Research On The Effect Of Silicon Content On The High Temperature Corrosion Resistance Of Ni-based Alloy Laser Cladding Layer

Based on "dual carbon" goals and strategic needs for energy transformation,coal-fired power generation has become a norm in undertaking the peak shaving function of the power system.The phenomenon of overtemperature in the water wall of boilers under deep peak shaving conditions frequently occurs,leading to severe corrosion of the water wall and causing leakage even tube explosion.With the improvement of clean energy power generation efficiency and the incineration power generation parameters,the high temperature corrosion of boiler heating surface caused by alkali metals,sulfur,chlorine in the fuel has become increasingly prominent.The oxide layer on the surface of heating surface materials has lost its protective role,bringing new challenges to the safe operation of boiler.Therefore,in response to the problem of intensified high-temperature corrosion on the heating surface of power plant boilers,the development of corrosion resistant nickel based alloy materials based on laser cladding technology is of great significance for the safe operation of power plant boilers.In order to study the high-temperature characteristics of nickel based alloy cladding layers,this paper uses laser cladding technology to prepare Ni-xCr alloy cladding layers with different Cr contents,as well as Ni-20Cr-xSi and Ni-24Cr-13Mo-xSi alloy cladding layers with different Si contents.Firstly,the high-temperature oxidation and high-temperature sulfate corrosion behavior of Ni-Cr alloy cladding layers with different Cr contents were studied to obtain the Cr content of the alloy with the best corrosion resistance.Subsequently,based on this material,the influence of Si content on the high-temperature oxidation,high-temperature sulfate,and mixed salt corrosion resistance of Ni-20Cr alloy cladding layer and Ni-24Cr-13Mo alloy cladding layer was investigated.To investigate the effect of Cr content on the high-temperature oxidation and high-temperature sulfate corrosion performance of Ni-Cr alloy cladding layers,Ni-xCr alloy cladding layers with different Cr contents(x=10wt.%,20wt.%,40wt.%,60wt.%)were prepared.The high-temperature oxidation and sulfate corrosion behavior of Ni-xCr cladding layers were studied.The results show that when the Cr content is 10,20,and 40 wt.%,the microstructure of the cladding layer is uniform without obvious precipitates.When the Cr content reaches 60 wt.%,Cr exhibits dendritic segregation in the cladding layer and produces a certain amount of large particles of Cr.The Cr20 and Cr40 cladding layers have good high-temperature oxidation resistance at 900℃,a continuous and dense Cr2O3 layer is formed on the surface of the cladding layer in high-temperature environment,which hinders the diffusion of O and Ni.Due to the segregation of Cr element,a large number of cracks have been generated in the surface oxide layer of Cr60 cladding layer,resulting in poor high-temperature oxidation resistance.In a sulfate corrosion environment of 600℃,the Cr content has a significant impact on the corrosion resistance of the cladding layer.The corrosion weight loss of Cr20 and Cr40 cladding layers is relatively small,and the surface corrosion layer can effectively prevent further corrosion.The Cr60 corrosion layer has cracked and peeled off,providing a good channel for the entry of corrosive media,causing internal corrosion and reducing the high-temperature corrosion resistance of the cladding layer.Ni-40Cr alloy cladding layer has the best resistance to high-temperature oxidation and high-temperature sulfate corrosion.In order to investigate the effect of Si content on the high-temperature oxidation and high-temperature sulfate corrosion performance of Ni-20Cr alloy cladding layers,Ni-20Cr-xSi alloy cladding layers(x=0,1wt.%,3wt.%,5wt.%)were prepared,and the high-temperature oxidation and sulfate corrosion behavior of Ni-20Cr-xSi cladding layers were studied.The results show that Ni-20Cr-3Si alloy cladding layer has excellent oxidation resistance at 900℃,and the SiO2 oxide film formed on the surface can effectively hinder the external diffusion of Ni and Cr alloy elements and internal diffusion of O2.When the addition amount of Si element is 5wt.%,the high-temperature oxidation products on the surface of the cladding layer will peel off,resulting in a decrease in antioxidant performance.In the sulfate corrosion experiment at 600℃,the corrosion products on the surface of the cladding layer are distributed in a sheet-like manner,the corrosion pits increase with the increase of Si element content,along with the corrosion resistance of the cladding layer decreases.The addition amount of Si element is 5wt.%,NiS2 is generated on the surface of the cladding layer.The Ni-20Cr-1Si cladding layer has excellent sulfate corrosion resistance at 600℃.The effect of Si content on the high-temperature mixed salt corrosion performance of Ni-20Cr alloy cladding layer was studied.The results show that in mixed salt corrosion experiments within the range of 550℃-650 ℃,the Ni-20Cr alloy cladding layer mainly produces a dense oxide layer on the surface,which hinders the penetration of corrosion media into the substrate of the cladding layer.Cr elements continue to diffuse from the substrate,forming a Cr deficient zone.The addition of Si element effectively improves the high-temperature corrosion resistance of Ni-20Cr alloy cladding layer in mixed salt.With a Si content of 1wt.%added,the Ni-20Cr alloy cladding layer has excellent corrosion resistance.The addition of Si element helps to improve the stability of Cr2O3 in mixed salts.The enrichment of Si element in the corrosion layer can effectively hinder the penetration of the outer corrosion medium,while reducing the depth of the Cr deficient zone.But when Si content≥ 3wt.%,the corrosion products on the surface of the cladding layer will peel off.In order to investigate the effect of Si content on the high-temperature mixed salt corrosion resistance of Ni-24Cr-13Mo alloy cladding layers,Ni-24Cr-13Mo-xSi alloy cladding layers were prepared(x=0 wt.%,1 wt.%,3 wt.%,5 wt.%),and the high-temperature corrosion behavior of Ni-24Cr-13Mo-xSi alloy cladding layers in mixed salt was studied.The results show that in a mixed salt corrosion environment between 550℃ and 650℃,a dense chromium rich oxide scale was formed on the surface of the Ni-24Cr-13Mo alloy cladding layer,which slowed down the corrosion process.The addition of Si element can effectively improve the high-temperature corrosion resistance of Ni-24Cr-13Mo alloy cladding layer.When the corrosion temperature is below 550℃,the Ni-24Cr-13Mo-5Si cladding layer has the best corrosion resistance,while when the corrosion temperature is above 600℃,the Ni-24Cr-13Mo-3Si cladding layer has the best corrosion resistance,and a layer of SiO2 is formed below the Cr-rich oxide layer.The increase in Si content not only contributes to the stability of the Cr-rich oxide layer,but also enhances the bonding between the Cr-rich oxide layer and the cladding layer through the "pinning" effect.