静水圧加圧成形体の均質性(第2報) : 成形圧力の影響  [in Japanese] Structural Homogeneity of CIP Formed Green Compacts (Part 2) : Influence of Applying Pressure  [in Japanese]

The influence of applying pressure on structural homogeneity such as density and microhardness distribution in CIP-ed powder compacts of silicon carbide has been investigated at the pressure from 100 to 900MPa. The green density of thin disks (φ10mm×3mm) varied according to Cooper's relation, which showed that the compaction of powders performed through two processes with different pressure dependence. A compaction process in the low pressure region (<200MPa) was packing which accompanies the deformation of agglomerated particles (Process I). and the following process in the high pressure region (>300MPa) was the rearrangement of primary particles (Process II). Vickers microhardness increased remarkably in the later process. As for larger powder compacts (φ52mm×25mm). inhomogeneous surface layer formed as the result of reduction of applying pressure by friction among particles and bridgings. The degree of the inhomogeneity varied de-pending on the applying pressure. Microhardness decreased gradually toward the center of compact at the pressure of 100MPa. where only Process I was predominant in the surface and also the center of compact during CIP-ing. At 200MPa, the difference in microhardness between the surface and center of compact increased because the pressure reduced to the level where Process I was predoninant at the center, on the contrary, Process was predominant near the surface. Above 500MPa. a homogeneous zone with almost constant microhardness values was formed in the compacts. The homogeneous zone developed with increasing applying pressure. At 900MPa, the compact showed the most homogeneous structure covered with a high hardness thin surface layer. Highly dense and homogeneous powder compacts could be formed by applying high CIP-ing pressure.