Structure and properties of laser cladding CoCrNi multicomponent alloy coating used in rain gauge

Rain gauge is an important measuring instrument, which is widely used for rainfall measurement under various conditions. However, since the rain gauge is used in outdoor exposed environment, its shell is easily corroded by rain, especially by acid rainwater, which will affect the service life. In order to improve the corrosion resistance and prolong its service life, CoCrNi medium entropy alloy (MEA) coating was prepared on the surface of rain gauge's shell by laser cladding. The microstructure and properties of the CoCrNi coating were studied comprehensively. The results show that the coating and the substrate form a metallurgical bond. The microstructure of CoCrNi MEA coating is mainly composed of two kinds of microstructures, and mainly containing face centered cubic (FCC) structure. The coatings have excellent corrosion resistance in acid rainwater with different pH. The corrosion current density of the laser cladding CoCrNi MEA coatings are lower than that of 304 stainless steel (SS), reduced by 2 orders of magnitude, the corrosion potential increased in varying degrees, with an increase range of 0.03∼0.47 V. The pitting corrosion resistance of the coating is excellent, with the increase of pH, the pitting resistance is enhanced. The corrosion resistance of the coating is related to the phase structure, uniformity and compactness of the microstructure as well as the corrosion resistant elements in the coating. The microhardness of the coating is 703.6 HV, the specific wear rate of the alloy is 1.4×10−4 mm3/Nm, and the friction coefficient is 0.47. Experiments show that the coating have excellent corrosion resistance and mechanical properties for the rain gauge's shell, which provides a guarantee for prolonging its service life.