High Temperature Oxidation Behavior of gamma-Ni+gamma'-Ni3Al Alloys and Coatings Modified with Pt and Reactive Elements

Mu, N.

doi:10.2172/933131

Cited by 7 publications

(7 citation statements)

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“…Given that the activity, , of a pure solid in their standard state is 1, (3)reduces to (4). [7,11,12] As shown with the Gibbs free energy calculations, thermodynamics predict stable oxides at various temperature and atmospheric conditions; however, it does not indicate the rate at which oxides grow; nor does it indicate the process in which oxygen is converted from a gaseous phase to solid oxide. Qualitatively, the oxidation of metals occurs as follows[7]:…”

Section: Background On High Temperature Oxidationmentioning

confidence: 99%

“…This process is characterized by the rapid growth of a very thing scale then severely limited growth after the initial formation. Within logarithmic growth, there is a logarithmic growth equation (7) and inverse logarithmic growth (8) [11,12]; graphically seen in Figure 9. Linear growth can be seen in a variety of metals and at varying temperatures.…”

Section: Kinetic Description Of Oxide Growthmentioning

confidence: 99%

“…Linear growth can result from surface reaction control or oxidant-supply control. [11,12]. This often indicates that the oxide scale is non-protective due to no reduced rate in growth.…”

Section: Kinetic Description Of Oxide Growthmentioning

confidence: 99%

“…1 k C ξ = + (9) Parabolic growth of oxides occurs above 400°C in most metals and is considered the characteristic rate for oxidation in bond coat TBC systems. Figure 9 shows a typical cross section and mass balance equations for parabolic oxidation, based on Wagner's model of oxidation [11,12]. Working from Fick's first law,…”

Section: Kinetic Description Of Oxide Growthmentioning

confidence: 99%

“…(10) expresses Fick's first law re-written in the terms of mass gain. Defining where m is the mass gain and r is the density of the oxide in question, (10)can be rearranged into (11). (12) shows the result of integrating with respect to…”

Section: Kinetic Description Of Oxide Growthmentioning

confidence: 99%

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Oxidation and hot corrosion of Pt- and Si-modified Ni-18Al-10Cr-0.1Hf and comparison compositions

Guyer¹,

Edward²

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Materials for high-temperature turbine environments face rigorous operating conditions. Not only are components exposed to high-temperature oxidation, but corrosive gasses that evolve during combustion and service operation can also lead to degradation. Ni-based superalloys are used in turbines for their strength and creep resistance at high temperatures. The compositions of these superalloys are such that they do not provide adequate environmental protection alone; therefore, coatings are used to protect the underlying materials from degradation. Currently, there is no coating that provides adequate protection to both oxidation and hot corrosion. In high-temperature areas where the main degradation mode is oxidation, β-NiAl-type diffusion coatings are often used. These metal coatings have a significant Al content to insure Al 2 O 3 -scale formation, which provides excellent oxidation protection but variable corrosion resistance that is highly dependent on composition. Conversely, MCrAlY overlay coatings (M=Ni, Co, or NiCo) provide superior corrosion resistance due to their relatively high Cr content (up to about 30at%), but cannot be used in applications exceeding 1000°C due to limited oxidation protection. A new generation of Al 2 O 3 -scale-forming coating, based on Hf+Pt-modified γ-Ni + γ'-Ni 3 Al, can show excellent oxidation protection and increased corrosion protection compared to β-type coatings. This research modifies the Hf+Ptmodified γ-Ni + γ'-Ni 3 Al coating composition with Cr and Si to increase the hot-corrosion resistance, while maintaining superior oxidation resistance. The best-performing γ-Ni + γ'-Ni 3 Al compositionwas found to be Ni-18Al-10Cr-3Pt-2Si-0.1Hf alloy (at%). Tests were conducted on both bulk alloys and coatings. Thermal spraying was used to generate the coatings for testing. A Pt-modification procedure was devised for the thermal-spray coatings. Oxidation testing and accelerated hot corrosion testing were used to assess performance. Metallography, SEM and EDS techniques were used to characterize samples and rank performance. As will be shown, the Ni-18Al-10Cr-3Pt-2Si-0.1Hf composition provided the best combination of oxidation and hot corrosion protection when compared to Ni-50Al-15Pt (Pt-modified β), Ni-20Al-20Pt-1wt%Hf (γ-Ni + γ'-Ni 3 Al), Ni-21.7Cr-19.5Al-0.5Y (β+γ MCrAlY), and Ni-17.6Cr-12Al-0.3Y (γ+γ' MCrAlY), with all compositions listed in at%.

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Section: Background On High Temperature Oxidationmentioning

confidence: 99%

Section: Kinetic Description Of Oxide Growthmentioning

confidence: 99%

“…Linear growth can result from surface reaction control or oxidant-supply control. [11,12]. This often indicates that the oxide scale is non-protective due to no reduced rate in growth.…”

Section: Kinetic Description Of Oxide Growthmentioning

confidence: 99%

Section: Kinetic Description Of Oxide Growthmentioning

confidence: 99%

Section: Kinetic Description Of Oxide Growthmentioning

confidence: 99%

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