Development of Chromium and Aluminum Coatings on Superalloys by Pack-Cementation Technique

Stéphane Mathieu,Xiaver Ledoux,Pascal Del-Gallo,Michel Vilasi,Marc Wanger,Pierre Jean Pantiex

doi:10.4028/www.scientific.net/amr.278.491

Stéphane Mathieu, Xiaver Ledoux + Show 4 more

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https://doi.org/10.4028/www.scientific.net/amr.278.491

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Abstract

Austenitic nickel-iron-chromium based superalloys are materials of choice for high temperature applications as they provide high temperature creep resistance associated with a suitable oxidation behavior in the temperature range of 600-1100°C. However, these properties are not sufficient for applications as Steam Methane Reformer (SMR). As a consequence, aluminum and chromium coatings are developed by the pack-cementation technique to improve their corrosion resistance. The oxidation behavior of the coated samples has been carried out in air at 1050°C. Chromium deposition leads to a layer of bcc chromium-iron solid solution. Oxidation tests indicated that a too high chromium concentration induces a too rapid growth of the chromia layer. In the case of aluminum coatings, a layer of -NiAl is formed at the surface of the alloy. It permits a significant decrease of the oxidation rate.

Highlights

Iron – Nickel – Chromium alloys have been proven to be resistant to corrosive environments at high temperatures (600-1000°C)
Chromium coatings should « play the role » of a chromium reservoir to avoid its fast depletion under the chromia layer while the aluminum coating should permit the formation of an Al2O3 layer which grows slower than the Cr2O3 layer [2]
The oxidation behavior of coated alloys was followed by TGA and samples were characterized by XRD, scanning electron microscope (SEM) and Electron Probe Microanalysis (EPMA)

Summary

Introduction

Iron – Nickel – Chromium alloys have been proven to be resistant to corrosive environments at high temperatures (600-1000°C) Their good resistance is due to the chromium content (22 to 28 wt.%) which allows the formation of a protective Cr2O3 layer [1]. For Steam Methane Reforming applications, operating conditions impose a carburizing atmosphere inside the reactor and an oxidizing one outside. In such conditions, Iron – Nickel – Chromium alloys do not permit a satisfactory life time of the reactor. Iron – Nickel – Chromium alloys do not permit a satisfactory life time of the reactor This is the reason why it could be of interest to improve the resistance of these alloys by forming coatings on the surface. The adhesion of the oxide scales has been evaluated by a cyclic oxidation test at 1000°C

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