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TECHNIC L INFORM TION

STRUCTURE AND PROPERTIES OF COATINGS MADE OF SELF-FLUXING ALLOYS

A. G. Sbrizher

UDC 621.793.7

Coatin gs of s elf-f luxin g alloys of the sy stem Ni--Cz--B--Si are used exten sivel y for

strengthening rapidly wearing and restoring worn machin e components. The process of prepar-

ing these coatings consists of two stages. The first is thermal spraying of the basic meta l

with self-fluxing alloy powders, and with this the cohesive strength of the sprayed coating

2

does not exceed 12-15 N/mm . The second stage is fusion of the applied coati ng which is ac-

complished as a result of heating the composite to 1000-1100°C and exposing the coating at this

temperature for a specific time necessary for complete emergence of slag at the surface. As

a result of fusion a monoli thic pore-free coating forms bonded by diffusion with the basic

metal. The cohesive strength of the fused coatings is determined by its tensile strength

(aco ~ a t since to tear the coatin g from the base is impos sible as a result of their dif-

fusion bonding, and failure during testing occurs through the coating. Consequently, in

order to evaluate the operating charact eristics of hardene d components it is important to

know the structure and properties of the coating of self-fluxing alloys.

Metallogra phic studies, involving measurement of microhar dness for the structural com-

ponents, anal ysis of the alloy comp osit ion diagr ams for the Ni--Cr--B--Si syst em [I], and the

results of studies carried out previous ly [2-4], have made it possible to establish that the

structure of self-fluxing alloy coatings (Fig . la) is a solid solution based in nickel

(H280...365), ni ckel eutec tic (H565...820), and crystalline formations of different shapes

and sizes (HI080...3800), whic h relate to carbides of chromium CrTCs, Cr2sCs, andM ~sC ~ (HI080...

1450), bo ride s of chro mium CrB2, CrB, Cr2B, Cr sBs and nicke l NiB, Ni=B, Ni3B (HI500...

2400). Results of studying the distrib ution of chromium, boron, and carbon in the coating

carried out inca Cameca MS-46 x-ray microan alyzer have shown (Fig . 2a) that complex compounds

of chromium with boron and carbon of the carboboride type M(C,B)3, M2 3(C,B)~ wi th microha rd-

ness H2800.. .3800 form in the structure of the coating.

Quantitative analy sis of the structural comp onents close in chemical compositi on and

hardness but obtained by different methods for self-fluxing alloys PG-SR4 (15...18 Cr,

2.8...3.8 B; 3...4.5 Si, 0.6...1.0 C ; < 5 Fe; balance nickel) and SNGN-60 (16...19 Cr;

4...4.7 B; 4...5 Si. 0.9...1.1 C; < 4.5 Fe; < 1.0 Mn; balance nickel), whic h are used

extensively in order to improve the wear resistance of the operating surface of machin e com-

ponents, were carried out in an electronic computing analyzer of the Quantimet 720 tele-

vision pictu re by scanni ng the television screen and resolving the light components. White,

light-gray, dark-gray, and dark components of the structure were separated du ring this study.

Fig. I. Microst ructure of a coating of the alloy system Ni--

Cr--B--Si (a) and the white compon ent of the coa ting o f self-

fluxin g alloys SNGN- 60 (b) and PG-SR4( c); a) x400; b-c) x1320.

t •

Minsk Branch of the Tekhenergokhimprom' Scientific Production Unit. Translated from

Metalloved enie i Termicheskaya Obrabotka Metallov, No. 4, pp. 42-44, April, 1988.

296 0026-0673/ 88/0304-0 296512.50 © 1988 Plenum Publishing Corporation



H

800

6O0

00

200

2 4

l t 4

o,m

0 , 1 0 o , 2 0 0 , 3 0 O , O h , m ~

Fig. 3 Fig. 4

F i g. 3 . M i c r o h a r d n e s s d i s t r i b u t i o n t h r o u g h t h e c o a t i n g

s e c t i o n a n d b a s i c m et a l . × 4 0 0.

F i g. 4 . D e p e n d e n c e o f m i c r o h a r d n e s s t h r o u g h a s e c t i o n o f

t h e c o a t i n g o n e x p o s u r e d u r i n g h e a t t r e a t m e n t , i ) 2; 2 )

5; 3) i0; 4) 15 sec.

T A B L E 2

PG-SR4

S N G N 6 0

Alloy

°f

°oo

N / m m z

E.IO 3 V

I

320 .350 1260 . 1380 ] 35,6 39,6

280 .300 1340 .1480 I 37,9 41,9

* P o i s s o n ' s r a t i o .

0 ,24 2 . .0 ,2 58

0,212. 0,240

t h e c o a t i n g ( Fi g. 2 b ) , w h i c h l e a d s t o f o r m a t i o n o f a t r a n s i t i o n z o n e c o n s i s t i n g o f n i c k e l e u -

t e c t i c a n d s o l i d s o l u t i o n b a s e d o n n i c k e l e n r i c h e d w i t h i r o n a n d w i t h o c c a s i o n a l i n c l u s i o n s

o f h a r d c r y s t a l l i n e f o r m a t i o n s .

