In situ nanotomography study of creep cavities in Al-3.6-Cu alloy

Abstract

Cavity growth during high temperature deformation has been extensively studied theoretically, but experimental investigation of nucleation and early stages of growth has been limited. In this work, in situ nanotomography investigation of cavity nucleation and growth during high temperature deformation (7.9 MPa, 698 K), has been carried out in Al −3.6 wt% Cu alloy. This model alloy allows controlled generation of second phase particles to promote cavity nucleation and has hence been chosen for the study. Fast 3D imaging using synchrotron X-Rays with 100 nm pixel size and scan time of 7 s has been done to track nucleation and volumetric growth of individual cavities during deformation. Using this, change in shape of cavities with straining has been studied. Also, the change of volumetric cavity growth rate vs equivalent radius of individual cavities has been compared to existing models of cavity growth by diffusion and plasticity. It was seen that several pre-existing porosities were present in the alloy, while very few cavity nucleations were observed. The experimental data of growth rate matched well with the studied models and it was concluded that cavities initially grew by diffusion, while the growth mechanism changed to plasticity near failure.