Morphology of random packing of micro-particles and its effect on the absorption of laser radiation during selective melting of powders

The results of analytical and numerical studies of the internal structure of random packed beds of metal micro-particles are presented. To construct packed beds from mono- and polydisperse solid spheres, an algorithm for their random generation based on the discrete element method is used. Analysis of the structure of the packed bed includes the determination of porosity, specific surface area and tortuosity of the pores when changing powder particle sizes. A theoretical conclusion of these structural parameters is proposed in the form of formulas. The data obtained characterize the percolation properties of the granular medium, which affects the propagation and absorption of laser radiation in the volumetric layer of particles. Analysis is made of the influence of the physical properties of particles on the limiting characteristics of the penetration of laser radiation into a packed powder layer; the effects of radiation absorption and scattering in the pore space of a granular medium are estimated. A comparative analysis of approximate analytical and numerical solutions with the data of known experiments is carried out. (C) 2020 Elsevier Ltd. All rights reserved.