Deposition Characteristic Of Cold Sprayed Ni And Coated Ni Particles

Cold spray(CS)technology has been widely used in the field of material surface modification due to its many advantages.It is a technology that uses low-temperature and high-pressure carrier gas to accelerate sprayed particles to a critical velocity and then impact the substrate.The coating is formed by the combination of sprayed particles and the substrate material itself,and the particles remain solid in the process of spraying.with the particles always remain solid state.Different from the conventional thermal spraying technique,the sprayed particles are kept at a low temperature during the cold spraying process,,therefore the adverse effects of high-temperature oxidation,melting,and decomposition can be avoided to the greatest extent,so that the original physical and chemical properties of the particles can be retained.For example,when oxidation-sensitive materials are accelerated by the carrier gas in the laval nozzle,oxidation of the materials can be avoided to the greatest extent,so that cold spraying has a greater advantage than thermal spraying in the preparation of pure oxidation-free coatings.These characteristics make cold spray technology have a broad application prospect in many engineering fields.However,considering the supersonic characteristics of the cold spraying process,the mechanism of particle deposition and its combination with the substrate is more complicated;Due to the extremely short timescale of the collision process,it is very difficult to observe the whole deformation history.The numerical methods,therefore,play an important role in researching the cold spraying deposition process.They provide quantitative and accurate details of the stress,strain,temperature and deformation region that would be difficult to measure experimentally.In view of the wide application of nickel-based coatings,this paper used a combination of finite element numerical simulation analysis and experiment to systematically study the collision process and deposition mechanism of nickel and its coated particles on a stainless steel substrate.In order to obtain the key influencing parameters and particle deposition characteristics of nickel-based coatings prepared by cold spray technology.The major creative contributions are summarized as follows:Low-pressure cold spray equipment was used to deposit nickel coating on the stainless steel substrate,and the morphology of the coating was characterized by optical microscope,scanning electron microscope,etc.for model verification and reference of the numerical calculations.By adopting the finite element analysis method and select the appropriate material model,the deposition process of the Cu particles onto the20 steel substrate was studied,in order to obtain the temperature distribution and deformation characteristics,and to compare with the experimental results from the literature to verify the model.Further more,The Euler algorithm in the finite element ABAQUS software was used to study the influence of the nickel particle initial velocity of the nickel particles,the incident angle of the particles,the preheating temperature of the particles and the substrate on the collision process of the cold sprayed nickel particles with the 20 steel substrate and the deposition mechanism.The results show that the increase of the initial velocity of nickel particles can promote the plastic deformation of the particles and the substrate,and the critical velocity at which the nickel particles can be successfully deposited on the 20 steel substrate is about 480m/s.When the particles impact onto the substrate at a non-vertical angle,the high strain and high temperature zone are focused on one side of the impacting zone,which leads tu the decreasing of the bonding strength between the particles and the substrate.While the preheating of the particles and the substrate can promote the thermal softening effect,which is beneficial to the effective deposition of the particles onto the substrate.Results of multi-particles deposition process show that increasing the initial speed of the particles is also beneficial to the mechanical engagement between the particles in the coating.The deformation behavior and deposition mechanism of nickel particles pre-coated with aluminum and copper coatings on 20 steel substrates were further studied.The results show that when the nickel particles pre-coated with metal aluminum coating collide with the substrate,the aluminum coating layer experiences plastic deformation firstly.Nickel particle deform slightly,and the deformation on both sides of the contact interface between the aluminum coating layer and the substrate is the most severe.The coating film was squeezed severely by the particles and substrate,and ti breaks and forms the metal jet.The calculation results of multi-particles show that the aluminum coating layer experiences strong plastic deformation and forms obvious jets,which fills up the gaps between the nickel particles,particle and substrate.Increaseing the initial velocity of the particles is also beneficial to the enhancement of the mechanical bonding in the coating.When the incident velocity of nickel particles pre-coated with the copper metal layer is 400 m/s,the metal jet also forms at the contact edge between the particles and substrate.The jet component includes the coating material and substrate material.When the incident velocity of the particles is increased to 400?500m/s,the copper coating remains intact,however,when the particle incident speed increases to 600m/s,the copper coating fractures at the interface of the contacting substrate area due to the action of the deformation and extrusion of the nickel particles.