Kiyohiko Tatsuzawa

Magnetic Properties of Nano-Particulate Cu-Co Alloy on the Route of Bulk Mechanical Alloying

Bulk mechanical alloying was used to fabricate the supersaturated solid solution of Cu 80 Co 20 . The nano-Co particulates Cu-matrix alloy was made by low-temperature annealing. Both the annealing temperature and time were parametrically varied to describe the relationship between process condition and magnetic properties. The maximum magnetoresistance ratio under 1.0 MA/m at room temperature of 4.9 % was measured for this nano-particulate material with the mean Co-particulate size of 6 nm. From the measured magnetic properties, the effect of particulate size of Co in Cu-matrix on the magnetic properties was discussed.

Processing and characterization of alumina wire by controlled fracture forming process:: (I) Forming behavior and evolution of green microstructure

Abstract The forming behavior of the Al 2 O 3 wire on the route of the controlled fracture forming (CFF) process, and the evolution of its green microstructure with respect to particle size and pore morphology are investigated. Results indicate that the 98% reduction in area is required to form the wire with high relative density (∼77% theoretical density) as well as homogeneous green microstructure. The intense compressive stress or strain resulted from the plastic deformation of the metal sheath material crushed the agglomerates or the larger grains in the presintered billet, and the flow and rearrangement of these constituent particles resulted in the elimination of the larger pores with coordination number more than 12. Because of the smaller particles and the homogeneous pore distribution, the formed wire can achieve full densification, which implies that the CFF process has a potential to fabricate the ceramic wire reinforced metal matrix composites.

Forming and microstructure control of ceramic/metal composite wires

The Al2O3/SUS 304 (JIS) and Al2O3/β–Ti alloy composite wires have been formed on the route of the controlled fracture forming (CFF) process. Factors affecting the forming limit of the composite wires and the morphology of the as-formed Al2O3 core are investigated. The forming limit is significantly dependent on the initial area ratio (IAR) of the metal sheath to the ceramic billet and more than 3.0 of IAR is required to form the composite wires without cracking or fracturing the metal sheaths. The pre-sintered billets and the metals with high fracture strength are favorable to increase the relative density and to improve the particle morphology of the as-formed Al2O3 core. The mechanisms for the densification and the morphological improvement are considered as follows: the compressive stress that results from the plastic deformation of the metal sheaths during the cold forming process is continuously applied to the Al2O3 core, making its particles refined and rearranged and resulting in homogenous microstructure as well as high relative density.

Processing and characterization of alumina wire by controlled fracture forming process: (II) Resintering behavior and mechanical properties

Abstract The resintering behavior of the CS-Al 2 O 3 wire, and its mechanical properties with respect to the Vickers hardness and the tensile strength has been investigated. Results indicate that the CS-98 wire can be fully densified without abnormal grain growth. The improved densification is attributed to the crushed constituent particles with new surfaces accelerating the matter diffusion. The retardation of grain growth is attributed to the homogeneously distributed pores in the green microstructure, which act the drag forces on grain boundary migration. The fracture mode of the resintered wire shows to be dependent on the residual pores, viz. the transgranular fracture is dominant at porosity 2%. The distribution of the Vickers hardness on the cross-sectional surface of the Al 2 O 3 core in the resintered Al 2 O 3 /SUS 304 composite wire indicates that the sheath material has a significant influence on the mechanical properties of the core.

High speed mechanical alloying for bulk amorphous intermetallics.

New alternative mechanical alloying is proposed and developed with active and intelligent use of local shear material flow and high hydrostatic pressure. Ag-Cu system is employed for verification of the present approach and investigation to discuss the relation between number of process cycles and broadening in X-ray diffraction.