Numerical Simulation And Technological Study For The Laser-assisted Cold Spray

Laser-assisted Cold Spray(LCS)is a new technology of material surface modification,which combines the supersonic powder beam found in Cold Spray(CS)with the deposition zone laser heating.So it not only retain advantages of CS:solid-state deposition,high build rate and the ability to deposit materials onto a range of substrates,but also with the help of laser heating,it can reduce the consumption of the carrier gas and the process cost of production and achieve coatings which is hard to deposit on the substrate,enlargeing the using range of the material and the substrate.LCS has broader application prospects than CS.The key in LCS is to control the parameters of cold spray and laser heating power to achieve the coatings.Since LCS is a process of a supersonic jet and high-speed collision between particle and substrate,the velocity of particle is not easy to be measured,which limits the study of LCS simply through experimental study.By using the numerical simulation,the distribution and variation of process parameters such as pressure,temperature,velocity etc.can be studied in detail.We can also optimize the standoff distance and laser power,which can greatly reduce the time and cost needed for experimental design.A new Laval nozzle is designed,and then the effect of different pressure,temperature,particles' material and size,standoff distance and laser power on the spraying has been investigated by employing the software Fluent and Ls-dyna.The results are as follow indicates that:(1)With the increase of gas pressure and temperature,air velocity also increases.A range of expansion waves and compression waves forms at nozzle exits,and bow wave will form when there is a substrate in the flow field.(2)The impact velocity of particles increases with the increase of standoff distance,but the dispersion phenomenon of particles is serious if the standoff distance is too large.(3)The laser power strongly affects coating deposition,the greater the power,the better the coating,but excessive power will lead to the increase of coating porosity.The CS and LCS experiment of Cu powder are carried out on the basis of the simulation,then the coating deposition rate,microhardness and the microstructure of substrate was studied.The experiment result shows that when the standoff distance is 30mm and the laser power is 800W,highest deposition rate,toughest microhardness and strongest bonding strength of coating can be achieved,the simulation meets the experimental result well.