Resistivity recovery in Ni-Al alloys after ultrasonic and static loading at 4.2 K

S c r i p t a METALLURGICA et M A T E R I A L I A

Vol. 26, pp. 877-881, Printed

1992

Pergamon P r e s s p l c

in the U.S.A.

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rights

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RESISTIVITY RECOVERY IN Ni-A/ ALLOTS AFTER ULTRASONIC AND STATIC LOADING AT 4.2 K

Institute

Y.A.Helobrovyi of M e t a l P h y s i c s of the Ukrainian of Sciences. SU-25E680 . Kiev . USSR (Received August (Revised January

6, 9,

Acade~

1991) 1992)

Introduction The p a r t i a l disordering of o r d e r e d alloys takes p l a c e u n d e r p l a s t i c deformation. It r e s u l t s in a c o n s i d e r a b l e increase in the stored ener~. Therefore. in o r d e r e d alloys, the r e c o v e r y p r o c e s s is g o i n g on f a s t e r than in the d i s o r d e r e d ones or in pure metals. It is i n t e r e s t i n E to s t u d y the r e c o v e r y p r o c e s s in a l l o y s in w h i c h the short o r d e r i n ~ state o c c u r s due to point defects m i g r a t i o n (for e x a m p l e in NiAI s o l i d solutions). The o r d e r i n ~ p r o c e s s in these a l l o y s has b e e n i n v e s t i E a t e d at the ~ e m p e r a t u r e s a b o v e 300 K (I-9). However, up to the p r e s e n t time, no i n v e s t i g a t i o n s into the o r d e r i n ~ of NiAI a l l o y s at low t e m p e r a t u r e s (from £.2K) have b e e n done. S t u d y of the l o w - t e m p e r a t u r e r e c o v e r y a f t e r d e f o r m a t i o n at 4.2K allows us to observe the wider spectrum of annealed point defects and to i n v e s t i g a t e the chanaes in the p h y s i c a l p r o p e r t i e s of alloys w h i c h are c a u s e d b y t h e i r m i g r a t i o n (in p a r t i c u l a r the c h ~ o c c u r r i n g because of o r d e r i n ~ p r o c e s s ) . In the present paper the results of investigation of the resistivity recovery in the s a m p l e s of s o l i d s o l u t i o n N i A 1 a f t e r u l t r a s o n i c a n d static d e f o r m a t i o n in l i q u i d h e l i u m are reported. Experimental

Procedure

S a m p l e s of a l l o y s N i - 7 . 5 a t ~ A 1 a n d N i - 5 . 5 a t ~ A 1 were a n n e a l e d for ~h at 1370 K in a v a c u u m of 10 -4 Pc, then furnace cooled. The ultrasonic deformation (17.SkHz) was p e r f o r m e d w i t h the t e c h n i q u e described in (10). By this mode of excitation of mechanical vibrations, the s t a n d i n ~ o s c i l l a t i o n s are f o r m e d in a h a l f - w a v e (i.e. half of the sonic wave l e n E t h A/2) sample. The d e f o r m a t i o n (stress) a m p l i t u d e a l o n ~ the s a m p l e is s i m i l a r to a s i n u s o i d a l one, w i t h a maximum in the m i d d l e of the sample at A/4. The magnitude of d e f o r m a t i o n (stress) a m p l i t u d e was e n o u @ h for i n t e n s i v e m u l t i p l i c a t i o n of structure defects in the sample. To avoid the supplementary heatln~, the samples w e r e d e f o r m e d b y short pulses (-I sec ). The static defox~n~tion was p e r f o r m e d b y t e n s i o n w i t h the rate 10-~sec -I . The r e s i d u a l d e f o r m a t i o n was 15~. The r e s i d u a l e l e c t r i c a l r e s i s t i v i t y was m e a s u r e d at the c e n t r a l part of the samples w i t h the s t a n d a r d 4 lead do. technique. Coercive force (Hc) was determined from a q u a s i s t a t i c h y s t e r e s i s loop. R e s i s t i v i t y r e c o v e r y was i n v e s t i g a t e d b y the isochronal annealing t e c h n i q u e up to 875 K. The samples were p u l s e - a n n e a l e d for 10 m i n in steps of 10 K from 4.2 K to 150 K a n d of 20 K from 150 to 675 K. The h e a t i n g rate was a K/min. Results

and Discussion

The relative residual resistivity chan~es (Ap/p,~) and the changes of Hc of N i - 5 . 5 a t . ~ A 1 a l l o y are s h o w n in Fig. 1 as a f u n c t i o n of the n u m b e r of u l t r a s o n i c deformation cycles. The r e s i s t i v i t y

