Effect of Co, Ni, Mo and W on the corrosion properties of amorphous electrospark coatings

Abstract

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, 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.

Electrospark deposition of coatings using Cr3C2 powder and their characterization

“…В наших более ранних работах был предложен способ осаждения электроискровых покрытий в среде гранул из осаждаемого материала, выполняющих функцию анода, который позволяет автоматизировать процесс осаждения покрытий [12]. Также была показана возможность одностадийного формирования многокомпонентных аморфных покрытий данным методом, используя гранулы, состоящие из разного набора элементов [13]. При осаждении металлокерамических покрытий традиционным ЭИЛ существуют ограничения по концентрации керамического компонента, вызванные высоким электрическим сопротивлением и низкой прочностью электродных материалов с высокой объемной долей керамики.…”