Effect of Process Parameters on Electrodeposited Nanocrystalline Chromium Coatings Investigated by an Orthogonal Experim
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ANOSCALE AND NANOSTRUCTURED MATERIALS AND COATINGS
Effect of Process Parameters on Electrodeposited Nanocrystalline Chromium Coatings Investigated by an Orthogonal Experiment Xinyue Wanga, Jihui Wanga, Zhiming Gaoa, *, Da-Hai Xiaa, and Wenbin Hua, b, ** a Tianjin Key Laboratory of Composite and Functional Materials, School of Materials Science and Engineering, Tianjin University, Tianjin, 300072 China bKey Laboratory of Advanced Ceramics and Machining Technology (Ministry of Education), Tianjin University, Tianjin, 300072 China *e-mail: [email protected] **e-mail: [email protected]
Received August 16, 2019; revised September 13, 2019; accepted March 15, 2020
Abstract—The microporous nanocrystalline chromium coatings were prepared on the H13 steel by electroplating in self-regulating baths. The effects of electroplating parameters including current density, compositions of baths, bath temperature and plating time on the surface quality, thickness of chromium coating and cathode current efficiency were investigated by an orthogonal experiment. Experimental results indicated that the surface quality, thickness of chromium coating and cathode current efficiency can be improved by adjusting these electroplating parameters. Furthermore, bath temperature has the greatest effect on the surface quality of chromium coating, and the high qualified surfaces were only obtained at higher temperatures of 55 and 65°C. Current density was the most significant factor for the thickness of coating and cathode current efficiency. Chromium coating with high surface quality, thickness and cathode current efficiency was obtained at current density 90 A/dm2, CrO3 250 g/L, K2SiF6 10 g/L, SrSO4 1 g/L, bath temperature 65°C and plating time 120 min, which is consisting of pure nanocrystalline chromium with a body-centered cubic structure. And the coating exhibits much higher microhardness and corrosion resistance than for H13 steel. Keywords: nanocrystalline chromium coating, electroplating, process optimization, microstructure, properties DOI: 10.1134/S2070205120040267
1. INTRODUCTION Chromium electroplating have been widely used in manufacturing industry of parts due to its special properties, such as the decorative appearance, high hardness, superior wear and corrosion resistance [1– 6]. However, the extreme hydrogen evolution occurred on the cathode surface resulted in the material embrittlement, decreasing the fatigue life under the loading condition [7, 8]. On the other hand, a chromic acid (CrO3) contained in plating bath was non friendly and was adverse to the environment because of the toxicity of hexavalent chromium [9, 10]. Nevertheless, the great properties of chromium coatings required by the industry can not be met by other materials. So the replacement of this process will be a lengthy evolution [11, 12]. Traditional chromium plating bath using sulfuric acid (H2SO4) as catalysts has been intensively applied in chromium plating industry. Its cathode current efficiency is only 6 ~ 16%, resulting in the increase of production
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