The Preparation of Ni-Cr Composite Coatings on Tungsten by Molten Salt Thermal Diffusion Method

Tungsten is a commonly used shielding material in Sr-90 Radioisotope thermoelectric generators; however, its resistance to high-temperature oxidation is relatively poor. This study aims to enhance the oxidation resistance of tungsten in high-temperature conditions. This study prepared a nickel-chromium composite coating on tungsten using the molten salt thermal diffusion method. The coatings produced at different molten salt temperatures were characterized using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Additionally, cyclic oxidation tests and isothermal oxidation tests were conducted to evaluate the oxidation resistance and spallation resistance of the coatings. The adhesion strength between the coatings and the substrate was also assessed using the indentation method.The results indicate that the primary phase composition of the coatings is γ-(Ni,Cr). When the molten salt temperature is 950 ℃, the coating surface is blocky. The impurity P element in it gradually disappears, and the prepared nickel-chromium coating is more pure, with good oxidation resistance and anti-spallation properties. The study reveals that a dense layer of Cr2O3 formed on the surface of the oxidized sample. Furthermore, this sample demonstrated the highest adhesion, and the coating exhibited a fine crystalline structure. Therefore, a temperature of 950 ℃ is optimal for preparing nickel-chromium coatings using the molten salt diffusion technique.