ANELASTIC BEHAVIOUR OF Ni100- xPx AMORPHOUS ELECTROLESS DEPOSITED ALLOYS DURING STRUCTURAL RELAXATION AND CRYSTALLIZATION

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ANELASTIC BEHAVIOUR OF Ni100- xPx

AMORPHOUS ELECTROLESS DEPOSITED ALLOYS

DURING STRUCTURAL RELAXATION AND

CRYSTALLIZATION

E. Bonetti, E. Lanzoni, G. Paparo

To cite this version:

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ANELASTIC BEHAVIOUR OF Nil,,-,Px AMORPHOUS ELECTROLESS DEPOSITED ALLOYS DURING STRUCTURAL RELAXATION AND CRYSTALLIZATION

E. BONETTI, E. LANZONIf AND G. PAPARO"

Dipartimento d i Fisica, Università d i Bologna, Via Irnerio 46, CISM-GNSM, Bologna, Italy

'Istituto d i Metallurgia, Università di Bologna, Viale Risorgimento 4, Bologna, Italy

"Istituto d i Acustica "O.M. Corbino", Via Cassia 1211, Roma, Italy

Resumé -

Le comportement anélastique d'une série d'alliages Ni-P obtenus par

v o i e i m i q u e a été etudié pendant la relaxation structurale et la cristal-

1 isation.

Abstract

-

The anelastic behaviour of

a

series of Ni-P alloys obtained by

electrolèss plating, during structural relaxation and crystallization, has

been investigated as a function of the metalloid content.

1 -

INTRODUCTION

Detailed studies have recently been made on the mechanical and transport properties

/1-3/ of amorphous Ni-P alloys, as well as on their anelastic behaviour /4/. In par-

ticular, in the electroless deposited alloys the metalloid content can be varied on

a wide range, making thus possible to obtain a series of alloys ranging fromamor-

phous to microcrystalline only as a function of bath composition /2/.

On the other hand it is well known that the mechanical behaviour of these alloys is

strongly influenced by the metalloid concentration which, during structural relax-

ation, may determine or not embrittlement effects /5/. Floreover, the metalloid con-

tent can strongly influencethe mechanisms and kinetics of amorphous to crystalline

transition /2,6/.

Aimofthis work is to extend previous interna1 friction and dynamic modulus measure-

ments to Ni-P alloys covering a wider P content range, to study the influence of the

chemical composition on the anelastic parameters during structural relaxation and

crystallization.

II

-

EXPERIP.tENTAL

The measurements were carried out on Pti-P sheets, 3 to 5 cm long with a(0.03x0.5)

cm2

cross section, obtained by electroless deposition from a chloride glycol late bath on

a stainless steel substrate.

Specimens with

differentphosphorcontents

Xpwere obtained by stepwise varying the pH

content in the bath (Table

1).

Table 1

PH

3.0

3.5

4.0

4.25

4.5 X,(at%)

22

20

18

16

14 Interna1 friction Q-l and dynamic Young modulus Md were measured from the flexural

vibration decay of specimens cantilever mounted in the frequency range 20-2000

Hz

under a 10-2 Pa vacumm. Strain amplitude was of the order of 10-6.

Al1 the

9-I

and Md measurements vs. T were performed at a constant heating rate of

2 deg/min.

Some measurements were made in isothermal conditions: typical times for thermal

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s t a b i l i z a t i o n , a t t h e measurement temperature, were o f t h e o r d e r o f 3

-

4 mins. III

-

RESULTS AND DISCUSSION

F i g u r e l a - b ) show c h a r a c t e r i s t i c Q - I ( T ) and Fld(T) trends f o r d i f f e r e n t Xp values. The curves r e f e r t o temperatures T

>

500 K above which, i n measurements c a r r i e d o u t a t a c o n s t a n t h e a t i n g r a t e , as i n t h e present case, i r r e v e r s i b l e v a r i a t i o n s o f t h e a n e l a s t i c parameters a r e observed: these a r e brought i n t o evidence by Q-1 maxima and Md steps.

Two d i s t i n c t processes a r e n o t i c e d f o r Xp < 20 at%.

