Yonosuke Murayama

High temperature strength, fracture toughness and oxidation resistance of Nb–Si–Al–Ti multiphase alloys

Abstract Nb–Si–Al–Ti quaternary phase diagram around three-phase region, which consists of niobium solid solution (Nbss), Nb3Al and Nb5Si3,is constructed in this study. The three-phase region exists up to titanium content of about 20 mol%. Based on the quaternary phase diagram, three-phase alloys containing Nbss from about 50 to 75% in volume are prepared to improve high temperature strength, room temperature fracture toughness and oxidation resistance simultaneously. When microstructure and composition are optimized (Nbss + Nb3Al + Nb5Si3) three-phase alloy with the addition of titanium exhibits higher compressive strength than nickel-based superalloys at room temperature to 1573 K. Fracture toughness at room temperature of (Nbss + Nb3Al + Nb5Si3) three-phase alloys is increased to over 12 MPa m1/2 by the addition of titanium without sacrificing high temperature strength. Oxidation resistance of (Nbss + Nb3Al + Nb5Si3) three-phase alloys is improved by the addition of titanium.

Analysis of orientation distribution in YBa2Cu3O7−x polycrystals by electron channeling patterns

A unit standard map for YBa2Cu3O7−x superconductors was constructed and indexed from a series of electron channeling patterns (ECPs). (001) pole figures of YBa2Cu3O7−x tapes and bulk specimens with various values of critical current density (Jc) were drawn by using the map covering [001‐110‐110] stereographic quadrant and ECPs taken from individual grains of the specimens. It was found that preferred orientation of (001) formed in the tape with a decreasing thickness of the tape, which raised Jc significantly. It is concluded that the ECP technique is very useful for the analysis of orientation distribution in small‐sized YBa2Cu3O7−x specimens such as tapes or thin films.

Dynamic recrystallization of Nb3Al produced from alloy powder

Abstract The deformation behaviour of Nb3Al compressed at above 1300 K was studied using off-stoichiometric, single-phase Nb3Al produced by consolidation of prealloyed and ball-milled powders. It was found that Nb3Al was able to be deformed plastically above 1400 K and the stress-strain curves showed deformation softening after a peak stress. Transmission electron microscopic observations revealed that this deformation softening was caused by dynamic recrystallization. The amount of deformation softening decreases and steady state deformation occurs at an early stage of compression, as the compression temperature increases.

Dissociated dislocations in deformed Nb3Al produced from alloy powder

Abstract Near-stoichiometric Nb3Al containing a small amount of niobium solid solution (3·7 vol%) and alumina (2·5 vol.%), which was produced from Nb-25 at.% Al alloy powders by hot isostatic pressing, was compression tested above 1300 K. The nature of dislocations induced by the plastic deformation was studied using transmission electron microscopy. The dislocations are dissociated into two partial dislocations which bound a stacking fault, These partial dislocations and the stacking faults belong to {100}. The Burgers vector of the partial dislocation and the displacement vector of the stacking fault are both determined to be (a/2)⟨001⟩.

Texture Study of Pressed YBa 2Cu3O7−x Polycrystals by Electron Channeling Patterns

(001) pole figures of YBa2Cu3O7−x tapes and bulk specimens with various values of critical current density (Jc) were drawn by analyzing electron channeling patterns (ECPs) taken from individual grains of the specimens. It was found that preferred orientation of (001) formed in the tape with decreasing thickness of the tape in agreement with the X-ray result. It is concluded that the ECP technique is very useful for the analysis of orientation distribution in small sized YBa2Cu3O7−x specimens such as tapes or thin films.