Direct laser manufacturing with coaxial powder injection: Modelling of structure of deposited layers

Direct Laser Manufacturing (DLM) with coaxial powder injection is applied for fabrication of near net shape objects from metallic powder. The proposed model includes analysis of the two-phase flow formed by the coaxial nozzle, particles heating by the laser beam, and deposit formation. The experimentally observed deposit looks like a porous array of separate intersecting particles. The density of the deposit is determined by competition between kinetic energy of the liquid droplets at impact and surface tension forces preserving their spherical shape. It is shown that the density, the mean coordination number and the maximum radius of the necks formed between particles increase with the impact velocity. The particles are bound preferentially in the vertical direction. The bounding anisotropy decreases with the impact velocity. The neck size distribution changes from a very narrow one at low velocities to a wide distribution at high velocities. The radial distribution function indicates that short linear chains of particles are formed at low impact velocities, these chains disappearing at higher velocities.