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Amorphous FeTi alloy formed by solid state reaction
0038-1098/88 $3.00 + .00 Pergamon Press pie
o> °+ Solid State Communications, Vol. 68, No. 9, pp.811-812, 1988. e-~ Printed in Great Britain.
AMORPHOUS
Fe-TI
ALLOY
FORMED
BY S O L I D
STATE
REACTION
Zhih,, a Y a m Imstitute
of P h y s i c s ,
Chinese
Academy
Wemkui Center
of C o n d e n s e d
Institute
of
Matter
and
of S c i e m c e s ,
Beijimg,
China
Wang
Radiation, and
CCAST(World
Laboratory)
Physics, Chinese Academy of Sciences, B e i j i n g ,
China
(Received I0 September, 1988 by W. Y. Kuan) T h e p r e s e n t p a p e r r e p o r t s the f o r m a t i o n of a m o r p h o u s F e ~ n T i ~ o a l l o y by the s o l i d s t a t e r e a c t i o n of p u r e p o l y c r y s t a l l i ~ Fe and Ti t'~in f i l m s at l o w t e m p e r a t u r e . X--ray d i f f r a c t i o n and reflectimg e l e c t r o n d i f f r a c t i o n w e r e u s e d to m o n i t o r the reaction. The amorphization p r o c e s s of t h i s a l l o y w i t h o u t l a r g e n e g a t i v e m i x i n g heat i s e x p l a i n e d in v i e w of the r e a c tion kinetics.
meter and JEM-2OOcx e l e c t r o n - m i c r o s c o p e respectively. The p r o f i l e in depth o f the a s - d e p o s i t e d sample is g i v e n by RBS,which i n d i c a t e s t h a t the samples b e f o r e r e a c t i o n are o f m u l t i l a y e r s . The o v e r a l l a l l o y c o m p o s i t i o n o f the m u l t i l a y e r samples was Fe~oh_Ti_o. F i g . 1 shows both X-ray d i f f r a c t i o n p a t t e r n s o f samples b e f o r e and a f t e r a n n e a l i n g . The d i f f r a c t i o n p a t t e r n o f the asd e p o s i t e d sample,as shown in F i g . 1 ( a ) , i s composed o f the peaks or Fe and T i . A f t e r s o l i d s t a t e r e a c t i o n at 3OO~ f o r 24 hours the amorphous Fe_^Tir^ a l l o y was formed w i t h tile appearance o f U U . a ~roa~ d , f r r a c t i o n p a t t e r n as in F i g . l ( b ) w h i l e sharp c r y s t a l l i n e peaks d i s a p p e a r . I t was f u r t h e r confirmed by r e f l e c t i n g e l e c t r o n d i f f r a c t i o n that amorphous Fe_^Ti_ O alloy can be obtaied by solid state reac~Yon~ The hemi-halos of the diffraction pattern indicate the formation of an amorphous Fe__Ti_^. This result sh~Idb~e interesting in the field of solid state reaction because the heat of formation of all alloys amorphized by solid
A COMPLETELY NEW APPROACH has been developed for synthesis of metallic glasses since amorphous La-Au alloy was formed by low temperature solid state reaction of elemental polycrystalline thin film(1). In this case the total free energy of system can be lowered by reaction in isothermal annealing to form ,,n amorphous phase,while the formation of a crystalline intermetallic compound is kinetically bypassed,at low temperature. It has.been suggested that the conditions on which solid state amorphization reaction can take place are related to fast interdiffusion as well as large negative heat of mixing(2). The heat of mixing of binary alloy can be estimated from ~Hf,the heat of formation,given by Miedema(3). So far all systems reported on amorphization in this way indeed have large negative heat of formation. One interesting problem is how negative the value or ~H. must be to ensure an amorphization by soli~ state reaction. It was the purpose of the present work to inves ~ tigate the possibility of performing a solid state amorphization reaction in the new alloy system with smaller negative AH f. In this paper Fe-Ti was selected because its heat of formation is negative but not so large as those before. In addition,an Fe-Ti alloy is difficult to form an amorphous phase by liquid quenching although amorphous Fe-Ti film has been prepared by vapor quenching(4). Elemental layers were alternatively deposited onto quartz and salt substrates in a dual source