Numerical Simulation of Droplet Impact and Solidification Including Thermal Shrinkage in a Thermal Spray Process

In this paper, we performed a numerical study on the effects of thermal shrinkage on deposition of molten tin and nickel droplets on a steel substrate in thermal spray processes using Volume-of-Fluid (VOF) method. Thermal shrinkage is a phenomenon caused by variation of density during solidification and cooling of molten metals. In our model, the Navier-Stokes equations along with energy equation including phase change are solved using a 2-D axisymmetric mesh. We used the VOF method to track the free surface of droplet. For solidification, we used an enthalpy-porosity formulation. The simulations performed in this study are accomplished using a commercial code (Fluent). Results of these scenarios are presented: the normal impacts of 2.7mm tin droplets at 1m/s and 2m/s, initially at 240°C, onto a 27°C steel substrate. When the droplet impacts the substrate with a velocity of 1m/s, the final splat has a single cavity inside due to shrinkage. In other cases with the scales of a typical thermal spray process, the results of normal impact of nickel droplets with a velocity of 73m/s, initial temperature 1600°C and diameter 60μm to steel substrate with different temperatures are presented. In these cases shrinkage decreases the droplet splashing on the substrate.