Finite Element Simulation Of Laser Cladding Nickel-base Composite Coatings

Nickel based superalloy has excellent comprehensive properties such as high temperature strength,good corrosion resistance and fatigue performance.It is widely used in the preparation of large hot end components such as aerospace engine,marine and industrial gas turbine.But the composition of nickel base superalloy is complex,easy to segregate and form brittle phase.Furthermore,the traditional preparation method restricts the full performance of this kind of alloy.The laser cladding method has the characteristics of high energy density and high heat and fast cooling,which can effectively solve the problem.Laser cladding is easy to have large residual stress,thus how to control the residual stress is an urgent matter.The current experimental method is difficult to get the data of temperature field and flow field in the preparation process,so it is very important to study the laser cladding process by computer simulation technology.In this paper,the process of Laser Cladding Ni base superalloy is studied by COMSOL Multiphysics software,and the model of four road coaxial powder feeding and cladding process is established by it.The following conclusions are obtained:(1)The density and dynamic viscosity coefficient of different inert gas has great difference.The smaller gas density and aerodynamic viscosity coefficient,the greater gas flow velocity.In the three inert gases of argon,nitrogen,and helium,the flow rate of helium gas is the highest.The convergence of powder flow is optimum when the vertical distance of the nozzle to the powder delivery head ranges from 14 mm to 18.2mm.When the particle diameter of the powder particles is 250-300 mesh,and the powder gas flow rate is 6-7L/min,the powder particles have the best convergence and the flow velocity of the powder particles in the converging region is about 3.2m/s.(2)Within the first 0.7 seconds of the cladding process,as the cladding time increases,the width of the cladding layer,the depth of the bath and the temperature in the bath gradually increase.After 0.7 seconds,the geometry and temperature distribution of cladding layer tend to be stable.Meanwhile,the energy of the system composed of substrate and cladding layer is close to conservation,and the transport of powder particles also tends to be stable.The temperature gradient of the rear end of the molten pool increases gradually from top to bottom,but the formation velocity of the interface decreases gradually.At the top of the cladding layer,the finer grain is formed,and the coarse dendrite or columnar crystal is easily formed at the bottom of the molten pool.By comparing the experimental data with the simulated data,the simulation results are in agreement with the experimental data.The error of the pool morphology,pool width with different laser power is 5.14%,and the error of the cladding layer height with various scanning velocity is 6.1%.(3)The flow velocity at the upper end of the molten pool is larger,and the upper part is annular.The flow velocity of the ring is the largest,and the flow velocity of the inner ring center and the pool boundary is smaller.The annular back end has a larger flow velocity than the front end.When the surface tension temperature coefficient is negative,the direction of the fluid flow on the left side of the molten pool transverse section is counterclockwise,and the right side is clockwise.The longitudinal section of the molten pool is located at the rear side of the plane fluid.The velocity under clockwise flow of the fluid is on the flow ring,meanwhile the front flow ring is clockwise.When the temperature coefficient of surface tension is negative,the fluid in the middle of the pool flows from bottom to top.When the temperature coefficient of surface tension is positive,the temperature coefficient of surface tension is in conjunction with the temperature gradient,and the direction of fluid flow in the middle of the bath will flow from top to bottom.