Phase Stability of Precipitates After Ion Irradiation and Creep Deformation in Cu Alloys

In this work two main research themes are studied in order to improve our understanding of how structural materials perform in extreme operating environment such as fission and fusion energy systems by utilizing advanced microstructural characterization to investigate the structure, precipitate-matrix orientation, and general stability of precipitates in model Cu-base structural alloys. Theme I focuses on fundamental understanding of phase stability of nanoscale precipitates within and beyond the ion displacement damage region in irradiated dilute Cu-base model alloys (Cu-1%Co, Cu-1%Fe and Cu-0.8%Cr). First, the in situ irradiation experiments with 1 MeV Kr++ ions provide some indication of the critical dose to induce loss of precipitate coherency. The observed effect of suppressed loss of coherency at high sink strengths might be due to nearly equal numbers of interstitial and vacancy defects arriving at the precipitate interface. At low sink strengths, there might be a preferential medium-range strain-induced bias for absorption of interstitial defects at the precipitates that accelerates coherency loss. Second, we use these coherent precipitates with different sink strengths as a ‘diagnostic monitor’ to provide an indicator of the radiation defect migration behavior via ex situ 1 MeV Ni+ irradiation. Evidence for pronounced defect migration well beyond the maximum range of the ion irradiation region suggests significant 1D migration of defect clusters.Theme II aims to analyze and understand the mechanical deformation mechanisms, especially regarding creep resistance, of newly designed CuCrNbZr alloys compared to commercial CuCrZr alloys for fusion energy applications. This new developed Cu alloy has been confirmed to have a multi-modal distribution of precipitates with fine Cr-rich precipitates and Cu5Zr intermetallic compounds in the matrix and coarse Laves-Cr2Nb phase at the grain boundaries. The matrix precipitates contribute to high tensile strength and resistance to dislocation power law creep whereas the grain boundary precipitates suppress grain boundary crack propagation and increase creep strength and life at test temperatures of 500 oC.