Simulazione numerica ed evidenza sperimentale della accelerata formazione di colli durante le fasi iniziali della sinterizzazione assistita da microonde di polveri metalliche

Coupling numerical simulation of the electromagnetic field during sintering of metallic powder compacts and metal-containing composites with the experimental results, it has been possible to demonstrate the existence of a microwave enhancement of the early stages of sintering, in particular the necks formation. The main phenomena involved resulted to be the electromagnetic field concentration in the regions among the conductive particles, as well as direct microwave absorption within the skin depth of the metal particles. This local concentration of the electric field, occurring exactly in the regions of necks formation, can have intensity higher than the dielectric strength of the medium, thus favouring breakdown phenomena, leading to arcing and local plasma formation, which trigger more efficient mass transport mechanisms during sintering. Three different cases has been numerically simulated and experimentally tested, in order to study the effects of particles dimension and shape: sintering of micrometric steel and brass spheres, sintering of millimetric pure metals and brass spheres, sintering of glass matrix composites reinforced with metal fibres.