DEFORMATION AND CRACKING OF METAL-DEPOSITED CERAMICS AND EFFECTS OF ION IRRADIATION

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DEFORMATION AND CRACKING OF

METAL-DEPOSITED CERAMICS AND EFFECTS OF ION IRRADIATION

S. Noda, H. Doi, T. Hioki, O. Kamigaito

To cite this version:

S. Noda, H. Doi, T. Hioki, O. Kamigaito. DEFORMATION AND CRACKING OF METAL-

DEPOSITED CERAMICS AND EFFECTS OF ION IRRADIATION. Journal de Physique Colloques,

1986, 47 (C1), pp.C1-147-C1-151. �10.1051/jphyscol:1986121�. �jpa-00225549�

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JOURNAL DE PHYSIQUE

Colloque Cl, supplément au n°2. Tome 47, février 1986 page cl-147

DEFORMATION AND CRACKING OF METAL-DEPOSITED CERAMICS AND EFFECTS OF ION IRRADIATION

S. NODA, H. DOI, T. HIOKI and 0. KAMIGAITO

Toyota Central Research and Development Labs., Inc.

Nagakute-cho, Aichi-gun, Aichl-'ken, 480-11, Japan

Résumé - Le dépôt de couches minces de Zr ou Ag et l'irradiation par des ions Ar+ augmentent de manière coopérative la résistance des saphirs à la fracture par rayure. Le dépôt de ces couches minces semble provoquer un adoucissement de la céramique.

Abstract - Deposition of Zr or Ag thin film and Ar ion

irradiation increases cooperatively the durability of sapphire against cracking by scratching. The deposition of the thin films were found to cause the softening of ceramics.

I - INTRODUCTION

The material is subjected to surface damage in mechanical use. The surface damage often leads catastrophic failure of a ceramic

component. Surface modifications of ceramics are expected to improve the mechanical properties. Ion irradiation has got increasing

interests in modifying the ceramic surfaces and has been found to affect the hardness/1,2/, the flexural strength/3/ and the fracture toughness/2,3/ of the ceramics. A thin Ti or Zr film deposition and the subsequent N ion irradiation has been found to increase the durability against cracking by scratching or the critical normal load, Lc to generate a crack in sapphire surface by scratching. The value of Lc varied with the dose; it increases with the dose in a low dose range, get the maximum and then decreases with the dose. The decrease has been tentatively attributed to film hardening due to formation of nitrides/4/. In this paper we studied the effects of chemically inert Ar+ion irradiation on the durability of sapphire itself as well as of sapphire with Zr or Ag thin film. The softening of ceramic surface due to the ion irradiation and due to metal film depositions were also studied.

II - EXPERIMENTAL METHODS

High purity single crystalline a-alumina(sapphire)specimens 5mmX25mm Xlmm in size were polished to a mirrorlike finish. The major surface was normal to a crystallographic<0001> axis. In order to remove mechanical damages, the specimens were annealed at 1773 K for 5 h in air. Zr or Ag films of ca.300 nm thickness were vapor-deposited on the specimens in vacuum and abbreviated Zr/ or Ag/sapphire hereafter.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986121

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cl-148 JOURNAL DE PHYSIQUE

E n e r g e t i c ~ r + i o n s were i r r a d i a t e d t o t h e specimens d i r e c t l y o r t h r o u g h t h e m e t a l f i l m . I n t h e l a t t e r c a s e t h e i o n e n e r g y was chosen s o t h a t t h e p r o j e c t e d r a n g e o f t h e i o n o r t h e a v e r a g e d e p t h o f t h e i m p l a n t e d i o n s was n e a r y e q u a l t o t h e f i l m t h i c k n e s s . The specimen s u r f a c e was s c r a t c h e d w i t h a cone-shaped diamond s t y l u s ( t i p r a d i u s : 75 u m ) . The s t y l u s was normally loaded and s l i d e d on t h e specimen s u r f a c e w i t h a r a t e o f 5 cm/min i n a n ambient atomosphere. The c r i t i c a l l o a d r e q u i r e d t o g e n e r a t e c r a c k s i n t h e s u r f a c e l a y e r , Lc was d e t e r m i n e d by o p t i c a l m i c r o s c o p i c e x a m i n a t i o n o f t h e s c r a t c h . The V i c k e r s m i c r o h a r d n e s s , Hv o f t h e m o d i f i e d s u r f a c e was a l s o measured.