As shown i n Fig. 1 t h e f i r s t dynamic modulus increase occurs i n p a r a l l e l w i t h t h a t o f i n t e r n a 1 f r i c t i o n l e a d i n g t o t h e f i r s t Q-1 maximum. The behaviour can be a t t r i b - u t e d t o a s h o r t range o r d e r i n c r e a s e o r t o some t y p e o f atomic c l u s t e r i n g i n t h e amorphous m a t r i x . The temperature o f t h e maximum s h i f t s t o h i g h e r values w i t h i n - creasing Xp, whereas t h e h e i g h t o f t h e maximum decreases i n t h e same way.

Th X-ray d i f f r a c t i o n p a t t e r n s o f t h e a l l o y s quenched a f t e r h e a t i n g up t o t h e f i r s t

Q-7

maximum /7/ do n o t d i f f e r s u b s t a n t i a l l y from those of t h e same a l l o y s as pre- pared, a p a r t from a d e f i n i t e sharpening o f t h e (111) Ni r e f l e x on an otherwise d i f - fused background. Our TEM observations (Fig. 2a-b) show t h a t a c l e a r b l a c k - w h i t e c o n t r a s t which c o u l d be c o r r e l a t e d t o a l o c a l enrichment i n t h e amorphous m a t r i x o f t h e metal atoms /7,8/, appears i n t h e a l l o y s w i t h Xp

<

18 a t % , quenched a f t e r a r u n

up t o t h e temperature o f t h e f i r s t Q-1 maxima.

Moreover, t h e Q-1 and Md isotherms performed i n t h e same T range (Fig. 3). a r e i n agreement w i t h t h e i s o c h r o n a l s p e c t r a of Fig. 1; i n p a r t i c u l a r t h e Q - l ( t ) curve shows a maximum which may be c o r r e l a t e d t o t h e appearance o f b l a c k - w h i t e zones i n t h e TEM micrographs and w i t h t h e sharpening of t h e (11 1) P l i r e f l e x i n XRD.

N i p r e c i p i t a t i o n around 600 K has a l s o been p o s t u l a t e d by o t h e r authors t o e x p l a i n r e s i s t i v i t y changes i n Ni-P a l l o y s o f t h e same nominal composition /9/.

The l a r g e Q-1 and Md v a r i a t i o n observed i n t h e 600-700 K range are connected w i t h t h e a l l o y c r y s t a l l i z a t i o n , i n agreement w i t h DSC and XRD measurements/6,8/, A t t h e c r y s t a l l i z a t i o n temperature t h e Q-1 behaviour i s c h a r a c t e r i z e d by a s t r o n g maximum f o l l o w e d by a drop, as n o t i c e d i n general d u r i n g s t r u c t u r a l i r r e v e r s i b l e t r a n s i t i o n s , d i f f u s i o n c o n t r o l l e d /10/and t h e dynamic modulus increases up t o 30%.

The Md minimum preceding t h e f a s t increase a t c r y s t a l l i z a t i o n may correspond t o t h e s o f t e n i n g o f t h e phonon mode r e l a t e d t o t h e C O - o p e r a t i v e d i f f u s i o n processes asso- c i a t e d t o c r y s t a l l i z a t i o n .

The temperature o f t h e maximum depends on t h e h e a t i n g r a t e b u t n o t on t h e measurement frequency. I n Fig. 4 t h e temperatures corresponding t o t h e f i r s t and second Q'I maximum T l , T2 a r e p l o t t e d as a f u n c t i o n o f X f o r a c o n s t a n t h e a t i n g r a t e o f E K / m i n . This p l o t compares w e l l w i t h t h e r e s u l t s o f tRe DSC analyses i n Fe-B a l l o y s /Il/. A two branch p l o t o f Tcr st vs. XB was observed a l s o i n t h a t case: t h e f i r s t one a t - t r i buted t o Fe j w e c i p i t a T i o n ( primary c r y s t a l l i z a t i o n )

,

t h e second s t a r t i n g from XB

-

15 a t % due t o an e u t e c t i c t y p e c r y s t a l l i z a t i o n .

