Nanolaminate - bulk multilayered Nb-Cu composite: Technology, Structure, Properties

摘要

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℃, 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 behaviour in the first and second cycles. A significant growth of hardness and the change over from the parabolic to the linear behaviour of the dependence is observable at a thickness of the layers less than 200 nm in the 3-rd cycle. The hardness amounting to 350 HB was observed at layers thickness of 11 nm. Noticeable changes of the hardness and halfwidth of X-ray peaks of Nb and Cu occur after annealing at temperatures above 400℃. After annealing at 1000 ℃ 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.