Modes of Deposit-Induced Accelerated Attack of MCrAlY Systems at 1100 °C

Gheno, Thomas; Gleeson, Brian

doi:10.1007/s11085-016-9669-1

Cited by 20 publications

(17 citation statements)

References 42 publications

(48 reference statements)

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“…Alloy composition effects were studied by varying the β phase fraction and the Cr content. In general, β-rich alloys were immune to the Na silicate (NS), and formed external Al 2 O 3 scales, while some γ-rich alloys suffered internal oxidation [2]. The situation of exclusive external scaling will be considered to evaluate the validity of the oxidation-dissolution analysis.…”

Section: Resultsmentioning

confidence: 99%

“…Any process consuming the scale would result in an increased oxidation rate. In recent studies [1][2][3], we showed that Al 2 O 3 -scale forming NiCoCrAlY compositions in air were susceptible to accelerated corrosion in the presence of oxide-sulfate deposits. Two modes of attack were identified, which involved Al 2 O 3 reaction with CaO to form Ca aluminates, and Al 2 O 3 dissolution in molten Na silicate.…”

Section: Introductionmentioning

confidence: 91%

“…% Na 2 SO 4 deposits in CO 2 -20H 2 O-1.6O 2 at 1100 • C. The experimental procedure is detailed in Ref. [2]. Briefly, 50 h isothermal corrosion experiments were conducted in a tube furnace under flowing gas, using cast alloys.…”

Section: Materials and Experimentsmentioning

confidence: 99%

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Kinetics of Al2O3-Scale Growth by Oxidation and Dissolution in Molten Silicate

Gheno

Gleeson

2016

Oxid Met

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During the high temperature oxidation of an alloy, the growth of a protective oxide scale selectively consumes one of the alloying elements. This can be accelerated if a molten deposit is present and dissolves the scale. The kinetics of Al 2 O 3-scale growth and dissolution in Na silicate were studied by considering the Al mass balance at the alloy/scale and scale/silicate interfaces. The analysis was applied to a single-phase γ-NiCoCrAlY alloy exposed to a SiO 2-Na 2 SO 4 deposit at 1100 • C, using an oxidation rate constant and effective Al diffusivity measured after deposit-free oxidation of the same alloy, and independent measurements of Al solubility and diffusivity in Na silicate. The simulated Al 2 O 3-scale thickness and Al depletion profile matched well with the experimental data. The model was then used to assess Al 2 O 3-scale failure on two alloys with particularly large Cr contents (27 and 35 at. %), which underwent internal oxidation when exposed to the SiO 2-Na 2 SO 4 deposit.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 91%

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Kinetics of Al2O3-Scale Growth by Oxidation and Dissolution in Molten Silicate

Gheno

Gleeson

2016

Oxid Met

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“…As beneficial as REs may be when added in the right proportion, overdoping can have detrimental consequences on oxidation resistance. Not only does overdoping increase overall scaling rates, but more critically, it produces oversized pegs which may favor scale failure during thermal cycling [15,16], or act as initiation sites for accelerated corrosion under sulfate [17] or oxide-sulfate deposits [18]. Controlling RE additions, together with impurities such as S or C, is therefore a critical aspect of material design and manufacturing.…”

Section: Introductionmentioning

confidence: 99%

A Thermodynamic Approach to Guide Reactive Element Doping: Hf Additions to NiCrAl

et al. 2017

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A method based on thermodynamic modeling was developed to determine optimal amounts of Hf additions to Al 2 O 3-forming, γ-γ NiCrAl alloys. The alloy ability to maintain Hf in solution was set by the Hf concentration required to form HfO 2 at the oxygen activity defined by the alloy/Al 2 O 3 equilibrium. This Hf tolerance decreased with increasing temperature and increased with increasing γ fraction. The latter was due to the higher solubility of Hf in γ , compared to γ. The validity of the procedure was evaluated by oxidizing a series of NiCrAl-Hf alloys in dry air at 1000-1200 • C. The experimental results followed the predicted trends, although the Hf tolerance tended to be overestimated. The applicability of the criterion, and potential routes for improved predictability, were discussed by considering the influence of the compositional changes occurring at the metal surface during the transient and steady-state stages of the oxidation process.

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“…Calcium chromate formation was a rapid, transient process, and the transition to a steady-state of slower Al 2 O 3 growth was favored by increasing the alloy β fraction. The thermallygrowing Al 2 O 3 reacted with the deposit to form calcium aluminates in a solid-state diffusion process, which led to an increased oxidation rate which has recently been attributed to hot corrosion [45,46].…”

Section: Implications: Cmas Degradation Mechanismmentioning

confidence: 99%

CMAS Effects on Ship Gas-Turbine Components/Materials

Shifler

Choi

2018

Volume 1: Aircraft Engine; Fans and Blowers; Marine

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Recent inspection of shipboard gas-turbine components under the platform has indicated the apparent presence of CMAS (calcium, magnesium, alumino-silicate) and its related attack. This type of attack has often been observed in aero gas turbine engines when sand and similar siliceous matter is ingested into the engine and the sand debris melts due to high engine operating temperature greater than 1150°C. Initial chemical analysis shows that the CMAS-affected areas of ship engine components versus aero engine components are similar. However, this phenomenon commonly observed in advanced aeroengines are not supposed to occur in the ship engine components since their probable temperature is known to be much lower than 1150°C (i.e., melting temperature of CMAS). As a consequence, some important questions arise as to: What caused this “CMAS” attack in ship engine components? Was this initiated by hot corrosion, which created a molten salt pool at a sufficient temperature to trigger CMAS attack? Did sodium chloride mixed with dust and debris lower the temperature at which molten CMAS would initiate? Past research provides a basic understanding of hot corrosion, but may ignore other reactants and other species inherently associated with ‘natural CMAS’ and mechanisms contributing to hot corrosion or CMAS attack. Further examination of ship and aero components will discern the local structure chemical profile of the component coatings, the chemical compositions of the alloy substrates, and the interface between the coating and the molten “CMAS” by several methods. Integrated computational materials engineering (ICME) and validating experiments will assist in developing degradation mechanisms. The environment complexity is also to be taken into account to determine whether salt-induced CMAS attack or CaO-induced hot corrosion may be dominant. The mechanisms need to be further studied and defined. The current work will address a series of systematic approaches to the aforementioned CMAS issues and will also present some recent results on CMAS-related effects on components and an elected alloy material system.

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Modes of Deposit-Induced Accelerated Attack of MCrAlY Systems at 1100 °C

Cited by 20 publications

References 42 publications

Kinetics of Al2O3-Scale Growth by Oxidation and Dissolution in Molten Silicate

Kinetics of Al2O3-Scale Growth by Oxidation and Dissolution in Molten Silicate

A Thermodynamic Approach to Guide Reactive Element Doping: Hf Additions to NiCrAl

CMAS Effects on Ship Gas-Turbine Components/Materials

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