Effect of Ni2+ concentration on microstructure and bonding capacity of electroless copper plating on carbon fibers

Many study utilize formaldehyde as a reducing agent to prepare copper coating on carbon fibers surface to improve the interface between carbon fibers and metal matrix. But formaldehyde is harmful to the environment and health. The copper coating on carbon fibers was plated in the electroless bath with hypophosphite as a reducing agent in this study. And the effect of Ni2+ concentration in the bath on the deposition rate, morphology, microstructure and binding capacity of copper deposits were investigated. The deposition rate increases with the increase of Ni2+ concentration in the bath. And the deposition particle sizes of the Cu–Ni composite coating become larger from 0.13 µm to 1 µm with the addition of Ni2+ in the bath, which is due to the increase of accumulation rate of copper atoms with the increase of coating rate. It has a small granular growth into an island shape with the aggregation and growth of the particles. The large particles cause deep grooves, which accelerate crack growth. The results of the thermal shock test shown that the binding capacity is best when the Ni2+ concentration is 3.8 mmol/L in the bath. The number of cycles is 50 when the coating begins to deteriorate. The final number of cycle is 62 and the coating accompanied by gradual weightle loss. At this time, the coating has the optimal thickness and shedding mode, which makes the crack propagation need more energy. This work also provides a reference for the electroless copper plating formula with sodium hypophosphite as the reducing agent.