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A new ordered phase in the AlPd system
Mat. Res. Bull. Vol. 13, pp. 1065-1070, 1978. Pergamon Press, Inc. PrInted in the United States.
A NEW ORDERED PHASE IN THE A1-Pd SYSTEM
G.V.S. Sastry and C.Suryanarayana Department of Metallurgical Engineering, Banaras Hindu University, Varanasi 221005 India
-
M.Van Sande and G.Van Tendeloo RijKsuniversitair Centrum Antwerpen~roenenborgerlaan171~-2020Antwerp(Bel~ium)
(Received August 9, 1978; Communicated by S. Amelinckx) ABSTRACT Using electron diffraction and electron microscopy a new phase has been observed in a rapidly solidified AI-6~Pd alloy. Depending on the cooling rate this phase is present in the as quenched cellular-dentritic structure along the cell boundaries or in finer precipitates mostly along the domain boundaries of the fcc solid solution. In both cases the precipitates agglomerate and grow to bigger size after heating in the electron microscope. The new phase having a complicated structure and a large unit cell is closely related to the A14Mn phase which is hexagonal.
I nt~o d~dJ~o n Formation o$ metastable phases is one of the many interesting results of rapid solidification of liquid alloys [1-4]. A metastable phase may form either directly on quenching the melt or during precipitation from an amorphous phase or extended terminal solid solution, when they formed %irst, The metastable phases formed under the above two conditions need not necessarily to be the same. Only a few of the metastable phases obtained so far are reported to be ordered [5]. According to Shunk [6] the equilibrium structure of the alloy consists of proeutectic AI along with the eutectic mixture AI+AIRPd. The intermediate o phase ~l~Pd has a % o r t h o r h o m b i c structure with the l~ttlce parameters a=7.09A, b=7.53A and c=5.09A. Magn613 et al reported the existence of a complicated phase with probable composition AI4Pd, isomorphous with A14Rh [7]. This paper describes the formation of a new phase observed for the first time in a rapidly solidified A1-6 at.~ Pd alloy and possibly related to the one observed by Magn~li et el [7].
1065
1066
G . V . S . SASTRY, etal.
Vol. 18, No. i0
Experiment~ Proced~re Thin foils of the alloy were obtained by rapid solidification of the melt using the well-Known "Gun" technique [8] capable of producing cooling rates in the range of 106 to 1010 °C/sec. Electron microscopy of these foils, before and after heating, was carried out in Philips EM 300, JEOL I00C and JEOL 1250 microscopes.
FIG. 1 a) typi~%l cellular dentritic structure in the as quenched AI-6%Pd bright field at 750 kV b) smaller precipitates in a material quenched at a different speed are concentrated along the domain bou~a~ies
FIG. 2 The same area as in fig. ib after heating for different times at 250 °C (a) after 30 seconds (b) after 2 minutes
Vol. 13, No. 10
THE A1-Pd SYSTEM
1067
Mi cr os t r u ct~re~ Fig. la shows the typical cellular-dentritic structure observed in the asquenched foils. The cells in this structure are of supersaturated f.c.c. AIsolid solution, while the cell boundaries contain a second phase. Depending on the quenching rate another morphology may also be possible : the precipitates are smaller and concentrate along the domain boundaries [fig.lb). A typical diffraction pattern from such a structure is shown as an inset. The intense spots marked by dots are fcc reflections belonging to the []12] zone of the matrix, while the closely spaced spots are due to the second phase. Upon heating inside the electron microscope, the cell boundaries desintegrate or agglomerate forming coarser grains. This phenomenon is well illustrated in fig.2 where the same area as in fig.lb is heated till about 250°C. After heating the positions of the reflections in the diffraction pattern have remained unchanged. Depending upon the local cooling rate in the foil, extended terminal solid solutions are also observed in this alloy. On heating this supersaturated solid solution precipitates out the excess Pd in the form of a second phase. The crystal structure and morphology of this phase were found to be the same as the one shown in fig.2b.
