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INTERNAL FRICTION STUDIES OF THE OXYGEN
SNOEK RELAXATION IN GROUP-Va TRANSITION
METALS
M. Weller, J. Diehl, G. Hörz, R. Mann, K. Schulze
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C10, suppldment au n012, Tome 46, dEtcembre 1985 page C10-47
INTERNAL FRICTION STUDIES OF THE OXYGEN SNOEK RELAXATION IN GROUP-Va TRANSITION METALS
M. WELLER, J.DIEHL, G. HORZ, R. MANN AND K. SCHULZE
Max-Planck-Institut fiir Metallforschunq, Institut fiir
Werkstoffwissenschaften, Seestrasse
92, 0-7000Stuttgart
1, F.R.G.Resum6
-
Les pics de Snoek de 0 (ou N) dans l e s m5taux Va montrent
u n
glarg-
7
~ s s e m e n t
extraordinaire
ddes concentrations 5lgv6es de 0 (N). Les expgriences
d g t a i l l g e s de frottement i n t g r i e u r s u r l e Nb-0.7% 0 ultrapure confirment que
c e t glargissement e s t symmgtrique e t correspond
2une d i s t r i b u t i o n des temps
de relaxation continue qui e s t a t t r i b u g e 6 une interaction repoussant des
atomes de 0 qui s15tend
dgrandes distances ( " a n t i c l u s t e r i n g " ) . Les r g s u l t a t s
ne sont pas en accord avec l e mode'le de "clustering" de Powers e t Doyle. En
ajoutant des f a i b l e s teneurs en
N ,on observe en plus
un Glargissement
asymm5trique du pic de Snoek de 0 au cat6 des tempgratures glevges.
Abstract
-
Snoek peaks of 0 ( o r
N )in
Vametals exhibit extraordinary broade-
ning a t higher 0
( N )contents. Detailed internal f r i c t i o n measurements on
ultrapure Nb-0.7% 0 confirm t h a t t h i s broadening i s symmetric and corresponds
to a continuous d i s t r i b u t i o n of relaxation times, which i s a t t r i b u t e d to a
long range repulsive i n t e r a c t i o n of 0 atoms
("anticlustering")
.
The r e s u l t s
disagree
w i t hthe predictions of Powers
'
and Doyle's clustering model.
Addition of small amounts of
Ncauses additional asymmetric broadening of
t h e 0 Snoek peak on i t s high temperature side.
I
-
INTRODUCTION
In recent internal f r i c t i o n ( I F ) experiments on ultra-pure tantalum and niobium doped
with oxygen only /1,2/ i t was shown t h a t with increasing oxygen concentration the
Snoek peak i s s h i f t e d t o somewhat higher temperatures and symmetrically broadened.
This observation i s not i n accordance with an early model derived by Powers and Doyle
from IF measurements on Ta-0 and Ta-N /3,4,5,6/ which was l a t e r also applied to Nb-0
and
Nb-N/7-9/. The basic assumption of t h i s model i s that the Snoek peak in concen-
t r a t e d solutions of i n t e r s t i t i a l foreign atoms (IFA) i s composed of a superposition
of several d i s c r e t e relaxation processes originating from the re1 axation of isolated
IFA, of IFA-pairs, t r i p l e t s e t c . being formed by a tendency towards clustering. The
main consequences of t h i s
clustering mode2a r e ( i
)an asymmetrical broadening a t the
high temperature s i d e of the peak, becoming the more pronounced the higher the IFA
concentration i s , ( i i ) no marked s h i f t of the peak temperature with the IFA content.
Our experimental r e s u l t s on Nb-0 and Ta-0 on ( i
)symmetrical broadening and ( i i
)peak-shi f t were interpreted with a long range repulsive interaction of IFA, a l s o
called
anticZustering/10/, leading t o a continuous d i s t r i b u t i o n of relaxation times.
In recent papers on Nb-0 / 1 1 , 1 2 / these r e s u l t s were questioned and the e a r l i e r clus-
t e r i n g model was favoured. This controversy prompted us t o study Snoek relaxations
in Nb-0 i n more detail /13/. Some of the r e s u l t s a r e presented i n t h i s paper.
