Abstract
At the interface between A15-phase layer and Nb solid-solution (NbS.S) region in a bulky Nb/Al composite, a layer of two-phase structure of Nb3Al plus NbS.S is formed when the composite is heated at 2073 K, whereas it is not formed when heated at 2023 K or less. The morphology and width of the two-phase structure layers are significantly influenced by the cooling rate from 2073 K and by the heating time at that temperature. These facts, as well as the theoretical consideration, suggests that the two-phase structure is formed during the cooling process from 2073 K. When cooled more slowly from 2073 K than a certain cooling rate, there observed anomalous growth of A15-phase, which is strongly correlated with formation of the two-phase structure. Most favorite performance of the bulky Nb/Al composite as the super-conducting material is obtained by cooling it at the slowest cooling rate after 1 h heating at 2073 K as far as the present study is concerned.
