Electrodeposited Ni-B-Si<inf>3</inf>N<inf>4</inf> composite coating: Preparation and evaluation of its characteristic properties

The preparation of Ni-B-Si3N4 composite coatings by electrodeposition technique and evaluation of their characteristic properties are addressed in this paper. The Ni-B-Si3N4 composite coatings were electrodeposited using a dimethylamine borane (DMAB)-modified Watt's nickel bath containing Si3N4 particles dispersed in it. The effect of chemical composition, structural and morphological characteristics, and hardness of electrodeposited (ED) Ni-B-Si3N4 composite coatings were evaluated and compared with that of ED Ni-B coatings. The study reveals that Si3N4 particles can be successfully codeposited in the ED Ni-B matrix. The maximum level of incorporation of Si3N4 particles, about 8 wt.%, is obtained at a bath loading of 50 g/l and at 1 A/dm2. The incorporation of Si3N4 particles decreases the metallic lustre, increases the surface roughness and alters the chemical composition of the ED Ni-B matrix. The average surface roughness of the ED Ni-B-Si3N4 composite coatings is 1.17 μm. The coating contains 89.6 wt.% Ni, 2.4 wt.% B and 8 wt.% Si3N4. The surface morphology of the coating reveals uniform distribution of Si3N4 particles in the ED Ni-B matrix. Incorporation of Si3N4 particles in the ED Ni-B matrix causes a change in crystal orientation. Heat treatment (400 °C for 1 h) increases the crystallinity and enables the formation of Ni3B phase. The Ni (1 1 1) texture is retained even after heat treatment at 400 °C for 1 h. The grain size of the coating is 6-8 nm in as-plated condition and it increases to 12-14 nm after heat treatment at 400 °C for 1 h. The microhardness of as-plated ED Ni-B-Si3N4 composite coating is 640 HV0.1 and it increases to 955 HV0.1 when the coating is heat treated at 400 °C for 1 h. © 2007 Elsevier B.V. All rights reserved.