Experimental and theoretical investigation of the dynamic properties of aluminum with helium bubbles

Abstract
The dynamic behavior of aluminum containing helium bubbles was investigated in shock wave experiments. The targets were obtained by mixing melted pure aluminum with 1800 appm ¹⁰B powder. After solidification, the targets were neutron irradiated to obtain helium atoms in the bulk from the reaction ¹⁰B+n→⁷Li+⁴He. Helium atoms further accumulated into bubbles by diffusion in the aluminum bulk. Shock wave experiments were performed by accelerating aluminum impactor into three types of samples: (1) pure aluminum, (2) Al-¹⁰B and (3) Al-¹⁰B with different concentrations of helium bubbles and different radii. The bubbles radii and concentration were determined experimentally using Transmission Electron Microscopy (TEM). The number of helium atoms in a bubble was calculated from the Electron Energy Loss Spectrum (EELS). The following results were obtained in the experiments: The maximum free surface velocity of shocked samples made Al-¹⁰B and Al-¹⁰B with different concentrations of helium bubbles and different radii was similar, implying that the pressure on the Hugoniot was the same. Moreover, it was found that the spall strength of these samples was the same. However, it was measured that the spall strength of pure aluminum samples was by 47% higher than that of Al-¹⁰B and Al-¹⁰B with bubbles samples. An equation of state (EOS) model was developed for describing aluminum with helium bubbles. The bubbles radii and concentrations were used as input parameters in the model. The calculated Hugoniot curve for aluminum with bubbles was not sensitive to the existence of helium, for mass ratio of 10⁻⁵ between helium and aluminum, typical for the experiments. This finding is in agreement with the experimental results.