Neutron diffraction measurement of residual stresses in CFC/Cu/CuCrZr joints for nuclear fusion technology

Residual stresses were experimentally determined in specimens of carbon-fibre composite (CFC) brazed to CuCrZr alloy, using neutron diffraction at the E3 instrument of HMI-BENSC (Berlin). The brazing was obtained by means of a Cu interlayer, one side of which was brazed to the CuCrZr alloy, after the other side was joined to CFC by a proprietary technique. Two different samples were investigated, the first one in the ‘as-brazed’ condition and the second one after thermal fatigue cycling [heating of samples up to 450 ◦C followed by a fast cooling (>1 ◦C s−1) to room temperature in air with water quench; the cycles were repeated 50 times for each sample]. Residual stresses were determined in the three principal directions, in the CFC and in the CuCrZr alloy, as a function of the distance from the interface with the Cu interlayer. The experimental results for the as-brazed specimen are in agreement with the results of FEM calculations available in the literature, while a relaxation of residual stresses in the thermally fatigued specimen is found to be probably ascribed to the formation of microcracks at the CFC/Cu interface.