Numerical modeling of sintering of two-component metal powders with laser beams

Abstract

Direct laser sintering of a mixture of two metal powders with significantly different melting points is investigated by numerical simulation. The model is based on self-consistent non-linear continuity equations for volume fractions of components and on energy transfer equations for the powder mixture. It includes the movement of the solid particles due to shrinkage because of the density change of the powder mixture and the liquid flow driven by the capillary and gravity forces. The liquid flow is determined by Darcy's law. The effect of surface settlement of the powder is obtained. The width increasing rate of the melting zone depend both on the parameters of the laser radiation (on the power of the beam) and on the physical parameters of the particle's material, and it increases with the increasing of the penetrability or the increasing of the phase-transition heat. The increasing of the laser power under other factors being equal results in the acceleration of the melting front propagation.

Heat and mass transfer under laser sintering of a powder mixture

“…As was found in [7], in the sintering of the two component powder, two modes of PT zone propagation are possible. The profiles of temperature corresponding to these regimes are shown in Figures 1-2.…”

“…This work, being a continuation of [7], takes into account the change in porosity and its effect of the evolution of temperature and phase saturations in sintering a two component powder compact. The essence of the model is that a fraction of the high melting phase cannot decrease on the fixed Lagrange coordinate as was the case in the model with constant porosity.…”

“…This system shown in Fig. 1 in [7] consists of ultradisperse particles of two metal materials with differing temperatures of particle melting. The starting temperature distribution of the powder mixture is homogenous.…”

“…As is small enough ( c) compared to the characteristic time of the sintering pro cess, further we will relate the starting condition will to zero ( ). In [7], the Lagrange volume (by volume of high melting component) coordinate was intro duced such that .…”

“…In our earlier work [7], the laser melting of two compo nent powders was considered within a model in which the porosity of the disperse medium was assumed to be constant. It was found that the width of the phase transfer (PT) increases with time, and the volume fraction of the low melt ing powder in the PT zone is greater than in the unmelted zone and that of the high melting powder is, on the contrary, smaller.…”