Diaelastic modulus change of aluminium after low temperature electron irradiation

The changes of the elastic shear moduli C44 and C' (C11 - C12)/2 have been measured after electron irradiation of aluminium at 4.5 K. Aside from dislocation pinning, a diaelastic effect which is proportional to the radiation-induced defect density has been observed. From these data the diaelastic polarizabilities under an external shear strain of the radiation-induced interstitials can be extracted. The results are very similar to those of Cu. The observed polarizabilities of α = - 23 and α' = - 13 are unusually large (for point defects) and highly anisotropic i.e. α/α ' approximately equal to 2. These findings can be understood quantitively on the basis of a model calculation which takes into account the <100> split configuration of the interstitial and the effect of the highly compressed atomic arrangement within the interstitial coreregion on the interatomic force constants. Thermal annealing studies indicate that di-interstitials present at the end of stage I have an even higher diaelastic polarizability than single interstitials and that the diaelastic polarizability decreases strongly when the interstitials form dislocation loops. (author)