111

-

RESULTS AND DISCUSTION

111-1 Sapph'ire. S a p p h i r e was i r r a d i a t e d w i t h 200 kev Ar'ions a t 100 K , The p r o j e c t e d r a n g e of t h e i o n i n s a p p h i r e was a b o u t 110 nm.

F i g u r e 1 shows t h e r e l a t i v e v a l u e o f Lc o f t h e i r r a d i a t e d s a p p h i r e a g a i n s t L$ (Lc o f t h e u n i r r a d i a t e d one) a s a

f u n c t i o n o f t h e i o n dose. The The Lc v a r i e s w i t h t h e d o s e i n a complex manner. The

Y f r a c t u r e t o u g h n e s s (K1 c ) of

t h e s u r f a c e l a y e r was

e v a l u a t e d by means o f V i c k e r s i n d e n t a t i o n ] 5 / and t h e

O 3

1- 1-

1

r e l a t i v e v a l u e i s a l s o shown

a s a f u n c t i o n of t h e d o s e i n F i g . 1. The K I C s i m p l y

i n c r e a s e s w i t h t h e dose. The s i m i l a r d o s e v a r i a t i o n o f t h e K I C h a s been r e p o r t e d f o r

s a p p h i r e i r r a d i a t e d w i t h ~ i + ions/6/. S i n c e b o t h Lc and

K1 c a r e d e t e r m i n e d from DOSEli~ns.cm-~ c r a c k s , t h e v a r i a t i o n w i t h

t h e d o s e s h o u l d be s i m i l a r . F i g . 1. Dose dependences o f Lc and A d i f f e r e n c e , however, i s i n K1c o f s a p p h i r e i r r a d i a t e d w i t h 200 t h e e f f e c t o f f r i c t i o n on t h e

keV Ar+ i o n s . s t r e s s f i e l d . T h i s i s much

more pronounced f o r a s c r a t c h t h a n f o r a s t a t i c i n d e n t a t i o n /8/. I n F i q . 2 t h e d o s e

I I I I I 325 dependence; o f Hv and a r e

shown f o r s a p p h i r e i r r a d i a t e d w i t h 200 keV -+ions. The h a r d n e s s was measured w i t h a l o a d o f 0.49 N and a l o a d i n g t i m e o f 30 ^Sa t a n ambient

-Q20

atmosphere. The i n d e n t a t i o n d e p t h was a b o u t 2 pm. The f r i c t i o n c o e f f i c i e n t was e v a l u a t e d f o r a s c r a t c h w i t h a normal l o a d below Lc -015 b e c a u s e t h e v a l u e of was

found t o i n c r e a s e when c r a c k s 121

1.0

*> 0.8

5 3

0.6-

a4

0.2

O : l

b i b

o c c u r e d . The s i m i l a r d o s e

v a r i a t i o n o f t h e h a r d n e s s h a s DOSElionscm~ been o b s e r v e d f o r ~ i + - o r ~ r +

- i r r a d i a t e d s a p p h i r e / 6 , 7 / and F i g . 2. Dose dependences o f p and Hv i n t e x p r e t e d a s a r a d i a t i o n

(0.49 N ) o f s a p p h i r e i r r a d i a t e d w i t h h a r d e n i n g o f c r y s t a l l i n e 200 keV A r + i o n s . s a p p h i r e i n a low d o s e and a

s o f t e n i n g due t o

-

^0-4

- ---

,

,A#

,

0'

-

⁰^'

*-I j

---

4'

-

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amorphisation of a sapphire surface layer in a dose range above a critical dose. In ~r+-irradiafed sapphire the occurrence of the amorphous layer was inferred from the analyses of the RBS-chanelling spectra. The concomitant changes of Hv and

p

shown in Fig. 2 are tentatively attributed to the change of the surface state(crystal1ine to amorphous). The increase of from 0.16 to 0.2 is expected to cause about 60

%

reduction of the Lc value if parameters other than p remain unchanged/8/. The dose dependence of Lc, shown in Fig. 1, seems to be determined by a complicated balance between the increase of KIC and that of the stress severity due to the

p

increase.

111-2 Zr/sapphire and Aq/sa~phire. In Fig.

3

typical scratches (normal load:4.9

N)

are shown for Zr/sapphire (film thickness d -260

nm)

a) unirradiated 16

b) 8.9

X 10

ions/cm2 c) as-deposited

Fig.

3.

Optical micrographs of scratches(upper:x 800, otherwise mentioned) and of their backside views(bottom:

X

200), scratched with a cone-shaped diamond stylus(tip radius:75 pm and normal

load:4.9

N ) :

a) and b), bare sapphire irradiated with 200 kev ~ r +

ions and c) to f), Zr/sapphire irradiated with 510 keV ~r+ions.

