Preparation, Characterization and Mechanical Properties of Cu-Sn Alloy/Graphite Composites
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I.
INTRODUCTION
II.
MATERIALS AND METHODS
THE Cu/graphite composites are promising sliding friction and electrical sliding materials owing to their good thermal and electrical conductivity.[1,2] Some advantages of Cu/graphite composites such as their ability to self-lubricate and be maintenance free make them a favorite for long-term service as sliding materials.[3] Graphite plays an important role in protecting the Cu matrix due to its good lubricating performance. However, poor wettability between Cu and graphite harms their ability to bond, causing damage to the composite during its service life. Thus, it is necessary to improve the interfacial bonding strength and wettability between the Cu matrix and graphite. An effective approach is to prepare a metallic coating on the surface of the graphite particles. Compared with electroplating, electroless plating could prepare a more uniform coating.[4,5] Much effort has been undertaken to improve the interface bonding by plating Cu,[6–10] Ni,[11–13] and Ni-based alloys[14,15] on graphite particles. The Ni-B alloy coating was expected to be a good candidate due to its high hardness and good wear resistance.[16–19] In addition, Cu alloys such as bronze and brass were also considered for use as matrix in order to improve the mechanical properties of the composites.[20] In the present work, Ni-B-coated graphite particles were prepared by the electroless plating method. The morphology and phase structure of Ni-B coating were investigated in detail. The Cu-Sn alloy/graphite composites were synthesized using the powder metallurgy method. A comparison study on the properties of Ni-B-coated and uncoated graphite composites was conducted (Table I).
The mean diameter of the graphite particles (SigmaAldrich Co., St. Louis, MO) was 20 lm. Before electroless plating, the graphite particles were sequentially immersed in acetone and HF solution (10 wt pct) with ultrasonic stirring for 5 minutes. Then the graphite particles were cleaned in distilled water. The Ni-B coating was prepared in a bath solution, which was composed of NaBH4: 6 g/L, NiCl2Æ6H2O: 10 g/L, and C6H5Na3O7Æ2H2O: 51.2 g/L. During the plating process, the bath temperature was maintained at 303 K ± 1 K (30 °C ± 1 °C) and the pH value was maintained at 13 using NaOH solution (20 wt pct). The electroless plating time was 10 minutes (Table II). Most of the electroless plating Ni-B coatings are amorphous.[21] The heat treatment (HT) [573 K (300 °C), 2 hours, argon atmosphere] was carried out in some Ni-B-coated graphite particles in order to analyze the phase structure of Ni-B coatings. The morphology of the coatings was characterized by the secondary electron images using a scanning electron microscope (SEM, Hitachi* 4800S, Tokyo, Japan). The
RUIFENG DONG, Student, ZHENDUO CUI, Professor, and XU XU, Student, are with the School of Materials Science and Engineering, Tianjin University, Tianjin 300072, P.R. China. SHENGLI ZHU, Professor, and XIANJIN YANG, Professor, are with the School of Materials Science and Engineering
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