Phase evolution and steam oxidation behavior of nickel-based composite coatings fabricated by laser cladding

Abstract

In this study, a variety of synthesized carbides are used as reinforcing phases for Inconel 625 alloy to enhance the performance of surface coatings. The effects of scanning rate and laser power on the microstructure and mechanical properties of coatings were studied, and specific energy was introduced to comprehensively evaluate the mechanisms of their influence. The results show that the percentage of macroscopic defects in the nickel-based composite coatings decreases and the dilution rate increases gradually with increasing specific energy density and the mechanical properties of the composite coating deteriorate gradually. It is worth noting that when the specific energy density is 153.33 J/mm2, the comprehensive performance of the composite coating is the best, which is mainly due to the uniform distribution of the contained (Ti, W)C and Cr carbides. The coating exhibits excellent hardness, corrosion resistance, and high-temperature oxidation resistance. In addition, after determining the optimal process parameter combination, the high-temperature steam oxidation performance of the nickel-based composite coating is analyzed in depth. At 1200°C, the corrosion degree of the composite coating gradually increased with increasing oxidation time. Research shows that the ceramic phase structure of (Ti, W)C and Cr plays a significant inhibitory role in high-temperature environment, effectively decelerating the increase of corrosion rate. Interestingly, before the first 48 h of the oxidation process, the thickness of the oxidation layer on coating surface increases slowly. However, when the oxidation time reaches 96 h, large amounts of WO3 and NiCr2O4 phases are formed, leading to the generation of pores and cracks in the coating. This causes the oxide film to fall off, resulting in a sharp increase in the corrosion layer thickness. The research in this paper is of great significance for optimizing coating materials and preparation processes, as well as improving the long-term high-temperature corrosion resistance of coatings.