Multi-Directional Solidification Model for the Description of Micro-Pore Formation in Spray Deposition Processes

Abstract This paper describes a numerical investigation of micropore formation in solidifying molten metal droplets impinging on a colder substrate. The velocity field inside the spreading liquid droplet is computed as a solution of the incompressible Navier-Stokes equations, and a Volume of Fluid function is defined in order to track the location of the free-surface. Computations based on a uni-directional solidification model show that, under conditions representative of spray deposition processes, the high-velocity liquid metal spreading on top of the solidifying layer overflows, and reattaches to the substrate at a further radial location where solidification also starts. A multi-directional solidification model is therefore implemented to simulate the formation of possible pores and/or troughs. This model is based on the application of a locally 1-D solution where the solid front advances in the direction normal to the solid/liquid interface. The multiple solid/fluid interfaces are tracked using uniformly distributed markers. The tracking algorithm allows for complex interface morphology representation as well as interface merging simulation. In the test case considered (high-velocity impact of a single droplet) no direct pore formation was observed. However, simulations predict the formation of an annular trough on the surface of the solidified splat. This feature may be a precursor of pore formation in multiple-droplet cases.