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Thin Solid Films, 95 (1982) 133-142
PREPARATION AND CHARACTERIZATION 133
MECHANICAL, T H E R M A L AND TRIBOL O G ICA L PROPERTIES OF ELECTRO- AND C H E M O D E P O S I T E D C O M P O S I T E COATINGS*
ERHARD BROSZEIT
Institut fiir WerkstoJ~unde, Teehnische Hochschule Darmstadt, Grafenstrafle 2, 61 Darmstadt (F.R.G.)
(Received March 29, 1982; accepted April 5, 1982)
By means of chemical (autocatalytic) and electrolytic codeposition of nickel and silicon carbide particles it is possible to produce coatings with enhanced wear and corrosion resistance on metallic and plastic substrates.
In the first part of the paper the basic plating technique in relation to the type, form, grain size and activation of the SiC particles will be described.
The mechanical properties of the coatings depend on the amount of in- corporated particles in the nickel matrix. By activation of the SiC powder the content of particles in the coating can be increased significantly. Mechanical properties such as hardness, strength and elastic modulus improve with increasing content of particles. It will be further shown that the negative influence of a pure nickel coating on fatigue is reduced with a coating of Ni-SiC. This result can be explained by the behaviour of the internal stresses in the coating as a function of the SiC content. The tribological properties of the coatings were tested by an abrasive wear mechanism under lubricated conditions combined with corrosion. The corrosive wear tests were performed under potentiostatically controlled conditions.
The high temperature application of these coatings is limited by the thermal decomposition of the SiC particles in the nickel matrix at about 500 °C. The coatings were examined by various techniques such as differential thermal analysis, X-ray diffraction and secondary ion mass spectrometry. The influence of different temperatures on the mechanical and tribological properties of the coatings will be described.
1. INTRODUCTION
Electrolytic and electroless deposition of composite coatings are well-known techniques for producing protective coatings on metallic and non-metallic parts ~-5. As the plating process takes place in aqueous solutions the maximum temperature in the bath is below 100 °C. This is one of the main advantages. A further advantage is the comparatively high deposition rate.
* Paper presented at the International Conference on Metallurgical Coatings and Process Technology, San Diego, CA, U.S.A., April 5-8, 1982.
0040-6090/82/0000-0000/$02.75 © Elsevier Sequoia/Printed in The Netherlands
134 E. BROSZEIT
The matrix materials mainly applied are nickel in the case of electroplating and Ni -P in the case of the chemical deposition. Several carbides and oxides such as SiC, TiC, WC, B4C, AI20 3 and SiO z have been used as the particulate material. Among these SiC is mainly applied. Normally the grain size of the SiC particles is 0-3 p~m. The concentration of the powder in the bath is in the range of 0-200 g I-~. To prevent separation of the suspension the bath is magnetically or mechanically stirred or air is blown into it.
The incorporation of the SiC particles in the nickel or Ni -P matrix depends on the activation of the SiC powder. Figure 1 shows the amounts of incorporated SiC for non-activated material and surface-activated material.
d,
0 I0 ~5 50 "/5 100 150 200
SiC- contenI in the both [~/I]
Fig. 1. Amount of SIC incorporated in Ni SiC coatings vs. SiC content in the electrolyte: 0, non- activated; C), surface activated.
2. MECHANICAL PROPERTIES
The hardness of the coating and the residual stresses depend on the amount of incorporated particles in the nickel matrix. In Fig. 2 the influence of the amount of incorporated SiC and AI20 3 on the hardness and the residual stresses for a dispersion coating plated in a Watts-type electrolyte is shown. For both dispersoids the hardness increases with increasing particle content; however, the increase in hardness is more marked for SiC. The internal stresses in the coatings decrease with increasing particle content. The mean grain size of the matrix material was measured with X-ray techniques and also showed a tendency to decrease (from 1200 to 600/~) with increasing particle content.
With several agents, e.g. saccharin, it is possible to produce electroplated coatings with increased hardness and compressive stresses. Figure 3 shows the influence of the saccharin content in the electrolyte (Watts type, containing 200 g A120 31- 1) on the hardness and the internal stresses. The hardness increases with increasing additive content, whereas the residual stresses change from tension at low saccharin concentration to compression at concentrations above 0.06 g 1 1
The incorporation of hard particles in the nickel matrix also influences the stress-strain behaviour of the material. Figure 4 shows the reduction in the strain. In
E L E C T R O - A N D C H E M O D E P O S I T E D C O M P O S I T E C O A T I N G S 135
5O0
# 0 0
300 I
ZOO
100
0 0
m I i J i 1 0
Z dt g 8 10 ~ %
°
r
\'~ "----L4 3
5 tO
DISPERSOID CONTENT % (a) BASE MATERIAL, UNCOATED (b)
F ig . 2. (a) H a r d n e s s vs. c o n t e n t o f i n c o r p o r a t e d S i C a n d A 1 2 0 3 ; (b) t ens i l e s t r e s se s in t h e c o a t i n g v s . S i C
c o n t e n t .
