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IEEE TRANSACTIONS ON MAGNETICS, VOL. 26, NO. 5, SEPTEMBER 1990

MAGNETIC PROPERTIES OF MELT SPUN SmFellTi-S%TMl7 PSEUDOBINARY ALLOYS

S.H. Huang, T.S. Chin, Y.S. Chen, S.K. Chen and C.H. L in Dept. of Materials Sc i . & Eng., Na t iona l Tsing Hua Un ive r s i ty , Hsinchu, 30043, Taiwan, Rep. o f China

P.Y. Lee Dept. of Materials Eng., Tatung I n s t i t u t e of Technology, Ta ipe i , 10451, Taiwan, Rep. of China

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SO a l l o y S10 a l l o y S20 a l l o y S30 a l l o y

spun anne'd spun anne'd spun anne'd spun anne'd

108.2 105.8 100.3 106.4 104.5 113.3 110.5 101.5

72.6 66.9 71.9 74.4 68.2 75.1 70.3 60.4

Abstract-Several a l l o y s i n t h e SmFe lTi-Sm TM (TM = Co/Fe/Cu/Zr) pseudobinary system conhaining20 L79O w t % Sm2TM17 were prepared by m e l t sp inn ing technique . A ma- ximum as-spun c o e r c i v i t y of 4.6 kOe is obta ined f o r t h e a l l o y con ta in ing 10 w t % Sm2TM17 a t a s u b s t r a t e v e l o c i t y of 15 m/s. The c o e r c i v i t y is enhanced t o 5.3 kOe after annea l ing a t 800 OC f o r one hour. XRD and TEM were used t o i n v e s t i g a t e t h e mic ros t ruc tu re of t h e a l l o y s . It w a s sugges ted t h a t g r a i n re f inement , doping of t h e 1-12 phase wi th Sm and o t h e r e lements , and reduced free i r o n might be t h e main r easons of c o e r c i v i t y enhancement.

INTRODUCTION

The d iscovery of p o s s i b l e h igh c o e r c i v i t y i n Sm-Fe-Ti a l l o y wi th ThMn (1-12) s t r u c t u r e [l], has drawn much a t t e n t i o n on t@ f e a s i b i l i t y of prepar ing permanent magnets from t h i s novel s t r u c t u r e [l-61.

Most of t h e works l e d t o remarkable i n t r i n s i c coe rc i - v i t y of t h e 1-12 a l l o y s were from s p u t t e r e d f i l m s [2 ] , or melt spun r ibbons of t h e Sm-Fe-M (M = T i , V, MO, C r , e t c . , ) sys tems [3-61. I n t h e la t ter cases, over quen- ched r ibbons were sub jec t ed t o a s u i t a b l e h e a t treat- ment, hence c o e r c i v i t i e s of from 2.5 kOe[3] t o 9.8 kOe [ 6 ] were obta ined . There were works on prepar ing them by mechanical a l l o y i n g which r e s u l t e d i n 3.8 kOe [7 ] , a l t hough i H c of g r e a t e r t h a n 50 kOe w a s ob ta ined , it was from a new composition Sm2Fe7Ti n o t of 1-12 s t r u c - t u r e [8].

I n t h i s s t u d y , we t r i e d t o dope t h e S iFe T i a l l o y wi th a h igh c o e r c i v i t y phase, Sm2T17 (TM=Co)$e/Cu/Zr) w i th commercially a v i l a b l e composition, f o r t h r e e des i - gned purposes o f (1 ) absorb ing t h e p o s s i b l e e x i s t i n g free i r o n s i n c e t h e 2-17 phase has a h igh s o l u b i l i t y of i r o n [9 ] , (2) s e rv ing as p o s s i b l e domain w a l l p inning sites should it be s t a b l y c o e x i s t i n g wi th t h e SmFe T i phase, and (3 ) i n v e s t i g a t i n g t h e p o s s i b l e extra p h i i e s between t h e 2-17 (or 1-8.5) and t h e 1-12 s t r u c t u r e .

