Electrospark deposition of chromium diboride powder on stainless steel AISI 304

Abstract

Introduction. Austenitic stainless steel AISI 304 is the most widely used type of stainless steel. However, it is subject to wear due to relatively low hardness, and also begins to oxidize intensively in air at a temperature above 800 °C. The use of coatings based on chromium boride can improve its tribotechnical properties and oxidation resistance. The purpose of the work: to study the effect of chromium diboride concentration in the anode mixture on the structure, wear behavior, oxidation resistance and corrosion properties of electric spark coatings on AISI 304 steel. The research methods. Electric spark treatment of AISI 304 steel was carried out in a mixture of iron granules with the addition of CrB2 powder in amount of 5, 10 and 15 vol.%. The structure of the coatings was studied by X-ray analysis, scanning electron microscopy, and electron dispersion spectroscopy analysis. The wear resistance of the coatings was studied under dry friction condition at a load of 10 N. The oxidation resistance test was carried out at a temperature of 900 °C for 100 hours. Results and Discussion. According to X-ray analysis, it is shown that under the conditions of electric spark exposure, CrB2 interacts with iron melt; this has resulted in the formation of chromium and iron borides. Corrosion properties, microhardness, coefficient of friction and wear are investigated in comparison with AISI 304 steel. Samples with coatings showed a lower corrosion potential and corrosion current density compared to the substrate in 3.5% NaCl solution and from 5 to 15 times higher oxidation resistance. The microhardness of the coatings increased from 6.25 to 7.60 GPa with an increase in the addition of chromium diboride in the electrode mixture. The coefficient of friction and the wear rate of all coatings were lower than that of AISI 304 stainless steel, while the coating prepared with the addition of 5 vol.% chromium diboride had the best tribotechnical characteristics.