Oxidation Behaviour of Si-Bearing Co-Based Alloys

Yeh, An‐Chou; Wang, Sheng-Chi; Cheng, C.; Chang, Young-Il; Chang, Shu‐Hao

doi:10.1007/s11085-016-9623-2

Cited by 22 publications

(6 citation statements)

References 27 publications

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“…It is clear that the three alloys investigated in this study have typical Cr 2 O 3 oxidation kinetics, despite the fact that they also form alumina layers. The parabolic constants determined in this study are lower than those determined by Yeh et al [ 16 ] for the oxidation of Co-30Ni-10Al-10W at 900 °C and Li et al [ 15 ] for the oxidation of Co-30Ni-5Cr-9Al-6W-4Ti-1Ta at 1000 °C. It should be noted that the growth of the oxide layer on the 5Cr alloy is significantly slower than that on the 3Cr and 1Cr alloys, which is primarily governed by the growth of Cr 2 O 3 and Al 2 O 3 .…”

Section: Discussioncontrasting

confidence: 80%

“…Generally, without the addition of Cr or Si, the oxidation resistance of Co-30Ni-10Al-based alloys is subpar [ 15 ]. The parabolic rate constants of the Co-30Ni-10Al-10W alloy after isothermal oxidation in air at 900 °C and 1000 °C, for example, are 0.00524 and 0.0302 mg 2 ∙cm −4 ∙s −1 , respectively [ 16 ]. It is well known that improving the high-temperature oxidation resistance of superalloys is also an important task of alloy design.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Chromium Content on the Oxidation Behavior of a Ta Stabilized γ’-Strengthened Polycrystalline Co-30Ni-10Al-4W-4Ti-2Ta Alloy

Qian

Shu

et al. 2022

Materials

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The high-temperature oxidation behaviors of polycrystalline Co-30Ni-10Al-4W-4Ti-2Ta superalloys with Cr contents ranging from 1 to 5 at.% are characterized at 900 °C to provide benchmark data for the alloy design of the CoNi-based superalloys. The mass gain curves for all three alloys exhibit parabolic growth, and the addition of 5Cr at.% is sufficient to decrease the oxidation rate by two orders of magnitude compared to the Cr-free alloy. Furthermore, cross-sectional findings reveal that these three alloys form qualitatively similar oxide scales composed of an outer oxide layer of Co3O4 and CoAl2O4 phase on top of an Al2O3 scale, following the inner oxide layers of Cr2O3, TiO2, and TiTaO4, and internally oxidized Al2O3 precipitate. The alloy forms a chromium-rich oxide scale as the Cr addition increased, and the concentration of Cr in the scale/alloy interface increases, promoting the growth of Cr2O3, while CoAl2O4 and Co3O4 nucleation is inhibited. The results further indicate that Cr has a superior effect on improving the oxidation resistance of CoNi-based alloys and that a higher content of Cr can assist the formation of a continuous Al2O3, Cr2O3, and TiTaO4 layers, which in turn hampers outer Co and Ni, and inward oxygen flux.

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Section: Discussioncontrasting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Effect of Chromium Content on the Oxidation Behavior of a Ta Stabilized γ’-Strengthened Polycrystalline Co-30Ni-10Al-4W-4Ti-2Ta Alloy

Qian

Shu

et al. 2022

Materials

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“…To reach higher melting points and therefore increase the potential service temperatures, the Ni level in novel Co-base alloys should be kept low. Taking into account that Cr-rich oxidic barrier layers are temperature-limited in applications, it is well justified to investigate the mechanisms behind alumina formation in Ni-free Co-base alloys [22]. Promising results have been gained recently by Stewart et al describing a more complex Co-base system with up to six elements.…”

