Pulse electrodeposition of Ni-P matrix composite coatings reinforced by SiC particles

Ni-P/SiC composite coatings were produced under both direct and extended pulse current conditions from an additive-free modified Watts type bath at various hydrodynamic conditions. Structural analysis revealed an amorphous phase of Ni-P matrix for the majority of coatings, except for those prepared under low duty cycle and high frequency pulses that exhibited mainly the crystalline Ni2P5 compound. The practice of pulse plating regime led to composite coatings with higher incorporation rate of SiC particles (up to 22 wt.%) and microhardness values (up to 7.2 GPa) than those produced under direct current conditions. It has been revealed that increased micron-SiC codeposition percentage resulted in decrease of P content in the amorphous matrix and increase of the deposits' hardness values. After annealing at 400 C the amorphous matrix was crystallized to phases of Ni, Ni2P, and Ni3P, the formation of which depends on the P content. As-plated deposits exhibiting Ni12P5 phase preserved this crystalline structure after thermal treatment. Annealed coatings exhibited almost double values of microhardness relative to those of the as-deposited coatings. (C) 2010 Elsevier B.V. All rights reserved.