I 1
-
EXPERIMENTS AND THEIR ANALYSIS
IF measurements were carried out with a computer-controlled inverted torsion pendulum
i n the frequency range of
1Hz. IF and r e l a t e d q u a n t i t i e s were determined from the
f r e e decay of the mechanical o s c i l l a t i o n s /13,14/. Measurements were taken with in-
creasing temperature a t a mean heating r a t e of 0.5
-
0.8 K/min. To enable r e l i a b l e
'data processing about 400 data points were taken f o r each sample-
C10-48 JOURNAL
DE
PHYSIQUEThe r e s u l t s o f two samples are presented i n F i g . 1. Sample A was prepared from u l t r a -
pure niobium /15/ and c a r e f u l l y doped w i t h 0.7 a t . % oxygen /16/ ( F i g . l a ) . Sample B
contained i n a d d i t i o n t o 0.7% 0 about 0.05% N ( F i g . l b ) . I t shows a small N-Snoek peak
i n a d d i t i o n t o t h e 0-Snoek peak ( h i g h e r than f o r s a m ~ l e A due t o d i f f e r e n t t e x t u r e ) . I n Fig.2 t h e 0-Snoek peaks a r e p1 o t t e d as l o g [Q-~/Q;~]vs. [ 1 / ~ - l / ~ , + ( k / ~ ) . l n f / f
]
-qil= h e i g h t o f I F peak, f,=frequency a t t h e maximum temperature T=Tm; H= 1.23 eD,
see below. The term k / H . l n f fm
h
c o r r e c t s a d i s t o r t i o n o f t h e I F curves due t o t h etemperature dependence o f f ( T ) (comp. F i g s . la,b,see /1,14/). The N-Snoek peak i n
F i g . l b was s u b t r a c t e d by assuming a Debye r e l a x a t i o n (which should be c o r r e c t f o r
t h e low N content o f 500 at.ppm) w i t h r e l a x a t i o n parameters from /1,17/. Whereas i n
F i g . 2 the data p o i n t s o f sample A,being doped o n l y w i t h 0, f a l l very c l o s e l y on a symmetrical I F curve, t h e data o f sample B, although t h e N peak i s subtracted, ex- h i b i t an a d d i t i o n a l asymmetrical broadening on t h e h i g h temperature s i d e .
I n F i g . 3 the I F data o f sample A a r e compared w i t h t h e o r e t i c a l c a l c u l a t i o n s . Curve ( 1 ) i s c a l c u l a t e d f o r a Debye r e l a x a t i o n w i t h parameters o f d i l u t e Nb-0 a l l o y s /14,17/. Curve ( 2 ) i s c a l c u l a t e d according t o t h e c l u s t e r i n g model by composing an I F curve o f f o u r Debye r e l a x a t i o n s , f o r which t h e parameters published by Gibala and Wert /7/ f o r a sample w i t h the same amount o f oxygen a r e used. The data i n F i g . 3 a r e again normalized w i t h r e s p e c t t o peak h e i g h t and peak temperature.
111
-
DISCUSSION AND CONCLUSIONSFrom t h e r e s u l t s i n Figs. 2 and 3 and from experiments p u b l i s h e d e a r l i e r /1,2/ t h e f o l l o w i n g can be s t a t e d :
Pure Nb-0.
-
( i ) The Snoek peak i s considerably broader than a Debye peak(Fig. 3).Continuous broadening o f Snoek peaks f o r h i g h e r IFA-concentrations was a l r e a d y ver-
i f i e d f o r Ta-0 and Nb-0 /1,2/. ( i i ) The broadening o f t h e peak occurs r a t h e r symmet-
r i c a l l y ( F i g . 3 /1,2/). ( i i i ) The broadened peak cannot be f i t t e d by curve ( 2 ) i n F i g . 3, c a l c u l a t e d by composing f o u r r e l a x a t i o n processes according t o t h e c l u s t e r i n g model. Curve ( 2 ) i s h i g h l y asymmetrical. I t coincides a t low temperatures w i t h t h e Debye curve. Above the peak temperature i t shows f l e x u r e s i n h e r e n t i n t h e ( d i s c r e t e ) c l u s t e r i n g model i n discrepancy w i t h t h e experimental curve. ( i v ) With i n c r e a s i n g
0-content Snoek peaks i n Ta-0 and Nb-0 a r e s h i f t e d t o h i g h e r temperatures /1,2/ i n -
d i c a t i n g an enhancement o f the a c t i v a t i o n enth'alpy H, which, according t o /13/, i n - creases from 1.15 eV f o r Nb w i t h 0.06% 0 t o 1.23 eV f o r Nb w i t h 0.7% 0.
