The Effects of Thermal Shrinkage on Coating Formation in Thermal Spray Processes: A Numerical Approach

Abstract

In this paper, we performed a numerical study on the<br><br>effects of thermal shrinkage on the deposition of<br><br>molten tin droplets on a steel substrate in thermal spray<br><br>coating process using Volume-of-Fluid (VOF) method.<br><br>Thermal shrinkage is a phenomenon caused by<br><br>variation of density during solidification and cooling<br><br>down of molten metal. The Navier-Stokes equations<br><br>along with the energy equation including phase change<br><br>are solved using a 2-D axisymmetric mesh. We used<br><br>the VOF method, applied to the fixed Eulerian mesh, to<br><br>track the free surface of the droplet. For solidification,<br><br>we used an enthalpy-porosity formulation. The<br><br>simulations performed in this study are accomplished<br><br>using both a commercial code (FLUENT) and an inhouse<br><br>developed program. The results of these<br><br>scenarios are presented: the normal impacts of 2.7mm<br><br>spherical tin droplets at 1m/s and 2m/s, initially at<br><br>240°C, onto a 27°C steel substrate. It is seen that when<br><br>the droplet impacts to the substrate with 1m/s velocity,<br><br>it spreads and solidifies and during the recoil of the<br><br>droplet, a single cavity forms within the splat which is<br><br>the source of porosity and is caused by shrinkage.