Properties of electrodeposited Ni-B-Al2O3 composite coatings
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Ni-B coatings have gained a great deal of attraction due to their promising mechanical properties. Owing to tempting properties, Ni-B coatings have succeeded to find their applications in automotive, aerospace, petrochemical, plastic, optics, nuclear, electronics, computer, textile, paper, food and printing industries. Despite having promising properties, further improvement in their properties is essential so that more challenging requirements and new developments can be successfully addressed. In the present study, novel Ni-B-Al2O3 composite coatings have been synthesized through electrodeposition process by reinforcing Ni-B matrix with Al2O3 particles. A comparison of properties of Ni-B and Ni-B-Al2O3 coatings in their as deposited states is presented to elucidate the beneficial role of Al2O3 addition. The structural analyses indicate that Ni-B coatings exhibit a single broad peak indicative of an amorphous structure. However, the addition of Al2O3 into Ni-B matrix considerably improves the crystallinity of the deposit. The surface morphology study reveals the formation of uniform, dense and fine-grained deposit in both Ni-B and Ni-B-Al2O3 composite coatings. However, addition of Al2O3 particles into Ni-B coatings results in high surface roughness. The nanoindentation results demonstrates that the addition of Al2O3 into Ni-B matrix results in significant improvement in mechanical properties (hardness and modulus of elasticity) which may be attributed to dispersion hardening of Ni-B matrix by hard Al2O3 particles. The linear polarization tests confirm that the addition of Al2O3 improves the corrosion resistance of Ni-B coatings. This improvement in corrosion behavior may be attributed to the reduction in active area of Ni-B matrix by the presence of inactive Al2O3 particles.
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