This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
8/10/2019 7.Structure and Properties of Coatings Made of Self-fluxing Alloys
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
8/10/2019 7.Structure and Properties of Coatings Made of Self-fluxing Alloys