[19] Electrocodeposition and Characterization of Nickel_titanium Carbide Composite

7/28/2019 [19] Electrocodeposition and Characterization of Nickel_titanium Carbide Composite

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SurJace and Coatings Technology, 67 (1994) 105-l 10 105

Electrocodeposition and characterization of nickel-titaniumcarbide compositesG. N. K. Ramesh BapuCentral Electroche mical Research institute, Karaikudi 623 006, Tamilnad u (India)(Received December 10,1993; accepted in final form January 30,1994)

AbstractDispersion-strengthened nickel was produced by an electrocodeposition technique using a nickel fluoborate suspension. The eff ectsof particle concentration in the bath. Furrent dens ity, pH and temperature on volume percentage incorporation ofTiC particles in thecomposite were studied. The hardness, wear resistance and oxidation behaviour of the composite in the as-plated and annealed statewere also examined and compared with those of nickel deposits. It was found that the volume percentage incorporation of TICparticles in the composite increased with increasing TIC content in the bath and with increasing current density. An optimum TICincorporation (13 vol.%) was possible by operating the bath containing 30 g I- of TiC particles in suspension at 5.0 A dm-*, atpH 3.0 and at 50C. The hardness and wear resistance of the composite were found to be more than twice those of the electrodepositednickel. The results of oxidation studies reveal that the composite oxidizes at a faster rate than nickel deposits and showed poorresistance to oxidation in tbe temperature range investigated.

1. IntroductionComposite materials can be defined as materials con-sisting of two constituents: the matrix and the distributedphase. It is well known that particle-dispersed metalcomposites can be produced by electroplating from asolution containing a suspension of chemically inertparticles [ 11. The presence o f fine dispersions of oxide,carbide, boride, sulphide, polymer etc. in a metal matrixgenerally leads to improved mechanical and chemical

properties resulting in a wide range of possible applica-tions. Electrodeposited nickel composites have beenproduced using sulphate- or sulphamate-based nickelbaths [Z] but there is no indication of the use offluoborate bath for production, although such baths arewell known for applications in electroforming andelectrotyping. In view of the high solubility of fluoboratesalts, the consequent possibility of high current densityoperation and other economic factors, an attempt wasmade to prepare and characterize electrodeposited nick-el-titanium dioxide [ 31, nickel-zirconium dioxide [4]and nickel-vanadium pentoxide [ 51 composites usingnickel fluoborate bath.More recently, nickel-based composites, particularlythose containing hard ceramic particles are receivingattention as possible wear-resistant coatings for hightemperature applications. Nickel composites containingTiC particles have been developed as hard facing forsteel mill rolls and as coatings for injection moulds [ 61.Most of the reports on electrodeposited Ni-TiC compos-ites are patented and operating details are not available.Hence in this investigation a detailed and systematicapproach is being made to study the effect of electro-chemical parameters of codeposition of TiC with nickel

on the volume percentage incorporation using a nickelfluoborate bath. The hardness and wear resistance ofthe composites were characterized in the as-plated andannealed state. The effect of dispersed TiC particleson the oxidation characteristics of nickel were aIsoinvestigated.2. Experimental details2.1. Electrocodeposition of Ni-TiC composites

The electrocodeposition of nickel was performed in asolution consisting of 280 g l- of nickel fluoborate,5 g 1-l of free fluoboric acid, 40 g 1-l of boric acid and0.1 g l- of sodium lauryl sulphate. The experimentalset-up has been described elsewhere [7]. By means of amechanically controlled glass stirrer, the TiC particlesof average size 6.5kO.5 pm were thoroughly stirred inthe above plating bath for 8 h and a uniform suspensionwa s obtained. In order to prevent agglomeration but toobtain uniform dispersion of particles in the bath, therequired amount of particles was first blended in amortar with a small amount of electrolyte and the slurrywa s transferred to the main electrolyte.The codeposition was carried out in a 1 1glass beaker.As anodes, two nickel pieces 5 mm thick were used.Stainless steel specimens 7.5 x 5.0 x 1.0 cm3 served ascathodes from which the coatings could be easilystripped of f for analysis. The extent of TIC incorpora-tions in nickel was studied with respect to particleconcentrations ranging from 5.0 to 50 g l-l, currentdensity ranging from 2.0 to 10.0 A dm-, bath pH from1.0 to 5.0 and a bath temperature range of 30-70C.The plating was carried out for a duration of 2 h in eachrun and the resultant deposit was analysed to determine