XRD observations on specimens quenched a t t h e onset of t h e second Q'I maximum /6/ show t h e appearance of t h e Ni3P r e f l e c t i o n . Thus t h e amorphous t o c r y s t a l l i n e t r a n s i - t i o n of t h e Ni-P e l e c t r o l e s s a l l o y s w i t h

P

c o n t e n t up t o 22 a t % occurs i n one o r more stages depending on t h e composition. The stage T2 observed i n a l 1 t h e a l l o y s (Fig. 4) corresponds t o Ni3P c r y s t a l l i z a t i o n . T h i s stage, i n t h e hypo-eutectic a l l o y s (Xp 5 18 a t %) i s preceded by a second one TI corresponding t o t h e appearance o f N i m i c r o c r y s t a l S.

F i n a l l y we consider t h e r e v e r s i b l e p a r t o f t h e Q - I ( T ) and Md(T) spectra f o r T

5

500K. T y p i c a l t r e n d s f o r a N i 4P16 a l l o y a r e shown i n F i g . 5, Here, as p r e v i o u s l y n o t i c e d i n NiB and Ni-P alloys O? near e u t e c t i c composition /4,12/, a r e l a x a t i o n peak i s some-

t i m e present. Even though i n t h i s case t e x t s have been c a r r i e d o u t on a wide

P

con- t e n t range no s i g n i f i c a n t f u r t h e r i n s i g h t i n t o t h e v e r y n a t u r e o f t h i s peak has been obtained. I n p a r t i c u l a r , a systematic dependence o f t h e peak parameters ( h e i g h t and temperature) on Xp has n o t been n o t i c e d even i f i n some cases (Xp a 20 a t % ) a

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h e a t i n g a t lower temperatures leads t o a r e l a x a t i o n s t r e n g t h i n c r e a s e ( F i g . 5). F u r t h e r work i s i n progress t o c l a r i f y t h e o r i g i n o f these peaks.

I V

-

CONCLUSIOIIS

The Q-1 and Md neasurements c o n f i r m t h a t t h e amorphous t o c r y s t a l l i n e t r a n s f o m a t i o n o f Ri-P a l l o y s i n t h e Xp range 14 t o 22 a t % occurs i n one o r two stages. The s i n g l e stage process i s l i m i t e d t o Xp values near t o t h e e u t e c t i c . I n t h e hypo-eutectic a l l o y s t h e hypothesis o f a s e p a r a t i o n i n t h e amorphous phase w i t h Ni r i c h c l u s t e r and subsequent m i c r o c r y s t a l f o r m a t i o n i s i n agreement w i t h Q-1 and TE!! observations. An a n e l a s t i c r e l a x a t i o n peak has been observed b e f o r e t h e onset o f t h e i r r e v e r s i b l e t r a n s f o r m a t i o n whose n a t u r e has n o t y e t been c l a r i f i e d .

V

-

ACKNOWLEDGEb.IEPJTS

T h i s work was c a r r i e d o u t w i t h M.P.I. funds. The.authors wish t o thank Miss. 1. Zuc- c h i and M r . R. B e r t i f o r t h e i r c o l l a b o r a t i o n ,

V I

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REFERENCES

/1/ Schmidt, T., Varga, L., Kemény, T., Kouczos, G., Tompa, K. and Kajcsos, ZS., Nucl. I n s t r . and Meth. 199 (1982) 353.

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-3

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f

Fig. 2 TEP1 images of I l i a f i P ~ a a s ~ r e ~ a r e d

'

(a7"and a f t è r heating a t 2K/min up t o 510 K and quenching (b). X 40.000 Fig. 4

-

1 -

S h i f t of t h e t e ~ p e r a t u r e of t h e Q-1 + 600 __-+ maxima vs Xp ( s e e Fig. 1 ) . 550 500 14 16 18 20 2 2 Xp (at %)

-

25

-1

a'yft;

and Md(t) s p e c t r a during anneal-

Fig. 5

Low temperature c y c l i n g e f f e c t on t h e Q - I ( T ) M ~ ( T ) s p e c t r a of a 14i84P 6 a l l o y . F i r s t run (-), second run

(---1.

300 400 500

TiK)-

ing a t 490 K f o r a bii84P16 a l l o y . Fre- quency

-

3x102

Hz. Mo:

modulus a t t h e

beginning of t h e isotherm. 5 - ₄

-

/,,"

:

_"

_-

_I

s