Anisotropy of secondary reaction zone formation in aluminized Ni-based single-crystal superalloys

2008 ◽  
Vol 59 (4) ◽  
pp. 428-431 ◽  
Author(s):  
H MURAKAMI ◽  
T SAKAI
Keyword(s):  
Single Crystal ◽  
Reaction Zone ◽  
Secondary Reaction ◽  
Zone Formation ◽  
Secondary Reaction Zone

scholarly journals Interdiffusion Behaviour of NiCoCrAlY Coating and N5 Single Crystal Superalloy

Coatings ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 393
Author(s):  
Jiaxu Cao ◽  
Yingkun Liu ◽  
Chunming Deng ◽  
Kun Yang ◽  
Feng Li
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Reaction Zone ◽  
Protective Coating ◽  
Energy Dispersive Spectrometer ◽  
Secondary Reaction ◽  
Single Crystal Superalloy ◽  
Interdiffusion Zone ◽  
Secondary Reaction Zone ◽  
Static Oxidation

This paper aims at investigating the microstructure and phases evolution of single crystal superalloy/high temperature protective coating during high temperature static oxidation, and exploring the influence of element interdiffusion behaviour on microstructure and phase evolution of the single crystal superalloy substrate. A NiCoCrAlY high-temperature protective coating was deposited on the Ni-based single-crystal superalloy by low-pressure plasma spraying technology. The coated samples were subjected to static oxidation for 200 h at a constant temperature of 1100 °C. Scanning electron microscope, energy dispersive spectrometer and X-ray diffraction were used to characterise the microstructure and phase after interdiffusion between the coating and the substrate at high temperature. The results showed that a dense thermally grown oxide layer was formed on the surface of the NiCoCrAlY coating after oxidation for over 100 h. The only interdiffusion zone was formed after oxidation for 50 h, while both interdiffusion zone and secondary reaction zone could be observed after oxidation for over 100 h. The thickness of interdiffusion zone and secondary reaction zone is increased with the extension of oxidation time, and the grain growth of topological close-packed phase in the secondary reaction zone is found. Al, Cr and Co in the coating diffuse from the coating to the substrate, while Ni and refractory materials like Ta, Mo, Re and W diffuse from the coating to the substrate. The interdiffusion of coating and substrate leads to the instability of γ/γ′ phase in the substrate, which finally results in the formation of W, Re and Cr-rich needle-like topological close-packed phase in the substrate.

The chemical structure of premixed fuel-rich methane flames: the effect of hydrocarbon species in the secondary reaction zone

1991 ◽  
Vol 433 (1887) ◽  
pp. 1-21 ◽  
Keyword(s):  
Reaction Zone ◽  
Chemical Structure ◽  
Reaction Rates ◽  
Secondary Reaction ◽  
Partial Equilibrium ◽  
Oh Radicals ◽  
Primary Reaction ◽  
Bimolecular Reactions ◽  
Atom Concentration ◽  
Secondary Reaction Zone

