Effect of alloy composition on the oxidation‐induced boron depletion in cast Ni‐base superalloy components

Abstract

Cover: High temperature corrosion attack of the surface of a heat resistant high-alloy steel for boiler tubes (DMV304HCu) after exposure to a chlorine-free coal-power-plant ash at 625 °C for 1000 hours (cross section/false colors): Coal-power-plant ash containing sulphur, sodium, potassium, calcium and iron-rich oxides (dark red and violet); outer iron-rich oxide scale (yellow); inward growing chromia scale containing sulphur (turquoise); small chromium sulphides at the corrosion front in the metal subsurface zone (pink). The corrosion test was conducted within a project of DECHEMA-Forschungsinstitut to investigate accelerated hot-corrosion through co-fi ring of "green fuels" in conventional coal-fi red power plants. The project was funded by Federal Ministry for Economic Affairs and Energy (BMWi) under contract No. 03ET7012D. More detailed information on the project can be found at http://dechema-dfi .de/en/L%C3%BCbkorr.html Aim of the study is to develop a simulation software for the prediction of internal corrosion during high-temperature applications. Within this study, the cellular automata approach was used to describe TiN formation in Ni-20Cr-2Ti, MnO formation in a Mn-steel containing 3.7 wt% Mn and intergranular Al 2 O 3 formation in Inconel 625Si. It is shown that experimental and simulated results are in good agreement. EFC-Workshop: Insight, mechanisms and modelling in high temperature corrosion M. Schütze and W. J. Quadakkers As a fi rst step toward multicomponent simulations of oxidation, simulations of oxidation of pure iron has been performed. The simulations were performed using a modifi ed version of the homogenization model as implemented in Dictra using Calphad databases. A reasonable agreement with experimental data has been obtained. An alumina forming austenitic steel is exposed in a nitriding atmosphere. The internal nitridation is compared with thermodynamic and kinetic modelling. The order of appearing nitrides from the surface of the sample is predicted by the modelling. However, the cubic chromium nitride was not detected in the sample and the experimental nitridation depth is smaller than the modelled nitridation depth. Isothermal, 500 h exposures at 750 °C in 1-300 bar CO 2 found little effect of pressure on the mass change or reaction rates for a group of chromia-and alumina-forming structural alloys. In addition to examining polished cross-sections, macroscopic evaluations via hardness and ex situ tensile properties did not reveal any evidence of signifi cant internal carburization under these conditions. During exposure of alloy 625 in wet air at 900-1000 °C chromium loss due to formation of volatile Cr species increases with increasing gas fl ow rate up to the maximum considered value of 6 m/s. Geometrical factors of the test specimen substantially affected the extent of volatile species formation; especially the specimen leading edge exhibited more extensive formation of volatile Cr species than other specimen areas. 159-170 Effect of gas fl ow rate on oxidation behaviour of al...

Surface preparation effect on oxidation kinetics of Ni-base superalloy

“…For ground specimen no boron peak is found. A similar effect of hampering boron diffusion through alumina scale was observed by Nowak et al [16].…”

Electrochemical synthesis and corrosion protection of poly(3-aminophenylboronic acid-co-pyrrole) on mild steel

“…In order to conrm the presence of both Py and APBA units in the p(APBA-co-Py) chains, its FESEM-WDX analysis 62,63 was performed together with those of homopolymers (Fig. 6).…”

Flash oxidation tests to evidence the segregation of boron at the grain boundaries of superalloy Inconel 718

“…Indeed, Binder et al [8] evidenced that increas ing the boron concentration in Cr Ni Co Fe alloys accelerated the devel opment of complex spinels at the expense of the more protective oxide Cr 2 0 3 • Similarly, Barrett et al [9] concluded for nickel basecl superal loys that boron favored the formation of NiO oxide at the expense of the more protective Al 2 0 3 and aluminate spinel oxides. Moreover, sev eral studies evidenced boron oxides in the oxide scale of nickel based alloys: CrB0 3 [10,11], Al 3 B0 6 [10], A1 4 Bi0 9 [12] and Ni 2 Cr0 2 (B0 3 ) [11]. Boron is incorporated in the oxide scale for two main reasons: the high thermodynamic stability of the boron oxides and the high diffusiv ity of boron in nickel [11] (the boron cliffusivity in nickel is between 3 and 4 orders of magnitude higher than that of Ni, Cr or Al [10)).…”

“…Moreover, sev eral studies evidenced boron oxides in the oxide scale of nickel based alloys: CrB0 3 [10,11], Al 3 B0 6 [10], A1 4 Bi0 9 [12] and Ni 2 Cr0 2 (B0 3 ) [11]. Boron is incorporated in the oxide scale for two main reasons: the high thermodynamic stability of the boron oxides and the high diffusiv ity of boron in nickel [11] (the boron cliffusivity in nickel is between 3 and 4 orders of magnitude higher than that of Ni, Cr or Al [10)). Then, the diffusion of boron towards the oxide scale can largely deplete the bulk alloy from boron, thus degrading the mechanical properties.…”

“…Then, the diffusion of boron towards the oxide scale can largely deplete the bulk alloy from boron, thus degrading the mechanical properties. In deed, Nowak et al [10] measurecl that, after 20 h of oxidation in air at E-mail addresses: suzanne.vernier@ensiacet.fr (S. Vernier), eric.andrieu@ensiacet.fr (E. Andrieu), lydia.laffont@ensiacet.fr (L Laffont). ht1ps://doi.org/10.1016/j.mtia.2020.100989 1050 °C, 90 % of the initial boron content had left a 2 mm thick sample of alloy Rene 80.…”