Aluminizing Behaviors of Vacuum Plasma Sprayed MCrAlY Coatings

2002 ◽  
Vol 124 (2) ◽  
pp. 270-275 ◽  
Author(s):  
Y. Itoh ◽  
M. Saitoh ◽  
Y. Ishiwata
Keyword(s):  
High Temperature ◽  
Diffusion Rate ◽  
Nickel Content ◽  
Reaction Diffusion ◽  
Vacuum Plasma Spraying ◽  
Temperature Oxidation ◽  
Vacuum Plasma ◽  
Mcraly Coatings ◽  
Heat Treated ◽  
Plasma Sprayed

The objective of this study is aluminide overlay coatings of MCrAlY sprayed by a vacuum plasma spraying (VPS) process for the protection against high-temperature corrosion and oxidation of gas turbine components. Diffusion coating processes have been applied for many years to improve similarly the environmental resistance by enriching the surface of nickel-based superalloys with chromium, aluminum, or silicon element. Recently, aluminizing of MCrAlY coatings is used for improving further the high-temperature oxidation resistance. However, the aluminizing properties of plasma-sprayed MCrAlY coatings, which have an important effect on the coating performance, have not been clarified. In this study, five kinds of plasma-sprayed MCrAlY (CoCrAlY, CoNiCrAlY, CoNiCrAlY+Ta, NiCrAlY, and NiCoCrAlY) coating were selected for pack-aluminizing tests. The as sprayed and the heat-treated (1393 K, 2 h, argon cooled and 1116 K, 24 h, argon cooled) MCrAlY specimens were Al-Cr-Al2O3-NH4Cl pack-aluminized at 1173, 1223, and 1273 K for 5, 10, and 20 h, respectively. The experimental results showed that the aluminizing process formed the aluminum rich layers of NiAl or CoAl phase. It also indicated that the thickness of the aluminum rich layer showed a parabolic time-dependence in all MCrAlY coatings. The order of reaction diffusion rate was NiCoCrAlY=NiCrAlY>CoNiCrAlY>CoNiCrAlY+Ta>CoCrAlY. There was a tendency that the reaction diffusion rate by aluminizing increased with increasing nickel content in the MCrAlY coatings and the reaction diffusion rate of as sprayed MCrAlY coatings is faster than that of the heat-treated MCrAlY coatings.

Mechanical Properties of Overaluminized MCrAlY Coatings at Room Temperature

2005 ◽  
Vol 127 (4) ◽  
pp. 807-813 ◽  
Author(s):  
Yoshiyasu Itoh ◽  
Masahiro Saitoh
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Volume Fraction ◽  
Bend Strength ◽  
Vacuum Plasma Spraying ◽  
Temperature Oxidation ◽  
Vacuum Plasma ◽  
Mcraly Coatings ◽  
Aluminum Compounds ◽  
Plasma Sprayed

The objective of this study is to compare the mechanical properties of overaluminized MCrAlY coatings sprayed by a vacuum plasma spraying process for the protection against high-temperature corrosion and oxidation in the field of gas turbine components. Recently, the overaluminized MCrAlY coatings are used for improving further the high-temperature oxidation resistance. However, the mechanical properties of aluminized MCrAlY coatings, which have an important effect on coating lives, have not been clarified. Five kind of freestanding MCrAlY specimens (CoCrAlY, CoNiCrAlY, CoNiCrAlY+Ta, NiCrAlY, NiCoCrAlY) were machined from the thick vacuum plasma sprayed (VPS) coatings. And, the heat-treated MCrAlY specimens (1393 K, 2 h, argon cooled and 1116 K, 24 h, argon cooled) and the overaluminized specimens (Al-Cr-Al2O3-NH4Cl pack, 1173–1273 K, 10 h) after the heat-treatment were used. The experimental results suggested that the volume fraction of precipitated aluminum compounds in the VPS MCrAlY coatings and the residual stress induced by the overaluminizing treatment had important effects on the mechanical properties. The Vickers hardness and Young’s modulus of the overaluminized MCrAlY coatings showed higher values in comparison with the VPS MCrAlY coatings. There was a tendency that the bend strength of overaluminized VPS MCrAlY coatings decreased by the aluminizing treatment and also with increasing volume fraction of precipitated aluminum compounds in the VPS MCrAlY coatings. It was also confirmed that the bend strength of aluminized layers themselves was reduced with increasing volume fraction of precipitated aluminum compounds in the VPS MCrAlY coatings. These tendencies were caused by the enrichment of brittle precipitates, such as NiAl and/or CoAl intermetallic compounds.

