown in Figures l through 6.
Two prominent characteristics are described in some
detail.
FIG. l Framesite microstructure striations revealed by relief-polishing. (As polished, 150X)
Grains and Grain Boundaries The highly irregular grain boundaries and rather open structure (Fig. I) are definitely not characteristic of the "equilibrium" grain boundary configuration seen in well-sintered materials.
There are many cracks and the
736
FRAMES1TE
Vol. 8, No. 6
FIG. 2 Framesite microstructure. More detailed view of 2 intersecting sets of striations, some of which show curvature. (As polished, 500X)
FIG. 3
Three sets of traces in a diamond grai,n of approximately { I l l } orientation. (As polished, 500X)
poor bonding mentioned earlier is confirmed by the polished section, There has been obvious removal of grain boundary material during polishing.
Vol. 8, No. 6
FRAMESITE
1
/
/
1 FIG. 4
Four sets of traces in diamond grain of approximately {315} orientation on basis of { I I I } traces. (As polished, 500X)
FIG. 5 Comparison of relief-polished microstructure.
a.
As polished, 150X
b.
Etched 3 minutes in molten KN03. 150X
737
738
FRAMESITE
Vol. 8, No. 6
FIG. 6 Interference and bright field photomicrograph of polished surface of framesite.
a.
TC~ = 5350.5~
385X
b.
Bright field
385X
Striation Within the Grains In many grains, sets of parallel striations or narrow bands can be seen as a result of r e l i e f polishing (Fig. I-4, 5a, 6b). Using light interference techniques, these striations (about l~ wide) have been found always to be higher in elevation than the polished surface of the grains in which they are found, and several different grain orientations are represented as seen from the different arrangements of the striations.
As measured with a Leitz
interference microscope, these ridges are about 400-600A high (Fig. 6a).
In
other words, their abrasion resistance is greater than that of the matrix grain.
The striations are variable in length--ranging from short spikes
ending within the grain to those completely crossing a large grain.
The
frequency of appearance of different directions or sets of traces per grain decreases in the order I>2>3>4. Four sets are rare (Fig. 4), and no examples of greater than four were found. Using a stereographic analysis (assuming all four traces were from the same family of Planes), the orientation of the
Vol. 8, No. 6
FRAMESITE
739
traces is consistent with { I I I }
planes in agreement with previously reported
s l i p planes for diamond (5-18).
This j u s t i f i c a t i o n
for the { I I I }
orientation
of the deformation lamellae is admittedly not completely satisfying.
All
attempts to obtain d i r e c t experimental confirmation via Laue photographs either of ( I ) a grain in a polished section, or (2) by removal of a polished grain were unsuccessful.
In the former, the small grain size coupled with the
depth of penetration of X-rays in diamond precluded unequivocal results. Because of the small grain size, removal of a single grain that also contained an adequate polished section revealing more than one set of traces was never achieved.
Attempts to polish two surfaces on the same grain so trace analysis
could be performed simultaneously on them were unsuccessful because of the difficulty
of polishing a sharp edge in this hard material with i t s r e l a t i v e l y
weak intergranular bonding and small grain size.
Etching has not been a useful
technique for determining orientation in framesite because the material f a l l s apart before etch p i t t i n g occurs.
In spite of the ambiguity, the p r o b a b i l i t y
of the traces being on planes other than { I I I }
is considered to be very low.
I t is quite common to see s t r i a t i o n s which show curvature (Fig. 2)--as i f a s t r i a t i o n cross-slipped to avoid another s t r i a t i o n from a nearby parallel plane.
Unequivocal
evidence of f a u l t i n g of one set of traces by an i n t e r -
secting set has not been found. Besides cleaning the sample and converting the dark gray, magnetic second phase to a red non-magnetic phase, the etching procedure described e a r l i e r also p r e f e r e n t i a l l y etches the s t r i a t i o n s .
Several examples of a one-to-one cor-
respondence between the r e l i e f - p o l i s h e d structure and the etched structure were easily found (Fig. 5).
However, the etching process also reveals
s t r i a t i o n s in grains that did not show any r e l i e f - p o l i s h e d microstructure. This may be due to an o r i e n t a t i o n e f f e c t , e.g., i f the planes responsible for the traces are nearly parallel
to the polished surface.
The etching rate of
the deformed regions was extremely rapid, and i t was not possible to etch long enough to develop etch pits related to dislocations before total disappearance of the sample.
