Curvature Reversal Condition During Pore Shrinkage or Fragmentation

Pore shrinkage is caused by sintering pressure, and is affected by the curvature of the grains within the surface of pores, as well as variables, like grain size, pore radius, and dihedral angle. The sintering pressure is greatly influenced by the direction of curvature of grains within the pores, which, during the shrinkage of the pore, is sometimes reversed; this is termed curvature reversal. This research aimed to present the curvature reversal condition by means of a geometrical model, and thus the radius of curvature of a grain surface within the pore was calculated according to the dihedral angle assuming a grain size of 0.1–0.3 μm and pore radius of 500 μm. Calculation of the pore shrinkage showed that the sign of the radius of curvature changed along with the rapid increase in absolute value, so this was physically interpreted as curvature reversal. This curvature reversal was observed in the process of shrinking pores, as well as in the change of dihedral angle; the larger the grain and the dihedral angle, the larger the pore radius at which reversal occurred. This paper presents the conditions of curvature reversal during the sintering of powder compact according to the dihedral angle, grain size, and pore size, and discusses the implications for actual sintering.