Electroless Ni–B–MMT nanocomposite on magnesium alloy

Abstract

Ni-B and Montmorillonite (MMT)-containing Ni-B deposits were electrolessly plated on AM60B magnesium alloy. The Ni-B coating showed cauliflower-like micromorphology, microcrystalline-amorphous microstructure, and thickness of about 15 μm, which was not influenced by the inclusion of MMT nanoparticles. The surface roughness of the Ni-B coating changed from about 376 to 328 nm after the inclusion of MMT. The boron content of the electroless deposit was mildly increased after MMT inclusion. Thermal shock and porosity examinations revealed suitable adhesion and pore-free structure of the coatings, respectively. Polarization resistance of the Ni-B deposit in 3.5 wt-% sodium chloride was increased about 1.5 times by MMT inclusion. The corrosion current of the substrate was remarkably diminished from 46.89 to 0.12 µA cm −2 by the Ni-B plating. Also, MMT incorporation causes to further decrement of the corrosion current to about 0.03 µA cm −2 .

Effect of heat-treatment temperature and borohydride concentration on corrosion behaviour of ENB coating

“…The thermal shock tests were conducted as per ASTM B733-04. 3,[29][30][31] The tests are carried out for each sample where the samples were kept at 200°C 6 10°C for 10 min and rapidly cooled by dipping them into the water at room temperature (25°C). The same has been carried out for 20 cycles and then the samples were investigated for the presence of any bubbles, cracks, peeling etc on the surface using an optical microscope (DM2700M, Leica).…”

“…The filter paper was removed after 10 min and checked for any red points on it which signifies the presence of porosity. 3,30,31 The porosity of the surface is calculated by the ratio of the total number of red points to the total contact area between the specimen and filter paper. 30 The corrosion behaviour of the ENB coatings was investigated through EIS and PDP test methods.…”

“…The tests have been carried out for each of the samples by heating them at 200°C and cooling them rapidly after keeping them for around 10 min in the heating chamber. 3,[29][30][31] The rapid colling was carried out by dipping the heated sample in ambient temperature (25°C) water. After the tests for 20 cycles of thermal shock, the samples were investigated for blisters, cracks, peeling, warping etc on the surface using an optical microscope (DM2700M, Leica).…”

“…5 While corrosion resistance may be improved with the addition of nano-particles in the Ni-B matrix. 3,19,20 Therefore, the coatings have been investigated with a certain concentration of borohydride and heattreated at 4008C and 4508C temperatures to study corrosion resistance behaviour. The corrosion also depends on phase structure which is a function of coating bath composition.…”

“…The borohydrides reduced ENB coatings normally show cauliflower or broccoli-like surface morphology in as-deposited conditions which helps in improving the tribological behaviour by reducing the actual surface contact area. 1–3 The presence of boron-like hard particles helps to improve the surface hardness of steel substrate due to the addition of an ENB alloy coating layer over it. 4 The ENB coatings have been studied on the basis of coating deposition rate, surface morphology and surface roughness etc.…”