In situ observation of microcrack growth in 8090-T 4 alloy

Abstract

Aluminum-lithium alloys have become of recent interest as potentially important aerospace structural materials because of their low density, high elastic modulus and strength. However, some Al-Li alloys show very low tensile ductility and fracture toughness, particularly at peak-aged conditions. Vasudevan and Starke et al. recognized that Al-Li alloys were highly sensitive to intergranular fracture. Noble emphasized the effect of strain localization at coarse slip bands. Although much research has been published, the problem still has not been satisfactorily resolved. In contrast, the 8090-T[sub 4] alloy exhibits good comprehensive properties. In this paper, in situ observations in a TEM were carried out in the 8090-T[sub 4] alloy in order to study the deformation characteristics near the crack tip as well as microcrack growth. The results can be used to define the microstructure/property relationship in Al-Li alloys. Some results on fracture mechanisms at peak-and over-aged conditions will be reported later, so that the relationship between fracture mechanism, tensile ductility and the resistance to crack growth can be elucidated.