Studies of electrodeposited chroniumcobalt alloy coatings by emission Co-57 Mössbauer spectroscopy

Ekctrochimka Acts, Vol. 39, No. 6, pp. 801405. 1994 copyrights 1594elaeviuscimceLtd.

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STUDIES OF ELECTRODEPOSITED CHROMIUM-COBALT ALLOY COATINGS BY EMISSION Co-57 Mt)SSBAUER SPECTROSCOPY I. CZAK~-NAGY,*~ M. K. EL-SIURIF,~ A. V&TBS~ and C. U. CHISHOLMS t Department of Nuclear Chemistry, E&v& University, Budapest, Hungary $ School of Engineering, Glasgow Caledonian University, Glasgow, Scotland (Received 21 June 1993; in revisedform 13 September 1993)

Abstract-Deposit of chromium+obalt (Cr-Co) alloys have heen prepared by direct current (dc) electrodeposition from chromium(III)diiethylformamide based electrolyte. By changing two electrolysis parameters (current density and electrolyte temperature) alloys of various cobalt content were obtained. Miissbauer spectroscopy (MS) measurements revealed that cobalt rich deposits (up to 80 w/o) consisted of a single ferromagnetic phase, an alloy of about 44 w/o cobalt contained a mixture of ferromagnetic phase and the paramagnetic phase. Measurements indicated that alloys with high chromium content (7242 w/o) consisted of a single paramagnetic Co/Cr phase. Key words: electrodeposits, cobalt alloys, emission Mdssbauer spectroscopy, codeposition, elkct of plating parameters.

INTRODUCTION Cobalt alloy electrodeposition promises a new type of material with unusual mechanical properties, such as resistance to creep, high-temperature oxidation and sulphidation wear and galling[ 1,2]. Chromium-cobalt alloys (Cr-Co) have recently received considerable attention both in biomedical and metallurgical fields, because such alloys provide excellent strength, toughness, corrosion and wear resistance[3-61. The properties of Cr-Co alloys depend on the composition and the conditions employed for depositing them. Yukawa et a/.[71 prepared alloy particles of Cr-Co by evaporation in argon atmosphere. They reported that alloys with low cobalt content (37.9 w/o) contain the a-Cr (bee) and the &(A-15) phases. Three phases (a, 6, a) were observed in alloys with cobalt content in the range 37.9 and 46.1 w/o. At higher cobalt concentration (over 48.1 w/o) two phases (the 6 and e phases) were observed. Gelchinski er a[.[83 prepared Cr-Co alloy deposits by pulsed plating. By changing two parameters of the electrolysis (off-time and amplitude) alloys of various compositions were obtained. X-ray diffraction measurements revealed that chromium rich deposits (75 w/o) consisted of A-15 (&Cr) phase along with the bee (a-Cr) phase. The bee lattice parameter decreased with the increase of the cobalt content of the alloy. An alloy of about 33 w/o Co l

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contained the intermetallic phase together with bee and the A-15 phase. Due to the complex nature of the deposition process from aqueous electrolytes the same tlnal composition of alloy can give rise to varying phase compositions. Alloys prepared by thermal methods and even by alternative plating methods can exhibit varying phase equilibria for the same alloy composition. This is often associated with the way in which small amounts of other elements or compounds are deposited with the main metals and this can vary depending on the composition of electrolyte. The aim of the present work is to study the effect of direct current (dc) plating parameters such as current density, bath temperature and plating time on the phase structure of the resulting Cr-Co electrodeposits using Co-57 emission Miissbauer spectroscopy. Since Co-57 is the parent element of Fe-57, the best known Miissbauer active nucleus, thus the electrodeposited samples of Cr-Co alloy coatings were doped with radioactive Co-57 and employed as sources in absorption Fe-57 Mossbauer measurements. The spectra recorded are actually Fe-spectra, but they directly reflect the chemical and magnetic state of cobalt[9].

EXPERIMENTAL The electrolyte for electrodeposition of Cr-Co alloys was as follows: 0.05 M CoC1,6H,O; 0.8M 801

