2.1. Sample Preparation

Pure Ni plated cBN grains and Ni/SiC plated cBN grains were electrolytically deposited in an additive-free nickel Watts type bath, respectively. The electroplate experiments were realized on a superhard materials barrel plating machine (JX41-5, Abrasives and Grinding Co. Ltd., Zhengzhou, China) with a rotation velocity of 3 rpm under direct current condition. The substrates that also used as cathode were cBN grains of 100/120 mesh (125–150 μm), which were processed through the following steps: oil removal, roughness, sensitization-activation, reduction and then chemical plating processing before electroplating [13]. Acid electroless plating bath was used in our work. Sodium hypophosphite was used as reducing agent. The electroless layer contained 13.09% P and an amorphous coating. The anode, which was a nickel foil of 99.9% purity with regular shape of 5 cm × 150 cm (wide and long), was positioned in the bath of the barrel plating machine. Before electroplating, the selected commercial SiC powders with a mean diameter of 5 μm were added to the bath. During electrodeposition, the temperature of the plating solution was maintained between 25 and 35 °C and the pH value of the electrolyte varied from 4.7 at the beginning of the deposition to 5.5 at the end. Plating current was kept between 1.0 and 1.5 A. Pure Ni plated cBN grains were also produced under the same experimental conditions for comparison. The composition of the plating solution and the deposition parameters for the preparation of plated cBN grains are presented in Table 1.

Overview of electrodeposition parameters for preparation of pure Ni plated cubic boron nitride (cBN) and Ni/SiC plated cBN.

After plating, cBN grains were cleaned in distilled water for 10 min so as to remove loosely adsorbed SiC particles from their surface. Thus, plated cBN grains samples (S1, S2, S3 and S4) could be obtained after being dried in vacuum oven at 80 °C for 5 h.