Kazuhisa Kita

Misorientation dependence of discontinuous precipitation in Cu-Be alloy bicrystals

The boundary-dependent discontinuous precipitation (DP) for various [001] symmetric tilt boundaries in Cu–5.2 at% Be alloy bicrystals has been examined in the temperature range 523–698 K. The precipitate phase maintains a constant interlamellar spacing under isothermal growth conditions. The interlamellar spacing increases with an increase in temperature. The incubation period τ to initiate DP and cell growth rate for DP against misorientation angle diagrams show local peaks and cusps at the same misorientation angles. The positions of the peaks and cusps agree with those of cusps in the boundary energy against misorientation diagram. The formation and growth of DP occur more easily at higher-energy boundaries. A detailed kinetic analysis of the experimental data using the models by Turnbull and Petermann–Hornbogen has enabled the determination of the grain-boundary diffusivity of Be along each boundary in the temperature range studied. A close correlation is found between the diffusivity and the energy of boundaries. A higher-energy boundary has a higher diffusivity with a smaller activation energy and a smaller pre-exponential factor.

High performance of mechanical and electrical properties of Cu-Cr-Zr alloy sheets produced by ARB process and additional thermo-mechanical treatment

The additional cold rolling and the aging process were applied to Cu-0.85Cr-0.07Zr alloy sheets processed by ARB, and mechanical properties and structural information were investigated for the purpose of further improvement of the mechanical properties and the electrical conductivity. From the results of the tensile test and the measurement of electrical conductivity, ARB/aged/CR was most appropriate processing in order to achieve technical advantages. The high tensile strength of 745 MPa and the high electrical conductivity of 68 %IACS were obtained simultaneously. In addition, the improvement of incomplete boundaries generated during ARB processing was possible by thermo-mechanical treatment.

Structure and Mechanical Properties of Severely Deformed Cu-Cr-Zr Alloys Produced by Accumulative Roll-Bonding Process

Aging behavior and mechanical properties of ultra fine grained Cu-Cr-Zr alloy sheet produced by accumulative roll bonding (ARB) process were investigated. A Cu-0.85Cr-0.07Zr (in mass%) alloy was solution treated and then cold-rolled at ambient temperature in the sheet of 1 mm thick. The sheets were heavily deformed by ARB process at ambient temperature up to 5 cycles. The grain size was reduced down to 210 nm and the fraction of high angle grain boundaries (HAGB’s) in the specimen after ARB process was 63%. The proof stress ( σ 0.2) and elongation were 540 MPa and 10%, respectively. Due to the aging treatment, a little grain growth took place (240 nm) and the fraction of HAGB’s was increased to 67%. The proof stress and elongation of the aged one increased to 605 MPa and 15%, respectively. It was noteworthy that the electrical conductivity remarkably increased from 35% to 79%IACS by the aging treatment. It was concluded that the aging treatment after ARB process enhanced not only the mechanical properties but also the electrical conductivity in the Cu-Cr-Zr alloys.