I. CZAKI~-NAGY et al.

802

[Cr(H,O),Cl,]Cl2H,O (green modification); 0.5 M NH&l; OSM NaCl; 0.15M B(OH),;5OOg N,N,dimethyl formamide and 5OOg deionised water. This electrolyte was developed by the authors. All solvents and reagents were of AnalaR grade. Before each deposition 0.1 mCi Co-57 in CoCl, was added to a 25 cm’ plating bath. Plating was carried out in a non-agitated electrolyte. When operating at high current densities, to keep the bath temperature constant, the electrolyte near the cathode was periodically agitated using an injection syringe tilled with fresh electrolyte. All plating experiments were conducted under galvanostatic control using Farenell constant current source L30-2. High conductivity AnalaR copper was used as the cathodes, the size of the working area exposed for deposition being 1.5 x 1.5cm’. The non-working area was insulated with a non-conducting lacquer. Insoluble high density graphite was employed as an anode (2 x 5cm2). The copper cathodes were prepared by degreasing in acetone, electropolishing at 9OOmV in a solution of 80% (v/v) phosphoric acid, 10% (v/v) water and 10% (v/v) methanol and finally rinsed with flowing deionised water and dried in air. The distance between the electrodes during the deposition was cc. 2 cm. Analysis of the deposits was carried out using the electron probe analysis unit on a Camscan electron microscope. The emission MGssbauer spectra were room temperature recorded at using a K,Fe(CN),2H,O absorber. Details of MS apparatus and data handling are summarized in [lo]. All the isomer shift data refer to u-iron. The errors of Miissbauer parameters are: rfr3 kOe in H, f 0.03 mm s-i in IS or AE and +5% in the area of the subspectra. The error associated with the measurement of the alloy composition was: +0.05%.

RESULTS (1) E&t

Table l(a). Composition of deposits prepared at various current densities

0.91 1.71 2.42 3.65 5.13

20.64 41.92 56.17 12.07 82.04 ._

79.36 58.08 43.83 21.93 17.96 --

I

ofcurrent density

Component 1

1.71 2.42 3.65 5.13

co

In Fig. l(a) the magnetically split spectrum with 320kOe hyperfine field and relatively narrow lines indicates the presence of a single ferromagnetic phase which can be interpreted as a solid solution of

4 0 v/mm s-l Fig. 1. Mijssbauer spectra of electrodeposits prepared at 25”C, for 5min with current density: (a) 0.97; (b) 1.71; (c) 2.42; (d) 3.65Admm2. -4

Table l(b). Results of Miissbauer analysis of Co-0

0.97

Cr

AND DISCUSSION

At constant temperature of 25°C and plating time of Smin the current density was varied from 0.97 to 5.13Adm-“. The compositions of the resulting deposits are shown in Table l(a). The emission Miissbauer spectra of the deposited samples are shown in Fig. l(a-d) and the results of the computer evaluation are summarised in Table l(b).

Current density Adm-s

Deposit composition (%)

Current density Adm-r

IS mms-’ 0.2 0.2 0.2

electrodeposits

Component 2

H l&e

r mms-*

Area %

IS mms-’

H kOe

r mms-’

320 310 310

0.4 0.8 0.8

100 100 19

0.2

276

1.3

Component 3 Area %

61

IS mms-’

0.3

AE mms-r

Imms-’

1.1 1.1 See Table 2 See Table 2

Area %

20

Electrodeposited chromium
-2

-1

1

0

2

v/mm s-l

Fig. 2. Miissbauer spectra of electrodeposits prepared at 25°C for Smin: (a) with 3.65Adm-‘; (b) with 5.13Adm-* current density. chromium in cobalt with a low chromium content. The pure metallic cobalt gives a hyperfine magnetic

field of cu. 337 kOe[ 1l] and increasing the chromium content decreases the value due to the chromium

803

alloy

substitution in the first or second co-ordination sphere of Co atoms[12, 133. The shape of the spectrum of Fig. l(b) is similar to that of Fig. l(a), but the line width (0.8 mm s-r) and the average hypertine field of 310kOe suggest that the spectrum can be considered as a superposition of more than one sixline subspectra, representing more different cobalt environments. It is worth noting that the line intensity ratios of both spectra differ from the 3:2:1 ratio characteristic of a random distribution of magnetization directions[14]. The increase of the intensities of the second and fifth lines indicates that the atomic magnetic moments are oriented parallel to the sample plane which is not surprising with thin layers. The spectrum in Fig. l(c) was decomposed for two sextets with average hyperfine fields of 310 and 276 kOe as well as a quadrupole doublet. The 276 kOe hyperfine field corresponds to a relatively high chromium concentration. The appearance of the quadrupole doublet indicates the formation of a paramagnetic Co/Cr phase which contains even more chromium than that of the ferromagnetic one. At high current densities, only the paramagnetic phase appeared as can be seen from Fig. l(d). The spectra of these deposits were recorded at a lower velocity to give further insight into the nature of the paramagnetic phase and are shown in Fig. 2. The Mossbauer parameters are summarised in Table 2. The two spectra could be well fitted with two doublets (QD) and one singlet. It is interesting that the parameters given in Table 2 are in a close agreement with those recently reported by Gupta et aI.[15] for a thermally prepared Fe/Cr a-phase. It can be assumed that the same paramagnetic phase is present in the electrodeposit prepared at 2.42Adme2 current density although its spectrum was not decomposed for doublets and singlets due to the weak statistics. (2) Efict

of temperature

To investigate

-4

4

0

v/mm s-l Fig. 3. Mijssbauer spectra of deposits electroplated for Smin with 3.65Adm-’ current density at: (a) 30°C; (b) 40°C.

