| Inconel 718 superalloy is a precipitation-enhanced nickel-chromium-iron-based alloy.It has good comprehensive properties such as oxidation resistance,radiation resistance,fatigue resistance,corrosion resistance,and weldability in the range of-253 to 650°C.It can be used to manufacture aviation on the engine,sheet metal welding parts,turbine disks and blades,compressor disks,casings,etc.Rocket engine components such as turbopumps,fuel chambers,fuel conduits,etc.It is the largest and most widely used superalloy material in aviation,aerospace and other fields.However,in the course of processing and service,alloy structural parts will inevitably be damaged,and direct scrapping will increase the production cost.It is of great significance to study the damage repair and strengthening of the alloy structural parts.In this paper,laser cladding technology is adopted to adjust the main process parameters that have a great influence on the quality of laser cladding coating,such as laser power,scanning speed,defocus amount,and preset powder thickness.Cladding coatings under different processes were prepared.Coatings were applied to analyze the influence of different process parameters on the forming parameters,dilution ratio,forming factor and microstructure of the cladding layer,and then the process was optimized.A single-pass,multi-pass coating with good forming quality was prepared.The microstructure,precipitating phase and mechanical properties of the cladding coating were studied.The results show:(1)The optimal laser processing parameters of laser single cladding are laser power 1300 W,scanning speed 2 mm/s,preset powder thickness 1mm and defocus 15mm.It is found that by appropriately reducing the laser power,increasing the scanning speed and the amount of defocusing,a good microstructure with fine grain size and large microhardness can be obtained.At the same time,the microstructure of the cladding layer which is relatively small in the precipitation of harmful Laves phase can be obtained.(2)The grain size of the first cladding microstructure of the laser overlap cladding with different scanning pitch is smaller than the grain size of the adjacent overlapping microstructure,and its microhardness is generally higher Lapping area section.(3)Comparison of the microstructures of the multi-layer coating and the original cladding state after different heat treatment shows that the content of Laves phase and segregation of niobiumcan in the 718 alloy coating can be effectively reduced by homogenization and standardization;After first order treatment,it was found that the coated dendrites prepared on the basis of 45~#steel had the tendency to shift to the isometric state,while the coatings prepared on the basis of the 718 forged alloy produced a large number of spherical?phases,and the obvious twinning structure appeared on the matrix.Meanwhile,the dendrite of the cladding layer was obviously coarsened.After secondary treatment,the dendrites of the cladding layer are obviously refined and the direction is strong;After the solution treatment,the fine needle like?phase is formed in the cladding coating based on the 45~#steel,and a large number of circular spherical?phase is formed in the cladding layer with the 718 forged alloy as the base.(4)The heat treatment has little effect on the hardness of the 718 coating on the45~#steel substrate,and has a very significant effect on the hardness of the coating on the 718 alloy substrate.By comparison,it was found that the selected matrix has a great influence on the microhardness value of the same coating after the same heat treatment.(5)Through the analysis of the electrochemical polarization curves of the coating based on 45~#steel and 718 forged alloys in the acidic medium,it is shown that the acid corrosion resistance of the coating can be significantly improved by the standardization,homogenization and first order heat treatment of the 718 coating based on 45~#steel.Its surface acid corrosion resistance can be significantly improved by Standardization or two stage heat treatment of 718 coating on the basis of 718forging alloy.By comparison,it is found that the selected base has great influence on the corrosion resistance of the same coating after the same heat treatment. |
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