Abstract
The fatigue behavior at room temperature and its influence on the superconducting properties of Nb3Al composite wire with a copper ratio of 1.55, containing 241 Nb3Al filaments with an average diameter of 34 μm, were studied. The main results are summarized as follows.
(1) Fatigue cracks nucleated and grew in the matrix (Cu), and thereby caused the fracture of Nb3Al filaments. The Nb3Al filaments themselves were not fractured by fatigue. (2) The growth pattern of the fatigue cracks depends on the maximum-applied-stress (σc, max) level. (a) At high σc, max, overall fracture of the composite occurs before the growth of fatigue cracks. The filaments are merely broken except in the fracture surface as in the case of the static test. (b) At intermediate σc, max, fatigue cracks can grow at several points before the breakage of the composite. Thus the breakages of the filaments are accumulated not only in the fracture surface, but also in the whole body. (c) At low σc, max, one fatigue crack grows in advance of others, causing the breakage of the composite. Thus the filaments are broken only in the fracture surface. (3) Corresponding to the growth patterns of the fatigue cracks mentioned in (2), the result of the measurement of critical current (Ic) using the rest part of the broken composite after the fatigue test shows the reduction in Ic at intermediate σc, max, but not at high and low σc, max.
