Mechanical Properties of Ni-P/Diamond Composite Films Processed by Electroless Plating Method

Abstract

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Recent advancements in various industries have necessitated the development of new engineering materials exhibiting superior properties of different character. For example, composite electroplating renders excellent corrosion- and wear-resistant materials with good lubrication behavior and chemical stability. Nanometer-sized diamond particles are expected to be good dispersion materials in electro-less composite plating. However, the processing conditions and characteristics of metal/diamond composites are not well understood so far. In this investigation, we developed new processes for co-deposition of Ni-P/diamond composite films on steel plates using the commercial electrolyte composed of nickel sulfate and sodium hypophosphite. No additives were applied in this process as in the conventional methods for the efficient dispersion of diamond particles. The diamond particles of a few hundred nanometer size were dispersed in an ultrasonic bath of de-ionized water. The zeta potential of the diamond solution was measured prior to the incorporation into the electrolyte. The morphology of the prepared films was characterized by FESEM. Based on the FESEM images, the size distribution of the diamond particles was determined using an image analyzer program. The micro-hardness, the coefficient of friction, and the corrosion potential were measured by Vickers hardness tester, tribometer and potentiometer, respectively. The present experimental results revealed remarkable differences in the values of the micro-hardness, the coefficient of friction, and the corrosion potential, compared to those of conventional diamond-free electro-less Ni-P plates. Process conditions were optimized in terms of the concentration of diamond particles, ultrasonic dispersion time, and pH of the electrolyte. As the concentration of diamond particles increased from 0.5to 3g/l, the zeta potential was decreasing with more particles aggregated. The higher the diamond concentration, the higher the volume fraction of diamond particles co-deposited in the nickel matrix. In turn, the coefficient of friction and corrosion potential increasd with the increasing diamond concentration. The particle size distribution was the most uniform in the samples prepared at the concentration of 1.0g/l. The best mechanical properties were obtained when the dispersion time was 30min. and the pH 5.