Section: Introductionmentioning

confidence: 99%

On the High-Temperature Oxidation Behavior of a Ta-Containing Quaternary Co-Base Model Alloy System with γ/γ′-Microstructure - Influence of γ′-Volume Fraction, Surface State, and Heating Condition on Alumina Growth

et al. 2020

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The improvement of the high-temperature oxidation resistance remains an ambitious goal for the design of new γ/γ′-strengthened Co-base superalloys, since their oxidation resistance beyond 800 °C still ranks behind their Ni-base counterparts. To better understand the origin of the poor oxidation resistance at higher temperatures, this study focuses on early stages of oxidation of four quaternary (Co-Al-W-Ta system) Co-base model alloys with a two-phase γ/γ′-microstructure and varying γ′-volume fraction at 800 °C, 850 °C and 900 °C. Based on time-resolved isothermal gravimetric analysis (TGA) in synthetic air and detailed electron microscopic analysis, the role of the γ-channel width (or γ′-volume fraction), the surface preparation prior to exposure (polishing versus shot-peening), and the heating conditions (synthetic air versus argon) on protective alumina growth is elucidated. Firstly, for alloys of increased γ′-volume fractions slower oxidation kinetics prevailed. Secondly, the two-phase microstructure was found to decisively affect the propagation of the internal oxidation front at the early stages of oxidation. Thirdly, shot-peening prior to exposure together with a lack of oxygen availability during heating was identified to foster protective alumina growth, accompanied by TCP-phase formation in the substrate. The critical role of a high Al availability in the alloy for a rapid growth of protective alumina and the relating challenges in alloy development regarding, for example, phase stability in this relatively novel Co-base alloy class are discussed in detail.

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“…13,14 However, at 900°C, only insufficient resistance against oxidation was repeatedly reported. [15][16][17] Interestingly, the formation of continuous alumina layers on the internal oxidation front (IOF) was observed in various polycrystalline Co-base model systems only at comparably low temperatures. 15,18,19 This oxidation behaviour is contradictory to the scaling mode of Alcontaining Ni-base alloy systems.…”

Section: Introductionmentioning

confidence: 99%

Transport mechanisms during the high-temperature oxidation of ternary γ/γ′ Co-base model alloys

et al. 2019

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Over a decade ago, γ′-strengthened Co-base alloys were introduced as potential replacement for conventional Ni-base Superalloys. Insufficient resistance against high-temperature oxidation restricts the number of possible applications. The present study contributes to the understanding of elementary mechanisms such as material transport during extensive oxide scale formation on γ/γ′ Co-base alloys to explain their inferior oxidation behaviour. A clear dependency of the scale growth kinetics on W content and oxidation temperature is demonstrated by thermogravimetry and subsequent analysis of cross-sections. By means of electron backscattered diffraction (EBSD), the evolution of microstructures in the outer oxide layers were examined depending on the oxidation temperature. Sequential exposure of samples in 16O2- and 18O2-containing atmospheres proved counter-current material transport. The combination of focused ion beam (FIB) and secondary ion mass spectroscopy (SIMS) visualised the formation of new oxide phases mainly on the outer and inner interface of the oxide scale. An elaborate review of available transport paths for oxygen is given during the discussion of results. All experimental findings were combined to a coherent explanation of the inferior oxidation resistance of this relatively new class of high-temperature materials at temperatures above 800 °C.

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Oxidation Behaviour of Si-Bearing Co-Based Alloys

Cited by 22 publications

References 27 publications

Effect of Chromium Content on the Oxidation Behavior of a Ta Stabilized γ’-Strengthened Polycrystalline Co-30Ni-10Al-4W-4Ti-2Ta Alloy

Effect of Chromium Content on the Oxidation Behavior of a Ta Stabilized γ’-Strengthened Polycrystalline Co-30Ni-10Al-4W-4Ti-2Ta Alloy

On the High-Temperature Oxidation Behavior of a Ta-Containing Quaternary Co-Base Model Alloy System with γ/γ′-Microstructure - Influence of γ′-Volume Fraction, Surface State, and Heating Condition on Alumina Growth

Transport mechanisms during the high-temperature oxidation of ternary γ/γ′ Co-base model alloys

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