elect~on beam evaporation system which was in 3xlO - torr~ The evaporation rate was controlled at about 2A/see to achieve the desired layer thickness. Samples were annealed isothermally in a vacuum to minimize the effect of oxidation. Rutherford Backscattering(RBS) was employed to to determine the c(~position profile in depth and overall alloy composition of the as-deposited samples. The overall composition of samples was also identified by quantitative chemical analysis. Both X-ray diffraction and r~flecting electron d i f f r a c t i o n were performed to measure the s t r u c t u r e change of samples b e f o r e and a f t e r r e a c t i o n . They were conducted w i t h Rigaku MDG D i f F r a c t o -
I
(~ -- -0
~c~
~_
l
01
I
III i
40
i
6O
8O
i
~
28 Fig, I: X-ray scattering intensity as a function of scattering angle, (a) as-deposited sample (b) sample annealed at 3OO"C for 24h
811
ALLOY FORMED BY SOLID STATE REACTION
812
Vol. 68, No. 9
Table I: Amorphous alloy formed by solid state reaction and their values of ~H..~n equiatomic concentration given ~y Miedema(3)
Alloy
Fe-Ti
Au-La
Au-Y
Co-Zr
Ni-Zr
Ni-Hf
Zr-Rh
N i -T £
-28
-92
-I09
-.59
-71
-62
-IO7
-57
KJ/g. atom
s t a t e r e a c t i o n are l a r g e n e g a t l v e , w i t h the e x c e p t i o n o f F e - T i . Table I l i s t s t h e ' v a b a e s Sf ~H.of these systems previously reported(1)(5-10). Ittlikely that,in choosing alloys as candidate for solid state amorphization reaction,the thermaldynamic limitation of A H . of them is less mix important than the kinetical process of reaction. So that the formation of predominant phases should depend mainly on the kinetics competing between them. In fact only if the heat of formation of a binary alloy is negative,its multilayer is metastable to a homogenous state in consideration of the high interracial energy of multilayer and mixing free energy difference between them. Therefore there is more or less a chemical driving force for multilayers to react to form some alloy phases. Even though annealing is performed at a low temperature,the interdiffusion occuring in
such a multilayer or modulated film may be still obvious,which was stated in detail by Greet and Spaepen(11). For Fe-Ti multilayer-sample annealed at 3OO°C,the temperature is too low For the crystilline compound FeTi to nucleate and grow although tile structure of FeTi is quite simple (cubic). As a result the disordered state induced by fast interdiffuslon on a large scale is " f r o z e n " to forln an, amorphous s t a t e . In summary the Formation of the amorphous Fe_^Ti~ 0 a l l o y can be a t t r i b u t e d to i t s k i n e t i c a l predominance o v e r ' the c r y s t a l l i n e compound. Candidates f o r the s o l i d s t a t e a m o r p h i z a t i o n r e a c t i o n should expand to more a l l o y systems w i t h n e g a t i v e m i x i n g heat.
Acknowledgement . . . . We wish to thank P r o f . Liu B a i x i n and his students f o r t h e i r help in p r e p a r a t i o n o f m u l t i l a y e r samples.
REFERENCES I. 2. 3. 4. 5. 6.
R.B.Schwarz and W.L.Johnson, Phys. Rev. Lett. 51,415(1983) R.B.Schwarz,P.R.Petrich and C.K.Saw, J.of Non-Cryst. Sol. 76,281(1985) A.R.Miedema, Philips Tech. Rev. 36,217(1976) K.Sumiyama et al, Acta Metall. 35,1221(1987) R.B.Schwarz,W.L.Johnson and B.M.Clemens, J.of Non-Cryst. Sol. 6}-62,129(1984) B.M.Clemens et al, J. of Non-Cryst. Sol. 61-62,817(1984)
7. 8. 9. 10. II.
H.Schroder,K.Samwer and V . K o s t e r , Phys. Rev. L e t t . 54,197(1985) M.Van Rossum e t a ] , Phys.Rev. B29,5498(1984) X.L.Yeh,K.Samwer and W.L,Johnson, App]. Phys. L e t t . 42,242(1983) Yan Zhihua and Wang Wenkui, Chinese Phys. L e t t . 4,569(1987) A . L . G r e e r and F . S p a e p e n , S y n t h e t i c Modulated S t r u c t u r e s , p 4 1 9 , A c a d e m i c Press,London(1985)
o> °+ Solid State Communications, Vol. 68, No. 9, pp.811-812, 1988. e-~ Printed in Great Britain.