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106 G. N. K. Ramesh Bapu 1 Electrocodeposition and characterization of Ni-TiCthe volume percentage incorporation of TiC in thecomposite as follows.The plated stainless steel samples were weighed (W,)with an accuracy of 0.1 mg and then stripped in 50 mlof 20% warm nitric acid. The resulting solutions weremade up to 100 ml in standard volumetric flasks. Afterstripping of f the deposits, the stainless steel substrateswere again weighed (W,). The difference W, - W, gavethe mass of the composite deposits. The nickel contentsof the composites were determined by analysing thesolutions using atomic absorption spectrometry with ahigh degree of accuracy. The TiC contents of the compos-ites could thus be deduced from the differences betweenthe values of the mass of each composite and the nickeltherein. The volume percentage contents of TIC wereevaluated as follows:the volume of nickel in the composite is

mass of Niv, = density of Nithe volume of TIC in the composite is

mass of TiCv, = density of TiCthe total volume isv=v,+v,and the volume percentage content of TiC is 100 V,/V.2.2. Characterization of Ni-TiC composites2.2.1. Microhardness

The Vickers microhardness of the as-plated compos-ites and composites vacuum annealed at 200-800Cfor 1 h was determined by an indentation technique at50 gf load with a diamond pyramid indentor. Hardnesswas calculated using the relationVickers hardness (kgf mm-) = 1854 x load (gf)d2where d is the indentation diagonal.

2.2.2. Wear resistanceThe abrasion wear resistance of the as-plated compos-ites and composites vacuum annealed at 200-800 C for1 h was determined with a Taber abraser using a CS-10calibrase wheel at 1000 gf load. The test sample(10 x 10 x 0.1 cm3) was weighed before and after abrasionfollowing each cycle consisting of 1000 revolutions andthe Taber wear index (TWI) which is the weight loss inmilligrams per cycle of abrasion was calculated.

2.2.3. Oxidation characteristicsA thermogravimetric technique was employed to studythe oxidation behaviour of electroformed nickel andNi-TiC (12.9 vol.%) composite 150 pm thick. Theweighed sample was kept in the reaction tube and

oxidized in an electric furnace at 600-900 C. After a2-8 h oxidation, the specimen was gradually removedfrom the hot zone of the furnace, cooled in a desiccatorand weighed. The weight gain was determined at varioustemperatures to give information on the oxidationcharacteristics.2.2.4. Structure of the depositsThe structure and distribution of TiC particles in thecomposite were examined using scanning electron micro-scopy. X-ray diffraction of the oxidized specimen was

also used to explore the possible structural changesduring oxidation.3. Results and discussion3.1. Effects of TiC concentration in suspension nd ofcurrent density on the volume percentage TiC content incompositeThe extents of TiC incorporation obtained at 5-50 g1-l of TIC particles in suspension over the 2-6 A dmm2current density range are shown in Fig. 1. Irrespectiveof the operating current density, the particle incorpora-tion increases sharply and attains an optimum value at30 g 1-l TiC in suspension. It was found that withfurther additions, the particles appeared to agglomeratein the bath and a decreasing trend was observed. Thedecreasing trend beyond this limit may be due to thestirring being insufficient to maintain all the TiC particles

13 -

; -e8 9w,I 7-zuf 5-0G

3tI I I I I I10 20 30 40 50TiC CONCENTRATIONN THE BATH g/l

Fig. 1. Effect of TiC concentration in the bath on the volume percen-tage incorporation at different current densities (pH, 3.0; temperature,50C): 0, 3 A dm-; n , 4A dm-; 0, 5 A dm-; 0,6 A dme2.


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(b)

G. N. K. Rarmh Baptr 1 Electrocodepositiou and characterization of Ni-TiC 107

(4Fig. 1. Scanning electron micrographs of the Ni-TiC comp osites with T iC concen trations of (a) 5 g I-, (b) 15 g I-, (c) 30 g I- and (d) 40 g I-.

in suspension and to the greater degree of agglomeration the nickel ions adsorbed on TIC particles and thein the bath [S]. cathode surface.The topography of the composites with varying TICincorporation is shown in Fig. 2. At 6.6 vol.% TIC (5 g1-l) the surface exhibited voids with a random distribu-tion of particles (Fig. 2(a)). With further TIC incorpora-tion (Figs. 2(b) and 2(c)) the surface coverage tended tobe uniform and the brightness on the periphery of theparticles increased. The agglomerated deposit wasrevealed clearly at 40 g 1-l of TIC suspension (Fig. 2(d))where the stirring is insufficient to maintain the suspen-sion, as noticed during codeposition.

3.2. EfSects qf pH and tenzperature on volume percentageTic content qfcompositeThe influence of pH on TIC incorporation is shownin Fig. 3. A smooth, uniform and semibright deposit

Over the range of TIC inclusions, maximum incorpo-ration could be seen at 5 A dm-, above which theextent of codeposition decreased. This trend is inconsis-tent with other types of metal-particle composites [ 3-5,91 where the metal is being deposited under conditionsof charge transfer overvoltage control. Above 5.0 Admm2, as the reduction of nickel ions is controlled byconcentration overpotential, the amount of codepositedTIC particles gradually decreased. As reported earlieron codeposition of alumina with the copper [lo], thedependence of codeposition on charge transfer overpo-tential control indicates that the rate of codeposition isdetermined by the formation of a real contact between

I 2 3 4 5PH

Fig. 3. Effect of pH on the incorporation of TiC (Tic concentration,30 g I-; current density, 5 A dm-l; temperature, 50C.


