Insight into the interfacial microstructure and chemistry of hot isostatically pressed AA6061-AA6061 bonds for U-10Mo fuel cladding application

Hot isostatic pressing (HIP) is performed on AA6061-AA6061 plates for U-10Mo monolithic fuel cladding application and this process allows us to bond multiple plates and large surface areas in a single run. In the current work, we HIP'd several plates of AA6061 with different HIP can dimensions at 560 °C and 103 MPa for 90 min to gain insight into the interfacial microstructure, chemistry and eventually bond strength. Interfacial microstructure characterizations were performed using scanning electron microscopy (SEM) combined with electron backscatter diffraction (EBSD) in conjunction with Transmission electron microscopy (TEM) to quantify precipitate fractions and study recrystallization, grain growth, and orientation relationships across the interface. Microstructural analyses revealed the precipitation of a large fraction of Mg2Si particles and a ∼50 nm thick Al-Mg oxide layer at the interface. Further TEM analysis confirmed that the oxide layer was not continuous, and Mg2Al2O5 oxide particles with an average size of 18 nm were present in the oxide layer. The bond strength of HIP-processed samples was correlated with peel testing and the bond strength was determined to be a direct function of the Mg2Si particle size at the interface. Finite element modeling analysis was performed to study the HIP can cooldown rate after HIP processing and was correlated with the interface precipitation.