Numerical Simulation Of Inconel 718 Alloy During Laser Cladding

Inconel 718 alloy has comprehensive properties such as oxidation resistance,radiation resistance,fatigue resistance,corrosion resistance and good weldability,so whether it is used as superalloy parts or coated alloys,it shows superiority in performance,it is the most widely used nickel-based superalloy.As a kind of secondary repair and surface modification technology,laser cladding has the characteristics of clean,high efficiency and little influence on the substrate,so in this paper,laser cladding of 718 alloy is taken as the research object,and the surface modification of 718 alloy on common alloy and the repair and remanufacturing of 718 alloy parts are systematically studied.Because of the characteristics of rapid melting,rapid solidification and local high heat input during laser cladding,great stress or deformation will occur after laser cladding,it is necessary to study the temperature and stress in laser cladding process.Due to the complexity of the cladding process,it is difficult to study the temperature and stress distribution and changes by experimental methods.The numerical simulation of laser cladding by computer technology is a hot research topic for domestic and foreign workers,and it has been obtained more and more applications.In this paper,ANSYS software is used and the method of combining simulation with experiments is adopted,a finite element model of 718 alloy preset-powder laser cladding was established.Optimization of process parameters for surface modification of 718 alloy by laser cladding and the repair and remanufacturing of 718 alloy by laser cladding which includes temperature and stress field of single channel laser cladding,temperature and stress field of single channel laser cladding of thin-walled parts with different thicknesses,the effects of temperature field on solidification of cladding layer,temperature and stress field of multi-channel overlapping laser cladding were systematically simulated and studied.In order to provide the theoretical basis for the process optimization of laser cladding surface modification and laser cladding repair and remanufacturing.The main research results include:For the surface modification of 718 alloy by laser cladding:The effect of process parameters on the quality of cladding layer was studied by temperature field,and the optimal parameters were finally determined.The results of temperature field calculation show that with the increase of defocusing amount,the maximum temperature of molten pool decreases,the forming coefficient increases and the dilution ratio decreases,and the forming effect becomes better;with the increase of scanning speed,the maximum temperature of molten pool decreases,while the forming coefficient increases and the dilution ratio decreases,the forming process becomes better;with the increase of laser power,the maximum temperature of molten pool becomes larger and larger.The forming coefficient is smaller and the dilution ratio is larger,and the forming effect is worse.The optimum proce ss parameters: defocusing amount is 15 mm,scanning speed is 2mm/s and laser power is 1300 W.For the repair and remanufacturing of 718 alloy by laser cladding:Temperature and stress fields of 718 alloy during single-channel laser cladding were simulated and analyzed.The results of temperature field calculation show that temperature profile can be used to reveal the characteristics of rapid melting and solidification of laser cladding and to explain the ablation of the end of the plate.The results of stress field calculation show that the residual stress is mainly concentrated in the cladding layer,the value of equivalent stress is greater than the yield limit(1125MPa),and the 4mm plate will be obviously deformed,but there is basically no crack in the cladding layer;the partial stress profiles on the different defined paths at the cross of the melting section shows that the longitudinal stress SZ is the tensile stress in the cladding layer,the transverse stress SX is complex,the value of SY is small.Through the numerical simulation of thin-walled parts with different thicknesses,the thickness of the substrate has a significant influence on temperature field during laser cladding 718 alloy.As the thickness of the substrate becomes larger,the maximum temperature of the molten pool decreases,the size of the heat-affected zone decreases,the forming factor becomes higher;the ―end effect‖ of laser cladding is less obvious.It can be seen from the results of the stress fields that in the cladding layers,under the same process parameters,the cladding stress of thin-walled parts with different thicknesses has little difference;the larger the thickness of the thin plate is,the larger the equivalent stress value is;the longitudinal tensile stress SZ increases with the increase of plate thickness in cladding layer;on the thin plate far away from the cladding layer,the larger the thickness is,the smaller the equivalent stress value is;the preheating is very effective for reducing the residual stress of the laser cladding,and the deformation amount after preheat ing is remarkably reduced.Temperature field simulation results of single channel laser cladding were used to obtain the cooling rate and temperature gradient,and then,the influence of temperature field on the solidification(microstructure,element dist ribution and performance)of the cladding layer was obtained.The results show that the cooling rate is increasing,and the temperature gradient is decreasing,the crystallization rate is increasing from the bottom to the top of the cladding layer.Under t he combined action of crystallization rate and temperature gradient,the grain growth morphology from the bottom to the top of the cladding layer presents the rule of ―cellular-columnar dendrite-equiaxed crystal‖.From the bottom to the top of the cladding layer,with the increase of cooling rate,the precipitation of Laves phase decreases;the faster the cooling rate,the smaller the segregation of Nb and the smaller the value of SR,but the value of SR is much larger than 1 in general;the micro hardness values are basically the same in different areas of the cladding layer.Temperature and stress fields of remanufacturing multi-channel overlapping laser cladding were simulated.The simulation results show that the temperature between the cladding layers is obviously affected,and the previous one will preheat the latter one,which will make the maximum temperature of the latter and the minimum temperature of the substrate increase;the maximum stress is in the overlapping zone of the cladding layer,the stress value is more than 1280 MPa,and the stress value in the cladding layer is between 1100-1280 MPa,which is greater than the yield limit of the material at normal temperature,so the plate will exist significant deformation.The probability of cracks appearing in overlapping zone is larger than that in cladding layer;the value of transverse tensile stress SX in the overlapping zone is bigger,while the value of longitudinal tensile stress SZ in the cladding layer is bigger;the cladding of the latter cladding layers will obviously reduce the equivalent stress in the previous cladding layers,and the weakening effect will decrease after the partition;After six channel cladding layers are completed,the weakening effect will make the stress value conform to the rule of step-by-step changing from bottom to top in cladding layers.