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108 G. N. K. Ranlesh Bapu / Electrocodeposition artd characterization 01 Ni-TiCcontaining 12.9 vol.% TIC was obtained at pH 3.0 for a The hardness of the annealed deposits was found toTiC suspension of 30 g 1-l in the bath at 5.0 A dm- be less and decreased considerably with increasingand 50C. Increasing the pH from 1.0 to 5.0 slightly annealing temperature compared with deposits in thelowered the volume percentage TIC incorporation. as-plated state. However, even in the annealed state theBelow pH 3.0 a dark grey deposit was obtained and composites retained more than 60% hardness comparedabove pH 4.0 a brittle deposit was obtained. The observed with the nickel deposit. During annealing, the disperseddecrease in TIC content may be due to a decrease in the particles were not able to diffuse in the deposit and theyefficiency of nickel deposition and an increase in the remained in positions taken during crystallization tillviscosity of the solution [S]. The decrease in efficiency the annealing temperature attained the temperature ofwas found to alter the rate of nickel deposition with a decomposition. Hence the composites retained moreconsequent decrease in the incorporation of Tic. hardness than nickel.It was found that the temperature of the plating bathmarkedly influenced the extent of codeposition (Fig. 4).TIC incorporation increased from 10.0 to 14.7 vol.%when the temperature was increased from 30 to 70C.A semibright deposit is obtained at 50C and temper-atures above this result in a burnt dark grey deposit.

3.4. Wear resistance

3.3. MicrohardnessWith incorporation of TIC, the hardness of the com-posite is increased to about 1.6-2.6 times more thanthat of the electrodeposited nickel (Table 1). Duringhardness measurements, the dispersed particles in thematrix may obstruct the easy movement of dislocationsand resist the plastic flow. This resistance to deformationis shown by an increased hardness value for Ni-TiCcomposite in the as-plated condition.

In the as-plated as well as the annealed condition,incorporation of TiC was found to improve significantlythe wear resistance o f nickel coatings (Table 2). Fornickel deposits, the principal mechanism of materialremoval by the abrasive particles was ploughing toproduce grooves [ 111. Because of the greater load-bearing capacity of the Ni-TiC composite, the abrasionon the composite was less than that seen on the nickelsurface. This can be seen more clearly in scanningelectron microscopy photography of wear tracks onnickel (Fig. 5(a)) and Ni-TiC surfaces (Fig. 5(b)).Extensive ploughing was observed in the ductile nickelwith the ridges formed between intersecting groovesbeing sheared off as wear proceeds. In the presence ofTIC particles, the contacts tend to become more elasticwith a resulting reduction in material loss.There was no significant change in wear index of the

I I I 1 130 40 50 60 70

TEMPERATURE (ClFig. 4. Effect of temperature on the incorporation of TIC (Tic concen-tration, 30 g 1-r; current densi ty, 5 A dm-*; pH, 3.0).TABLE 1. Microhardness of nickel and Ni-TiC compositesDeposit Hardness (VHN,,)

As plated 200C 400C 600C 800CNickel 195 185 150 110 65Ni-6.6vol.%TiC 315 300 280 235 210Ni-9.3vol.%TiC 460 440 410 330 280Ni-12.9vol.%TiC 530 485 465 390 330Annealing temperature.

TABLE 2. TWI of nickel and Ni-TiC compositesDeposit TWI

As platedNickel 28.2Ni-J.lvol.%TiC 8.4Ni-12.9vol.%TiC 6.8Annealing temperature.

200C 400C 600C 800C24.4 21.2 17.0 14.07.3 6.5 6.3 6.35.9 5.4 5.0 5.0

TABLE 3. Weight gain of nickel and Ni-TiC composites at differentoxidation temperaturesSpecimen Oxidation Weight gain (mg cm-*)temperature (C) 2h 4h 6h 8hNickel 600 0.19 0.23 0.25 0.28

800 0.70 1.20 1.58 1.84900 2.70 3.28 3.69 3.91Ni-12.9vol.%TiC 600 0.23 0.28 0.31 0.35800 1.16 1.67 2.15 2.36900 2.59 3.50 4.22 4.95

Time of oxidation.