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JOURNAL DE PHYSIQUE

except smaller Lc values in Fig. 4. Dose dependences of relative the low dose in the former.

values of Lc of Zr/ and Ag/sapphire The maximum value of Lc was irradiated with 510 and 680 keV ~ r + nearly the same in both cases.

ions, respectively.

A good adhesive contact irradiated with 510 keV Ar'ions. For comparison those for sapphire before and after the 200 keV ~ r + i o n irradiation are presented. Their backside views are also shown in Fig.

3.

These pictures show that the Zr deposition and the ion irradiation dramatically change the crack patterns and that the Zr films 'tirradiated are not removed by the scratching. The. relative value of Lc aqainst

LC'

(Lc of the unirradiated sapphire) is shown as a function of the dose in Fig. 4.

The as-deposited Zr film

between the metal film and

7

5 0 3 4 -

'

2

aligned

channel number

O

lh5 DOSElion~cm-2

'

^lb6

' ^at' as that in the Zr/sapphire the dose in a similar manner

I I I I

/ ^-

- .+ L

v ~ 0 0 6 0 @ ~ ~ q / s a p p h i r e

A '

^I

-

- -

1 - 0

-

sapphire is not necessarily required for the Lc increase.

The amorphisation of the sapphire surface may be responsible for the sharp increase of Lc ar und the dose of

I

1016ions/cm9 in both cases. The amorphisation was inferred from the analyses of the RBS-channeling spectra of the Ag/sapphire as shown in Fig. 5. It is noted that little changes of

p

and Hv with the dose were found either Zr/ or Ag/sapphire; the values of

p

for Zr/ and Ag/

sapphire were

.v

0.35 and

.v

0. l?, respectively. The deposition of the metal film and the ion irradiation cooperatively increase Lc of sapphire but the mechanism for the Lc increase is not clear.

remarkably increase Lc and the ion irradiation further

dependence increases it. of The Lc is dose also shown in Fig.

4

for Ag/sapphire

(d-

240

m )

irradiated with 680 keV ~r+ions. The as-deposited Ag film slightly increases Lc.

The Ag film, irrespective of the ion irradiation, was completely removed when scratched with the load much smaller than

Lc

and

is

in sharp contrast with the Zr film in this respect. The Lc in Ag/sapphire increases with

Fig. 5. RBS-channeling spectra of Ag/sapphire irradiated with ~ r + i o n after removal of Ag film by

chemical etching

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111-3 Softening of ceramics by thin metal film deposition.

In Adsapphire Hv was found smaller by more than 20% than that of bare-&appLire in case of the normal load of 1.98 N and the ~ r + i o n irradiation caused little change of HV up to the dose of 2

X

1016ions/

cm2. The size of the indent was reexamined after removing the Ag film by chemical etching and it was confirmed that the Ag film deposition reduces Hv of sapphire or sapphire deforms a little more easily upon indentation when it is covered with a thin Ag film. The Hv reduction was also found in Zr/sapphire but it was smaller than that in Ag/

sapphire. The similar Hv reduction was also found in sintered silicon nitride with a thin metal film. The A1 film of ca.300 nm thickness caused the Hv reduction of-30%(from 14.8 GPa to 10.4 GPa at 0.98 N).

The depth of the indent was about 2.6 um and is nearly 10 times larger than the thickness of the metal film. The Hv reduction of silicon nitride was also found for Ti film deposition. It seems to be the general phenomena that a thin metal film deposition results in the hardness reduction of ceramics. It has been well recognized that a tensile stress occurs on ceramic surface upon indentation/9/.

A metal film should reduce the tensile stress on ceramic surface by its plastic deformation. The stress modification on ceramic surface by a metal film may alter the deformation behavior of ceramics under

the indenter.

IV - ^SUMMARY

Either an ion irradiation or a metal film deposition increased

the

durability of sapphire against cracking by scratching. The metal film deposition followed by an ion irradiation resulted in the cooperative increase of the durability. It will be effective for ceramics other than sapphire and the application to ceramic

components is expected to improve the reliability of the components in use. A larger deformation of ceramics occurred upon indentation when ceramics was coated with a thin metal film. Mechanisms for the mechanical property changes due to the metal film deposition and the

ion irradiation remain to be studied.

We would like to thank Dr.

J.

Kawamoto for his helpful discussions and Mr. M. Kakeno, Mr. A. Itoh and Mr. M. Ohkubo for their

experimental supports.

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