Influence of Ion Treatment of Cr-Coated Zirconium Alloy (E110) on Resistance to High-Temperature Oxidation

Two series of Cr coatings were deposited on E110 zirconium alloy by magnetron sputtering using different modes of ion surface treatment. The crystal structure and microstructure of the Cr coating and its adhesion and corrosion resistance during high-temperature oxidation in air at a temperature of 1100°C with isothermal exposure for 20 and 60 min were studied. The short-term Ar+ irradiation of the Zr alloy with a current density of less than 1.6 mA/cm2 caused a preferential growth of Cr crystallites in (200) plane, an increase in the size of columns in the “coating-alloy” zone, and a high uniformity of the columnar microstructure over the thickness. Without ion treatment, the Cr coating was less resistant to cracking and more vulnerable to high-temperature oxidation. Due to the high permeability of the Cr coating to oxygen and nitrogen, the oxidation of Zr alloy occurred with the formation of (ZrO2 + ZrN) layer underneath the coating. The Cr coating with (200) texture was more resistant to cracking during scratch testing. Because of a lower permeability of oxygen and nitrogen through the Cr (200) coating, the extended dendritic structures α-Zr(O,N) were formed in the Zr alloy up to a depth of 250–270 μm during prolonged air oxidation.