Derivation of Temperature-Estimation Equation Based on Microstructural Changes in Coatings of In-Service Blades of Gas Turbines

2010 ◽  
Author(s):  
Mitsutoshi Okada ◽  
Tohru Hisamatsu ◽  
Terutaka Fujioka
Keyword(s):  
High Temperature ◽  
Diffusion Layer ◽  
Gas Turbines ◽  
Aluminum Content ◽  
Oxide Formation ◽  
Diffusion Layer Thickness ◽  
Temperature Estimation ◽  
Diffusion Layers ◽  
Barrier Coating ◽  
Trailing Edges

A CoNiCrAlY-coated blade of an in-service gas turbine is analyzed, and a diffusion layer is formed along the boundary between the coating and the substrate due to the interdiffusion in the middle and tip of the blade. Such a layer is not observed in the vicinity of the blade root because of a comparatively low temperature during the operation. Coated specimens are prepared from the portions of the blade devoid of the diffusion layers, and the specimens are exposed to a high temperature in air. On the basis of the increase in the diffusion layer thickness, an equation for estimating the temperature of the blade is derived. Analysis of another in-service blade with a thermal barrier coating (TBC) is carried out. The aluminum-content decreases below the bond coat surface due to Al diffusion caused by the Al-oxide formation. This results in the formation of an Al-decreased layer (ADL) along the leading and trailing edges. The ADL is not observed at the center of the blade chord. The specimens are extracted from the portions of the blade that are devoid of ADL, and they are subjected to a high temperature in air. On the basis of the increase in the ADL thickness, a temperature-estimation equation is derived.

Derivation of Temperature-Estimation Equation Based on Microstructural Changes in Coatings of In-Service Blades of Gas Turbines

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Mitsutoshi Okada ◽  
Tohru Hisamatsu ◽  
Terutaka Fujioka
Keyword(s):  
High Temperature ◽  
Diffusion Layer ◽  
Gas Turbines ◽  
Aluminum Content ◽  
Oxide Formation ◽  
Diffusion Layer Thickness ◽  
Temperature Estimation ◽  
Diffusion Layers ◽  
Barrier Coating ◽  
Trailing Edges

A CoNiCrAlY-coated blade of an in-service gas turbine is analyzed, and a diffusion layer is formed along the boundary between the coating and the substrate due to the interdiffusion in the middle and tip of the blade. Such a layer is not observed in the vicinity of the blade root because of a comparatively low temperature during the operation. Coated specimens are prepared from the portions of the blade devoid of the diffusion layers, and the specimens are exposed to a high temperature in air. On the basis of the increase in the diffusion layer thickness, an equation for estimating the temperature of the blade is derived. An analysis of another in-service blade with a thermal barrier coating is carried out. The aluminum content decreases below the bond coat surface due to Al diffusion caused by the Al-oxide formation. This results in the formation of an Al-decreased layer (ADL) along the leading and trailing edges. The ADL is not observed at the center of the blade chord. The specimens are extracted from the portions of the blade that are devoid of ADL, and they are subjected to a high temperature in air. On the basis of the increase in the ADL thickness, a temperature-estimation equation is derived.

Stability Study of EBC/TBC Hybrid System on Si-based Ceramics in Gas Turbines

2012 ◽  
Vol 1519 ◽  
Author(s):  
JiaPeng Xu ◽  
Vinod Sarin ◽  
Soumendra Basu
Keyword(s):  
High Temperature ◽  
Hybrid System ◽  
Hot Corrosion ◽  
Gas Turbines ◽  
Ceramic Matrix Composites ◽  
Functionally Graded ◽  
Air Plasma ◽  
High Temperature Stability ◽  
Chemical Attack ◽  
Barrier Coating

ABSTRACTCurrently, ceramics are being used under increasingly demanding environments. These materials have to exhibit phase stability and resist chemical attack during service. This research involves the study of the high-temperature stability of ceramic materials in gas turbines. SiC/SiC ceramic matrix composites (CMCs) are being increasingly used in the hot-sections of gas turbines, especially for aerospace applications. These CMCs are prone to recession of their surface if exposed to a flow of high-velocity water vapor, and to hot-corrosion when exposed to molten alkali salts. The objective of this investigation was the development of a hybrid system containing an environmental barrier coating (EBC) for protection of the CMC from chemical attack and a thermal barrier coating (TBC) that allows a steep temperature gradient across it to lower the temperature of the CMC for increased lifetimes. The EBC used was a functionally graded mullite (3Al2O3∙2SiO2) coating deposited by chemical vapor deposition (CVD), while the TBC layer was yttria-stabilized zirconia (YSZ) deposited by air plasma spray (APS). The stability of this system was investigated, via adhesion between the two coating layers and the substrate, the physical and chemical stability of each layer at high temperature, and the performance under severe thermal shock and exposure to hot corrosion.