300 I I
WATTS-nickel (200g/[ AtzO 3) variable saccharine-content
",-,,.v-,-.:
200
E
i~100
_,oo 0 20 40 60 80 I00
coating thickness [pm]
Fig . 3. H a r d n e s s a n d i n t e r n a l s t r e s s e s as f u n c t i o n s o f t h e a d d i t i v e c o n t e n t .
500
j J 4OO
e:ff 31111, .
zoo
100
0 I I I I I saccharine -content I00
0 gll - - - ~ , , - ~ , , , - - , - , ~ ,
E 50
° \ : z 0
O.08g/t . . . . ~-- -50 - - - - [1.1 g/I . . . . . . . . . -- - -- - - ~ " ~ ' - " ' ~ - ~
/ -100
o o.oz 0.04 o.o6 o.~ {~ socchorine-content [gill
Fig. 5 the change in the Young's modulus as a function of the amount of incorporated SiC is shown. Figures 6 and 7 demonstrate the influence of SiC on the yield limit and the strength.
Figure 8 shows the crack surfaces of a pure nickel specimen (Figs. 8(a)-8(c)) and of an Ni-7~oSiC specimen (Figs. 8(d)-8(f)). The ductility of the pure nickel and the brittleness of the composite coatings are clearly demonstrated. The microstructure of the fracture surface (Fig. 8(f)) shows the dispersoids and the plastic deformation of the nickel matrix material. The mechanical properties of the composite Ni-SiC material depend on the amount of dispersoid in the metallic matrix. The hardness, Young's modulus, yield limit and strength increase with increasing SiC concen-
1 3 6 E. BROSZEIT
~,00
200
o
o
Ni
Ni-SiC (co. 2% SiC)
o 8o0
~OL}
200
0 8gC
2~
Ni-SiC (co 4%SIC)
210000
E
x, >-
E
~L. ~6o0o0 .g-
0 20~(11
E 19~[11 z
~ 17O000
160000 .g.
o
Ni-SiC (CQ 7=/= SiC)
o ~ 4 5
strain c[%]
Fig. 4. Stress-strain behaviour of various coatings.
Oo .~o ....z--~ % o Q ~ C
o / , , 8 1 i
. . . . . .
--~--i-o~?.pos!,~-~ Yo:,l,I ~--
o
- - i I - - ~ O0°C/ lh ,
J [ I I I I I
,.s~ ; . . - .--~
i I I
[ I l [ I i l 1 2 3 5 6 7 8
SiC f n c o r p o r o b o n [w t % i
Fig. 5. D y n a m i c Y o u n g ' s m o d u l u s v s . SiC c o n t e n t .
=o 1" I
4oo - ---s q w,~ )o °
,::,: Ni-SiC oWb. /
o ooo ~ l 1 ~ 600 400 °C/ lh
= i ] ~ 0
6oo°c/lh ! i /
o / o,z'/,t ~ lLo, 0 1 2 3 4 5 6 7 8
SiC CONTENT
Fig. 6. Yie ld l imi t v s . SiC c o n t e n t .
%
ELECTRO- AND CHEMODEPOSITED COMPOSITE COATINGS 137
BOO 700 600 500, 400,
z 300 ,~ zoo
100 0
800 70O 600
I E I ~= 500 ~ 400'
E-I ~ 380' o e zoo
100
8oo 7O0 600 500 400, 3~, zoo I00
0 0
- l Ni-SiC owb. t~t',
J J I B
, ~ '
400"C/lh - ~ - - ,
W -
' i 600%/lh I
1 2 3 4
SiC CONTENT
Fig. 7. Strength v s . SiC content.
I
? Y ] fL/to G 7
(a) (b) (c)
(d) (e) (f)
Fig. 8. Crack surfaces of (a)-(c) a pure nickel and (d)-(f) a composi te coating.
tration, while the ductility decreases. As the residual stresses also decrease, the fatigue life under rotating-bending conditions in air is raised in comparison with that of the specimens coated with pure nickel (Fig. 9).
1 3 8 E. BROSZEIT
#6
:",,I # Z - -
m ) + o - / . /
, ° . / / +
~ a2 --
ZO
.... S.