the effect of temperature on the phase composition of the electrodeposited Cr-Co alloy coatings, the current density and the plating time were kept constant at 3.65 A dme2 and 5min, respectively. Figure 3 summarises the experimental results, and Table 3 illustrates the data from the computer evaluation. While at 25°C the single paramagnetic phase was formed, at 30°C ferromagnetic and paramagnetic phases were obtained together. At 40°C the quantity of the paramagnetic component decreased significantly. The electrodeposition was carried out at 25X, 3.65 A dm-’ and plating times of 5, 10 and 20min,

Table 2. Mossbauer parameters of the paramagnetic phase Current density Adme 3.65 5.13

QD,

Qb

IS mms-’

AE mms-*

Imms-’

0.26 0.36

0.94 0.86

0.49 0.49

Area % 17 22

Singlet

IS mms-’

AE mms-’

Imms-’

Area %

IS mm s-i

Imms-’

0.05 0.06

0.13 0.23

0.36 0.36

19 24

0.40 0.39

0.72 0.70

Area % 64 54

Cr

72.01 68.07 33.36

Temperature “C

25 30 40

21.93 31.93 66.64

co

Deposit composition (%)

0.2 0.2

IS mms-’ 306 310

H kOe 0.6 0.8

lmms-’

Component 1

20 100

Area % 0.2

IS mms-’

lnuns-’

See Table 2 271 1.3

H kOe

Component 2

55

Area %

0.2

IlUlls-

IS

Table 3. The effect of temperature on the deposit composition and the MGssbauer parameters

1.1

lllllls-’

AE

I-

1.2

IMI-’

Component 3

25

%

Area

P

Electrodeposited chromium-cobalt alloy respectively. The average compositions of the electrodeposited samples were all the same, as shown in Table l(a), the deposit thicknesses were: 0.41, 0.75 and l.Xpm, respectively. The spectra did not change with the plating time, the same quadrupole doublet showed up in the spectra of the deposits. CONCLUSIONS

The experimental results show that a strong correlation can be made between the applied current density and the phase composition of the electrodeposits. At low current density a high cobalt content was found and in this case the Miissbauer analysis showed the formation of a ferromagnetic Co/Cr alloy. With increasing current density the cobalt content decreased and in parallel a paramagnetic Co/Cr phase appeared with the ferromagnetic phase. At 3.65Adm-’ and above, where high chromium contents were obtained the Co-alloy exhibited the paramagnetic Co/Cr phase. A similar trend was obtained with varying plating temperature. The higher the temperature the higher the cobalt content of the electrodeposit. At 25°C the paramagnetic Co/Cr phase was found while at 30°C this one together with the solid solutions of chromium in cobalt with various cobalt environments and at 40°C only the latter phase with low chromium substitution was observed. Since deposition time did not affect the deposit composition significantly, it is not surprising that the MGssbauer spectra indicated the presence of the same Co/Cr phase, namely the paramagnetic phase, in agreement with the actual composition.

805 REFERENCES

1. M. E. Browning and E. W. Turns, ASTM Spec. Tech., Publ. No. 318, 107-121 (1962). 2. C. U. Chisholm, Electrodep. and Su$ce Treatment 3, 321 (1975). 3. J. B. Vandersands, J. R. Coke and J. Wulff, Metal. Trans. 7A-389 (1976). 4. H. S. Dobbs and J. L. M. Robertson, J. Mater. Sci. 18, 391(1983). 5. S. D. Cook, A. M. Weinstein, T. A. Sander and J. J. Klawitter, Biomater. Med. Deu. Art$ Organs 10, 123 (1982). 6. E. Angeline and F. Zucchi, J. Mater., Sci. Mater Med. 2,27 (1991). 7. N. Yukawa, M. Hida, T. Imura, M. Kawamura and Y. Mizuno, Metal. Trans. 3,887 (1972). 8. M. H. Gelchinski, L. Gal-Or and J. Yahalom, J. electrochem. Sot. Electrochemical Science and Technology, 129, (1 I) 2433 (1982). 9. G. W. Simmons, H. Leidheiser Jr., Application of Miissbauer Spectroscopy, Vol. 1, pp. 85-129, Academic Press, New York (1976). 10. A. Vtrtes and I. Czakb-Nagy, Electrochim.Acta 34,721 (1989). Il. A. V&es, I. Czakb-Nagy, P. Deck and H. Leidheiser Jr., J. electrochem. Sot. 134, 1628 (1987). 12. C. E. Johnson, M. S. Ridout and T. E. Cranshaw, Proc. of Phvs. Sot. 81. 1079 (1963). 13. i. k. Dubiel .and i. ZGkrowski, J. Magn. Magn. Material lS-18,655 (1980). 14. L. TakLs, A. V&tes and H. Leidheiser Jr., Phys. Stat. Sol. (a) 74, K45 (1982). 15. A. Gupta, G. Principi and G. M. Paolucci, Hype&e Interactions 54,805 (1990).