Effect of Co, Ni, Mo and W on the corrosion properties of amorphous electrospark coatings
Letters on Materials
Влияние Co, Ni, Mo и W на коррозионные свойства аморфных электроискровых покрытий
Coatings based on amorphous metals with a different number of elements: nickel, cobalt, molybdenum and tungsten, were obtained on steel 35 by electrospark deposition in a mixture of crystalline granules.The thickness of the deposited coatings was 20 to 33 μm. X-ray diffraction analysis showed a wide halo in the range of angles 20 -43° that indicates on a predominance of the amorphous phase in the coating composition. The content of the amorphous phase, depending on the coatings composition,
... gs composition, varied from 81 to 99 vol.%. The smallest fraction of the amorphous phase was observed in the coating without molybdenum. According to the EDS analysis, it was shown that the concentration of elements along the cross-section of coatings was constant that indicates on a homogeneity of the composition of the deposited coatings. A study by the scanning electron microscopy in phase contrast mode showed that the coatings had a homogeneous structure and did not have a precise boundary with the substrate demonstrating a good adhesion of the coatings to the substrate. Potentiodynamic polarization tests in 3.5 % NaCl solution have shown that amorphous coatings can improve the corrosion resistance of the steel 35 surface by up to 5 times. Tungsten reduced the rate of electrochemical corrosion of coatings, while cobalt lowered the corrosion properties of the coatings. A high-temperature corrosion test for 100 hours at temperature of 700°C showed that the samples with coatings were oxidized 3.4 to 7.9 times less than steel 35. Barrier properties of coatings without tungsten under high-temperature gas corrosion were 2.3 times lower than those of coatings without cobalt. This means that tungsten improves the corrosion resistance of amorphous alloys, whereas cobalt reduces it.