ELECTRON CHANNELLING CONTRAST IMAGING OF DEFECT STRUCTURES IN NEUTRON IRRADIATED ALUMINIUM D.R.G. Mitchell and R.A. Day Materials Division, Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234, Australia (Received March 12, 1998) (Accepted June 5, 1998) Introduction Electron channelling contrast (ECC) may be obtained using a scanning electron microscope (SEM) in backscattered electron imaging mode. The penetration depth of electrons into a material is dependent upon, amongst other things, the crystal orientation, with strong channelling occurring when the electron beam satisfies the condition for Bragg diffraction. Under such conditions the electron beam penetrates deeply into the material and the backscattered intensity is reduced greatly. Zauter et al (1) have employed ECC to study the microstructures of a range of deformed materials, highlighting the complementarity of the information gained from this seldom applied technique with that obtained from transmission electron microscopy (TEM). Iba ´n ˜ez et al (2) have used ECC to monitor the development of sub-grain structure in aluminium during in-situ straining in a scanning electron microscope. They demonstrated that sub-grain contrast in high purity annealed aluminium became apparent after only 2.5% strain, and were able to monitor both sub-grain development and movement. They also showed that the sub-grain structure observed at the surface was representative of that of the bulk, and the ECC-derived microstructural information correlated well with that obtained using TEM. More recently Gong et al (3) have used ECC to correlate macro deformation bands formed on the surface of copper with the corresponding dislocation structures as observed with both TEM and ECC, and Schwab et al (4) have performed similar studies on nickel. SEM-based diffraction techniques have been the subject of a recent comprehensive review by Wilkinson and Hirsch (5). The ECC technique is powerful and versatile, requiring little specimen preparation, other than electropolishing to remove surface deformed layers (1). It can provide some of the information that conventional TEM can supply, and more importantly, it can do so over regions orders of magnitude greater than can be imaged in typical TEM studies of thin foils. This permits dislocation features in many tens or even hundreds of grains to be examined. It can also permit the relationship between specific features, such as cracks, twins and slip bands, and their corresponding dislocation microstruc- tures to be revealed (1,2). Such imaging is often very difficult to achieve using TEM. This paper reports our ECC and TEM studies on dislocation structures present in cold worked aluminium, neutron irradiated to various fluences. Pergamon Scripta Materialia, Vol. 39, No. 7, pp. 923–930, 1998 Elsevier Science Ltd Copyright © 1998 Acta Metallurgica Inc. Printed in the USA. All rights reserved. 1359-6462/98 $19.00 + .00 PII S1359-6462(98)00245-0 923