AMORPHOUS
Fe-TI
ALLOY
FORMED
BY S O L I D
STATE
REACTION
Zhih,, a Y a m Imstitute
of P h y s i c s ,
Chinese
Academy
Wemkui Center
of C o n d e n s e d
Institute
of
Matter
and
of S c i e m c e s ,
Beijimg,
China
Wang
Radiation, and
CCAST(World
Laboratory)
Physics, Chinese Academy of Sciences, B e i j i n g ,
China
(Received I0 September, 1988 by W. Y. Kuan) T h e p r e s e n t p a p e r r e p o r t s the f o r m a t i o n of a m o r p h o u s F e ~ n T i ~ o a l l o y by the s o l i d s t a t e r e a c t i o n of p u r e p o l y c r y s t a l l i ~ Fe and Ti t'~in f i l m s at l o w t e m p e r a t u r e . X--ray d i f f r a c t i o n and reflectimg e l e c t r o n d i f f r a c t i o n w e r e u s e d to m o n i t o r the reaction. The amorphization p r o c e s s of t h i s a l l o y w i t h o u t l a r g e n e g a t i v e m i x i n g heat i s e x p l a i n e d in v i e w of the r e a c tion kinetics.
meter and JEM-2OOcx e l e c t r o n - m i c r o s c o p e respectively. The p r o f i l e in depth o f the a s - d e p o s i t e d sample is g i v e n by RBS,which i n d i c a t e s t h a t the samples b e f o r e r e a c t i o n are o f m u l t i l a y e r s . The o v e r a l l a l l o y c o m p o s i t i o n o f the m u l t i l a y e r samples was Fe~oh_Ti_o. F i g . 1 shows both X-ray d i f f r a c t i o n p a t t e r n s o f samples b e f o r e and a f t e r a n n e a l i n g . The d i f f r a c t i o n p a t t e r n o f the asd e p o s i t e d sample,as shown in F i g . 1 ( a ) , i s composed o f the peaks or Fe and T i . A f t e r s o l i d s t a t e r e a c t i o n at 3OO~ f o r 24 hours the amorphous Fe_^Tir^ a l l o y was formed w i t h tile appearance o f U U . a ~roa~ d , f r r a c t i o n p a t t e r n as in F i g . l ( b ) w h i l e sharp c r y s t a l l i n e peaks d i s a p p e a r . I t was f u r t h e r confirmed by r e f l e c t i n g e l e c t r o n d i f f r a c t i o n that amorphous Fe_^Ti_ O alloy can be obtaied by solid state reac~Yon~ The hemi-halos of the diffraction pattern indicate the formation of an amorphous Fe__Ti_^. This result sh~Idb~e interesting in the field of solid state reaction because the heat of formation of all alloys amorphized by solid
A COMPLETELY NEW APPROACH has been developed for synthesis of metallic glasses since amorphous La-Au alloy was formed by low temperature solid state reaction of elemental polycrystalline thin film(1). In this case the total free energy of system can be lowered by reaction in isothermal annealing to form ,,n amorphous phase,while the formation of a crystalline intermetallic compound is kinetically bypassed,at low temperature. It has.been suggested that the conditions on which solid state amorphization reaction can take place are related to fast interdiffusion as well as large negative heat of mixing(2). The heat of mixing of binary alloy can be estimated from ~Hf,the heat of formation,given by Miedema(3). So far all systems reported on amorphization in this way indeed have large negative heat of formation. One interesting problem is how negative the value or ~H. must be to ensure an amorphization by soli~ state reaction. It was the purpose of the present work to inves ~ tigate the possibility of performing a solid state amorphization reaction in the new alloy system with smaller negative AH f. In this paper Fe-Ti was selected because its heat of formation is negative but not so large as those before. In addition,an Fe-Ti alloy is difficult to form an amorphous phase by liquid quenching although amorphous Fe-Ti film has been prepared by vapor quenching(4). Elemental layers were alternatively deposited onto quartz and salt substrates in a dual source elect~on beam evaporation system which was in 3xlO - torr~ The evaporation