Synthesis and characterization of electrodeposited Ni-B-Tl2O3 composite coatings

Abstract Ni-B coatings are promising materials for several applications in electronics, nuclear, automotive, aerospace, petrochemical and food industries owing to their exceptional mechanical and chemical properties such as, high hardness, high wear resistance and good corrosion resistance. However, the literature indicates that there is still significant scope for further improvement in properties of these coatings in order to improve their in-service performance and/or total service life. Considering this fact, a novel Ni-B-Tl 2 O 3 composite coatings has been developed via electrodeposition technique by reinforcing Tl 2 O 3 particles into the Ni-B matrix. The effect of addition of Tl 2 O 3 particles on the morphology, structure and electrochemical properties of Ni-B-Tl 2 O 3 coatings was investigated and compared with that of the Ni-B coatings. A substantial change on surface roughness, thermal properties, crystal structure, mechanical properties and corrosion resistance was observed due to the addition of Tl 2 O 3 particles to the Ni-B coatings. The as-deposited Ni-B coatings were found to be amorphous in nature, however the crystallinity of the composite coatings was significantly improved by the addition of the Tl 2 O 3 particles. Surface analyses showed an increase in surface roughness due to the addition of Tl 2 O 3 particles, which confirms the formation of fine and dense structures in both Ni-B and Ni-B- Tl 2 O 3 coatings. There is significant improvement in microhardness (by 80%) and elastic modulus (by 60%) of Ni-B-Tl2O 3 composite coatings as compared to Ni-B coatings mainly due to the addition of Tl 2 O 3 particles. Corrosion resistance was found to be improved significantly after the incorporation of Tl 2 O 3 into the Ni-B matrix which may be attributed to reduction in active area of Ni-B matrix.