Metal droplet deposition on non-flat surfaces: effect of substrate morphology

In droplet-based deposition processes, substrate morphology plays an important role in the bonding quality between splats and substrate. This paper presents a numerical investigation of metal droplet impact and solidification on two types of non-flat surfaces, namely a pre-molten pool and a wavy surface. We solve the axi-symmetric incompressible Navier–Stokes equations and an enthalpy formulation of the energy equation to simulate both the flow field and the heat transfer during droplet spreading and solidification. The results show that for efficient droplet deposition on molten pools, the pool size and droplet impact velocity should be kept relatively small. Droplet impingement on non-flat surfaces is almost always accompanied by splashing. The degree of splashing decreases with the increase in surface roughness height. Increasing surface roughness wavelength improves droplet spreading and hence solidification.