R e s u l t s o f m e a s u r i n g m i c r o h a r d n e s s s h o w e d t h a t i n t h e d i f f u s i o n z o n e f o r i r o n it d e c r e a s e

(Fig. 3).

S h o w n i n F i g. 4 i s m i c r o h a r d n e s s d i s t r i b u t i o n i n t h e b i m e t a l . T h e m a r k 0 o n th e a b s c i s -

s a a x i s c o r r e s p o n d s t o t h e c o n t a c t ( f u s io n ) o f t h e P G - S R 4 a l l o y c o a t i n g w i t h t h e b a s i c m e t a l ,

i.e., steel 45. To the l eft of the zero ma rk is basic metal, and to the right is the coating.

W i t h a n i n c r e a s e i n e x p o s u r e a t t h e c o a t i n g f u s i o n t e m p e r a t u r e t h e z o n e o f r e d u c e d m i c r o h a r d -

n e s s i n t h e c o a t i n g s h i f t s t o w a r d s i t s s u r f a c e a s a re s u l t o f a n i n c r e a s e i n th e d i s t a n c e o f

d i f f u s i o n d i s p l a c e m e n t o f i r o n f r o m t h e b a s i c m e t a l . W i t h e x p o s u r e f o r 15 s ee t h e m i c r o h a r d -

n e s s i s r e d u c e d s t a r t i n g f r o m t h e s u r f a c e t o a t h i c k n e s s o f 0 . 5 m m , w h i c h i n d i c a t e s d i f f u s i o n

o f i r o n t h r o u g h t h e w h o l e c o a t i n g t h i c k n e s s .

C o a t i n g t e n s i l e a nd c o m p r e s s i v e s t r e n g t h , e l a s t i c i t y m o d u l u s a n d P o i s s o n ' s r a t i o , w h o s e

c o n f i d e n c e r a n g e s a r e g i v e n i n T a b l e 2 , c h a r a c t e r i z e s e l f - f l u x i n g a l l o y s P G - S R 4 a n d S N G N - 6 0

a s b r i t t l e m a t e r i a l s .

T h e w e a r r e s i s t a n c e o f a l l o y s S N G N - 6 0 a n d P G - S R 4 d u r i n g l i m i t e d f r i c t i o n w i t h a l u b r i c a n t

i n t h e r a n g e o f r e l a t i v e s l i d i n g r a t e s v = 0 . 7 8 . . . 3 . 9 3 m / s e c a n d s p e c i f i c l o a d p = 4 . 9 . . . 2 4 . 5

N/mm 2 is higher than for steel 45 (HRC 46-48) by factor s of nine to ten and six to seven re-

s p e c t i v e l y .

C O N C L U S I O N S

I. The st ruct ure of co atings of alloys of the syste m Ni--Cr--B--Si cons ists of a solid solu-

t i o n b a s e d o n n i c k e l , n i c k e l e u t e c t i c , c h r o m i u m c a r b i d e s , c h r o m i u m a n d n i c k e l b o r i d e s , a n d

c o m p o u n d s o f t h e c a r b o b o r i d e t y p e.

298



2. Hard crys talline formations in coatings of alloy SNGN-60 are greater by a factor of

2.5 than in allo y PG-SR4.

3. Self-fluxing alloys are brittle materials.

4. With an increase in the depth of iron diff usion the boundary for a reduction in micro

hardness shifts towards the coating surface.

5. The wear resistance of coatings of alloy SNGN-60 is greater by a factor of 1.5 than

for alloy PG-SR4, whic h is due to the greater conte nt of hard crystalline formations in alloy

SNGN-60 and their more un iform di stributio n in the structure.

LITERATURE CITED

i. O. Knot ec and E. Lugsc heider , On the structure of Ni--Cr--B--Si hard faci ng alloys and

their bonding reacti on, J. Vacuum Sc i. Technol., ii, No. 4, 798-801 (1974).

2. Yu. A. Otradi nskii, M. S. Matvee va, and G. V. Kozlova, Study of the micr ost ruct ure of

self- fluxi ng ha rd allo ys of the Ni--Cr--B--Si syste m, in: Repair of Artic les by Wear- Resi s

ant Fusion and Welding [in Russian], Mos cow (1972).

3. S. I. Rumyants ev and V. E. Astrakhantsev, Restoration of articles by plasma metalli zing

followed by fusion, Avtomobi l'nyi Transport, No. 6, 13-14 (1972).

4. Yu. P. Oshchen kov and N. V. Oshchenkova, Features of structure formation for alloys of

the Ni--Cr--B--Si syste m with i nduct ion melt ing, Metall oved. Term. Obrab. Met., No. i0,

14-18 (1979).

9 9

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