• Aucun résultat trouvé

THE INFLUENCE OF THERMAL CYCLING ON THE ACOUSTIC EMISSION DURING HYDRIDE FORMATION IN NIOBIUM

N/A
N/A
Protected

Academic year: 2021

Partager "THE INFLUENCE OF THERMAL CYCLING ON THE ACOUSTIC EMISSION DURING HYDRIDE FORMATION IN NIOBIUM"

Copied!
5
0
0

Texte intégral

(1)

HAL Id: jpa-00221018

https://hal.archives-ouvertes.fr/jpa-00221018

Submitted on 1 Jan 1981

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

THE INFLUENCE OF THERMAL CYCLING ON

THE ACOUSTIC EMISSION DURING HYDRIDE

FORMATION IN NIOBIUM

C. Cannelli, R. Cantelli

To cite this version:

(2)

JOURNAL DE PHYSIQUE

CoZZoque C5, suppZ4ment au nO1O, Tome 42, octobre 1981 page C5-947

THE INFLUENCE OF THERMAL CYCLING ON T H E ACOUSTIC EMISSION DURING

HYDRIDE FORMATION IN NIOBIUM

C . Cannelli and R. Cantelli

ConsigZio NazimaZe deZZe Ricerehe, I s t i t u t o d i Acustica "O.M. Corbino" Via Cassia 1216, 00189 Roma, I t a l y

A b s t r a c t . - T h e effect i s studied of r e p e a t e d thermal cyclings onthe a c o u s t i c acti- vity of t h e Nb-H system d u r i n g hydride p r e c i p i t a t i o n .

1 . l n t r o d u c t i o n . - Recently it h a s been shown by t h e a u t h o r s that hydride formatisn i s t h e s o u r c e of i n t e n s e a c o u s t i c emission (AE)in the Nb-H, Ta-H and V-H ~ ~ s t e m s ~ ~ ~ . ~ h e a c o u s t i c emission phenomenon was c h a r a c t e r i z e d by a n emissivity which s t a r t e d , o n c o o l i n g , a t t e m p e r a t u r e s c o f ~ r e l a t e d with the s o l v u s of the metal-hydrogen system and proceeded d u r i n g evolution of preci- pitation; or. heating no a c o u s t i c acitivity w a s p r e s e n t . O n e of the c h a r a c t e r s of the AE phenome non not sufficiently i n v e s t i g a t e d , i s the e f f e c t of a g e i n g and thermal cycling o n the behaviour of the emissivity d u r i n g p r e c i p i t a t i o n . I n o r d e r to c l a r i f y t h i s . a s p e c t , a c o u s t i c emission ex- p e r i m e n t s combined with ageing t r e a t m e n t s have been performed on the Nb-H system between 330 and 225 K

.

2 . Experimental. - F o r the p r e s e n t experiment a niobium specimen w a s c h o s e n i n which emis- s i d n had been previously stimulated by a s e v e r e h y d r i d e p r e c i p i t a t i o n . The sample w a s a c i r - c u l a r p l a t e of 99.9% p u r e p o l y c r y s t a l l i n e niobium(30 mm in d i a m e t e r and 3 mm thick).Prio13 t o the p r e s e n t hydrogen doping, the specimen w a s annealed a t 2000°C f o r I h in a vacuum of

-8

t h e o r d e r of 10 T o r r . T h e h y d r o g e n c h a r g e was conducted a t 550°C i n a c o n t r o l l e d 99.999% p u r e H atmosphere, and the resulting concentration of 4.0 a t % H was determined by a vacuum e x t r a c t i o n method. The a c o u s t i c emission measurements w e r e performed by Dunegan-Endevco instrumentation by v a r y i n g the t e m p e r a t u r e from 330 t o 225 K a t a r a t e of 0.6 K/min using a n iron-constantan thermocouple d i r e c t l y a t t a c h e d t o the specimen. The s i g n a l s from t h e P Z T t r a n s d u c e r w e r e p r e a m p l i f i e d . b y 4 0 d B i n the frequency band 100-300 kHz and then fed into a

l a g amplifier followed by a d i s t r i b u t i o n a n a l y z e r providing t h e t o t a l number of b u r s t s (events) Ne and t h e i r amplitude d i s t r i b u t i o n . A b u r s t s i g n a l that o c c u r r e d more than 1 0 ms a f t e r the 1% v e l o f the p r e c e d i n g b u r s t had decayed below the a d j u s t a b l e t h r e s h o l d of t h e amplitude detec- t o r , was counted a s one s e p a r a t e e v e n t . T h e e v e n t s w e r e d i s t r i b u t e d in 100 l e v e l s a c c o r d i n g t o t h e i r amplitudes e x p r e s s e d in d B above the value of 1 pV a t the t r a n s d u c e r output.

(3)

JOURNAL DE PHYSIQUE

3. R e s u l t s . - I n o r d e r t o have a more complete understandinp ot t h e emission pherromenon, i n t e r n a l f r i c t i o n , ~ - ' , a n d r e s o n a n c e frequency,f , m e a s u r e m e n t s w e r e conducted on the specimen c o n c u r r e n t l y with the AE e x p e r i m e n t s . T h i s p r o c e d u r e allowed t h e h y d r i d e p r e c i p i t a t i o n t e m p e r a t u r e Tt and t h e p l a s t i c deformation p r o c e s s e s o c c u r r i n g d u r i n g the formation of the m j

-1

st'itting hydride p r e c i p i t a t e s t o be r e v e a l e d F i g u r e 1 d i s p l a y s t h e i n t e r n a l f r i c t i o n

