| In order to improve energy efficiency,reduce coal consumption and reduce carbon emissions,thermal power units are bound to develop towards ultra-supercritical units with high capacity and high parameters.However,the high-temperature and high-pressure environment in the units will aggravate the corrosion of boilers and other equipment,which makes the selection of high-temperature materials the top priority.In this paper,Inconel 625 superalloy cladding layers with different Si contents(0wt.%,1wt.%,3wt.%)were prepared on Q235 steel by laser cladding technology.Based on the experiments,the microstructure,mechanical properties and high temperature oxidation resistance of the alloy laser cladding layers were studied.It provides theoretical basis for the application of high temperature materials in power station.The cladding layer of Inconel 625 alloy is mainly composed of primary phase and eutectic phase,in which the segregation of Si and Mo elements occurs.With the addition of Si,the segregation of elements is aggravated and the grain boundary deteriorates.When Si is added 3 wt.%,cracks can be observed.The hardness of Inconel 625 alloy increases with the addition of Si.The average hardness of 3 wt.%Si and 0 wt.%Si alloy at the cladding layer is 277.9HV and 247.6HV,respectively.The hardness of the cladding layer is 1.5～2 times that of the matrix.The results of compression and tensile tests at room temperature indicate that the Inconel 625 alloy cladding layer has the highest tensile strength and plasticity in the step direction.With the increase of Si content,the tensile strength and yield strength increase,while the elongation and reduction of area decrease significantly.The results of tensile fracture analysis show that the dimple fracture occurs mainly in 0wt.%Si alloy cladding layer,and the dimple size and depth are more uniform compared with the scanning direction when the tension direction is stepping direction.When Si content is 1wt.%,the microcracks occur at the fracture,and some dimples can be observed,which are mainly the mixed fracture mechanism of dimple fracture and intergranular fracture.When Si content is 3wt.%,long and deep cracks and dimples are observed at the fracture,and the fracture mechanism is mainly intergranular fracture.The cladding layer of Inconel 625 alloy shows excellent oxidation resistance at high temperature,and the oxidation resistance increases with the increase of Si content.The oxidation kinetics curves all show a parabolic rule.The increase of Si content significantly reduces the oxidation rate of cladding layer during the interfacial reaction stage.Especially,when the temperature is 900℃,the oxidation rate constant a of 0wt.%Si cladding layer is 100 times that of 3wt.%Si cladding layer.The addition of Si makes the outer oxide gradually change from loose NiO to compact Cr2O3 and NiCr2O4 with strong oxidation resistance,and forms SiO2 below the Cr2O3 layer,preventing the diffusion of elements such as Ni,Cr,Mo,Fe,and external O elements in the matrix,avoiding the occurrence of internal oxidation. |