I
i Z60 5 ?o
SiC-CONTENT %
1100
1000
900
800
700
"o .~ BOO
5OO
400
300
0
o n n e o l i n g hme
L L ~ L
i . . . . %[- Ni-P- SiC - ~ [co 5%1
- - ~ N ! - P -
I i i too 2oo 3oo 4oo soo 000 ?oo 0o0 0oo 1ooo
lemperolure [ °C ]
Fig. 9. Fatigue strength vs. SiC o r A 1 2 0 3 content: 0, SiC; O, A 1 2 0 3 ; - - -, uncoated specimen.
Fig+ 10. Hardness vs. annealing temperature.
x
At2 03-J~qP qPJ F specim+n
I 4 . ~ + I - - l + Ni -S iC
Ni c
I - ~ (a )
m ~ e c i ~ Ni-P-SiC ,
- - _ (
,~ (a )
~ E *l ~ E
• 580"C 800% 36o, % +2o % +5o, °~ 88o,.c ~ . . . . ~ , .
~ 340 lOO 200 300 400 500 600 700 800 900 I000 0 100 200 ~,00 ~00 500 600 700 BOO gO0 1000
(b) temperolure ~ [°C ] (b) temperoture ~ [% ]
Fig. l 1. Differential thermal analysis results for nickel and Ni-SiC coatings (inert material, ~-A1203; dO~dr = 20 ~'C rain- 1); (b) difference curve (Ni-SiC values minus nickel values).
Fig. 12. Differential thermal analysis results for Ni-P and Ni -P SiC coatings (conditions as in Fig. 11); (b) difference curve (Ni-P-SiC values minus Ni -P values).
ELECTRO- AND CHEMODEPOSITED COMPOSITE COATINGS 139
3. INFLUENCE OF HEAT TREATMENT
The properties of the chemically deposited Ni-P coatings can be improved by heat treatment. Figure 10 shows the variation in the hardness of Ni-P and Ni-P-SiC films with the annealing temperature (annealing time, 2 h) in the range from room temperature to 800 °C. The hardness has a maximum at 350 °C and decreases at higher temperatures. Except for the hardness values at 800°C the hardness curves are similar for both coatings.
Electroplated nickel and Ni-SiC coatings show decreasing hardness with increasing annealing temperature. Using differential thermal analysis we demon- strated that at several critical temperatures crystallographic changes and chemical reactions take place (Fig. 11). Strong exothermal peaks are observed at 650 and 880 °C.
For the Ni-P and Ni-P-SiC coatings differential thermal analysis again shows several critical temperatures (Fig. 12): at 340°C (formation of Ni3P ) for both coatings, at 580 °C (Ni-SiC reaction) for the Ni-P-SiC coating and at 880 °C (partial melting of the eutectic Ni-10~/oP alloy) for both coatings.
~ ' , ~ <, 'Egrg
r~ . ; "~
'.¢,*)21
(a) (b) (c) (d)
Fig. 13. Structure of Ni-SiC coatings annealed at 650 °C for (a) 10 s, (b) 5 rnin, (c) 30 min and (d) 2 h.
Figure 13 shows cross sections of an Ni-7~oSiC coating after various heat treatment times at 650°C. After 10s no change in the structure is observed. However, after 5min the SiC particles have decomposed and a dark phase (presumably Ni3Si ) has formed in the bright nickel phase. After 30 min a third phase (presumably carbon) has formed at the grain boundaries and in the interior of the dark phase. A 2 h heat treatment changes the structure of the coating again: in a uniform grey matrix (Ni-Si) only black lines (carbon) remain.
4. TRIBOLOGICAL PROPERTIES
The tribological properties of the electroplated and chemically plated nickel and nickel dispersion coatings were tested in the abrasive wear regime for mild and
140 E. BROSZEIT
i J Ni i
Ni-TiC 1o - (co 2°1o TiC) - - -
anneetin 9 time 2h
E I I I
/
--anneeling time 2h--@~/ -lh j z4h__ / , " I '
15 7% SiC)
- - 5 0
• 40
0 tO0 200 300 z,~ 500 600 700 800 gO0 I000
lemperoture [ °C ]
Fig. 14. Abrasive wear of nickel, Ni SiC and Ni TiC coatings v s . the annealing temperature.
severe abrasive conditions. For the tests a Taber abraser was used. Figure 14 shows the weight loss per revolution in micrograms for Ni-SiC and
Ni -T iC after heat treatment at temperatures up to 1000 °C (annealing time, 2 h). For the pure nickel coating the wear (mild abrasive conditions) decreases slightly with increasing temperature.
