Papers by Author: Akira Chiba

Abstract: Hot dynamic densification method was developed by combining self-propagating high temperature synthesis (SHS) with explosively shock powder compaction technique. This method is extremely short time processing. The main purpose in this study is to perform from synthesis to densification of TiB₂-TiN system high temperature ceramic composites and TiB₂-TiNi-Cu system functionally graded materials (FGMs) in one step. In TiN-TiB₂ ceramic composites, they showed up to 95% of relative density. It was appeared by TEM observations that both the two phases joined tightly each other. The FGMs also were produced by the same technique. They indicated no interlayer exfoliation and no macro cracks after thermal shock tests from 973 K to room temperature. It was shown that thermoelastic property of intermetallic TiNi phase as intermediate layer between ceramics and metal layers operated effectively.

Abstract: Metallic glass or amorphous alloys have been gaining popularity due to their low density, high strength, high fracture toughness, good corrosion and good wear resistance. Especially, bulk metallic glasses (BMGs), which are made in bulk form with a thickness of ~10mm at slow cooling rates of the order of 1~100K/s, have been noted as an industrial application. The welding to other materials becomes very important. Explosive welding of most popular Zr41.2Ti13.8Cu10Ni12.5Be22.5 bulk metallic glass to crystalline pure Cu plate is investigated in this paper and the BMG was found to retain the amorphous structure. The sound bonding with other materials is expected to push forward the application of BMGs for industrial usage.

Abstract: Recently, a number of amorphous alloys that possess high glass-forming ability and a wide supercooled liquid region before crystallization have been discovered. Especially, bulk metallic glasses, which are made in bulk form with a thickness of ~10 mm at slow cooling rates of the order of 1~100 K/s, have been noted as an industrial application. Hence the welding of bulk metallic glasses to other materials is very important. Explosive welding of most popular Zr41.2Ti13.8Cu10Ni12.5Be22.5 bulk metallic glass to crystalline pure Ti and SUS304 plates is investigated in this paper. The BMGs was found to retain the amorphous structure and the original mechanical properties. The sound bonding with other materials is expected to push forward the application of bulk metallic glass for industrial usage.

Abstract: Sm2Fe17Nx compound is a prospective candidate as a material for high performance permanent magnets because of its good intrinsic magnetic properties with a Curie temperature of 747K, a room-temperature anisotropy field of 14T and a room-temperature saturation magnetization of 1.5T. However, Sm2Fe17Nx compound decomposes to
-Fe and Sm nitride above 873K and conventional powder metallurgy processing techniques fail to meet the processing requirements. Shock consolidation is a viable alternative to process this compound. Fully dense Sm2Fe17Nx bulk materials were fabricated by cylindrical explosive consolidation technique using water as a pressure transmitting medium. Explosive consolidation is performed under cold state and fully dense materials can be obtained without any degradation of the characteristics of the powder states. Sound compacts were obtained without any cracks or teas, and the value of (BH)max of Sm2Fe17Nx compact is 23.8 MGOe.