Associate Professor, Yokohama National University, Japan

Dr. Makoto Hasegawa obtained his Doctor of Engineering from Yokohama National University, Japan in 2002. He worked as a postdoctoral research fellow and research associate in The University of Tokyo from 2002 to 2006 and a research associate in Yokohama National University from 2006 to 2010. From 2011, he became an associate professor in Yokohama National University. His is currently focused on the researches of the high temperature processing on intermetallic compounds and alloys for preferential orientation control and an orientation control of metals and ceramics coatings by aerosol deposition method which will form the coatings under room temperature processing.

Speech Title: Fracture toughness of a lamellar orientation controlled TiAl intermetallic compounds

Aims: Improving the fracture toughness of TiAl intermetallic compounds is currently an important issue, since these materials are candidates for various high-temperature structural applications. In this work, the effects of lamellae orientation and the distribution of fine grains and fine lamellar colonies on the fracture toughness of orientation-controlled Ti-43mol%Al intermetallic compounds were examined.

Methods: Fracture toughness was determined by three-point bending tests following the introduction of a chevron notch, and thermomechanical processing to control lamellar orientation consisted of high temperature compression in the α single-phase and (α+γ )two-phase regions.

Results: Materials processed by one-step compression in the α single-phase region exhibited tilting of the lamellae interface by approximately 20° to 30° relative to the compression plane. Further compression in the (α+γ )two-phase region (termed two-step compression) arranged the lamellae interface nearly parallel to the compression plane. Fine grains were also observed around the orientation-controlled lamellar colonies, and were converted into fine lamellar colonies during heat treatment following processing in the (α+γ) two-phase region. Specimens processed by one-step compression had fracture toughness values lower than those of two-step compression specimens. In addition, specimens processed using two-step compression and exhibiting a crack arrester orientation had higher fracture toughness values than those with a crack divider orientation.

Conclusions: Materials processed by two-step compression exhibited higher fracture toughness than materials to which only one-step compression was applied. Specimens having a crack arrester orientation were found to have higher toughness values than those with a crack divider orientation among the material processed via two-step compression.