Numerical Simulation Of Particle Deposition Process In Cold Spraying Based On Material Point Method

The cold spraying process is widely used in the field of coating preparation and surface repair in the aerospace field because of its ability to prepare thermally sensitive material coatings by low temperature spraying.The process of particle deposition is an important part of cold spraying,and it is of great significance to study the bonding mechanism of particles and substrates to guide the production of cold spraying.The particle deposition process is a large deformation problem due to high-speed collision which may lead to the problems of grid distortion existing in traditional numerical simulation methods.The deposition process of cold spray particles will be simulated by the material point method.The influence of different collision parameters on the particle substrate deformation behavior and spray effect will be discussed.The governing equation of the material point method was deduced.The explicit material point method solution format for the cold spray problem was established.The solution process of the display solution format was written.The material program was written in Fortran language based on the material point method theory.The deposition process of cold spray particles was simulated by self-written material point method program.The particle deformation law and the particle height after spraying by simulation were in good agreement with the experimental results in the literature,which verifies the self-written material point method program to simulate the cold spray problem feasibility and validity.The numerical simulation of the particle deposition process of cold spray was carried out based on the material point method.The effects of collision velocity,preheating temperature,collision angle,particle diameter and surface roughness on the particle deposition process were discussed respectively.The spray effect was evaluated by flat rate and deposition depth.The results show that,with the increase of collision speed and preheating temperature,the surface roughness,the degree of particle deformation,the degree of flatness and deposition depth increase,and the spraying effect is better.With the collision angle increases,the particle tends to slide to the right,the deposition depth decreases,and the spraying effect is worse.When the particle is deposited on the rough surface,with the surface roughness increases,the flattening trend of the particle increases under the effect of the wave peak,and the rebound kinetic energy decreases.The particle jet will form a mechanical occlusal structure with the substrate while the surface roughness is sufficient.When the particle is deposited at the trough,the particle will be difficult to be flattened by the wave peaks on both sides,and the spraying effect will be weakened with the increase of the peak height.When the particle is deposited at the half waist,a secondary contact will be formed between the particle and the substrate under the effect of the tangential velocity component,which lead to a longer jet flow and increase of the bonding strength.When the particle diameter is smaller,the substrate has less influence on the particle deposition,but the length of jet flow and effective contact area will be smaller,the spraying effect will be poor.The larger diameter particles deposition at the trough will form a longer jet flow and a larger effective contact area which makes the spraying effect is better.A four-factor and three-level orthogonal test was carried out with the test factors of particle collision speed,particle preheating temperature,particle diameter.It can be concluded the best process parameter combination to the flat rate,which Collision velocity is 700m/s,substrate surface roughness is 5μm,particle preheating temperature is 900K,particle diameter is 10μm.The significance level relationship of the four factors is particle collision velocity>substrate surface roughness>particle temperature>particle diameter.The research in this paper provides a novel method for the numerical simulation of the bonding process of cold spray particle deposition,and also provides some guidance for the production of cold spray processes.