Numerical Simulation Of Heat And Mass Transfer In Laser Cladding Of Nickel-based Alloy

Large ships and marine drilling equipment have been severely corroded in the marine environment with high salinity for a long time.Corrosion can not only reduce the strength of marine equipment structure,shorten the life of marine equipment,but also affect the performance and safety of operations.Effective corrosion control methods are an important issue of concern in China's industrial development.With its high temperature resistance,corrosion resistance,and complex stress resistance,nickelbased superalloys have a wide range of applicability in the production of hightemperature parts for turbine engine working blades,guide blades,aircraft engines,and industrial gas turbines.With the development of industrialization,nickel-based superalloys are also gradually used in energy and power industries such as supercharged turbines,industrial gas turbines,internal combustion engine valve seats,steering rollers,transportation,petrochemical industry,metallurgical mines and glass building materials.Laser cladding has unique advantages for the manufacture of nickel-based superalloys.Not only can it shorten production time and reduce production costs,but it can also give priority to functional design.It is very suitable for forming and manufacturing hotsegment components such as nozzles,blades,combustion chambers in aero engines and gas turbine wheels,as well as complex parts such as space vehicles and rocket engines.At present,the microstructure and element composition control in the forming process of nickel-based superalloys are the key to restricting the further development of laserclad preparation of nickel-based alloys.Both of these issues are related to the heat and mass transfer phenomena in the molten pool.How to understand and Regulating complex thermophysical processes in the molten pool is the main trend of current research,and it is also the basis and premise for further predicting and controlling the microstructure and mechanical properties of nickel-based superalloy parts prepared by laser cladding.Therefore,this article mainly includes two research contents:First of all,this paper mainly discusses the temperature field and flow field distribution of the molten pool in the laser cladding process of the circular spot,and the influence of the marangoni effect on the shape and solidification parameters of the molten pool.The results show that Marangoni convection caused a double peak phenomenon in the velocity of the molten pool surface.The temperature gradient(G)and solidification rate(S)of the cladding layer were calculated to predict the morphology and size of the solidified microstructure.The simulation results show that during the solidification process of the molten pool,the cooling rate(G × S)decreases from the top region of the cladding layer,and the solidification rate of the cladding layer gradually decreases from top to bottom.The experimental results are very consistent,and when the simulated melt pool depth is less than the thickness of the previously placed powder layer,the metallurgical bond between the substrate and the cladding layer is not very good.Secondly,this paper mainly studies the laser cladding process of rectangular spot.At a laser power of 4000 W and a scanning speed of 3 mm / s,the maximum temperature gradient G of the cladding layer surface is 500 K / mm,the maximum cooling rate ? is 600 K / s,and S is 1.20 mm / s.As the distance from the surface of the cladding layer increases,G,?,and S all decrease.As the distance from the top surface of the cladding layer increases,G / S first decreases slightly,then rises again,and the cooling rate ? decreases.It laid a foundation for predicting and controlling the microstructure and properties of the cladding layer in the future.This thesis includes 40 figures,4 tables,and 105 references.