冷喷涂金属颗粒变形行为数值模拟研究进展

Research Progresses in Numerical Simulation of Deformation Behavior of Cold Sprayed Metal Particles

理解冷喷涂中的颗粒变形和沉积行为一直是科学工作的焦点。由于颗粒撞击基底后的瞬时变形行为难以通过实验观测,因此多数研究工作聚焦于数值模拟。总结了一些颗粒撞击基底的建模方法,在前人研究的基础上,针对每个模型的原理及优缺点,分析了每个方法的适用场景,给出了改善模型的方法。综述了颗粒特性、入射角度、气体预热温度等对颗粒变形行为的影响,其中粒径大小、颗粒形状等是影响颗粒变形行为的主导因素,因此重点探讨了颗粒特性的影响。颗粒的撞击变形是影响冷喷涂涂层残余应力分布的重要因素,对涂层残余应力的相关数值模拟研究进行了综述,分析了颗粒变形与颗粒残余应力的关系。最后就目前冷喷涂残余应力建模较单一的形势,探讨了如何建立一种新模型以分析涂层残余应力。

The temperature of cold spray is very low,so the quality of the coating depends on the deformation behavior of particles impacting the substrate.Since it is difficult to observe the instantaneous deformation behavior of particles impacting the substrate through experiments,most research work focuses on numerical simulation.The commonly used simulation method is the finite element method,and the mesh is a key step in the finite element method.The quality of the mesh determines the accuracy of the computation results.There are other methods that do not require meshing.The finite element methods can be also divided into Lagrangian method,Euler method,Arbitrary Lagrangian Euler method(ALE)and Coupled Lagrangian Euler method(CEL).The Lagrangian method can effectively simulate the deformation behavior of a single particle impacting the substrate,but the distorted mesh which can cause computation termination makes it unsuitable for particles at too fast speed.This extends to the ALE method.When the mesh distorts,it can have adaptive changes.Although it overcomes the problem of mesh distortion in the Lagrangian method,its computational accuracy is not as good as Lagrangian method.The Euler method is more accurate,and will not terminate the computation due to mesh distortion.The biggest problem is that it is difficult to track the particle/substrate interface.Although the CEL method can clearly see the particle/substrate interface,the problem of mesh distortion in the Lagrangian method still exists.There are some methods without mesh,such as Smooth Particle Hydrodynamics(SPH)and Molecular Dynamics(MD).They adopt a series of particle combinations with material properties to determine the deformation behavior of particles through changed in particle aggregation,effectively avoiding mesh distortion and difficulties in monitoring particle/substrate interfaces.They can complete some work that can not be completed by the finite element method.The deformation behavior of particles is closely related to the residual stresses of the coating.For example,shot peening effect caused by high-speed impact of metal particles will cause residual compressive stresses in coatings.Some commonly used modeling methods were reviewed,the applicable scenarios of each model were analyzed based on their advantages and disadvantages and the effects of process parameters such as particle properties,spray angle,and gas preheating temperature on particle deformation behavior were summarized.The effect of particle properties on particle deformation was dominant,and particle hardness,particle size,particle oxidation difficulty and particle shape had a significant effect on particle deformation.Therefore,the focus was on exploring the effect of particle properties.At last,some models for residual stresses in coatings were summarized,starting from particle deformation to explore the causes of residual stresses in coatings.The modeling researches on residual stresses in coatings mainly focus on the model of particle impact on the substrate,which is limited to the"shot peening stresses"of particles,while the"birth and death methods"can analyze the formation of other residual stresses,which is widely used in the field of thermal spray.A model that combines the advantages of the both is proposed as future work content.