Nanolaminate - bulk multilayered Nb-Cu composite: technology, structure, properties

The Cu-Nb multilayered composite as a ribbon 50 mm in width and 0,35 mm in thickness was produced by the following procedures constituting a technological cycle: integration of a packet of specific number of layers (16 layers 0,35 mm in thickness both for Cu and Nb), rolling of the packet in vacuum at a temperature of 750-800 oC, cold rolling in air down to the thickness equal to that of one initial layer constituting the composite. The structure of the composites was examined by optical and electron microscopy, x-ray diffraction at all the stages. The hardness was measured in the course of cold rolling for each of 3 technological cycles. Upon completion of 3 cycles a nanolaminate was produced consisting of 32768 layers of 11 nm in thickness, the ribbon thickness being 0,35 mm. A change in the hardness as a function of true deformation has an ordinary parabolic behavior in the first and second cycles. A significant growth of hardness and the change over from the parabolic to the linear behavior of the dependence is observable at a thickness of the layers less than 200 nm in the 3rd cycle. The hardness amounting to 350 HB was observed at layers thickness of 11 nm. Noticeable changes of the hardness and half width of x-ray peaks of Nb and Cu occur after annealing at temperatures above 400 oC. After annealing at 1000 oC copper grains of about 200 - 600 nm in size form which comprise niobium inclusions of about 1-10 nm in size. The hardness drops down to 135 HB. (author)