Life Prediction of High-Temperature MCrAlY Coatings Based on Microstructural Observations

2014 ◽  
Vol 922 ◽  
pp. 143-148 ◽  
Author(s):  
Robert Eriksson ◽  
Kang Yuan ◽  
Sten Johansson ◽  
Ru Lin Peng ◽  
Xin Hai Li
Keyword(s):  
High Temperature ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Gas Turbines ◽  
Life Prediction ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Mcraly Coatings ◽  
Barrier Coating ◽  
Coating Composition

Thermal barrier coatings are commonly used in gas turbines for protection against high tem-perature and oxidation. Life prediction of oxidation protective coatingsmay be done bymicrostructure-based techniques such as -depletion based life criteria. In this study, a thermal barrier coating sys-tem, with an overlay NiCoCrAlY coating as bond coat, was oxidised up to 10000 h at 900 C. Themicrostructure was studied and related to Al depletion. It was found that a -depletion based lifecriterion could not be used for the studied coating composition and temperature as it would be tooconservative. A 0-depletion based model was instead suggested and supported by interdiffusion sim-ulation.

scholarly journals Evolution of the Diffusion Layer in a CMSX4 Single Crystal Superalloy

2011 ◽  
Vol 278 ◽  
pp. 521-526 ◽  
Author(s):  
Elisabetta Gariboldi ◽  
Xing Hua Han ◽  
Giulioantonio Longo ◽  
Giovanni Paolo Zanon
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Diffusion Layer ◽  
Crystallographic Orientation ◽  
Vapour Phase ◽  
Process Conditions ◽  
Surface Layers ◽  
Diffusion Layers ◽  
Phase Type ◽  
Low Activity

Aluminising processes are well-known techniques industrially adopted to enrich of aluminium the surface layers of Ni-based alloys thus improving their resistance to environmental interaction at high-temperature. The results of aluminising processes are typically described in terms of the presence, compositions and thickness of the sequence of layers at the surface of the treated parts. Following this approach, the microstructural features of the diffusion layers obtained under different holding times via vapour-phase type high-temperature low-activity process were experimentally investigated on single crystal CMSX4 alloy. The attention was particularly focused on the effect of the crystallographic orientation of the crystal on the coating features. The evolution of the diffusion layers under different process conditions was then taken into account.

Compositional Factors Affecting the Oxidation Behavior of Pt-Modified γ-Ni+γ’-Ni3Al-Based Alloys and Coatings

2008 ◽  
Vol 595-598 ◽  
pp. 239-247 ◽  
Author(s):  
N. Mu ◽  
Takeshi Izumi ◽  
L. Zhang ◽  
Brian Gleeson
Keyword(s):  
High Temperature ◽  
Gas Turbines ◽  
Cyclic Oxidation ◽  
Oxidation Behavior ◽  
Thermally Grown Oxide ◽  
Factors Affecting ◽  
Barrier Coating ◽  
Α Al2o3 ◽  
Slow Growing ◽  
Tbc Systems

Many high-temperature coatings rely on the formation of a continuous and adherent thermally grown oxide (TGO) scale of α-Al2O3 for extended resistance to degradation. For instance, the durability and reliability of thermal barrier coating (TBC) systems in gas turbines are critically linked to the oxidation behavior and stability of an alumina-forming β-NiAl-based bond coat. This study focuses primarily on the development of unique Pt+Hf-modified γ′-Ni3Al+γ-Ni coating compositions that form highly adherent, slow-growing TGO scales during both isothermal and cyclic oxidation at high temperature. Recent findings on the isothermal and cyclic oxidation behavior of γ′+γ alloys and coatings will be discussed, with particular emphasis on the effects of Pt, Al and Hf contents and distributions. Inferred reasons for the observed “Pt effect” will also be presented.

Phase structures and thermophysical properties of ZrO2-doped SmTaO4 ceramics

2019 ◽  
Vol 33 (11) ◽  
pp. 1950132 ◽  
Author(s):  
Ying Zhou ◽  
Guoyou Gan ◽  
Zhenhua Ge ◽  
Jianhong Yi ◽  
Jing Feng
Keyword(s):  
Thermal Conductivity ◽  
High Temperature ◽  
Thermophysical Properties ◽  
Gas Turbines ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Next Generation ◽  
Phase Structures ◽  
Barrier Coating ◽  
Ion Doping

The [Formula: see text] ceramics have excellent high-temperature phase stability and mechanical properties and show great potential for use as next-generation thermal barrier coating (TBC) materials. However, the thermophysical properties of [Formula: see text], especially [Formula: see text]-doped, were not clearly established. The [Formula: see text] ceramics doped with different contents of [Formula: see text] (0%, 2%, 4%, 6%, and 8%) by high-temperature solid-state reaction were studied in this paper. The phase structures and microstructures of the samples were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and EDS. The thermophysical properties of the samples including specific heat, thermal diffusivity, and thermal conductivity were measured systematically. The results show that [Formula: see text]-doped [Formula: see text] ceramics have a single monoclinic phase, and that [Formula: see text] ion doping does not change the crystal structure. The bandgap of 2% [Formula: see text]-doped [Formula: see text] ceramics was narrow (4.48 eV), indicating that heat is conducted by phonons in ceramics. The [Formula: see text] doped with 2% of [Formula: see text] had lower thermal conductivity [Formula: see text] at [Formula: see text] than [Formula: see text] [Formula: see text] at [Formula: see text]. This indicates that 2% [Formula: see text]-doped [Formula: see text] ceramics have the potential to be employed as TBCs in next-generation gas turbines.

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