Study On Characteristics And Mechanism Of Laser Cleaning Of Oxide Film On Superalloy Surface

Nickel base superalloys are widely used in high temperature parts of aerospace,energy,chemical and other industries because of their good high temperature strength,oxidation resistance and thermal corrosion resistance.However,in the process of forming,transportation and storage,the alloy surface will be oxidized to form a layer of oxide film,which greatly affects the post-treatment quality of the alloy.Therefore,the oxide film on the alloy surface needs to be removed during use.At present,traditional surface cleaning methods will cause substrate damage,low efficiency and pollution.Green efficient and high-precision laser cleaning technology can be used as an effective means of oxide film cleaning.In view of this,this paper takes the oxide film on the surface of GH3128 nickel base superalloy as the research object,and carries out the cleaning experiment with a nanosecond pulse laser to explore the influence of laser process parameters on the cleaning effect of the oxide film on the surface of GH3128 alloy and the mechanical properties of the substrate after cleaning.Combined with the relationship model between laser and material temperature,the removal mechanism of oxide film is analyzed.The research contents and results are as follows:(1)Orthogonal experiment and single factor experiment were designed to explore the influence of different process parameters(laser energy density and scanning speed)on the surface cleaning effect of GH3128 nickel base superalloy.By comparing the surface morphology,element content and surface roughness after cleaning at the energy density of 0.50J/cm~2-1.99J/cm~2 and the scanning speed of 6000mm/s-10000mm/s,it is concluded that the cleaning effect is the best when the energy density is 0.88J/cm~2 and the scanning speed is 7000mm/s.The surface roughness is reduced to 0.171μm.The oxygen content decreased to the valley value of2.42wt.%.The surface roughness and oxygen content decreased first and then increased with the increase of laser energy density or scanning speed.The ring-shaped craters,splash particles and residual oxide film on the cleaned surface are the main reasons for the increase of roughness.(2)Combining the relationship model between laser energy and material temperature with the micro morphological characteristics of the cleaned surface,the removal mechanism of oxide film on the surface of GH3128 alloy by laser cleaning is revealed.When the laser energy density is less than 0.88J/cm~2,the thermal expansion explosion mechanism occurs.When the laser energy density is greater than 1.57J/cm~2,the recoil pressure sputtering mechanism occurs.(3)The surface microhardness,room temperature tensile properties,high temperature tensile properties and friction and wear properties of the samples before and after cleaning with different process parameters(laser energy density,scanning speed)were tested.The effects of different laser processing parameters on the mechanical properties of GH3128 alloy were analyzed.The results show that when the energy density is less than 0.88J/cm~2,the surface microhardness has no obvious change.In the range of 0.88J/cm~2 to 1.99J/cm~2,the microhardness of the substrate will increase slightly.Changing the scanning speed has no effect on the microhardness of GH3128 alloy.Laser cleaning can slightly improve the high temperature tensile properties and wear resistance of GH3128 alloy,but has no effect on the tensile properties at room temperature.