Understanding and Modelling the Damage Evolution in CuCrZr via Mechanical Testing, Electron Microscopy, X-ray Tomography and Finite Element Simulation Techniques

Abstract

Achieving nuclear fusion is paramount in meeting the increasing global demand for clean, abundant and affordable energy. A key challenge in the realization of fusion energy is the design and manufacture of plasma-facing reactor components, which must withstand extreme thermal and neutron loads. The longevity of these components is critical in the minimization of reactor down-time and cost in case of component replacement. Reliable material models are required to design components against failure.
Copper-Chromium-Zirconium (CuCrZr) is a candidate material for the cooling pipes within the divertor, a plasma-facing component which extracts the heat and ash from the fusion reaction. The two key contributing factors to the failure of the material are the multiaxial stress state and irradiation-induced change in ductility, which the pipe will experience under plasma operation. This work aimed to analyse the effect of ductility on the material failure, and to validate a damage model for CuCrZr which could accommodate stress multiaxiality.
Three different heat treated conditions for smooth and notched tensile geometries were tested. It was found that void nucleation, growth and coalescence was the prominent failure mechanism in CuCrZr, with an increased shear contribution observed with increase in ductility and lower stress triaxiality. Coarse Cr and Zr-rich precipitates were identified as void-nucleating, and fine Cr and Zr-rich precipitates were responsible for material strengthening.
Qualitative and quantitative analysis of the void behaviour during deformation was conducted through in-situ X-ray computed tomography measurements and analysis of the fracture surfaces with scanning electron microscopy. It was found that the model, which defined damage in terms of void volume fractions (VVFs), could be calibrated for a smooth round bar geometry, but could not be validated against notched geometries exhibiting a higher stress triaxiality. Furthermore, VVFs derived by experimental methods could not be used as direct inputs for the damage model.

Date of Award	10 Dec 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	David M Knowles (Supervisor), Mahmoud Mostafavi (Supervisor) & Yiqiang Wang (Supervisor)