Formation process of A15 type Nb3Al phase by the solid/liquid interfacial reaction

Methods for fabricating A15 type Nb3Al superconducting materials based on t he solid Nb/liquid Al interfacial reaction have recently drawn the strong a ttention of workers in this field around the world. It seems, however, that the details of the formation process of the A(15)(Nb3Al) phase in these me thods are not yet clear. Therefore, in the present study, we have performed some experiments in order to obtain some basic information about the proce sses involved. As a consequence, the following data were obtained; For Nb/A l composites with a single Al rod covered by a Nb tube heated at 1723 simil ar to 2073 K for given times, 1) the sigma(Nb2Al)-phase grows rapidly from the solid/liquid interface toward the interior of liquid Al, and 2) the A15 phase grows very gradually, with its grown width being about 40 mu m at mo st for the sample heated at 2073 K for 1 h.