Using Rapid Thermal Annealing for Studying Early Stages of High-Temperature Oxidation of Superalloys

Kubacka, Dorota; Eggeler, Yolita M.; Volz, Nicklas; Neumeier, Steffen; Spiecker, Erdmann

doi:10.1007/978-3-030-51834-9_74

Cited by 1 publication

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“…Previous studies demonstrated a significant impact of the W-content in ternary Co-base alloys, with nominal similar Co-and Al-levels, on the formation of lateral alumina scale sections [23,24]. Therefore, a decelerating influence of higher concentrations of heavy elements such as Ta and W on diffusiondriven processes can be assumed [25][26][27][28]. Additionally, the role of the two-phase microstructure on elemental transport, especially during the early stages of oxidation, can be seen as a crucial.…”

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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