Natsuo Yukawa

Electronic effect on the ductility of alloyed TiAl compound

Abstract Alloying effects on the electronic structure of a TiAl compound have been investigated systematically using the discrete variational (DV) Xα cluster calculation. It has been shown that the existence of directional Al p-Ti d covalent bonds causes this compound to be brittle. The addition of those elements into TiAl which weaken p-d interactions but enhance d-d interactions is most effective in improving the ductility.

Alloying effect on the electronic structure of BCC Fe

The influence of a number of alloying transition elements on the electronic structure of BCC Fe has been studied by the DV X alpha cluster method. The calculated electron density of states of BCC Fe, which resembled the result of band calculations, was modified by the alloying. This modification occurred mainly due to the appearance of the new d orbital levels of the alloying transition metal above the Fermi level. Such metal d levels changes systematically with the order of elements in the Periodic Table and correlated with the electronegativity and atomic radius of the metal. The ionicity and the bond order of various alloying elements were estimated and used to elucidate the nature of the bonds between solute and solvent atoms in the BCC Fe phase. The importance of the second-nearest-neighbour atomic interaction in BCC metals, assumed a priori to be large in a previous study, was confirmed. In particular, it was found to be remarkably high in those BCC metals which exhibit an allotropic transformation to the close-packed FCC or HCP phase. The problem of the solid solubility of BCC Fe alloys was also discussed in terms of the metal d levels and the bond order.

Rapidly solidified MC carbide morphologies of a laser-glazed single-crystal nickel-base superalloy

Rapidly solidified MC (TiC type) carbide morphology and its evolution with solidification cooling rate were studied comprehensively for a laser-glazed hot-corrosion resistant single-crystal nickel-base superalloy. The rapidly solidified interdendritic MC carbide was found in flower-like or radially branching morphologies which are closely related to the solidification cooling rate. At a relatively low cooling rate (9 X 10(3) K s-1), the carbide takes up the flower-like morphology, in which a few thick plates grow radially from the central nucleus. As the cooling rate increases, the growth morphology changes from flower like to radially dendritic and finally to well-developed radially branching colonies. The growth mechanism of the rapidly solidified MC carbide was confirmed to be lateral growth from the ledges or steps existing on the growing interface. The branching of the well-developed highly branching carbide occurs from the twins or twin intersections on the advancing fronts.

Design and development of hot

AbstractAs the first step to design and develop the new hot corrosion-resistant nickel-base single-crystal superalloys by thed-electrons alloy design theory (or the New PHACOMP), an evaluation of the phase stability of the modified hot corrosion-resistant IN738LC nickel-base superalloys (Ni-16Cr-9.5Al-4.0Ti-8.0-Co-0.55Nb-0.06Zr-0.05B-0.47C-(0~3)Ta-(0~3)W-(0~3)Mo (in atomic percent)) was conducted with the alloy design theory. The critical conditions for suppressing the precipitation of the brittle σ phase can be described by the electronic parameters

Alloying effect on the electronic structure of aluminium

\overline {Mdt} \leqslant 0.991

An electronic approach to alloy design and its application to Ni-based single-crystal superalloys

and

Design and development of hot corrosion-resistant

\overline {Md\gamma } \leqslant 0.93