High-temperature oxidation resistance and diffusion analysis of Al/Ni-WC composite coating

LI Deyuan; SUN Jibo; LI Guangquan; ZHANG Nannan; ZHU Cheng

doi:10.7688/j.issn.1000-1646.2025.02.09

Abstract：[Objective]The use of carbon steel in high-temperature working conditions is strictly limited due to its poor oxidation resistance.Ni-Al intermetallic compounds have many practical industrial applications due to their high melting points and good high-temperature oxidation resistance.In this study,a Ni-Al reaction-modified coating was prepared on the surface of carbon steel to explore the further application of coatings containing Ni-Al intermetallic compounds with high-temperature oxidation resistance and improve the high-temperature service life of carbon steel.[Methods]A Ni-WC coating was prepared on the carbon steel substrate by high-velocity oxygen-fuel(HVOF)spraying,and then an Al coating was prepared on it by arc spraying.The Ni-Al within the coating reacted under diffusion treatment for different time at 800 ℃ to afford intermetallic compounds and thereby enhance high-temperature oxidation resistance.The high-temperature oxidation resistance of the coating was tested by recording their oxidation weight gain curves.[Results]The results show that the Al/Ni-WC composite coating generates Al-rich Ni-Al intermetallic compounds by in-situ reaction at the Al/Ni interface during high-temperature oxidation.The Al/Ni-WC coating forms Al-rich NiAl3 during diffusion treatment at 800 ℃,and the Al atoms on the surface react with the atmospheric oxygen atoms to form Al2O3.With the extension of the reaction time,the NiAl3 phase formed at the Al/Ni interface is transformed into the Ni2Al3 phase with better high-temperature oxidation resistance.The two Ni-Al intermetallic compounds have high melting points and high-temperature oxidation resistance,and Al2O3 formed on the surface of Al/Ni-WC composite coatings slows down the diffusion of O atoms.The thickness of the diffusion layer of the Al/Ni-WC composite coating increases almost linearly with the prolongation of the diffusion treatment time.The thickness of the NiAl3 layer of the Al/Ni-WC coating after the diffusion treatment at 800 ℃ increases at a fast rate,and a thicker Ni2Al3 layer is generated by in-situ reaction after 10 h of heating.After 20 h of diffusion treatment at 800 ℃,a Ni2Al3 layer slightly thicker than the NiAl3 layer is generated by in-situ reaction.Due to the higher melting point and stability of the Ni2Al3 layer,the Al/Ni-WC coating after diffusion treatment at 800℃ has better high-temperature oxidation resistance.After cyclic oxidation,there are ceramic phases Al2O3 and WC as well as NiAl phases in Al/Ni-WC coating subjected to 50 h of diffusion treatment at 900 ℃.which also show better high-temperature oxidation resistance under the combined effect of ceramic phases and NiAl phases.In this paper,the thickness of the diffusion layer of the Al/Ni-WC coating after diffusion treatment for different time was also measured,and the diffusion relationship between Ni and Al was obtained.The kinetic index of diffusion reaction is 0.790 45.The protective effect of the composite coatings on the carbon steel substrate is improved significantly.[Conclusion]The high-temperature oxidation resistance of the carbon steel substrate is significantly improved under the combined effect of the Ni-Al intermetallic compounds and Al2O3 film formed during the oxidation process as well as the original WC in the coating.As indicated by the oxidation weight gain experiment,after the introduction of ceramic phases in the Ni layer,the high-temperature oxidation resistance of the metal-ceramic composite coating is significantly better than that of the carbon steel substrate,namely that the carbon steel substrate can be better protected by the coating.