Electrodeposited Ni–B–Si3N4 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.