Papers by Author: Yuushi Sakai

Abstract: The deformation and fracture behavior at 1773-2023K of the unidirectionally solidified eutectic Al2O3/YAG (Yttrium-Aluminum Garnet with the composition of Y3Al5O13) ceramic composite was investigated. The stress-stain curve and strength of unnotched and notched specimens, measured by bending and tensile tests, showed that (a) both unnotched and notched specimens fractured in a brittle manner at low temperatures and at high displacement speeds, but in a ductile manner at high temperatures and at low displacement speeds, and (b) the notched strength increased, reaching maximum, and decreased with increasing temperature and decreasing displacement speed. The increase in the notched strength with increasing temperature and decreasing displacement speed up to the maximum value was accounted for by the increase in plastic zone size ahead of the notch, and the decrease with further increasing temperature and decreasing displacement speed by the loss of the stress carrying capacity of the yielded ligament, based on the finite element analysis.

Abstract: Several Fe – O samples containing different fractions of dispersed oxides were processed by mechanical milling followed by consolidating rolling. The samples were annealed at 1000oC and then compressed to strains of 0.35, 1.2, and 1.9 at an ambient temperature. Dispersed oxides with size of about 20 nm were homogeneously distributed throughout the ferrite matrix and their volume fractions varied from about 0.3% to 2.0%. To study the annealing softening mechanisms, the coldworked specimens were annealed for an hour at 700oC and 800oC. The fine dispersion of oxide particles was very effective to suppress any softening processes. Primary recrystallization fully developed in the samples with volume fraction of dispersed oxides of about 0.3%. Increase in the fraction of dispersed oxides resulted in decrease of the fraction recrystallized. In the samples containing 2.0 vol.% of dispersed oxides, only recovery was the annealing softening process irrespective of the preceding cold strain. The critical volume fraction of dispersed particles for development of the primary recrystallization is considered to range from 0.5 to 2.0%.