Diffraction
effects
Since the unit cell has large lattice parameters in three directions a large number of reciprocal lattice sections can be obtained; the most dense diffraction pattern is represented in figure 3a. A pseudo hexagonal pattern of int@nse spots can be recognlsed, their d~ value corresponding approximately to 2 . 1 A . The distance in between two such spots [indicated by arrows)ols subdivided into eight parts corresponding to a repeat unit of about 17 A. In directions perpendicular to these, streaking and spot splitting is observed indicating some disorder or a mixing of different but related structures. Upon heating or by looKing at more Pd rich alloys such as Al4Pd larger crystals containing less faults could be obtained. Different regions show diffraction patterns closely related to each other having the same periodicity in one direction but a different in the second one [fSg.4a,b).
F~G.3 a) Diffraction pattern of the new AI-Pd phase. b) Similar diffraction pattern of an unknown phase in a nominal A l ~ M n l I N i 4 phase More intense reflections forming a pse~5o hexa,9on are indicatedV~y ~C~roWs
1068
G.V.S. SASTRY, et ~I.
Vol. I~, No. I0
FIG. 4a & b Diffraction patterns of two closely related superstructures observed in an as quenched AI4Pd specimen. The intense pseudo hexagon can be easily re-
cognized.
. . + . . ; : - + . . ++- t - ,+. , ~ , + ~ . . . . , , , m ~ t - e - . ~ , , . ~ , , + , o ' . + + " l
" + " , % " . +'9.", " " " +" . ' . +" '
+
"
........ +" ............ ++
w, .
•
•
"+~
+
+
" + e " +
t + ~
++ 2
,
•
+
:'+;, + ' : " : + ++++,
~_,
e.
"+,'.%,, "~ . . " "+ +" +.' " +," +-~ + . " ~ ' k ' : ' " + ' - ' 2 . T " : ~ " % . . . . . , + '+" "-+ " ' % " % " ,~..,+.,.. • . , • • .,,.+. +,,..++~- +,.- +
+ Ii
+
o. • I
. . . . ++ +" . . . .
+'++++
++:";'.::A.
~ " . s+ . . . . . . . . . , l . . ~ . .+ ~It+ + +++' +
',,., , , , ; . . a , - .+." ++ "
++
+ e
•
_++
•
+
.
_ +. . . .
L..
_
_
-
-
I"
" °"
"DI°eIlP~llv~+
~a.B~
FIG.
5
High resolution bright field micrographs correspond~ung to the diffraction patterns shown in figure 3. (a) in A1 - 6% Pd (b) in A I 6 ~ I I N i 4
Vol. 13. No. i0
THE
AI-Pd SYSTEM
mixing of both related phases perfectly explaines the splat cooled material [fig.3a).
1069
the observed patterns in
Till now no structure could be determined mainly due to its complicated nature and the small crystal sizes. However very similar diffraction patterns are observed in nominal alloys A 1 M n , A 1 M n and A1 Mn INi A diffraction 6 4 ~ 4" pattern of the ternary alloy is reproduced in figure 3~ and has to be compared with the one obtained from AI-Pd alloys; all features are similar except that the distance between corresponding intense pseudo hexagonal reflections is subdivided into 8 for A1-Pd and into 6 for AI-Mn-Ni. For AI4Mn showing an analogue diffraction pattern as A1-Mn-Ni the exact structure is unknown but its unit cell is claimed to be hexagonal with a = 28.4 A and c = 12.4 A [B]. Since both structures are so closely related it is probable that a simpler structure might be found from which both structures here are direct superstructures.
Lattice resolution In view of the large lattice parameters of t h ~ e phases direct structure imaging can be easily obtained in bright field. In figure 5 two high resolution pictures of Al-6%Pd and Al~_Mn,,Ni 4 are rebU produced; the corresponding diffraction patterns are shown in ~igure 3. It is ~lear that also sub-unit cell details are similar, however no further information can be obtained from those images since no exact structure has been determined till now. Figure 6 is a direct image corresponding to another section of the reciprocal lattice which is shown as an inset; note its pseudo pentagonal symmetry. In the direct image, antiphase boundaries A, twin boundaries T as well as periodic twin boundaries [region X) can be observed.
FIG. 6 High resolution microgral~h corresponding to a different section (shown as an inset)where different interesting crystallograhic l ~ h ~ can be o b s e r v e d
1070
G . V . S . SASTRY, et al.
