Manufacturing of steel hollow spheres using commercial iron powders and investigations of their mechanical properties and microstructure

In this study, steel hollow spheres were manufactured using commercial iron powders by powder metallurgy technique. For manufacturing the hollow spheres, iron powders, copper powders (10 wt. %) and carbon powders (0.5 wt. %) were firstly mixed and then were added to the sodium silicate (10 wt. %) as binder to produce a homogenous suspension. Then, prepared suspension was coated on the polystyrene spheres. After drying the green spheres, two different heat treatment processes were carried out on the spheres including the melting and thermal de-binding and the sintering processes. The microscopic evaluations were performed by optical microscope and scanning electron microscope and mechanical properties of steel hollow spheres were investigated by the compression test. The results shown that sphere walls composed of four different regions including: the sintered iron powders region, the dispersed copper powders region, remained sodium silicate region and porosities region. In addition, the force-displacement curves of compressed spheres were revealed no significant differences in spheres with different sphere sizes. The fractures of spheres in compression forces were occurred based on the presence of the micro-cracks in the sphere walls and growth of them.