3D reconstruction and analysis of GP zones in Al-1.7Cu (at%): A tomographic atom probe investigation

The tomographic atom probe (TAP) has been used to analyse Guinier-Preston (GP) zones in an Al-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 Al and preferential retention of Cu atoms.