Vacuum Plasma Spraying of Pre-reacted MoSi2 and SiC-Reinforced MoSi2 Produced by a New Kind of Powder Processing

2000 ◽  
Author(s):  
B. Wielage ◽  
S. Steinhäuser ◽  
G. Reisel ◽  
I. Morgenthal ◽  
R. Scholl
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Plasma Spraying ◽  
Powder Processing ◽  
Protective Coatings ◽  
High Energy ◽  
Vacuum Plasma Spraying ◽  
Temperature Oxidation ◽  
Vacuum Plasma ◽  
Brittle Ductile Transition

Abstract Molybdenum silicides have the potential as protective coatings for high-temperature applications because of their high melting point and their high-temperature oxidation resistance. Reinforcing MoSi2 with SiC shows an improvement of its low toughness at room temperature and low creep resistance at temperatures above the brittle-ductile transition temperature of approximately 700-1000 °C. A new kind of powder processing was used to produce MoSi2 and MoSi2-SiC as a feedstock for thermal spraying. Mixtures of the elemental powders, molybdenum and silicon, were prepared by milling and subsequent heat treatment to get highly dispersed, pre-reacted powders. As high-energy milling equipment, a planetary ball mill was used to prepare the powders. In the case of reinforcement, SiC was mixed to the pre-reacted MoSi2 at the end of the milling process, that means before heat treatment. On these as-milled powders, X-ray diffraction characterization (XRD), scanning electron microscopy (SEM), electron probe micro analysis (EPMA) and determination of the oxygen level were carried out. Vacuum plasma spraying has been used to deposit the powders onto a carbon steel substrate. Evaluated coating characteristics were the microstructure (SEM), phases (XRD), EPMA, oxygen content, microhardness and surface roughness. Tests at high temperatures will be considered in future work.

Microstructure Characteristics and High-Temperature Oxidation Behavior of Plasma-Sprayed and Laser-Remelted MCrAlY Coatings on TiAl Intermetallics

2011 ◽  
Author(s):  
Zongjun Tian ◽  
Lida Shen ◽  
Zhidong Liu ◽  
Yinhui Huang
Keyword(s):  
High Temperature ◽  
Oxidation Resistance ◽  
Plasma Spraying ◽  
High Temperature Oxidation ◽  
Intermetallic Alloys ◽  
Laser Remelting ◽  
Temperature Oxidation ◽  
Mcraly Coatings ◽  
Tial Intermetallics ◽  
Plasma Sprayed

In order to further improve the high-temperature oxidation resistance of TiAl intermetallic alloys, MCrAlY coatings were fabricated by plasma spraying and plasma spraying-laser remelting technologies. The microstructures of the as-sprayed and laser-remelted MCrAlY coatings were studied. In addition, the oxidation behaviors at 850 °C for three samples were investigated. One sample is the matrix of TiA1 intermetallic alloys, the other one is processed by plasma-spraying MCrAlY coatings, and the third one is processed by plasma-spraying and laser-remelting MCrAlY coatings. It was revealed that the oxidation resistance of TiAl intermetallics is weak due to lack of protection of Al2O3 film formed on the surface. The plasma-sprayed MCrAlY coatings have better oxidation resistance than the TiAl intermetallics although the plasma-sprayed MCrAlY coatings have high density of porosity and a typical layered structure. It is demonstrated that most of the holes can be eliminated by laser remelting, leading to the best oxidation resistance of the third sample with the laser-remelted coatings. The high oxidation resistance of the laser-remelted coatings is mainly attributed to three aspects: firstly, an Al enriched zone on the coating surface is formed during laser remelting, which is transformed into a protective Al2O3 film during oxidation process. Secondly, laser remelting eliminates most of the defects in plasma-sprayed coatings and enhances its density, thus decreases the channel of oxidation diffusion in high temperature oxidation process. Thirdly, rapid cooling of laser remelting results in a grain refinement and a preferred oxidation of Al at the initial stage, leading to a reduction of oxidation rate.

