a~J surface science ELSEVIER Applied Surface Science 94/95 (1996) 261-266 3D reconstruction and analysis of GP zones in AI-I.7Cu (at%): a tomographic atom probe investigation A. Bigot *, F. Danoix, P. Auger, D. Blavette 1, A. Menand LMIE - URA CNRS 808, UFR Sciences Universit~ de Rouen, 76821 Mont Saint Aignan Cedex, France Received 6 August 1995; accepted 2 October 1995 Abstract The tomographic atom probe (TAP) has been used to analyse Guinier-Preston (GP) zones in an A1-1.7Cu (at%) single crystal alloy aged at 373 K for 30 h, known to contain a majority of monolayer GP(I) zones. This work is a challenge for the TAP because of the extreme thinness of the metallurgical objects to be analysed and reconstructed. The GP zones whose habit plane is parallel to the analysis direction are quite successfully reconstructed in the form of thin copper rich platelets. However, the expected single layer structure is not preserved, due to a local magnification effect. Despite the high depth resolution of the TAP, the investigation of the GP zones perpendicular to the analysis direction, that was carried out at 35 K, did not provide any direct quantitative data related to the real thickness and the composition of GP zones. The observed phenomenon can be interpreted in terms of preferential evaporation of AI and preferential retention of Cu atoms. 1. Introduction The GP zones formed in an aged A1-4Cu (wt%), i.e. AI-I.7Cu (at%) alloy are known to be copper rich platelets parallel to the {200} matrix planes. Since the pure Cu single layer model proposed by Gerold [1], extensive studies performed with various techniques including atom probe field ion mi- croscopy (APFIM), brought new and sometimes con- tradictory information about both the composition and structure of GP zones. The present study is confined to GF'(I) zones which appear during the first stage of decomposition of the supersaturated A1-Cu solid solution. FIM observation by Wada et al. [2] of an AI-1.7Cu (at%) * Corresponding author. Tel.: +33 35 14 66 53; fax: +33 35 14 66 52; e-mail: annabelle.bigot@univ-rouen.fr. Also with the Institut Universitaire de France. alloy annealed at 403 K for 1000 h revealed that most of GP(I) zones are single {200}AI layer thick. This result is confirmed by a recent high resolution electron microscopy (HREM) study of a same alloy annealed at 373 K for 10 h performed by Karlik [3]. More than 80% of the zones are found to have a single layer structure. As far as the composition of GP(I) zones is concerned, the results published during the last 10 years converge on a copper content lower than 50 at%. James and Liedl [4] had already suggested this upper limit on the basis of X-ray diffuse scattering measurements. The model they developed relies on a central copper rich plane adjoining side planes of much lower copper content ( < 3%). The AP analysis of multilayer GP(I) zones by Hono and coworkers [5,6] revealed that the maximum copper concentra- tion of 4 layer thick zones is approximately 30-40 at%. Jouffrey and Karlik [7] performed X-ray analy- 0169-4332/96/$15.00 © 1996 Elsevier Science B.V. All fights reserved SSDI 0169-4332(95)00384-3