Vol. 13, No. i0
Acknowledgemen~ The a u t h o r s are t h a n k 4 u l to D r . H . A . D a v i e s o4 the U n i v e r s i t y o4 S h e 4 4 i e l d 4or s u p p l y i n g t h e a l l o M used i n the i n v e s t i g a t i o n . Two o4 t h e a u t h o r s [GVSS, CS) would l i k e to thank the Oepartment o4 S c i e n c e and Technology, Government o4 I n d i a , New O e h l i and t h e U n i v e r s i t y Grants Commission, New D e h l i , 4or 4 i n a n c i a l assiSaance.
Ref~enc~ 1. T.R.Anantharaman and C.Suryanarayana, J . M a t e r . S c i . , 6, 1111 ( 1 9 7 1 ) . 2. H.Jones and C.Suryanarayana, J . M a t e r . S c i . , 8, 705 ( 1 9 7 3 ) . 3. T.R.Anantharaman, P.Ramachandrarao, C.Suryanarayana, S . L e l e , K.Chattopadhyay and G . V . S . S a s t r y , Pape£ to be p r e s e n t e d at t h e t h i r d i n t e r n a t i o n a l conference on R a p i d l y Ouenched M e t a l s , B r i g h t o n , U.K. ( 1 9 7 8 ) . 4. A . K . S i n h a , B . C . G i e s s e n and D . E . P o l k , i n " T r e a t i s e on S o l i d S t a t e C h e m i s t r y " , p . 1 , v o l . 3 , ed. by N.B. Hannay, Plenum P r e s s , New York (1976). 5. B . C . G i e s s e n i n " R a p i d l y Ouenched M e t a l s " , N . J . G r a n t and B . C . G i e s s e n , eds. o,119, Massachusetts I n s t i t u t e o f Technology ( 1 9 7 6 ) , 6. F.A.Shunk, C o n s t i t u t i o n o4 b i n a r y a l l o y s p . 3 5 , Mc Graw H i l l (1969). 7. A.Magn61i, L.E.Edsha~Tnar, T.Dagerhamn. F i n a l T e c h n i c a l Report n ° l under c o n t r a c t DA-91-591-EUC-2734 (AD426927) (1963) 46-49. 6. P.Duwez and R . H . W i l ! e n s , T r e n s . M e t . S o c . A I M E , 227, 362 (1963). 9. M . A . T a y l o r , Acta M e t . 6 , 256-262 (1960).
A NEW ORDERED PHASE IN THE A1-Pd SYSTEM
G.V.S. Sastry and C.Suryanarayana Department of Metallurgical Engineering, Banaras Hindu University, Varanasi 221005 India
-
M.Van Sande and G.Van Tendeloo RijKsuniversitair Centrum Antwerpen~roenenborgerlaan171~-2020Antwerp(Bel~ium)
(Received August 9, 1978; Communicated by S. Amelinckx) ABSTRACT Using electron diffraction and electron microscopy a new phase has been observed in a rapidly solidified AI-6~Pd alloy. Depending on the cooling rate this phase is present in the as quenched cellular-dentritic structure along the cell boundaries or in finer precipitates mostly along the domain boundaries of the fcc solid solution. In both cases the precipitates agglomerate and grow to bigger size after heating in the electron microscope. The new phase having a complicated structure and a large unit cell is closely related to the A14Mn phase which is hexagonal.
I nt~o d~dJ~o n Formation o$ metastable phases is one of the many interesting results of rapid solidification of liquid alloys [1-4]. A metastable phase may form either directly on quenching the melt or during precipitation from an amorphous phase or extended terminal solid solution, when they formed %irst, The metastable phases formed under the above two conditions need not necessarily to be the same. Only a few of the metastable phases obtained so far are reported to be ordered [5]. According to Shunk [6] the equilibrium structure of the alloy consists of proeutectic AI along with the eutectic mixture AI+AIRPd. The intermediate o phase ~l~Pd has a % o r t h o r h o m b i c structure with the l~ttlce parameters a=7.09A, b=7.53A and c=5.09A. Magn613 et al reported the existence of a complicated phase with probable composition AI4Pd, isomorphous with A14Rh [7]. This paper describes the formation of a new phase observed for the first time in a rapidly solidified A1-6 at.~ Pd alloy and possibly related to the one observed by Magn~li et el [7].
1065
1066
G . V . S . SASTRY, etal.
