超音速火焰喷涂镍基涂层颗粒沉积特性的数值模拟

Numerical Simulation of Particle Deposition Behavior of Ni-based Coatings by High-velocity Oxy-fuel Spraying

目的 考虑后续不同粒径颗粒随机冲击的影响,探索热喷涂涂层颗粒的沉积特性。方法 利用ABAQUS建立颗粒与基底冲击模型,通过颗粒冲击的凹坑深度和应力分布进行网格收敛性研究。通过实验验证模型的可行性。随后,应用验证模型研究颗粒以不同入射角和速度冲击基底时的沉积特性,以及4个颗粒重叠冲击基底及多颗粒随机冲击基底表面时的沉积特性。结果 在颗粒入射角从15°增至60°时,颗粒更好地附着于基底表面;当颗粒速度从350 m/s增至500 m/s时发生了溅射现象,可能造成绝热剪切失稳现象,形成有效结合;在4个颗粒冲击基底时,第2个颗粒对第1个颗粒及基底的影响都最明显;当多颗粒随机冲击基底时,在后续颗粒的冲击和沉积作用下,填充颗粒的形状不规则,同时第1层颗粒可能与基底形成机械咬合。结论 在超音速火焰喷涂时应当倾斜一定角度,同时提升颗粒速度,这对制备涂层更有利;在颗粒重叠冲击时,后续颗粒增大了第1个颗粒的压缩效果,且更深入地嵌入不锈钢基底,这有利于颗粒与颗粒之间的后续黏结;当多颗粒随机冲击基底时,在第1层沉积颗粒与基底之间,以及涂层内相邻颗粒之间均观察到高塑性应变,表明涂层出现黏结,同时后期沉积的颗粒未完整压缩变形。

In order to explore the deposition characteristics of thermal spraying coating particles,it is necessary to consider the effect of subsequent random impact of particles with different particle sizes.In the research related to deposition characteristics of coating particles,many researchers mainly focus on the particles with the same particle size to impact together in neat rows.However in the actual spraying,the powder particles are interval powders,with particles with different particle sizes,and the impact on the substrate is also random.Therefore,few people consider this problem.In this work,a particle and substrate impact model was established in ABAQUS to study grid convergence based on dent depth and stress distribution of particle impact.At the same time,the reliability of the model was verified by experiments.Then,the deposition characteristics of the substrate impacted by particles at different incident angles,and the deposition characteristics when four particles continuously overlapped and impacted the substrate and multiple particles randomly impacted the substrate surface were analyzed with the validation model.The optimal grid number of the sediment model was 1 752 912,which not only reduced the calculation cost,but also obtained accurate results.The particle with a particle size of 20 μm had a large impact speed,but a large resilience,and poor adhesion to the substrate.The particle with a particle size of 40 μm had a moderate speed,but a large impact energy,so it had a good interface with the substrate.The incident angle of particles increased from 15° to 60°,and the particles were better attached to the substrate surface,when the particle velocity increased from 350 m/s to 500 m/s,sputtering may occur,which may cause adiabatic shear instability and form effective bonding.When four particles impacted the substrate,the deformation of the second particle and its effect on the substrate were the most obvious.When multiple particles with different particle sizes impacted the substrate at random,the shape of the filling particles was irregular due to the impact and deposition of subsequent particles,and the first layer of particles may form a mechanical bite with the substrate.Thermal spraying should be inclined at a certain angle and increased at a certain speed,which can expand the contact area between particles and substrate.At the same time,the deposition depth increases continuously to enhance the adhesion,so it is more conducive to the preparation of the coating.When the particles overlap and impact,the subsequent particles make the first particle increase the compression effect and embed more deeply into the stainless steel substrate,which is conducive to the subsequent bonding between particles and makes the coating more compact.When a number of particles with different particle sizes impact the substrate at random,due to the different initial velocities and temperatures obtained by the subsequent particles in the thermal spraying gun tube,the particles impact and deposit in the later stage,and there is no good flatness or deformation.At the same time,high plastic strain is observed between the first layer of deposited particles and the substrate,as well as between adjacent particles in the coating.This situation indicates that the coating is bonded,so it is necessary to increase the full combustion of oxygen and kerosene to fully soften particles with different particle sizes during the actual thermal spraying.At the same time,the best efforts should be made to obtain higher speed under the gun barrel air pressure.When impacting the substrate,it can be completely deformed,so as to obtain an ideal high-quality coating.