The Ni-SiC composite coating shows little wear for temperatures up to 350 °C in comparison with the nickel coating at the same temperatures. For heat treatment temperatures above 350°C the weight loss rises to a maximum at 650°C; above 650 °C the wear decreases again.
The TiC-containing coatings (2'~o TiC) show the best results over the full range of temperatures. This is due to the better thermal stability of the TiC particles in the nickel matrix.
In Fig. 15 the wear behaviour of the chemically deposited N i -P and Ni -P -S iC coatings is shown for annealing temperatures up to 800 °C. The weight loss for the N i - P coating is relatively high for low annealing temperatures (200°C). Heat treatment above 300 °C improves the wear properties. A wear minimum was found at 650"C. The dispersion coating N i -P -S i C shows little wear at annealing temperatures up to 350 °C. Thermal treatment at high temperatures (400-800 °C) leads to a deterioration in the wear properties under mild abrasive conditions.
In Fig. 16 the wear properties of a nickel diamond composite coating are compared with the wear behaviour of a boride layer (Fe2B). Under mild and severe conditions the weight losses of the brittle boride layer are respectively 2 and 30 times that of the ductile nickel-diamond composite coating.
ELECTRO- AND CHEMODEPOSITED COMPOSITE COATINGS 141
"T\ b-...
_ cslox::~ ~ I,~ ~: "-
I I I I
~ 10
~ o 2O
i Ni- P - SiC ( 5 7*•, SiC) '°1 ~ /
0
] I
Ni-P
/ o
o
onneohng lime 2h I I I
r-I
~0 ~in£1inn time 2h ? , 0 ~00 200 300 400 500 600 70o ~00 goo ~000
temperature [ °C ]
Fig. 15. Abrasive wear of Ni P and N i -P SiC coatings v s . the annealing temperature.
250 25
200 :
~5o
100
50
I severe obroslon
/
/' - A~sp =0,2127 ?
/ /~msp "0'00727 m-~U
,__..~__~_-.-..-.~ 500 1000 rev
TABER-~SER
'r%, ' , ~ : ' . ~:, • j,~ ? ! l
i lOOpml |
oboridloyer (Fe28) 1650 HV 0,2
ZO
• I0
5Opm .,I
• chern nicke[composHe Coohng 5 ( dlomond porticles) @I0 RV 0,2
I mild obrosion
CS I ~
1
/ /
5000 10000 fev
Fig. 16. Mi ldand severeabras ivewearofachemica l lydepos i t edcoa t ingofn icke landd iamondpar t i c l es and of a boride layer•
142 E. BROSZEIT
5. SUMMARIZING REMARKS
Nickel dispersion coatings containing the dispersoid SiC have acceptable wear properties. Their application is limited, however, with respect to the maximum temperature. A major field of application is the cylinder bore and Wankel trochoid coating for combustion engines. For temperatures above 400°C TiC or A120 3 should be used as dispersoids.
Further results about the properties of dispersion coatings have been described in detail in refs. 6-14.
ACKNOWLEDGMENT
This work was supported by the Deutsche Forschungsgemeinschaft.
REFERENCES
l V.P. Greco and W. Baldauf, Plating (East Orange, N J), 55 (1968) 250. 2 P.K. Sinha, N. Dhananjayan and H. K. Chakrabarti, Plating (East Orange, N J), 60 (1973) 1, 55. 3 M. Viswanathan, Met. Finish., 73 (1975) 38. 4 E.C. Kedward, C. A. Addison and A. A. B. Tennett, IMF (Inst. Met. Finish.) Symp. Publ., 54
(1976) 8. 5 W.F. Sharp, Wear, 32 (1975) 315. 6 E. Broszeit, G. Heinke and H. Wiegand, Metall (Berlin), 25 (1971) 470 475. 7 E. Broszeit, G. HeinkeandH. Wiegand, Metall(Berlin),25(1971)lllO 1114. 8 E. Broszeit, F. J. Hess and E. Wagner, Wear, 30 (1974) 311-319. 9 E. Wagner, H. J. Schwalbe and E. Broszeit, Z. WerkstoJJ~ech., 8 (1977) 225-228.
10 K.H. Kloos, E. Wagner and E. Broszeit, Metalloberft6ehe, 32 (1978) 321-328; 384-388. 11 K.H. Kloos, E. Wagner and E. Broszeit, Z. WerkstofJ?ech., 9 (1978) 305-310. 12 E. Wagner and E. Broszeit, Schmiertech. Tribol., 26 (1979) 17 19. 13 E. Wagner and E. Broszeit, Wear, 55 (1979) 235-244. 14 K.H. Kloos, E. Wagner and E. Broszeit, Z. Werkstoff?ech., 11 (1980) 77 82.