In a previous paper the analysis of a fuel-rich, ф =1.60, methane flame using a four-stage molecular beam inlet to a quadrupole mass spectrometer was described. The results were used to investigate the chemical structure of the primary reaction zone of the flame. In this paper, results from a richer flame, ф = 2.00, are presented and analysed. This premixed, laminar, flat flame had the following composition (all molar percentages) and conditions: 35.0% (CH 4 ), 35.0% (O 2 ), 30% (Ar); pressure = 8.00 kPa; cold-gas velocity at 293 K = 0.47 m s -1 . Mole fraction profiles through each flame were measured for a large number of stable and radical species, and those for the ф = 2.00 flame are presented in this paper and are compared with the results from the ф = 1.60 flame published earlier. Analysis and discussion in the present paper concentrates on the secondary reaction zone of both fuel-rich flames. Comparison of the profiles shows that hydrocarbon species survive the primary reaction zone in increasing concentrations as ф increases. It is shown that the reaction H + O 2 ⇌ OH + O (21, -21 ) does not achieve the partial equilibrium condition that is found in leaner flames, although the remaining bimolecular reactions of the H 2 -O 2 system do so. The competition between various species for the H, O and OH radicals is analysed using a convenient parameter which allows comparison of reaction rates and which has been called the 'characteristic reaction time’, r . It is concluded that the direct cause of the inability of (21, -21) to achieve partial equilibrium is the removal of O atoms from the available pool of H, O and OH radicals by reaction with hydrocarbon species, particularly C 2 H 2 . The rate of decrease of the H atom concentration in the secondary reaction zone is shown to be too fast to be the result of termolecular recombination reactions; it is suggested that the cause is the rapid response of the fast bimolecular reactions of the H 2 -O 2 system to the removal of O atoms via OH + H → O + H 2 , (-22) OH + OH → O + H 2 O (-23) thus reducing the concentrations of H and OH radicals. This mechanism explains the reduction in the excesses of the H, O and OH radicals above their thermodynamic equilibrium levels that is observed with increasing ф . It is concluded that it is possible to view a rich flame as consisting entirely of an extended primary reaction zone in which the concentrations of the H, O and OH radicals are controlled by bimolecular reactions throughout.

scholarly journals Secondary Reaction Zone Formations in Pt-Aluminised Fourth Generation Ni-Base Single Crystal Superalloys

2011 ◽  
Vol 278 ◽  
pp. 78-83 ◽  
Author(s):  
Aya S. Suzuki ◽  
Catherine M.F. Rae ◽  
R.A. Hobbs ◽  
Hideyuki Murakami
Keyword(s):  
Cross Section ◽  
Reaction Zone ◽  
Alloy Composition ◽  
Effective Cross Section ◽  
Secondary Reaction ◽  
Fourth Generation ◽  
Microstructural Stability ◽  
Secondary Reaction Zone ◽  
Negative Effect ◽  
Factorial Design Of Experiments

Fourth generation superalloys are characterised by the addition of Ru which contributes to improved creep resistance whilst improving the microstructural stability. However, Ru additions have a negative effect on coated Ni-base superalloys, promoting Secondary Reaction Zone (SRZ) formation. Formation of a layer of SRZ beneath an aluminised or Pt-aluminised coating has the potential to reduce the effective cross section of a blade by in excess of 100 μm or 10% of the wall thickness. In this paper the effects of alloy composition on the formation of the SRZ in Pt-Aluminised fourth generation alloys were investigated systematically. A series of experimental fourth generation alloys was used having two distinct compositions of Co, Mo, W and Ru and conforming to a four factorial 'Design of Experiments' model. These alloys showed significant and consistent changes in the SRZ depending on alloy composition. These were in distinct contrast to the effects of these elements on stability in the bulk. Mo was demonstrated to be by far the most effective element suppressing SRZ formation, followed by Co. In contrast, both W and Ru enhance SRZ formation.

Microstructure Development of an Electroplating Coated Nickel-Base SC Superalloy in Oxidation Processes—Simulation Results

2021 ◽  
Author(s):  
Kang Yuan ◽  
Zhaoran Zheng
Keyword(s):  
Kinetic Model ◽  
Single Crystal ◽  
Diffusion Zone ◽  
Microstructure Development ◽  
Diffusion Kinetic ◽  
Oxidation Processes ◽  
Secondary Reaction Zone ◽  
Tcp Phases ◽  
Simulation Results ◽  
Nickel Base

Abstract In this paper; a diffusion kinetic model was applied to simulate the microstructure development in a MCrAlY-superalloy system at high temperatures. Both simulation and experimental results showed that γ+γ’ microstructure was obtained in the coatings due to Al depletion after oxidation. With the help of the modelling; the mechanism of the formation of the diffusion zones in the single crystal (SC) superalloy can be also analyzed. The results revealed that the inward diffusion of Al from coating affected the depth of secondary reaction zone (SRZ) with the precipitation of TCP phases while the depth of inter-diffusion zone (IDZ) was decided by the inward diffusion of Cr.

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