Solid state transformations from spheres to polyhedrons in hollow Fe spheres

The present work analyzes the sintering conditions for ∼ 3 mm inner diameter hollow iron spheres, sintered for manufacturing composite structures. Optimal sintering variables were investigated modifying temperature from 700 to 1200◦C, while times were between 1 and 3 h. Results showed that packing of the spheres increased with time and temperature: at 700◦C sintering was not enough; at temperatures from 800◦ to 1000◦C spheres were well sintered with porosity between them; while at higher temperatures were completely packed. Densities ranged from 0.6 gcm−3 to a maximum of 1.1 gcm−3 for spheres 100% packed, where it was observed a sphere-to-polyhedron shape transformation, with maximum values of penetration (0.39 mm) and sintering neck width (1.42 mm). Complete packing of the Fe particles of the sphere walls was also observed. The use of Design of Experiments made possible to establish correlations between sintering variables and characteristics such as neck width, penetration, porosity and packing. These results could be used as a starting point for the adequate selection of the sintering conditions of hollow Fe spheres for manufacturing hollow composite structures, taking into account not only the characteristics of the sintered hollow spheres but also of the Fe particles forming their walls.