Microstructural evolution of a low-alloy steel / nickel superalloy dissimilar metal weld during post-weld heat treatment

The microstructural evolution of a dissimilar metal weld (DMW) obtained by narrow-gap gas tungsten arc welding (NG-GTAW) was investigated after it was subjected to a post-weld heat treatment (PWHT). The case studied here is a joint between low-alloy steel pipes and a stainless steel steam generator using a nickel based alloy as filler material. The fusion boundary that was the focus of this work was that between the low-alloy steel (2.25Cr-1Mo) and the nickel alloy (alloy 82). The difference in matrix phase and chemical composition between the two alloys leads to a large difference in chemical potential for carbon, which is mobile at the PWHT temperature. A number of advanced characterization techniques were used to assess the gradient of composition, hardness and microstructures across the fusion line, both as welded and after PWHT. This complete analysis permits to highlight and understand the main microstructural changes occurring during the PWHT

Electrochemical testing of the sensitivity to exfoliation corrosion of high strength 7XXX series aluminium alloys: Towards the understanding of the corrosion mechanisms » in:

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In-situ study of precipitate composition in 7000 series aluminium alloys by Anomalous Small-Angle Scattering

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Electrochemical aspects of exfoliation corrosion of aluminium alloys: The effects of heat treatment

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Relationship between alloy composition, microstructure and exfoliation corrosion in Al-Zn-Mg-Cu alloys

International audienceThe exfoliation corrosion (EFC) susceptibility of several 7000 Aluminium alloys has been studied after a variety of heat treatments using two independent corrosion tests (standard EXCO test and an electrochemical test based on potential transients analysis), together with detailed microstructural examinations. It is proposed that depending on heat treatment EFC may occur via two different mechanisms: inter-granular dissolution induced damage (IDD) or inter-granular fracture induced damage (IFD). The coexistence of these two mechanisms, leading to EFC, and their relative predominance explain the influence of alloy composition and heat treatment on EFC susceptibility via the confrontation of the two corrosion tests. (C) 2011 Elsevier Ltd. All rights reserved

Influence of alloy composition and heat treatment on precipitate composition in Al-Zn-Mg-Cu alloys

International audienceThe composition of precipitates in three alloys of the Al-Zn-Mg-Cu system has been investigated for different heat treatments, including peak-aged and over-aged states as well as near-equilibrium conditions, by combining atom probe tomography and systematic anomalous small-angle X-ray scattering experiments. We show that the concentration of Cu in the precipitates changes during heat treatments and is alloy dependent. At low ageing temperature (120 degrees C) the Cu content in the precipitates is close to the alloy content. The precipitate Cu content is shown to increase with increasing temperature and Cu alloy content. We show that in near-equilibrium conditions the precipitate compositions are 33 at.% in Mg, about 15 at.% in Al, about 13 at.% in Cu and balance Zn. Our results strongly suggest that the gradual incorporation of Cu in the precipitates during the heat treatment is essentially related to the slower diffusivity of this element in aluminium