The Numerical Investigation Of Particle Impact Behavior On Substrate During High Velocity Oxy-Fuel Spraying

High velocity Oxy-fuel spraying technology, a branch of thermal spraying technology, had replaced plasma spraying technology as the mainstream of thermal spraying technology. Spraying particle was heated and accelerated to a certain degree in the high velocity and high temperature flame ejected from a Laval nozzle, followed by impacting on the substrate. The bonding of particle and substrate depended on the plastic deformation of particle and substrate and the part-melting of particle. During the spraying process, particle's velocity being relatively high, the impact to substrate was strong and the bonding strength was fine. And particle's temperature being relatively low, high performance coatings with high compactness could be formed easily because of particle oxidation and thermal impact to substrate were low.In this study, a comprehensive investigation on the impact process of particle on substrate was conducted by numerical method. Initial particle states and substrate conditions were studied in this paper. Numerical simulation results showed that:Particle deformation mainly took place in the beginning of the deformation process. 90% of the particle deformation occurred in half the deformation time. Diameter of particle had no effect on the deformation of particle and substrate. But it was important to the dynamic duration of the impact process. The duration of particle impacting substrate was proportional to initial particle diameter. The larger the initial particle diameter was, the longer the duration of the impact process was. With the increase of particle initial velocity, the flatting of particle was weakened. The contact area of particle and substrate and the longitudinal component of reactive force imposed to particle increased along with particle initial velocity, good for the bonding strength and the compactness of coatings. Higher particle initial temperature would lead to larger flatting of particle and larger contact area. So Higher particle initial temperature was good for forming high bonding strength and good compactness coatings.The initial conditions of substrate also had important effect on the impact process. Contact area increased with substrate initial temperature, so did the bonding strength. The strength of substrate did the opposite. The higher the strength of substrate was, the less the contact area was. So the bonding strength decreased when the strength of substrate increased.It should be noticed that when particle initial velocity decreased to some degree or the strength of substrate increased to some degree, the splashed part would contact with substrate. Though this pact contact area couldn't improve the bonding strength, it's useful to avoid or reduce splashing.