Hideo Awaji, Takuya Matsunaga and Seong-Min Choi
Nagoya Institute of Technology, Materials Science and Engineering, Gokiso-Cho, Showa-Ku, Nagoya 466-8555
In order to improve the fracture toughness of ceramics, we need to develop a new material design concept. One of the suitable concepts is to utilize dislocation activities even in brittle ceramics. Intra-type nanocomposites use dislocation activities to enhance the strength and fracture toughness. The dislocations are caused by sintering residual stresses around the second-phase nano-particles dispersed within the matrix grains. In this research, first, we clarified the relation between the strength, fracture toughness, and critical frontal process zone (CFPZ) size using alumina ceramics. The fracture toughness of ceramics is related closely to the CFPZ size, because ceramics with larger CFPZ size consume higher fracture energy during crack extension and indicate larger fracture toughness. Second, we fabricated toughened alumina-nickel nanocomposites using a soaking method which we developed recently to create an intra-type nano-structure, and found that the suitable annealing after sintering could achieve toughened nanocomposites. Finally, we discussed the relation between the fracture toughness and CFPZ sizes of the monolithic alumina, as-sintered nanocomposites, and annealed nanocomposites. The results revealed that the annealed nanocomposites had the highest CFPZ size and fracture toughness, because it was conceivable that the sessile dislocations in the CFPZ became nuclei of nano-cracks, created many nano-cracks, and expanded the CFPZ size.
ceramics, strength, fracture toughness, frontal process zone, nanocomposites
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