Improving hardness and tribological characteristics of nanocrystalline Cr–C films obtained from Cr(III) plating bath using pulsed electrodeposition

doi:10.1016/j.ijrmhm.2011.10.006

International Journal of Refractory Metals and Hard Materials

Volume 31, March 2012, Pages 281-283

$International Journal of Refractory Metals and Hard Materials$

https://doi.org/10.1016/j.ijrmhm.2011.10.006 Get rights and content

Abstract

Effect of pulsed electrodepostion on the nanocrystal size, composition, hardness, coefficient of friction and wear resistance was investigated for the Cr–C electrodeposits obtained from a trivalent chromium bath. The electrodeposits were shown to contain about 9% of carbon. Pulsed electrodeposition does not virtually affect the carbon content. At the same time, an increase in the off time duration leads to a decrease in the nanocrystals size. The hardness and wear parameters of the electrodeposits may be sufficiently improved when using pulsed current. For instance, at t_on = t_off = 1 s, the hardness reaches the values of ~ 1200 ÷ 1300 HV (meanwhile, it is close to 850 ÷ 950 HV at a steady-state electrolysis).

Highlights

►Cr–C electrodeposits obtained from a trivalent chromium bath under pulsed current. ►An increase in the off time duration results in a decrease in the nanocrystal size. ►Hardness and wear parameters may be sufficiently improved when using pulsed current.

Introduction

Hard chromium electroplating is widely used in modern industry for improving hardness, wear and corrosion resistance, decorative appearance of different tools and machines. Usually, chromium is deposited from solutions containing highly toxic compounds of Cr(VI). Because of the great toxicity and carcinogenicity, the Cr(VI) baths are now under pressure and numerous efforts have been made in order to develop eco-friendly processes based on Cr(III) compounds.

In recent years, a number of publications were devoted to Cr–C electrodeposition from Cr(III) baths [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. Such chromium–carbon coatings were shown to distinguish by their valuable physicochemical and mechanical properties. It was established in our works [12], [13] that the nanocrystalline Cr-C deposits may be obtained from sulfate trivalent chromium bath containing carbamide and formic acid. The hardness of these coatings does not differ substantially from the hardness of electrodeposits which are obtained in a Cr(VI)-based bath. Their wear characteristics are somewhat better than those obtained from the common Cr(VI)-bath. It is clear that further improvement of hardness and wear parameters of deposits under consideration is desirable.

Recently, the authors of study [14] showed that nanocrystalline Cr–C layers with excellent anti-wear performance can be prepared by electrodeposition in Cr(III) bath with subsequent annealing. However, annealing is a rather power-consuming procedure.

Improvement of different properties of Cr electrodeposits has also been reported using pulsed electrolysis [15], [16], [17], [18]. Therefore, the aim of the present work was to study effect of pulsed current deposition on hardness and wear characteristics of Cr–C coatings from Cr(III) bath containing carbamide and formic acid.

Section snippets

Material and methods

A sulfate trivalent chromium bath with the following composition was applied (mol L^− 1): 1 Cr(III), 0.5 HCOOH, 0.5 CO(NH₂)₂, 0.15 Al₂(SO₄)₃⋅ 18H₂O, 0.3 Na₂SO₄, 0.5 H₃BO₃ and 0.1 g L^− 1 of sodium dodecyl sulfate [12], [13]. Chromium was deposited at current densities of 30, 35, and 40 A dm^− 2; the temperature of the chromium bath was equal to 35 °C; the bath pH was 1.5.

Chromium electrodeposition was carried out both at a steady value of current density and at pulsed current with square wave in a usual

Results and discussion

It was stated that the electrodeposits obtained from the bath under study contain about 9% of carbon. Varying off time duration from 0 to 2 s (at a constant pulse duration time of 1 s) does not practically affect the carbon content at current densities of 30, 35 and 40 A dm^− 2. Thus, one can assert that using pulsed electrodeposition virtually has no effect on the composition of Cr–C deposits obtained from the plating chromium bath under study.

The radius of gyration in nanocrystalline structure (R₀

Conclusions

Thus, the application of pulsed electrolysis leads to the decrease in the nanocrystals size when Cr–C coatings are deposited from the trivalent chromium bath. The hardness and tribological parameters of the electrodeposits under consideration may be sufficiently improved when using pulsed current.

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Short communicationImproving hardness and tribological characteristics of nanocrystalline Cr–C films obtained from Cr(III) plating bath using pulsed electrodeposition

Abstract

Highlights

Introduction

Section snippets

Material and methods

Results and discussion

Conclusions

Surf CoatTechnol

Appl Surf Sci

Electrochim Acta

Surf CoatTechnol

J Alloys Compd

Surf CoatTechnol

Electrochim Acta

Thin Solid Films

Surf CoatTechnol

Electrochim Acta

Appl Surf Sci

Short communication
Improving hardness and tribological characteristics of nanocrystalline Cr–C films obtained from Cr(III) plating bath using pulsed electrodeposition