Effect of the Current Density on Morphology, Porosity, and Tribological Properties of Electrodeposited Nickel on Copper Vanessa F.C. Lins, Erik S. Cecconello, and Tulio Matencio (Submitted July 4, 2007; in revised form January 11, 2008) In the steel industry, nickel coating on copper has increased the lifespan of continuous ingot casting molds. The objective of this work is to estimate the porosity of nanocrystalline nickel electrodeposited onto copper. Characteristics of nickel coating such as hardness, wear resistance, porosity, morphology, and adhesion are very important for maximum performance of molds. The effective porosity in nickel coating was deter- mined by using anodic voltammetry. The porosity of electrodeposited nickel onto copper increased from 0.16% up to 6.22% as the current density increased from 1.5 up to 8.0 A dm -2 . The morphology of the nickel electrodeposited at lower current densities was more compact. Tribological properties were studied using hardness measurements, and calotest. Results of calotest indicated a wear coefficient of 10 -6 for all samples. An extremely low friction coefficient of 0.06-0.08 was obtained for the sample deposited with a current density of 1.5 A dm -2 , and a friction coefficient of 0.15-0.21 was measured for the nickel coating electrodeposited at a current density of 5 A dm -2 . Effects of the current density of the electrodeposition process on the morphology, porosity, and tribological properties were evaluated. Keywords electroplating, nanocrystalline nickel, porosity, wear 1. Introduction Hard coatings with potential wear resistance are capable of improving the tribological performance and lifespan of com- ponents (Ref 1). One needs to consider the great difference between the substrate hardness and the coating hardness, which may generate localized failure and loss of adhesion. Thermal treatment used after the coating deposition process optimizes the coupling of materials with different hardness values. Electroplating is one of the most economic methods for the application of metallic coating onto an endless list of engi- neering components. Electroplated coatings are employed in industry to improve the appearance of surfaces, to protect substrates from corrosion, and to provide good electrical and thermal contact (Ref 2). Electroless nickel coatings show good tribological properties due to their high levels of hardness, which can be increased through thermal treatment (Ref 3). In the steel industry, nickel coating on copper has increased the lifespan of continuous ingot casting molds. Electrodepos- ited nickel increases resistance to friction and abrasive wear between on steel and copper used in the molds. Nanocrystalline electrodeposited nickel with a grain size of 10-20 nm showed 100-170 times higher wear resistance and 45-50% lower friction coefficient than polycrystalline nickel with 10-100 lm grain size in the pin-on-disk test (Ref 4). Characteristics of nickel coating such as hardness, wear resistance, porosity, morphology, and adhesion are very important for maximum performance of molds. For many engineering applications, wear resistance is one of the most important mechanical properties because wear accounts for more than 50% loss of all materials in service (Ref 5). Correlations between electrodeposition parameters and prop- erties of coatings can be evaluated. Krishnaveni et al. (Ref 6) reported a strong correlation between the current density and the crystallographic texture of the electrodeposited nickel. Research into tribological behavior of the electrodeposited nanocrystalline nickel has been undertaken (Ref 6-9), but in these studies, the effect of porosity on morphology, hardness, and tribological properties has not been taken into consider- ation. The importance of this work is to apply an electrochem- ical technique to evaluate porosity of electrodeposited nickel and to correlate the results of the material resistance to wear. The tribological properties of the electrodeposited nickel are fundamental for industrial applications, and porosity of the electrodeposits affects this wear behavior significantly. The objective of this work is to evaluate the porosity of the electrodeposited nanocrystalline nickel on copper by means of five different current densities. The porosity measurements were carried out using voltammetric anodic dissolution. The morphol- ogy of the electrodeposited nickel was also evaluated using scanning electron microscopy. Tribological properties were stud- ied using hardness measurements, and the calotest. Results of porosity, grain size, hardness, and wear properties of the electro- deposited nanocrystalline nickel were discussed and compared. Vanessa F.C. Lins, Corrosion and Surface Engineering Laboratory, Chemical Engineering Department, Federal University of Minas Gerais, 35 Espirito Santo Street, 30160-030 Belo Horizonte, Brazil; Erik S. Cecconello, Companhia Vale do Rio Doce, Rio De Janeiro, Brazil; and Tulio Matencio, Chemical Department, Federal University of Minas Gerais, 6627 Antonio Carlos Avenue, Belo Horizonte 31270-901, Brazil. Contact e-mail: vanessa.lins@terra. com.br. JMEPEG (2008) 17:741–745 ÓASM International DOI: 10.1007/s11665-008-9205-9 1059-9495/$19.00 Journal of Materials Engineering and Performance Volume 17(5) October 2008—741