Ba-フェライト焼結体の微細構造および機械的性質に及ぼす押し出し加工の効果

抄録

In order to examine the possibility of hot-forming of ceramics by utilizing their plastic property and to elucidate the mechanism of the process, a hot-extrusion processing was applied to polycrystalline Ba-ferrite (BaO·6Fe₂O₃). The effects of the stem speed and area contraction ratio on the microstructure and mechanical properties of the extruded Ba-ferrite were studied.
Sintered Ba-ferrite samples were capsulated into stainless steel (SUS 304) to prevent the fracture of the ceramic, and heated from 1100°C to 1390°C. The heated capsule was immediately transferred into the container and then extruded at a stem speed of 3.5mm/sec to 17.5mm/sec with varying area contraction ratios from 48% to 84%. The extruded Ba-ferrite ceramic was found to exhibit finer and denser microstructure than the non-extruded. These effects were accelerated with larger deformation and lower stem speed. The Vickers hardness (H_v) and fracture toughness (K_c) of the extruded Ba-ferrite increased remarkably and their values were comparable to those observed for a hot-pressed body. As for K_c, anisotropy was observed: K_c perpendicular to the extruding direction was higher than that of the parallel direction. In the case of extrusion of the billet at large contraction ratios, smooth extrusion of the ceramic could not be realized due to the difference in deformation resistance between the capusule and Ba-ferrite.