EXPERIMENTAL

1 9Fe10 - The s t a r t i n g m a t e r i a l s were p rea l loyed Sm Ti l and Sm(Coo 65Fe0.27Cu0 g6Zrp 022k 44 &oys (?CP ana lyzed composition.), respeC i v e 9. By were ground, a x e d a t l U w t L i n t e r v a l s , then induc t ion mel tea unQer A r p ro t ec t ion . For s i m p l i c i t y , t h e SmFe T i added wi th 10, 20, 3Owt% etc., 2-17 composition i s ' aes igna ted as S10, S20, and S30, etc. The m e l t chunks were r a p i d l y s o l i d i f i e d by m e l t sp inn ing a t d i f f e r e n t wheel speeds (Vs) of 10, 15, 30, and 40 m / s . Some r ibbons were fu r - t h e r annea led a t 600, 800, 1000 OC f o r 10 minutes t o an hour.

C r y s t a l s t r u c t u r e w a s s t u d i e d wi th X-ray d i f f rac tome- t r y (XRD). The magnetic p r o p e r t i e s were measured by a v i b r a t i n g sample magnetometer. Mic ros t ruc tu re w a s s t u - d i ed by a t r ansmiss ion e l e c t r o n microscope (TFM). Cur ie zemperature (Tc) was determined by a thermal magnetic ba lance a t a f i e l d s t r e n g t h of 400 Oe.

RESULTS AND DISCUSSION

The A s - m e l t Spun P r o p e r t i e s

Fig. 1 shows i n t r i n s i c c o e r c i v i t y (iHc) and (0 /a ), where 0 is t h e s p e c i f i c magnet iza t ion a t t h e d x i & m f i e l d ofS17 kOe, ve r sus t h e 2-17 a d d i t i o n s of t h e r i b - bons obta ined a t a wheel speed (Vs) of 15 m/sec. It is ev iden t t h a t 10 w t % a d d i t i o n (S10 a l l o y f o r s i m p l i c i t y ) h a s t h e maximum iHc of 4.6kOe, which is h ighe r t h a n t h e r e p o r t e d b e s t as-spun c o e r c i v i t y , 3.6 kOe o f a SmFe lTi a l l o y [61. a maximum of h.69 f o r t h e S10 a loy . r Tfhs is of g r e a t i n d u s t r i a l import- ance s i n c e on ly minor amount o f t h e 2-17 composition is necessary t o a t t a i n h igh spun c o e r c i v i t y . Table I shows s p e c i f i c magnet iza t ion va lues .

The (0 / U ) a l s o r eaches

Table I S p e c i f i c magnet iza t ion (emu/g) of t h e a l l o y s

F ig .1 The composition dependence of iHc and ( as)

XRD p a t t e r n s of t h e as-spun S10, S20, and S30 a l l o y s are shown i n Fig. 2. The 1-12 s t r u c t u r e is t h e major phase wi th minor 2-17H phase and trace f r e e i r o n i n t h e S10 and S20 a l l o y s . For t h e S30 a l l o y , t h e 2-17H t u r n s o u t t o be t h e major phase wi th inc reased amount of free i r o n and decreased 1-12 phase. Over 50 w t % a d d i t i o n , no more 1-12 phase and free i r o n could be found. E f f e c t of wheel speeds on t h e as-spun c o e r c i v i t y of t h e S10 a l l o y was s t u d i e d , as shown i n Fig. 3. It is clear t h a t t h e speed of 15 m/sec is opt imal for t h e doped a l l o y s . A Vs o f ' 10 m/sec r e s u l t e d i n undercool ing , w h i l e 40 m/sec overcool ing , as concluded from t h e degree of XRD peak broadening.

E f f e c t o f Annealings.

The spun S10 r ibbons were annea led a t 600, 800 and me 6OO0C annea l ing 1000°C, r e s p e c t i v e l y f o r one hour.

0018-9464/9010900-1391$U1.00 0 1990 fEEE

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.-

1 -

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0 , - .-.- c - - 0 -

0 - O W - .