877 0036-9748/92 $5.00 + .00 Copyright (c) 1992 Pergamon Press

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decreases despite intensive & ~ n e r a t l o n of struotux-e defects ; the latter p o i n t i s p r o v e d b 7 t h e Ho i n o r e a s i r ~ . It takes place because of the destruction of the short-razOrs order created durir~ hlshtemperature e~nealiz~. One c a n s e e t h a t the main increase o f Ap/p ooou.z~ c~b~iz~ t h e initial sta~e of deforau~tion, when the plastic strmin amplitude is hi4£h. The n o r ~ i z e d Isoc~r~ r e c o v e r 7 curves of NI-5.Sat.~AI alloy samples a~'ter low-temperature ultre~sontc ( 1 ] and static (2) deformations a n d q u e n c h i n g f r o m g73 K t o 3 0 0 K ( 3 ) a r e sh o w n i n F i g . 2 . Curve i dieple~s five sta4~s of the resisttvt~ recovery. The l o w - t e m p e r a t u r e sta41es a x e o f p a . x . t t o u l a r i n t e r e s t . In the first (T<125 K) steq;e, the reslstivl~-~ i n c r e a s e s i n spite o f probable processes o f p o i n t d e f e c t s eltmiz~tion on sinks ( t h e l a s t p r o c e s s mu~t g i v e r i s e to decrease of resistivity). The diffusion m o b i l i t y of defects is known to be small at such low t e m p e r a ~ s , i.e. processes c a u s e d by the atoms m i s T a t l r ~ lazes distances (as in se~gation or antiphase domain formation) are impossible. The r e s i s t i v i t y increase can probably be u n d e r s t o o d in remus of short-reulge orderlr~. The s h o r t - r ~ order formation in Ni-AI solid solutions is assumed to increase the electrical resistivity. The latter was s u g g e s t e d by some authors (2,8,9). Aocordi~ to the works (3, 4), in deformed Ni-AI alloy (6.3 at~Ll ), local resions (with ~ degree and different t~e of short-reusEs order) ezlTiohed or "impoverished" with A1 atoms are formed at the b e g l n n l n ~ of isotherm~l anneallns. The existence of this regions of so-called "local order" was p r o v e d by means of X-rs~7 technique, electrical and me~netic measurements. In experlments r e f e r r e d to, the transition from "local order" to h o m o g e n e i t y order took place at the increase of eu~nealln8 time (more than 30 rain at T>500 K) (3). It results in considerable decrease of resistivity. U s l n ~ the fact of the same behaviour of deformed Ni-5.5at~Al alloy at isothermal, anneallr~ at T>300 K, it is possible to suppose that the structure char~es are the same at the annealin~ of Ni-6.3at~Al and NI-5.5at~&l alloys. In our experiments, Increasir~ r e s i s t i v i t y is observed du~In~ the Isochron~l eulnealir~ up to 600 K. Therefore. one can consider that the t~rpe of order c~eated at low temperatures (T<125 K) are kept durln~ the isoohronal a n n e a l l n ~ up to 600 K in Ni-5.5at~Al alloy. T a k l n ~ into account the data p r e s e n t e d (the existence of "local order" in Ni-AI solid solution aooordlr~ to the experiments w h i c h are r e f e r r e d to above and non-decrease of r e s i s t i v i t y at isochronal annealln~ in our experiments up. to 60~ K) it is reasonable to consider that the order occurred in this temperature reul~e (T<125 K) w o u l d be "local order". Besides that if to assume that the "local order" is created durlr~E anneallz~E w h e n lon~-ran&~ m i g r a t i o n of atoms is impossible then it is necessary to consider that the regions of concentration Ir~homogeneltles are arisen u n d e r cyclic deformation already, i.e. orderlr~ durir~ anneallr~ takes place in local region~ which were enriched w i t h atoms (in the interstitial confi&~ration) of one of the components du~Ir~ the loadln~ or "impoverished" with ones (supersaturated by vacancies). The activation energy ( ~ a ) of the annealin~ process in the first st~e, determined by the m e t h o d of " t ~ n t s " , was found to be 0.3~0. I eV. This me4~nitude is close to the activation energy of Interstitials for pure Ni after electron irTadiation (I I ). It can therefore be supposed that the defects movir~ in the low temperature rar~e ale Interstitials and their concentration may be high due to the

