Research On Formation Mechanism Of H₂S Ion Sulfuration On Laser Cladding Layer

The failure of mechanical and material caused by friction and wear can be effectively solved by preparing solid lubrication coatings.Solid lubrication coatings prepared by laser cladding-ion sulphurizing process can reduce the friction coefficient on the surface of materials and improve the service life of workpieces.However,most of the current studies focus on the preparation of metal sulphide films such as Fe S and Mo S₂,focusing on the micro-Characterization and friction and wear properties of lubrication films.There is no in-depth study on the formation mechanism of sulphide films.In this paper,Ni-based alloy cladding layer and Fe-based alloy cladding layer were prepared by laser cladding technology,and ion sulfurizing was carried out on the surface of different cladding layers.Select temperature and different holding time as variables in sulphurization experiments.By analyzing the role of sulphurized gas in the process of sulphurization,the changes of micro-morphology and composition of sulphurized layer on the surface of two kinds of cladding layers under different temperature and holding time,the formation process and mechanism of sulphurized layer on the surface of different cladding layers under H2S atmosphere were studied based on the principle of plasma reaction.The main phases of Ni-based alloy cladding layer are(Fe,Ni)solid solution,Cr₇C₃,WC,etc.The sulphide phase are Fe S,Fe S₂ after suiphring.During the process of sulfurizing,the bombardment of hydrogen ion and argon ion on the surface make changes to the morphology of Ni-based alloy cladding layer changes,but has little effect on the composition.Sulfide preferentially occurs in the phase with low Cr and high Fe content.When the holding time is35-40 minutes,the surface of Ni-based alloy cladding layer is completely covered by fine sulfides.With the extension of holding time,the sulfides are easy to form Fe S₂ and S₈ besides Fe S.After holding time exceeds 1.5 hours,the prolongation of sulphurizing time has little effect on the change of element content in sulphurized layer.The main phases of Fe-based alloy cladding layer are(Fe,Cr)solid solution,compound of Cr-Fe-B and(Fe,C)solid solution.,the main sulfide phases are Fe S and Fe S₂ after sulphurization.The bombardment of hydrogen ions and argon ions during heating process has limited influence on the surface morphology of the cladding layer of iron-based alloys,and has great influence on its composition.Sulfide is preferentially formed in the area with low Cr content during sulphurization,and the surface of iron-based alloy cladding layer is completely covered by fine sulphide and the distribution of sulphide is uniform when the holding time is 15 minutes.After holding for 1 hour,the surface of iron-based alloy cladding layer has formed a higher and more Fe S content.The sulphurized layer is smooth,compact and uniform.The efficiency of sulfide formation on the surface of Fe-based alloy cladding layer is higher.After heat preservation for more than 1 hour to 1.5 hours,the prolongation of desulphurization time has little effect on the change of element content in desulphurization layer.The process of H₂S ion sulphurization can be divided into three parts:chemical reaction of sulphurizing medium,migration of sulphur medium,and formation of sulphide layer.Sulphur is supplied by H₂S gas in the heat preservation process,and H₂S in the furnace will not decompose directly at the experimental temperature.The H₂S molecule collides with the high energy electron e^-*to become the excited state H₂S^*or to be ionized into the positive ion H₂S⁺and decomposes further.At the same time,H₂S molecule collides with the positive ions H₂⁺,H⁺and Ar⁺to form H₂S⁺,S and other particles.The sputtered iron atoms in the cladding layer react with the active sulfur atoms in the atmosphere to form Fe S and other iron sulfides which preferentially adsorb to the crystal defects and grain boundaries of the cladding layer to form Fe S nuclei.Sulfides are continuously formed and accumulated into sulfurized layer.