Vol. 18, No. i0
Experiment~ Proced~re Thin foils of the alloy were obtained by rapid solidification of the melt using the well-Known "Gun" technique [8] capable of producing cooling rates in the range of 106 to 1010 °C/sec. Electron microscopy of these foils, before and after heating, was carried out in Philips EM 300, JEOL I00C and JEOL 1250 microscopes.
FIG. 1 a) typi~%l cellular dentritic structure in the as quenched AI-6%Pd bright field at 750 kV b) smaller precipitates in a material quenched at a different speed are concentrated along the domain bou~a~ies
FIG. 2 The same area as in fig. ib after heating for different times at 250 °C (a) after 30 seconds (b) after 2 minutes
Vol. 13, No. 10
THE A1-Pd SYSTEM
1067
Mi cr os t r u ct~re~ Fig. la shows the typical cellular-dentritic structure observed in the asquenched foils. The cells in this structure are of supersaturated f.c.c. AIsolid solution, while the cell boundaries contain a second phase. Depending on the quenching rate another morphology may also be possible : the precipitates are smaller and concentrate along the domain boundaries [fig.lb). A typical diffraction pattern from such a structure is shown as an inset. The intense spots marked by dots are fcc reflections belonging to the []12] zone of the matrix, while the closely spaced spots are due to the second phase. Upon heating inside the electron microscope, the cell boundaries desintegrate or agglomerate forming coarser grains. This phenomenon is well illustrated in fig.2 where the same area as in fig.lb is heated till about 250°C. After heating the positions of the reflections in the diffraction pattern have remained unchanged. Depending upon the local cooling rate in the foil, extended terminal solid solutions are also observed in this alloy. On heating this supersaturated solid solution precipitates out the excess Pd in the form of a second phase. The crystal structure and morphology of this phase were found to be the same as the one shown in fig.2b.
Diffraction
effects
Since the unit cell has large lattice parameters in three directions a large number of reciprocal lattice sections can be obtained; the most dense diffraction pattern is represented in figure 3a. A pseudo hexagonal pattern of int@nse spots can be recognlsed, their d~ value corresponding approximately to 2 . 1 A . The distance in between two such spots [indicated by arrows)ols subdivided into eight parts corresponding to a repeat unit of about 17 A. In directions perpendicular to these, streaking and spot splitting is observed indicating some disorder or a mixing of different but related structures. Upon heating or by looKing at more Pd rich alloys such as Al4Pd larger crystals containing less faults could be obtained. Different regions show diffraction patterns closely related to each other having the same periodicity in one direction but a different in the second one [fSg.4a,b).
F~G.3 a) Diffraction pattern of the new AI-Pd phase. b) Similar diffraction pattern of an unknown phase in a nominal A l ~ M n l I N i 4 phase More intense reflections forming a pse~5o hexa,9on are indicatedV~y ~C~roWs
1068
G.V.S. SASTRY, et ~I.
Vol. I~, No. I0
FIG. 4a & b Diffraction patterns of two closely related superstructures observed in an as quenched AI4Pd specimen. The intense pseudo hexagon can be easily re-
cognized.
. . + . . ; : - + . . ++- t - ,+. , ~ , + ~ . . . . , , , m ~ t - e - . ~ , , . ~ , , + , o ' . + + " l
" + " , % " . +'9.", " " " +" . ' . +" '
+
"
........ +" ............ ++
w, .
•
•
"+~
+
+
" + e " +
t + ~
++ 2
,
•
+
:'+;, + ' : " : + ++++,
~_,
e.
"+,'.%,, "~ . . " "+ +" +.' " +," +-~ + . " ~ ' k ' : ' " + ' - ' 2 . T " : ~ " % . . . . . , + '+" "-+ " ' % " % " ,~..,+.,.. • . , • • .,,.+. +,,..++~- +,.- +
+ Ii
+
o. • I
. . . . ++ +" . . . .
+'++++
++:";'.::A.
~ " . s+ . . . . . . . . . , l . . ~ . .+ ~It+ + +++' +
',,., , , , ; . . a , - .+." ++ "
++
+ e
•
_++
•
+
.
_ +. . . .
L..
_
_
-
-
I"
" °"
"DI°eIlP~llv~+
~a.B~
FIG.