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Fig . 5. Scanning electron micrograph of abraded surfaces after 3000 revolutions: (a) nick& (b) Ni 12.9vo l.!~. TiC

26

22

16

\fk IL"r-4; ICnc-4

z Ea"2 2Pg- 0.1 2

O.Of

O.Of

a-a NiCKELm-m Ni-TiC (12.9 VOL%)

7 7 I I120 240 360 LEO

JTIME, t ( min )

Fig. 6. Parabolic plots for oxidation of nickel (0) and Ni-TiC compos-ite (B) in different temperature ranges.

composite on annealing at 600-800 C. The outstandingwear resistance of this material in the annealed statemay be due to its ability to form a glaze-like materialwhich prevents metal-metal contact [ 121. Incorporationof TIC may promote the mechanism of glaze-oxideformation and possibly improves the load-bearing char-acteristics of the oxide by reinforcing the matrix.

The Ni-TiC composite used in the oxidation studycontained 12.9 vol.% TIC. In Table 3 are given theweight gain values for nickel and Ni-TiC compositesoxidized in air at 600-900C. The weight gain due tothermal oxidation can be related directly to the quantityof metal being oxidized under given conditions andhence can be taken as a measure of resistance to oxida-tion [ 131. In the investigated temperature range, it wasfound that the weight gain values were always higherfor Ni-TiC composites than for electrodeposited nickel.This result is in accord with that of Wagners theory[ 141 in that the substitution of TiJ+ ions in NiO wouldincrease the number of vacancies in the scale and activatethe adsorption of oxygen on the NiO film. In the presentcase, the occluded TIC particles would have increasedthe diffusion rate of Ni+ ions in NiO, thereby favouringthe oxidation of composites to a greater extent.

Plots of the square of weight gain US. time for theoxidation of Ni-TiC and nickel are shown in Fig. 6.

Fig . 7. Scanning electron micrographs of Ni-TiC composite oxidizedat 800 C.


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110 G. N. K. Ramesh Bapu f Electrocodep osition and characterization of Ni-TiC

6L 70 60 50-29

Fig. 8. X-ray diff raction pattern of Ni-TiC composite oxidized at 800 C.

LO 30

Adherence to a straight line in such a plot suggestedthat the systems were found to approximate the para-bolic rate law and the kinetics of oxidation was governedby a diffusion process [ 143.At the oxidation temperature (800 C) the incorpo-rated TiC particles were found to undergo partial dis-solution, forming N&C phase and internal oxides withtitanium. This internal oxide formation might havecaused the observed increase in weight gain in the caseof composites during oxidation (Table 3). Surface exami-nation of the composite at 800C clearly revealed thecracked pattern indicating the possible breakdown ofcarbide particles and formation of needle-shaped crystal-lites consisting of internal oxides of titanium (Fig. 7).Additional evidence of the formation of N&C phase at800 C can be seen in the X-ray diffractogram (Fig. 8)of the oxidized Ni-TiC composite.4. Conclusions

Ni-TiC (12.9 vol.%) composite can be obtained fromthe fluoborate bath containing 30 g 1-l particles insuspension at pH 3, temperature 50 C and operatingthe bath at 5 A dm-. The hardness and wear resistanceof the composite were found to be more than twice thoseof the electrodeposited nickel. The composite oxidized

at a faster rate than electrodeposited nickel and showedpoor resistance to oxidation in the temperature rangeinvestigated.

References1 F. K. Sautter, J. Electrochem. Sot., 1 IO (1963) 557.2 J. P. Celis and J. R. Roos, Rev. Coat. Corros., 5 (1982) l-4.3 G. N. K. Ramesh Bapu and K. I . Vasu, Bull. Electrochem, 5

(1989) 435.4 G. N. K. Ramesh Bapu and K. I . Vasu, Bull. Electrochem., 6(1990) 37.

5 G. N. K. Ramesh Bapu and M. Mohammed Yusuf, Mater. Chem.Phys., 36 (1993) 134.

6 E. C. Kedward, K. W. Wright and A. A. B. Tennett, Tribol. Ink, 7(1974) 221.7 G. N. K. Ramesh Bapu, V. S. Muralidharan and K. I. Vasu, P/at.Surf. Finish., 78 (1991) 126.8 V. 0. Nwoko and L. L. Shreir, J. Appl. Electrochem, 3 (1973) 137.

9 J. P. Celis and J. R. Roos, J. Electrochem. Sot., 124 (1977) 1508.10 J. P. Celis, Ph.D. Thesis, Catholic University of Leuven, 1976.11 D. S. Rickerby and P. J. Burnett, Sur$ Coat. Technol., 33 (1987) 191.12 B. P. Cameron, J. Foster and J. A. Carew, Trans. Inst. Met. Finish.,

57 (1979) 113.13 P. K. Sinha, H. Dhananjayan and H. K. Chakrabarthi, Plating, 60(1973) 55.14 K. Hauffe (ed.), Oxidation of Metals, Plenum, New York, 1965.

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[19] Electrocodeposition and Characterization of Nickel_titanium Carbide Composite