Q

and the t o t a l number of e v e n t s r\i, (broken l i n e s ) of the H-free specimen a f t e r the annealing a t 2000°C. After doping the specimen with 4.0 a t % H , i n t e r n a l f r i c t i o n and r e s o n a n c e f r e q u e p cy measurements w e r e simultaneously undertaken on cooling (with the same r a t e of the AE ex- ~ e r i m e r i t ) until the a b r u p t inflection of both p a r a m e t e r s o c c u r r e d ( a t T =273 K),indicating i n i t i a

t

tiorl of hydride formation. At this t e m p e r a t u r e the measurement w a s stopped and t h e specimen heated to room t e m p e r a t u r e .During subsequent cooling the A E m e a s u r e m e n t , ~ w a s conducted ( F i g . 1 from 330 t o 2 2 0 K , l s t cooling). I t i s s e e n that a c o u s t i c activity s t a r t s a t the tempe- r a t u r e 1' =269 K,which i s a l i t t l e l o w e r than the s o l v u s t e m p e r a t u r e T ,and p r o c e e d s on co-

AE t

oling with evolution of p r e c i p i t a t i o n . At 225 K the thermal cycle was inverted;during heating no a c o u s t i c activity was d e t e c t e d . T h e n , the specimen w a s a g e d . a t 150°C f o r 2 h o u r s a n d sub- sequently t h e AE cooling r u n was r e p e a t e d . T h i s p r o c e d u r e was i t e r a t e d f o r 6 t i m e s . I n F i g . 1 a r e r e p o r t e d the c u r v e s c o r r e s p o n d i n g t c the 4 t h , 5th and 7th c o o l i u g , e a c h of them was p r e c e ded by the 1 5 0 ° C ageing t r e a t m e n t . I t c a n be s e e n that the AE i n t e n s i t y d e c r e a s e s with p r o c e g

TEMPERATURE ( K 1 --- H - W E E t I. 0-' PRECOOLlHG ?--b.,

...

1

_

1st CDOLmG 4 - 4 t h " ef1.r 3rd tt.15ffC

'-.

5 - 5 t h " " 4 t h " 7 - 7 t h " " 6 t h

-

h

.

,

-1

. .

F i g . 1 : Vibration frequency f and i n t e r n a l f r i c t i o n Q i n d i c a t i n g t h e hydride formation t e m p e r a t u r e Tt of t h e Nb-4at%H system.The c u r v e s of the t o t a l n u m b e r of e v e n t s Ne d i s p l a y t h e a c o u s t i c activity of the same system with p r o c e e d i n g t h e r m a l c y c l i n g s .

- t ( Hz )

(4)

ding thermal cycling and a g e i n g , until it i s n o l o n g e r d e t e c t a b l e .

4 . D i s c u s s i o n . - The a c o u s t i c emission c u r v e s r e p o r t e d i n F i g . 1 must be d i s c u s s e d taking 1 .

i n t o account r e s u l t s previously r e p o r t e d I t was found that the t h e r m a l cycling of a same hy- d r o g e n a t e d specimen a c r o s s t h e s o l v u s t e m p e r a t u r e gradually a t t e n u a t e s the AE down t o i t s s u p p r e s s i o n in a few c y c l e s , but a t h e r m a l treatment a t 150°C p a r t i a l l y r e s t o r e s t h e emissivi- t y . This means that thermal cycling and a g e i n g affect a c o u s t i c emission in the opposite way. T h e r e f o r e t h e values of t h e Ne c u r v e s 4 , 5 and 7 of F i g . 1 a r e h i g h e r than they would be wi- thout the e f f e c t of thermal treatment a t 1 5 0 ° C , but t h i s r e c o v e r y of emissivity by a g e i n g gra-

1

(5)

C5-950 JOURNAL DE PHYSIQUE

p r e c i p i t a t i o n s c a u s e a p r o g r e s s i o n of d e t e r i o r a t i o n only when s t r e s s waves a r e emitted by the m a t e r i a l .

R e f e r e n c e s

1. G .Cannelli and R . Cantelli

,

J .Appl. P h y s

.

3,

5666 (1979).

2. G .Cannelli a n d R . C a n t e l l i

,

J

.

Appl. P h y s

.

51,

1955 (1980). 3. G .Cannelli and R. C a n t e l l i , S c r i p l a Met.

3,

731 (1980). 4. G .Cannelli a n d R . C a n t e l l i , Appl. P h y s .

3,

325 (1974).

5. 0. B u c k , D . v . Thompson, and C.A.Wert, J . P h y s . Chem. S o l i d s

3,

2331 (1971).

Références

Documents relatifs

To test whether the vesicular pool of Atat1 promotes the acetyl- ation of -tubulin in MTs, we isolated subcellular fractions from newborn mouse cortices and then assessed

Néanmoins, la dualité des acides (Lewis et Bronsted) est un système dispendieux, dont le recyclage est une opération complexe et par conséquent difficilement applicable à

Cette mutation familiale du gène MME est une substitution d’une base guanine par une base adenine sur le chromosome 3q25.2, ce qui induit un remplacement d’un acide aminé cystéine

En ouvrant cette page avec Netscape composer, vous verrez que le cadre prévu pour accueillir le panoramique a une taille déterminée, choisie par les concepteurs des hyperpaysages

Chaque séance durera deux heures, mais dans la seconde, seule la première heure sera consacrée à l'expérimentation décrite ici ; durant la seconde, les élèves travailleront sur

A time-varying respiratory elastance model is developed with a negative elastic component (E demand ), to describe the driving pressure generated during a patient initiated

The aim of this study was to assess, in three experimental fields representative of the various topoclimatological zones of Luxembourg, the impact of timing of fungicide

Attention to a relation ontology [...] refocuses security discourses to better reflect and appreciate three forms of interconnection that are not sufficiently attended to