rate was controlled at about 2A/see to achieve the desired layer thickness. Samples were annealed isothermally in a vacuum to minimize the effect of oxidation. Rutherford Backscattering(RBS) was employed to to determine the c(~position profile in depth and overall alloy composition of the as-deposited samples. The overall composition of samples was also identified by quantitative chemical analysis. Both X-ray diffraction and r~flecting electron d i f f r a c t i o n were performed to measure the s t r u c t u r e change of samples b e f o r e and a f t e r r e a c t i o n . They were conducted w i t h Rigaku MDG D i f F r a c t o -
I
(~ -- -0
~c~
~_
l
01
I
III i
40
i
6O
8O
i
~
28 Fig, I: X-ray scattering intensity as a function of scattering angle, (a) as-deposited sample (b) sample annealed at 3OO"C for 24h
811
ALLOY FORMED BY SOLID STATE REACTION
812
Vol. 68, No. 9
Table I: Amorphous alloy formed by solid state reaction and their values of ~H..~n equiatomic concentration given ~y Miedema(3)
Alloy
Fe-Ti
Au-La
Au-Y
Co-Zr
Ni-Zr
Ni-Hf
Zr-Rh
N i -T £
-28
-92
-I09
-.59
-71
-62
-IO7
-57
KJ/g. atom
s t a t e r e a c t i o n are l a r g e n e g a t l v e , w i t h the e x c e p t i o n o f F e - T i . Table I l i s t s t h e ' v a b a e s Sf ~H.of these systems previously reported(1)(5-10). Ittlikely that,in choosing alloys as candidate for solid state amorphization reaction,the thermaldynamic limitation of A H . of them is less mix important than the kinetical process of reaction. So that the formation of predominant phases should depend mainly on the kinetics competing between them. In fact only if the heat of formation of a binary alloy is negative,its multilayer is metastable to a homogenous state in consideration of the high interracial energy of multilayer and mixing free energy difference between them. Therefore there is more or less a chemical driving force for multilayers to react to form some alloy phases. Even though annealing is performed at a low temperature,the interdiffusion occuring in
such a multilayer or modulated film may be still obvious,which was stated in detail by Greet and Spaepen(11). For Fe-Ti multilayer-sample annealed at 3OO°C,the temperature is too low For the crystilline compound FeTi to nucleate and grow although tile structure of FeTi is quite simple (cubic). As a result the disordered state induced by fast interdiffuslon on a large scale is " f r o z e n " to forln an, amorphous s t a t e . In summary the Formation of the amorphous Fe_^Ti~ 0 a l l o y can be a t t r i b u t e d to i t s k i n e t i c a l predominance o v e r ' the c r y s t a l l i n e compound. Candidates f o r the s o l i d s t a t e a m o r p h i z a t i o n r e a c t i o n should expand to more a l l o y systems w i t h n e g a t i v e m i x i n g heat.
Acknowledgement . . . . We wish to thank P r o f . Liu B a i x i n and his students f o r t h e i r help in p r e p a r a t i o n o f m u l t i l a y e r samples.
REFERENCES I. 2. 3. 4. 5. 6.
R.B.Schwarz and W.L.Johnson, Phys. Rev. Lett. 51,415(1983) R.B.Schwarz,P.R.Petrich and C.K.Saw, J.of Non-Cryst. Sol. 76,281(1985) A.R.Miedema, Philips Tech. Rev. 36,217(1976) K.Sumiyama et al, Acta Metall. 35,1221(1987) R.B.Schwarz,W.L.Johnson and B.M.Clemens, J.of Non-Cryst. Sol. 6}-62,129(1984) B.M.Clemens et al, J. of Non-Cryst. Sol. 61-62,817(1984)
7. 8. 9. 10. II.
H.Schroder,K.Samwer and V . K o s t e r , Phys. Rev. L e t t . 54,197(1985) M.Van Rossum e t a ] , Phys.Rev. B29,5498(1984) X.L.Yeh,K.Samwer and W.L,Johnson, App]. Phys. L e t t . 42,242(1983) Yan Zhihua and Wang Wenkui, Chinese Phys. L e t t . 4,569(1987) A . L . G r e e r and F . S p a e p e n , S y n t h e t i c Modulated S t r u c t u r e s , p 4 1 9 , A c a d e m i c Press,London(1985)