5
High resolution bright field micrographs correspond~ung to the diffraction patterns shown in figure 3. (a) in A1 - 6% Pd (b) in A I 6 ~ I I N i 4
Vol. 13. No. i0
THE
AI-Pd SYSTEM
mixing of both related phases perfectly explaines the splat cooled material [fig.3a).
1069
the observed patterns in
Till now no structure could be determined mainly due to its complicated nature and the small crystal sizes. However very similar diffraction patterns are observed in nominal alloys A 1 M n , A 1 M n and A1 Mn INi A diffraction 6 4 ~ 4" pattern of the ternary alloy is reproduced in figure 3~ and has to be compared with the one obtained from AI-Pd alloys; all features are similar except that the distance between corresponding intense pseudo hexagonal reflections is subdivided into 8 for A1-Pd and into 6 for AI-Mn-Ni. For AI4Mn showing an analogue diffraction pattern as A1-Mn-Ni the exact structure is unknown but its unit cell is claimed to be hexagonal with a = 28.4 A and c = 12.4 A [B]. Since both structures are so closely related it is probable that a simpler structure might be found from which both structures here are direct superstructures.
Lattice resolution In view of the large lattice parameters of t h ~ e phases direct structure imaging can be easily obtained in bright field. In figure 5 two high resolution pictures of Al-6%Pd and Al~_Mn,,Ni 4 are rebU produced; the corresponding diffraction patterns are shown in ~igure 3. It is ~lear that also sub-unit cell details are similar, however no further information can be obtained from those images since no exact structure has been determined till now. Figure 6 is a direct image corresponding to another section of the reciprocal lattice which is shown as an inset; note its pseudo pentagonal symmetry. In the direct image, antiphase boundaries A, twin boundaries T as well as periodic twin boundaries [region X) can be observed.
FIG. 6 High resolution microgral~h corresponding to a different section (shown as an inset)where different interesting crystallograhic l ~ h ~ can be o b s e r v e d
1070
G . V . S . SASTRY, et al.
Vol. 13, No. i0
Acknowledgemen~ The a u t h o r s are t h a n k 4 u l to D r . H . A . D a v i e s o4 the U n i v e r s i t y o4 S h e 4 4 i e l d 4or s u p p l y i n g t h e a l l o M used i n the i n v e s t i g a t i o n . Two o4 t h e a u t h o r s [GVSS, CS) would l i k e to thank the Oepartment o4 S c i e n c e and Technology, Government o4 I n d i a , New O e h l i and t h e U n i v e r s i t y Grants Commission, New D e h l i , 4or 4 i n a n c i a l assiSaance.
Ref~enc~ 1. T.R.Anantharaman and C.Suryanarayana, J . M a t e r . S c i . , 6, 1111 ( 1 9 7 1 ) . 2. H.Jones and C.Suryanarayana, J . M a t e r . S c i . , 8, 705 ( 1 9 7 3 ) . 3. T.R.Anantharaman, P.Ramachandrarao, C.Suryanarayana, S . L e l e , K.Chattopadhyay and G . V . S . S a s t r y , Pape£ to be p r e s e n t e d at t h e t h i r d i n t e r n a t i o n a l conference on R a p i d l y Ouenched M e t a l s , B r i g h t o n , U.K. ( 1 9 7 8 ) . 4. A . K . S i n h a , B . C . G i e s s e n and D . E . P o l k , i n " T r e a t i s e on S o l i d S t a t e C h e m i s t r y " , p . 1 , v o l . 3 , ed. by N.B. Hannay, Plenum P r e s s , New York (1976). 5. B . C . G i e s s e n i n " R a p i d l y Ouenched M e t a l s " , N . J . G r a n t and B . C . G i e s s e n , eds. o,119, Massachusetts I n s t i t u t e o f Technology ( 1 9 7 6 ) , 6. F.A.Shunk, C o n s t i t u t i o n o4 b i n a r y a l l o y s p . 3 5 , Mc Graw H i l l (1969). 7. A.Magn61i, L.E.Edsha~Tnar, T.Dagerhamn. F i n a l T e c h n i c a l Report n ° l under c o n t r a c t DA-91-591-EUC-2734 (AD426927) (1963) 46-49. 6. P.Duwez and R . H . W i l ! e n s , T r e n s . M e t . S o c . A I M E , 227, 362 (1963). 9. M . A . T a y l o r , Acta M e t . 6 , 256-262 (1960).