Abstract Copper molds are considered as the main part of continuous casting machine. This part is under difficult working conditions and must be able to withstand ferrostatic pressure, high working temperature, creep and having high abrasion resistance and corrosion resistance. To achieve corrosion and abrasion properties, hard chrome coatings is applied on the inner surfaces of these molds. Despite the positive features, this coatings has disadvantages such as environmental problems, the presence of many microcracks and non-uniform thickness. So far, many attempts have been made to replace hard Chrome coatings or eliminate the disadvantages of it, each of which has been associated with problems. Using electroless nickel-phosphor coatings and compositing it with nanoparticles to improve the properties can be a good solution for this issue. Carbon Nano Tube (CNT) with its tubular structure and very small diameter to length ratio has ideal mechanical properties, high thermal conductivity, lubricity and high corrosion resistance. Also, calcium fluoride (CaF2) as a solid state lubricant has a very high ability to reduce the coefficient of friction. In this study, electroless nickel phosphor composite coatings with CNT-CaF2 particles was applied on copper substrate for 1.5 hours at 90 ° C and pH = 4.7. Nano Tube particles with a concentration of 1 g / l and CaF2 with a concentration of 2 g / l were added to the bath with the relevant preparation. Coatings was characterized by X-ray diffraction (XRD) analysis, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Also, the effect of surface roughness and sandblasting of the substrate on the distribution of particles in the coatings was investigated. The results showed a 30 μm thick dense deposit in which the particles were evenly distributed and lacked extensive microcracks. To eva‎luate the corrosion properties, polarization tests and Electrochemical Impedance Spectroscopy (EIS) were performed in 3.5 wt% sodium chloride solution. Due to the presence of carbon nanotubes and their ability to block coatings defects, the composite coating had a much higher corrosion resistance than the non-composite nickel-phosphor coatings and the corrosion current density decreased from 0.76 μA / cm2 to 0.0016 μA / cm2. By adding particles to the coatings, the charge transfer resistance increased from 43.8 KΩ.Cm2 to 58.5 KΩ.Cm2. Also, with the uniform distribution of nanotube particles, the corrosion potential was transferred from -396 mV to -336 mV. By examining the EIS curves, the highest load transfer resistance was related to the composite coatings. To investigate the tribological behavior of the samples, the pin on disk test was performed at 400 ° C. The lubrication of carbon nanotubes and calcium fluoride improved the wear properties of the coatings and reduced the coefficient of friction from 0.56 to 0.19. Key Words Composite Coating, Copper Mold, Carbon Nano Tube, Calcium Floride, Corrosion resistance, Ni-P Electroless, Wear Coefficient.

مسعود عطاپور، مرتضي شمعانيان

محمود منيرواقفي، عبدالمجيد اسلامي