Reaction Diffusion Behaviors for Interface Between Ni-Based Super Alloys and Vacuum Plasma Sprayed MCrAlY Coatings

1999 ◽  
Vol 121 (3) ◽  
pp. 476-483 ◽  
Author(s):  
Y. Itoh ◽  
M. Tamura
Keyword(s):  
Simulation Analysis ◽  
Reaction Diffusion ◽  
Compound Layer ◽  
Vacuum Plasma Spray ◽  
Aluminum Compound ◽  
Vacuum Plasma ◽  
Diffusion Layers ◽  
Mcraly Coatings ◽  
Plasma Sprayed ◽  
Diffusion Behaviors

The object of this study is overlay coatings of MCrAlY alloy sprayed by a vacuum plasma spray (VPS) process for the protection against high-temperature corrosion and oxidation in the field of gas turbine components. Reaction diffusion behaviors at the interface between the MCrAlY coatings and the substrate, which have an important effect on coating degradation, have not always been clarified. Three kinds of substrate, equiaxis IN738LC, directional solidified CM247LC and single-crystal CMSX-2, and the four kinds of vacuum plasma sprayed MCrAlY coating have been selected for these experiments. The experimental results showed that the reaction diffusion layers consisted of aluminum compound layer and aluminum depleted layer, excepting that the aluminum depleted layer could not be observed in the case of CoNiCrAlY and NiCoCrAlY coatings. It also indicated that the diffusion thickness could be observed to follow a parabolic time dependence. The order of reaction diffusion rate was NiCrAlY > CoCrAlY > CoNiCrAlY > NiCoCrAlY independent of the substrates. A convenient computer-aided system was developed for analyzing the reaction diffusion behaviors at the interface between coating and substrate. It was also clear that the estimated results of long time diffusion behaviors by simulation analysis was in good agreement with experiments.

Study on the Oxidation Behavior of LPPS MCrAlY Coatings at High Temperature: Part II Coating Microstructure Development

2021 ◽  
Vol 1035 ◽  
pp. 584-590
Author(s):  
Kang Yuan ◽  
Zhao Ran Zheng
Keyword(s):  
High Temperature ◽  
Thermodynamic Simulation ◽  
Thermal Barrier ◽  
Microstructure Development ◽  
Temperature Oxidation ◽  
Bond Coats ◽  
Β Phase ◽  
Mcraly Coatings ◽  
Coating Microstructure ◽  
Simulation Results

MCrAlY can be used as bond coats for thermal barrier coatings (TBCs) with good ductility and excellent resistance against high temperature oxidation and hot corrosion. The behavior of the microstructure development in the MCrAlY coatings plays a key role on the oxidation resistance. In this paper, the microstructure in the coatings oxidized at 750~1100 °C was analyzed. The formation of the phases and their fraction were studied by comparing thermodynamic simulation results with the experimental observations. At higher temperatures (>1000 °C) β-to-γ’-to-γ phase transformation took place while at lower temperatures (<1000 °C) β phase would transfer to γ directly. The results show that the simulation can semi-quantitatively predict the microstructure formed in the coating.

High Temperature Oxidation and Microstructural Evolution of Modified MCrAlY Coatings

2013 ◽  
Vol 45 (3) ◽  
pp. 1401-1408 ◽  
Author(s):  
Giovanni Pulci ◽  
Jacopo Tirillò ◽  
Francesco Marra ◽  
Fabrizio Sarasini ◽  
Alessandra Bellucci ◽  
...  
Keyword(s):  
High Temperature ◽  
Microstructural Evolution ◽  
High Temperature Oxidation ◽  
Temperature Oxidation ◽  
Mcraly Coatings

Study of Damage Processes in Plasma Sprayed Bond Coat Under Thermal Cycling

1998 ◽  
Author(s):  
P. Bonnet ◽  
S. Abboudl ◽  
B. Normand
Keyword(s):  
High Temperature ◽  
Thermal Cycling ◽  
Bond Coat ◽  
Gas Turbines ◽  
Temperature Oxidation ◽  
Bond Coating ◽  
Engine Efficiency ◽  
Thermal Barriers ◽  
Plasma Sprayed ◽  
Damage Processes

Abstract Plasma sprayed thermal barriers are used as insulating materials in the hot sections of gas turbines to decrease the metal temperatures during service and men allow a higher combustion temperature for better engine efficiency. They usually contain a bond coating to protect the substrate from high temperature oxidation and a top coat with a low thermal conductivity. This study evaluate and identify the mechanisms of degradation of a vacuum plasma sprayed NiCoCrAlYTa bond coat subjected to thermal cycling at high temperature. The microstructure and micro-composition of the coating layer were analyzed by scanning electron microscopy and energy dispersive X-ray analysis to elucidate the improvement and degradation mechanisms of the material. The thermal cycling provokes some morphological and chemical modifications changes within this material. These modifications provoke a perturbation of the heat transfer within the material.

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