Improvement of Surface Characteristics by Electroplating Hard Chromium Coating Post Treated by Nanocrystalline Plasma Electrolytic Carbonitriding Seyed Haman Hedayat Mofidi, Mahmood Aliofkhazraei, * Alireza Sabour Rouhaghdam, Ehsan Ghobadi, Ehsan Mohsenian Introduction One of the disadvantages of hard chromium coating [1] with respect to other method of coatings is represented by microcracks that cannot be avoided in the industrial electroplating processes. Microcracks can have a severely adverse effect on the corrosion resistance and tribological behaviors of the tools. A duplex treatment is used in order to resolve this problem. The proposed treatment is a combination of conventional electroplating of chromium and pulsed plasma electrolytic carbonitriding. [2,3] This treatment is based on atmospheric pressure plasmas which are relatively new in plasma technology and have been used successfully for application such as low alloy ferrous materials. [4–6] The characteristics of this treatment such as atmospheric pressure and its rapidity make it suitable for mass treatment of complex shaped tools in the industry. [7,8] Furthermore, this technology can be per- formed in order to clean the inner and outer surfaces that are not easily reached. [7] In this research, duplex treatment is applied on the AISI 1035 steel. Experimental Part Coin like samples with 20 mm diameter and 5 mm thickness were made from AISI 1035 steel and then submitted to chemical cleaning and hard chromium electroplating. The bath contained 300 g  L 1 chromium oxide(VI) and relative catalyst. The current density of bath was 40 A  dm 2 and the temperature of the bath was set on 60 8C. These samples were connected to the negative output of a pulsed power supply. The average thickness of the coating was 75 mm. The anode was a stainless steel container which filled with an organic based solution. Its exposed area was Full Paper S. H. H. Mofidi, M. Aliofkhazraei, A. S. Rouhaghdam Department of Materials Engineering, Faculty of Engineering, Tarbiat Modares University, P.O. Box: 14115-143, Tehran, Iran E-mail: maliofkh@gmail.com E. Ghobadi Department of Polymer Engineering/Polymer Physics, Technical University of Berlin, Fasanenstraße 90, D-10623 Berlin, Germany E. Mohsenian University of Potsdam, Potsdam, Germany Nanocrystalline carbonitrides were performed by pulsed plasma electrolytic carbonitriding on hard chromium coating deposited on AISI 1035 substrate by electroplating. The electroplated samples were connected cathodically to a high-current pulsed power supply and biased to a negative voltage. The treatment times were 30, 60 and 60 min. A thick compound layer was formed on the surface of Cr coating with microhardness of about 1 200 HV 0.15 . The nano- structure of the treated layers depends strongly on the applied voltage. The wear resistance of the treated layers depended on process parameters. Overall mechanical properties of treated samples show strong relation to morphology and distribution of complex carbonitride nanocrystallites. Plasma Process. Polym. 2009, 6, S297–S301 ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/ppap.200930702 S297