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Ereat size effect of N i - A I alloy. The m i g r a t i o n of i n t e r s t i t i a l s and their a n n i h i l a t i o n w i t h inTnobile v a c a n c i e s can r e s u l t in the orderir~E p r o c e s s a n d i n c r e a s i r ~ r e s i s t i v i t y . O r d e r i r ~ occurs in local r e g i o n s s u p e r s a t u r a t e d b y point defects, a n d this p r o c e s s does not r e q u i r e the lor~ m i g r a t i o n of i n t e r s t i t i a l s . Unfortunately, w i t h the a v a i l a b l e d~ta, it is d i f f i c u l t to m a k e a more p r e c i s e c o n c l u s i o n o r to say w h i c h of the i n t e r s t i t i a l c o n f i g u r a t i o n s is most p r o b a b l e a n d mobile. Figure 3 shows that the d i s p l a c e m e n t of curve to the lowtemperature r ~ occurs with increasin~ aluminum concentration. It takes place probably because of an increase in the relative c o n t r i b u t i o n of o r d e r i n g p r o c e s s e s to the total chan~e of r e s i s t i v i t y of N i - 7 . 5 a t ~ A ! a l l o y c o m p a r e d w i t h N i - 5 . S a t ~ A l alloy. In the second stage (-125 K-S00 K), a slow increase of r e s i s t i v i t y (1.Fig. l) is observed. This sta~e c o u l d be a t t r i b u t e d to the r e l e a s e of i n t e r s t i t i a l s t r a p p e d by impure atoms. This p r o c e s s p r o m o t e s the f u r t h e r orderln~. The r e s i s t i v i t y b e h a v i o r at the h i g h temperature (T>300 K) sta~es I I I , I V , V is the s a m e in the p r i n c i p a l features for those samples treated by the various methods (ultrasonic(1) a n d static(2) l o a d i n g and q u e n c h i n ~ from 973 K (3)). The i n t e n s i v e o r d e r i n g of these s t a g e s in the samples a f t e r u l t r a s o n i c treatment takes place due to sannealin~ of v a c a n c y agglomerates (lll stage -300 K - 4 2 5 K), non-equilibrium single vacancies (lV stage -425 K - 5 5 0 K) a n d v a c a n c y self d i f f u s i o n (V stage - a b o v e 550 K) (12). The similarity between the hi@h-temperature recovery ste4Ees for the samples a f t e r u l t r a s o n i c t r e a t m e n t (curve I) a n d a f t e r quenchin~ (curve 3) c o n f i r m s the a s s u m p t i o n of i n t e r s t i t i a l mi~Tation leading to the resistivity increase in the low-temperature r a n g e in the samples t r e a t e d b y u l t r a s o n i c . One can see that the shapes of r e s i s t i v i t y curves d e p e n d on the m e t h o d of d e f o r m a t i o n (ultrasonic or static deformation). E s p e c i a l l y stror~g d i f f e r e n c e s are o b s e r v e d for two first l o w - t e m p e r a t u r e stages. The first stage (up to 150 K) for s t a t i c a l l y d e f o r m e d samples is not observed, a n d the small d e c r e a s e of r e s i s t i v i t y takes place d u r i n 8 the s e c o n d stage (150 K - 3 0 0 K). It is p o s s i b l e that the v a r i a b l e defect s t r u c t u r e is c r e a t e d under the static and cyclic deformation with condition of the invariable mechanism of p o i n t defects generatln~ (non-conservative m o t i o n of JoEs on s c r e w d i s l o c a t i o n s or the m u t u a l a n n i h i l a t i o n of ec~ge d i s l o c a t i o n s ) . The a n n e a l l n g of point defects in the samples a f t e r static l o a ~ does not r e s u l t in a n o t i c e a b l e increase of r e s i s t i v i t y at the first stage due to ordering, in the case of the resistivity recovery of the o r d e r e d alloys, it is difficult to s e p a r a t e the c o n t r i b u t i o n of two p r o c e s s e s to the r e s i s t i v i t y change : the point defects elimination itself leads to the resistivity decrease, a n d the o r d e r i n g p r o c e s s itself leads to the r e s i s t i v i t y increase due to the m l g r a t i o n of p o i n t defects. Therefore, it can be supposed that e i t h e r on the first a n n e a l i n g stage of the static t r e a t e d a l l o y s the c o m p e n s a t i o n of two opposite c o n t r i b u t i o n s takes place or no mobile interstitial configuration at first-stage t e m p e r a t u r e s is c r e a t e d u n d e r the static loading. On the s e c o n d stage the p r o c e s s of i n t e r s t i t i a l s e l i m i n a t i o n (it is p o s s i b l e at d e t r a p p l n ~ from impurities) predominates. Thus, the data p r e s e n t e d in d i c a t e the e x i s t e n c e of s t r u c t u r a l effects s p e c i f i c to the N i - A 1 a l l o y s a f t e r u l t r a s o n i c treatment a n d a l l o w us to a s s u m e that. in c o n t r a s t to static loadir~g, some regions (local regions in which the internal stress level is high)