+ X ' O w l 0 -0- x -10 w l o -0- x = 2 o w / o -+ X = 3 0 w / o 1 %4

530

70 6 0 5 0 40 30 - 2 0

Flg.2 XRD patterns of as-spun al.l.oys at Vs=15 m/sec

I I I I

Y z 3 2

1

-8- x = 0 W/(

-0- x =IO Wll

I I

40 60 Annealing Time(min)

Fig.4 Effect of annealing time at 800 OC on coercivity 2

1.5

c' N

N s 1 7 e- - 0 %?

0.5

0

vs=15m/s Anneali ng

. 800'C

20 min Q

6 0 min + - 30 Sm2TMii (wt%)

Fig.5 Free iron content vs. that of the 1-12 phase

alloys were measured, as typically shown in Fig. 6 for the S10 alloy. There are two Tc's during heating up, and this is similar for all the above as-spun alloys. The former, Tcl, was adopted from heating curve, while Tc from cooling curve. After 6OO0C annealing the Tc sth1 exists yet shifts to higher temperature, whid after 800 OC annealing Tc disappears. This indicates the possible existence 02 a metastable phase, which disappears after high temperature annealing, not iden- tifiable from XRD pattern though. Tc2 is representative of the major 1-12 phase. Tc varies with composition, annealing and wheel speed as shown in Fig. 7. Tc values increase with doped 2-17 amount, Fig. 7a, depicting the incorporation of CO in the phase. Tc and Tc2 for the as-spun S10 alloy show a peak at Vs 15m/s, Fig. 7b, depicting possible difference in element partitions, notably CO, with wheel speed. at 30 and 40 m/s, 193OC is believed to belong to an amorphous phase. After annealing, TC ' s of all the alloys increase as

increasing the 2-17 azdition amount due to increased CO incorporation, as shown in Fig. 7a.

Microstructural Features

The low Tcl value

Fig. 8 shows two TEM micrographs taken from a S10 al- loy prepared by Vs=15 and 30 m/s, and annealed at 8OO0C for an hour(Vs=15) and 10 minutes(Vs=30), respectively. The grain size ran es from 50 to 100 nmfor the 15 m/s quenched alloy, w k t o 50 nm f o r the 30 m/s quen- ched alloy. This is comparable to that of other works [ 6 ] . The extremely fine grain such as this may be in part responsible for the high coercivity.

1393

I annealing a t

IOOO'C lhr \> \ ' c 2 I

eoo'c lhr Y1 100 200 300 400 500 600

Temperature {C)

Fig.6 Magnetization vs. Temp. curves of the S10 al.l.oy

k = 1 5 rnls ~As-spun Tc,

$300 +As-spun TC;

+Annealing8dO'C 60 rnin

/I As-spun

Fig.7 Curie temperatures vs. composition (a) and Vs (b)

Possible Mechanisms of Coercivity

- -

From the fact that the as-spun SO (pure Sm;F&Ti) al- loy has an iHc of 1.5 kOe, it is evident grain refinement itself bestows coercivity. The addition of 10 w t % Sm2TM17 composition provides excess Sm and dop- ing elements in the 1-12 phase hence increases greatly the coercivity at the as-spun state. Annealing at 800°C reduces the free iron content, Fig. 5, hence improves the coercivity further. The existence of the 2-17H phase might not be beneficial since the as-spun 2-17 rich alloys (S50, S80 and S90) showed low coercivity.

CONCLUSION

Magnetic properties of melt spun SmFellTi - Sm TM alloys were investigated. A 10 w t % addition of the22-13 composition greatly enhanced the as-s un coercivity from 1.5 to 4.6 kOe. Annealing at 800 C further im- proves it to 5.7 kOe. The mechanisms of coervivity are attributed to refinement of grain size, stabilization of the 1-12 phase, and reduced free iron content. The 2-17H phase was identifiable in the 10-30 w t % addition alloys, while it is dominating when weight fraction of the 2-17 composition is over 50. A metastable phase was detected in Tc measurements, however it was not resol- vable in the XRD patterns.

8

Fig.8 TEM micrographs of annealed spun S10 at (a) Vs=15 m/s and 800°Cxlh annealed, (b) Vs=30 m/s and 800' CxlO min annealed; the marker represents 50 nm

Acknowledgements

The authors are grateful for the sponsorship of this research by the National Science Council of the Rep. of China under the contract number NSC 79-0416-E007-06.

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