Sakae Saito

In situ observations of crack propagation and role of grain boundary microstructure in nickel embrittled by sulfur

In situ observations of crack propagation in sulfur-doped coarse-grained nickel were performed for the specimens with grain boundary microstructure pre-determined by SEM/EBSD analysis. The role of grain boundary microstructure was studied in the crack propagation in nickel embrittled by grain boundary segregation of sulfur. It was found that the main crack tends to predominantly propagate along random boundaries, and the crack propagation rate can be locally accelerated at the grain boundary network with a high connectivity of random boundaries. On the other hand, the cracks can propagated along fracture-resistant low-Σ coincidence site lattice (CSL) boundary only when the trace of the grain boundary is arranged being almost parallel to slip bands in the adjacent grains. The local crack propagation rate was found to become lower when a crack propagated along low-Σ CSL boundaries. Moreover, when the crack propagation is inhibited by low-Σ CSL boundaries, the branching of propagating crack occurs at partially cracked triple junctions. The crack propagation can locally slow down due to the occurrence of crack branching. The optimum grain boundary microstructure for the control of sulfur segregation-induced brittle fracture is discussed on the basis of new findings obtained from the in situ observations on crack propagation and fracture processes in polycrystalline nickel.

Superconducting properties of Nb3Al wire fabricated by the clad-chip extrusion method and the rapid-heating, quenching and transformation treatment

Abstract The study of a fabrication process for Nb 3 Al intermetallic compound wire and measurements of its superconducting properties are presented. The adopted process of fabrication for the superconducting wire consists of the clad-chip extrusion (CCE) method and the rapid-heating, quenching and transformation (RHQT) treatment. The former (CCE) is the processing of Nb/Al composite wire characterized by the extrusion of thin chips of Nb/Al clad-sheet in which the thickness ratio of the Nb-layer to the Al-layer corresponds to Nb 3 Al. The latter (RHQT) is the heat-treatment method to transform the CCE-processed Nb/Al composite wire into the Nb 3 Al intermetallic compound, which gives a nearly stoichiometric composition and a fine grain of Nb 3 Al for high performance of superconductivity. The experimental results show that the wire is successfully fabricated by the CCE method and the RHQT treatment, and its superconducting properties are improved to 18.02 K of T c and 318 A/mm 3 of J c at 20 T and 4.2 K. It is also shown that 26.3 T of H c2 is estimated by a Kramer plot.

Manufacturing processes and properties of clad metals by plastic working

Abstract Intermetallic compound Nb3Al superconducting wires were successfully fabricated by newly developed process, in which thin chips of Nb sandwich-rolled with Al were used as starting materials. This was termed the Clad-chip Extrusion (CCE) process. The fabrication process and the effects of several factors on the wires performance were studied. Furthermore, the workability of the high Tc superconducting ceramics (YBa2Cu3Oy) was improved by the Peripheral Shear Bonding (PSB) process, where a preformed ceramic core is tightly joined with a metal sleeve. Properties of the joint interface and workability of the multi-type billet for the advanced material products were discussed. These CCE and PSB processes research have proven to raise the level of workability for intermetallic compounds and ceramics and the possibilities look favorable for hard alloys.

Superconducting properties depending on the processing parameters of Nb/sub 3/Al wires by the clad-chip extrusion method and the rapid-heating, quenching and transformation treatment

Superconducting properties depending on the processing parameters of Nb/sub 3/Al wire fabrication are presented. The adopted process consists of the clad-chip extrusion (CCE) method and the rapid-heating, quenching, and transformation (RHQT) treatment. The former (CCE) is a fabrication method for Nb/Al composite wire. It is characterized by the extrusion of thin chips of Nb/Al clad-rolled sheet. The latter (RHQT) is a heat-treatment method to transform the CCE-processed Nb/Al composite wire into the Nb/sub 3/Al intermetallic compound. The focused processing parameters are the chemical composition and the thickness of Nb/Al layers in the composite, and the cold working of the bcc supersaturated solid solution Nb(Al)/sub ss/ wire after the rapid-heating and quenching treatment. The results are as follows. A nearly stoichiometric composition of the CCE-processed precursor wire is optimum for enhancing the critical transition temperature T/sub c/ and the critical current density J/sub c/ of the Nb/sub 3/Al wire after the RHQT treatment. The thinner the Nb/Al layers in the CCE-processed wire, the higher the J/sub c/ and T/sub c/ of the RHQT-treated Nb/sub 3/Al wire. The as-quenched Nb(Al)/sub ss/ wire can be drawn to nearly 50% reduction at room temperature. Such cold working of the Nb(Al)/sub ss/ wire before transformation is an effective operation to improve J/sub c/-B property of the transformed Nb/sub 3/Al wire by the following treatment.

Superconducting Properties of

Fabrication and superconducting properties of Sn added Nb3 Al wires are presented. The wire fabrication process consists of the clad-chip extrusion (CCE) method and the rapid-heating, quenching, and transformation (RHQT) treatment. The former (CCE) is a metal-composite fabrication method and characterized by the extrusion of thin chips of Nb/Al clad-rolled sheet. It can produce the Sn-adding Nb/Al microcomposite precursor with the intended chemical composition. The latter (RHQT) is a heat-treatment method to transform the precursor to the Nb3Al wire by way of the bcc-structured supersaturated solid solution, Nb(Al)ss. It can produce not only the nearly stoichiometric composition but also fine grain of Nb3Al, which is favorable for upgrading the superconducting properties. The combined process of the CCE method and the RHQT treatment successfully fabricated the Sn added Nb3Al wires with Sn-addition from 0.25 to 5 atomic percent (at%). Sn-addition to Nb/Al composite wires affected the phase transformation at RHQT treatment. With increasing Sn-addition, the Nb(Al)ss became unstable and A15 phase was dominant at the stage of rapid-heating and quenching. The RHQT-treated Nb3Al wire with nearly 2 at% Sn-addition showed the maximum transition temperature Tc but the more addition decreased Tc. The small Sn-addition within 2 at% improved both of the critical field and the critical current density, although the more addition decreased them drastically