This r e s u l t emphasizes the high degree of strain associated
with the deformation structures. Electron microprobe scanning of the polished surfaces showed no chemical differences between s t r i a t i o n s and the matrix. Discussion The above observations on the s t r i a t i o n s seen in polished sections of framesite are all consistent with localized strain along d e f i n i t e c r y s t a l l o -
740
FRAMESITE
Vol. 8, No. 6
graphic planes. The greater abrasion hardness of the striations, their preferential etching behavior, and the zoned strain birefringence seen in single grains are all compatible with such an interpretation.
In common with many
other examples in physical metallurgy, i t is d i f f i c u l t to distinguish between slip and deformation twinning.
Fromconsiderations of the diamond structure
and from the experimental studies of the deformation of diamond and related materials at one atmosphere,(14) both types of plastic deformation would be expected to take place predominantly on the { I l l } planes. From studies of natural diamond crystals, i t seems likely that the deformation mode would be similar at high pressures and temperatures also (5,15). By analogy with previous work, there is a marked resemblance of the structures described here to some of those seen by Phaal (lO) in a diamond deformed with an indenter at high temperatures at one atmosphere and to structures identified as slip lines in a p~per by Varma (18). In Phaal's study, the surface traces of planes were attributed
to both slip and deformation twinning--the latter being the only
structure remaining after repolishing the sample. One set of slip lines was consistent with { I l l } while another appeared to correspond with {123} (lO). Varma used the criterion of whether or not the sets of traces cross each other to distinguish slip from deformation twinning in diamond (18). Sets of slip traces can cross while deformation twins tend to end at another intersecting twin. Growth twinning occurs on { I l l } in diamond and is recognizable by r e l i e f polishing in framesite and in other polycrystalline diamonds as a single line or a wide band extending completely across a grain.
These are much more gross
features than the fine striation structure emphasized here. Although they were not a prominent feature in framesite, occasional growth twins were seen as a single straight line--a relief-polished step resulting from the orientation dependent hardness difference on either side of the boundary. A set of striations from the deformation structure has been seen to intersect a growth twin boundary. Although { I l l } twinning can exist on a fine scale in diamondtype structures, intersecting sets of growth twins on the fine scale seen here are considered highly unlikely.
I t would be expected also that i f the s t r i -
ations were due to fine scale growth twinning, for some orientations the striations would be lower than the matrix rather than higher as found by r e l i e f polishing.
I f the phenomenon is due to a twinning or faulting mechan-
ism, i t is more likely by deformation twinning than by growth twinning. Because there are no apparent chemical differences between the matrix and the striations, a precipitation mechanism for their origin seems remote. The
Vol. 8, No. 6
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nitrogen precipitate found in Type la diamond is an extremely fine scale feature which lies along {lO0} planes (19) and is certainly not revealed by r e l i e f polishing. Oriented graphite has been reported in a framesite sample studied by X-ray techniques (2). No evidence for graphite was seen in the specimens studied here. However, the relationship of graphite formation to the structures seen should not be discounted completely without further study.
I t has been noted
that diamond is highly strained near graphitized regions (8,9). I t would be interesting to know the structure of a slip plane in diamond and its possible relationship to graphite-related structures.
Although a layer of graphite on
edge might be expected to be harder than diamond from a simple C-C bond length argument, i t seems an unlikely explanation for the properties of l~ thick deformation structures reported here. In conclusion, i t seems clear that framesite was subjected to stress probably while hot and some of the individual crystals in a polycrystalline aggregate recorded that event by deforming plastically under conditions in which b r i t t l e fracture was inhibited.
Following Frank (21~ i t can also be
stated that not much annealing took place after that event. Within the grains, the deformation process--either slip or deformation twinning--produced oriented lamellae which are harder in an abrasion test than any orientation of the matrix diamond grain.
These strain-hardened zones are probably the reason for
the observations that framesite is d i f f i c u l t to cut and grind much in the same manner that a "knot" is a problem in polishing gem diamonds. Acknowledgments Several people have become involved in this work. their various contributions:
I thank all of them for
M. Houle (who, indeed, may have been the f i r s t
person to reveal the fine structure of framesite), E. Raviola, C. Robb, E. Lifshin and Carol Kirk, E. Koch and A. Ritzer for metallography and microscopy; L.Osika and S. F. Bartram, for X-ray characterization; K. Darrow, for much teaching and encouragement in revealing and observing the microstructure, for providing samples of framesite and for making polishing equipment available; W. Roth, for helpful discussions; W. G. Johnston and J. Westbrook for their interest and helpful discussions on interpretation of deformation structures; Rod Hanneman and P. D. S. St. Pierre for critical reading of the manuscript.
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This paper was pr e s e nt e d at the Annual Meeting of the A m e r i c a n C e r a m i c Society, 1972.