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supersaturated by defects can arise durin~ the ultrasonic loadln~ and in these regions the structure transformation governed by atom transfers takes place at low temperatures. Conclusions The resistivity variations during the isochronal annealin~ of low-temperature deformed Ni-AI solid solutions have been interpreted in terms of defect annihilation and short-rar~e orderir~.The shape of resistivity curves w a s found to depend on the me~hod of deformation (ultrasonic or static deformation). Especially stror~ differences are observed for two first low-temperature recovery stages (T<300 E). This difference has been explained as result of interstitial annealing leadlnE to short-rmr~Ee orderin~ in local regions enriched by point defects under ultrasonic treatment. References 1.E.A.Starke, V.Gerold and A.G.Guy, Acts Metall.13,957 (1965) 2.E.Hornbogen a n d H.Kreye, Z.Hetallkunde, 57,122 (1955) 3.A.A.Katsnel'son, A.M.Silonov and V.M.Silonov, Fiz. Metal. Hetalloved, 33,1267 (1972) ~.A.A.Katsnel'son and P.DaJaev, Izv.Vuzob Fizika. 4,23 (1970) 5.A.G.Gtkv, Trans.ASM,55,737 (1962) 6.F.Chassagne, M.Bessiere, Y.Calvayrac. P.Cenedese and S.Lefebvre, Acts Metall. 37,2329 (1989) 7.F.Elaiber, B.Sohonfeld and G.Eostorz, Acts Crystall.A43,525 (1987) 8.M.Afyouni, V.Pierron-Bohnes and M.C.Cadeville, Acts Metall.37,2339 (1989 ) 9.B.Sitaud and O.Dimitrov, J.Phys. Condens.Matter, 2.7061 (1990) 10.V.F.Belostotskii and I.G.Polotskli, Fizika Niz.Temp.10,129a (1978) 11.A.V.Volobuyev, V.V.Gann, I.M.Neklydov, Yu.T.Petrusenko and A.N.Sleptsov, in Proc.of the Int.Conf.on Radiation Materials Sciense (Alushta, USSR), 58 (1990) 12.V.F.Belostotskii, Fiz.Metal.Metalloved. 1,173 (1990)

Hc, kA/m 10.3

I

0 ~ ~ _ 60

1 N.105 ~ ,,

o 120

ap "-,nOra. c m~

2 ~" 1

~--,a ~

:j

Fig. I .The char~Ee of the residual electrical resistivity Ap (at v~rious deformation stress amplitudes-U} and coercive force(Hc) of Ni-5.5at~Al with number of deformation cycles (N). The change of Hc corresponds to curve I of the resistivity chan~e. 1-U=I00 EPa.2-U=125 ~Pa.3-U=150MPa.

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881

Ap/p,~

1.5

2 I

a 0.5 ....

.

100

.

.

200

.

- -300

AO0

500

600

700 T,K

-0.5

Fig. R . T h e r e l a t i v e r e s i d u ~ l r e s i s t i v i t y changes of N i - B . 5 a t ~ A l a l l o y d u r i n g i s o c h r o n a l a n n e a l i n g at i n c r e a s i n g t e m p e r a t u r e (l-after u l t r a sonic loadir~g, 2 - a f t e r static loading, 3 - a f t e r q u e n c h i n g from 973K).

0..6

ap/p,

0,3

0

:::-

-

I OO

T, K

200

Fig. S . T h e r e l a t i v e r e s i d u a l r e s i s t i v i t y chanEes of N i - A I a l l o y s d u r i n g isochronal anneali21E at increasinE t e m p e r a t u r e f, - Ni-5.5at%A!. 2Ni-T.5at~Al) after ultrasonic l o a d l n ~ at U ( a m p ! i t u d e of stress )=I 50 MPa.