I n f l u e n c e o f n i t r o g e n .
-
N i t r o g e n causes a d d i t i o n a l broadening o f tbe oxygen Snoek peak on i t s h i g h temperature side,which apparently i s due t o an 0-N i n t e r a c t i o n . A t h i g h e r N-concentrations t h i s behaviour was already r e p o r t e d by Powers and Doyle /6/f o r Ta-0
+
N, and by Gibala and Wert / l 8 1 as w e l l as by Ahmad and Szkopiak /19/ f o rNb-O+N. Whether t h i s 0-N i n t e r a c t i o n i s a t t r a c t i v e o r r e p u l s i v e i s an open question.
Comparison w i t h a f t e r - e f f e c t (AE)-experiments.
-
The r e c e n t controversy /11,12/ men-t i o n e d i n t h e i n t r o d u c t i o n i s mainly based on AE-experiments w i t h samples c o n t a i n i n g
smaZZ
amounts of nitrogen /7,12/. Okamoto /12/ r e p o r t e d t h a t t h e i r AE-curves o f Nb-0 c o u l d n o t be f i t t e d w i t h a symmetrical lognormal d i s t r i b u t i o n . This may be e x p l a i n e d by t h e a d d i t i o n a l 0-N i n t e r a c t i o n . By r e a n a l y s i n g experiments o f Gibala and Wert /7/, Cost /11/ d e r i v e d 3 r e l a x a t i o n times f o r Nb-0 which a r e approximately i d e n t i c a l w i t h those used f o r c a l c u l a t i o n o f curve ( 2 ) i n F i g . 2. Cost furthermore analysed AE curves obtained i n o u r l a b o r a t o r y f o r a d i l u t e , u l t r a p u r e Nb-0 a l l o y c o n t a i n i n g 0.063% 0. He e s s e n t i a l l y obtained a s i n g l e r e l a x a t i o n time o n l y and argued t h a t the experiments were n o t c a r r i e d on l o n g enough f o r a l s o f i n d i n g l o n g e r r e l a x a t i o n times. However, f o r t h e low 0-concentration i n v o l v e d 0-0 i n t e r a c t i o n s ( c l u s t e r i n g o r a n t i - c l u s t e r i n g ) a r e n o t t o be expected a t a l l , and these experiments were used t o measure the temperature dependence o f t h e r e l a x a t i o n t i m e f o r d i l u t e Nb-0 a l l o y s /14/ and n o t as an evidence a g a i n s t t h e c l u s t e r i n g model.Conclusions.
-
The continuous broadening o f t h e I F curves w i t h i n c r e a s i n g 0 concen- t r a t i o n r e p o r t e d e a r l i e r i s t h o u g h t t o be c o n f i r m e d by t h e p r e s e n t i n t e r n a l f r i c t i o n experiments on u l t r a - p u r e Nb doped w i t h 0.7% 0. T h i s broadening i s accounted f o r by a continuous d i s t r i b u t i o n o f r e l a x a t i o n times, which i s a t t r i b u t e d t o a l o n g r a n g e . r e p u l s i v e i n t e r a c t i o n o f oxygen atoms. The a d d i t i o n a l asymmetrical broadening o f t h e 0 peak caused b y even s m a l l t r a c e s o f n i t r o g e n o b v i o u s l y i n d i c a t e s an i n t e r a c t i o n between N- and 0-atoms, t h e n a t u r e o f w h i c h has t o be c l e a r e d up s t i l l .Acknmledgements. - We a p p r e c i a t e t h e t e c h n i c a l a s s i s t a n c e o f Miss M. Hamm, Mr. B. Rahn and Mr. M. T i e t z e .
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31, 1799 (1970).340
T [K1
T
[K1
F i g . l a
-
I F and f 2 vs. T p l o t s F i g . l b-
I F and f 2 vs. T p l o t sf o r Nb w i t h 0.7% 0 (sample A). f o r Nb w i t h 0.7%
+
0.05% N (sample B).JOURNAL DE PHYSIQUE
