基于Eulerian法计算多颗粒冷喷涂Ti-6Al-4V涂层的孔隙率和残余应力

Calculation of Porosity and Residual Stresses of Multi-particle Cold Sprayed Ti-6Al-4V Coating Based on Eulerian Method

冷喷涂涂层具有喷涂温度低、沉积效率高和结合强度高等特性,在航空航天等工业领域具有广阔的应用前景,但关于喷涂参数对涂层孔隙率和残余应力影响的研究较少.考虑送粉速度和涂层厚度的影响,建立不同颗粒密度和数量的随机分布颗粒冲击模型,采用Eulerian法模拟TC4(Ti-Al-4V)涂层的孔隙率和残余应力分布规律.结果表明,此方法能够很好地预测颗粒的沉积行为,揭示颗粒的原位夯实致密化效应,获得冷喷涂涂层的孔隙率和残余应力分布规律.颗粒密度减小,孔隙率略有降低;颗粒数量增加,孔隙率减小;当颗粒温度在一定范围(523~823K)时,孔隙率随温度上升呈线性降低.同时,不同颗粒密度和数量的模型获得的残余应力分布规律相似.计算结果可为冷喷涂涂层在航空航天等工业领域中的应用提供理论和数据支持.

Cold-sprayed coatings have a low spraying temperature,high deposition efficiency,and high bonding strength,which have broad application prospects in aerospace and other industrial fields.Porosity and residual stresses are important parameters that affect the mechanical properties of coatings.However,only a few studies have been conducted on the effects of spraying parameters on the porosity and residual stresses of coatings.In the actual cold-spraying process,the increase in the powder feeding rate decreases the gap between particles during particle deposition.The initial coating layers are affected by the repeated impact of the subsequently deposited particles,and the coating thickness increases with the increase in the number of deposited particles.Therefore,the powder feeding rate and coating thickness can be equated with the density and number of particles to study their effects on the porosity and residual stresses of coatings.The particle diameters of general metal powders follow the Rosin-Rammler distribution.The diameter difference between particles was set as 1μm;thus,the proportion of particles under each diameter can be calculated.According to the actual particle diameter distribution,multiparticle impact models with different densities and number of particles were generated by Python Script.Then,the Eulerian method was used to simulate the porosity and residual stress distribution of TC4(Ti-Al-4V)coatings.Five groups of models were calculated,and the results were compared and analyzed.This method can effectively predict the deposition behavior of particles;reveal the effects of in-situ compaction and densification of particles;and determine the porosity and residual stress distribution of cold-sprayed coatings.When the particles were deposited,the deformation at the interface was much larger than that inside the particles.Overall,the temperatures of the initial coating layers were higher than those of the upper layers.The particle deformation of the initial coating layers was larger and the particles were more densely distributed.To further explore the effects of different parameters on the porosity,the porosity was calculated by extracting 100μm×100μm×30μm squares from the center of each coating.It was found that the porosity slightly decreased with the decrease in the particle density.As the number of particles increased,the porosity decreased,indicating that increasing the number of deposited particles could lead to repeated impacts on the initial layers.By changing the temperature of the particles in the model(523-823 K),it was found that the porosity linearly decreased as the temperature increased.This indicates that increasing the particle temperature can improve the coating performance.However,the residual stress distributions were similar for models with different densities and number of particles.There were mainly compressive residual stresses in the coatings,along with tensile residual stresses that were mainly on the substrates.The maximum residual stress was found at the interface between the substrates and coatings.The residual stress distribution trend was basically the same when the particle temperature was changed.The calculated results are in good agreement with previous experimental studies,indicating that the model effectively simulated the multiparticle deposition behavior of cold spraying.The results reveal the porosity formation law and residual stresses of the coatings,and provide theoretical support for future studies on the influence of spraying parameters on the mechanical properties of coatings and the application of cold-sprayed coatings in aerospace and other industrial fields.