Microstructural features in multicore cu–nb composites

The study is devoted to heavily drawn multicore Cu–18Nb composites of cylindrical and rectangular shapes. The composites were fabricated by the melt-and-deform method, namely, 600 in situ rods of Cu–18%Nb alloy were assembled in a copper shell and cold-drawn to a diameter of 15.4 mm (e = 10.2) and then rolled into a rectangular shape the size of 3 × 5.8 mm (e = 12.5). The specimens were analyzed from the viewpoints of their microstructure, microhardness, and thermal stability. The methods of SEM, TEM, X-ray analysis, and microhardness measurements were ap-plied. It is demonstrated that, at higher strain, the fiber texture < 110 > Nb || < 111 > Cu || DD (drawing direction), characteristic of this material, becomes sharper. The distortions of nio-bium lattice can be observed, namely, the {110} interplanar distance is broadened in longitudi-nal direction of specimens and compacted in transverse sections. The copper matrix lattice is dis-torted as well, though its distortions are much less pronounced due to its recrystallization. Evolution of microstructure under annealing consists mainly in the coagulation of ribbon-like Nb filaments and in the vanishing of lattice distortions. The structural changes in Nb filaments start at 300–400 °С, then develop actively at 600 °С and cause considerable decrease of strength at 700–800 °С.