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Effect of Rare Earth Cerium Addition on Oxidation Behavior of Co-Al-W Alloys at 800°C

Migas Damian, Liptáková Tatiana, Moskal Grzegorz

Archives of Metallurgy and Materials

2022

Vol. 67, iss. 1

203--208

The γ/γ′ Co-based alloys are a new class of cobalt superalloys, which are characterized by remarkable high temperature strength owing to strengthening by γ′-Co3(Al, X) phases. In this investigation, the effect of cerium addition on oxidation behavior of model Co-Al-W alloys was studied. The introduction of Ce aimed at improvement of the oxidation resistance of γ′-forming Co-based superalloys. The minor additions of cerium (0.1, 0.5 at.%) were added to the base alloy Co-9Al-9W. The alloys were prepared via induction vacuum melting (VIM). Further, a primary microstructure of the alloys was analyzed with particular regard to a segregation of Ce. The thermogravimetric analysis (TG) under non-isothermal conditions was used to preliminary estimate the oxidation behavior of alloys at different temperatures. During experiment, differential thermal analysis (DTA) was performed simultaneously. After this test, cyclic oxidation expermients was carried out at 800°C for 500 h. In as-cast state, Ce segregates to interdendritic areas and forms intermetallic phases. The effect connected with melting of interdendritic precipitates was observed at 1160°C. Ce-containing alloys were less prone of oxide spallation. Moreover, oxidation rate of these alloys substantially decreased after 100h of oxidation, whereas mass of the sample corresponding to base alloy continued to increase.

Cyclic oxidation resistance of Co–9Al–9W new cobalt-based superalloy

Moskal Grzegorz, Tomaszewska Agnieszka, Migas Damian, Niemiec Dawid

Inżynieria Materiałowa

2019

Vol. 40, nr 2

39--45

Cobalt-based superalloys are class of new heat-resistant materials for components of turbine engines. The γ/γʹ phase microstructure similar to nickel-based analogue, provide excellent creep resistance as well as resistance to corrosion and oxidation. Superior high temperature resistance drives intensive development of Co-based superalloys. The aim of paper is assessment of high temperature oxidation behaviour of Co–9Al–9W alloy in as-cast state. The cyclic oxidation performance of Co–9Al–9W alloy was studied at temperature 800°C and 900°C. The cyclic oxidation test was carried out under laboratory air atmosphere with time of exposure 25 hours and multiplicity of it. The scale morphology after cyclic oxidation test was investigated. The evaluation of scale concerned macrostructure, microstructure, chemical and phase composition of surface. Surface of tested alloys after oxidation was characterized using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and light microscopy (LM). Obtained data revealed that Co–9Al–9W alloy showed acceptable resistance to cyclic test at temperature 800°C. The oxide scale at this variant showed mainly Co oxides as an dominant phase. At higher temperature – 900°C the strong effect of spallation of scale was observed as results of CoWO4 complex oxide formation.

Celem pracy była charakterystyka odporności na utlenianie nowego typu stopów na bazie kobaltu umacnianych fazą Co3(Al, W). Ocenie poddano stop Co–9Al–9W (% at.) w stanie po odlaniu i homogenizacji. Wykonano próby odporności na utlenianie cykliczne w cyklach 25-godzinnych w atmosferze powietrza. Zakres prezentowanych badań obejmował pomiary masy próbek po kolejnych cyklach, ocenę stanu powierzchni z uwzględnieniem procesów jej odpadania, jak również charakterystykę składu chemicznego i fazowego powstałej zgorzeliny oraz jej budowę morfologiczną.