scholarly journals Phase Analysis and Microstructural Investigations of Ce2Zr2O7 for High-Temperature Coatings on Ni-Base Superalloy Substrates

2019 ◽  
Vol 38 (2019) ◽  
pp. 773-782 ◽  
Author(s):  
G. Venkatesh ◽  
R. Subramanian ◽  
L. John Berchmans
Keyword(s):  
High Temperature ◽  
Parabolic Rate Constant ◽  
Xrd Analysis ◽  
Thermally Grown Oxide ◽  
Coated Sample ◽  
Inconel 625 ◽  
Oxide Growth ◽  
Air Plasma ◽  
Microscopy Characterization ◽  
Base Superalloy

AbstractCrystalline cerium-zirconate (CZ) powders were synthesized via solution-assisted combustion synthesis route and calcined at 850°C for 8 h to obtain coarse crystalline powders. SEM (scanning electron microscopy) characterization studies were done to evaluate the morphology of the powders. XRD analysis of the resulting powder confirmed the presence of crystalline α-Ce2Zr2O7 along with a Ce2Zr2O8 phase having a disordered fluorite cubic lattice. Phase composition, lattice parameters, and the atomic positions were also investigated. Refinement of XRD data was done to quantify the amount of α-Ce2Zr2O7 and Ce2Zr2O8 phases. Ni-base superalloy Inconel 625 was chosen as the coating substrate, and the powders were coated using an air plasma spraying (APS). A thermally grown oxide (TGO)/Al2O3 layer was observed owing to the high temperature of the substrate as well as the diffusion of bond coat material into the substrate. Coated samples were characterized by SEM to study the surface morphology, coating thickness, and interface microstructures. The thickness of the coated sample was found to be 400 μm. Thermal cycling test of the coated sample was carried out at 750°C for 50 h to evaluate the thermal shock resistance of the coating as well as the spalling behavior of the coating. Preliminary oxidation tests were carried out for 50 h at 750°C to evaluate the oxide growth by measuring weight gain of the oxide layers formed. Oxide growth signifies the gradual increment of layers over a period with a parabolic rate constant of about Kp= 1.18 × 10–3 mg2 cm–4 h–1.

TGO Formation with NiCoCrAlYTa Bond Coat Deposition Using APS and HVOF Method

2015 ◽  
Vol 1125 ◽  
pp. 18-22 ◽  
Author(s):  
S. Mohd Zulkifli ◽  
Muhammad Azizi Mat Yajid ◽  
Mohd Hasbullah Idris ◽  
M. Daroonparvar ◽  
Halimaton Hamdan
Keyword(s):  
Bond Coat ◽  
Oxidation Process ◽  
Thermally Grown Oxide ◽  
Inconel 625 ◽  
Thermal Barrier ◽  
Air Plasma Spray ◽  
Air Plasma ◽  
Continuous Layer ◽  
Barrier Coating ◽  
Coating Failure

Formation of thin and continuous layer of thermally grown oxide (TGO) in thermal barrier coating (TBC) are essential in order to avoid coating failure for high temperature applications. As-sprayed high velocity oxy-fuel (HVOF) bond coat can provide more uniform TGO layer in TBC system and much less oxide compare to air plasma spray (APS). In this paper, both APS and HVOF method are used to deposit NiCoCrAlYTa bond coat on Inconel 625 substrate followed by topcoat, YSZ deposition. Pre-oxidation process was done in normal oxygen furnace at 1000°C for 12 to 24 hours to study the characteristic of TGO formation via these two different methods. From the result obtained, it shows that HVOF method provide better TGO formation as compared to APS.

scholarly journals Performance of air plasma sprayed Cr3C2-25NiCr and NiCrMoNb coated X8CrNiMoVNb16-13 alloy subjected to high temperature corrosion environment

2022 ◽  
Author(s):  
P Subramani ◽  
M Sathishkumar ◽  
M Manikandan ◽  
S Senthil Kumaran ◽  
V Sreenivasulu ◽  
...  
Keyword(s):  
Weight Gain ◽  
High Temperature ◽  
Bond Strength ◽  
Molten Salt ◽  
Environmental Conditions ◽  
Xrd Analysis ◽  
Vital Role ◽  
Air Plasma ◽  
Air Oxidation ◽  
Plasma Sprayed

Abstract Thermal barrier coating plays a vital role in protecting materials' surfaces from high-temperature environment conditions. This work compares the demeanour of uncoated and air plasma sprayed Cr3C2-25NiCr and NiCrMoNb coated X8CrNiMoVNb16-13 substrates subjected to air oxidation and molten salt (Na2SO4 + 60%V2O5) environment condition at 900°C for 50 cycles. Coating characteristics have been analyzed through microstructure, thickness, porosity, hardness, and bond strength. SEM, EDS and XRD analysis were used to analyze corrosion's product at the end of the 50th cycle. Coating microstructures showed a uniform laminar structure that is adherent and denser with a coating thickness of 150 ± 20 μm and porosity less than 3.5%. The Microhardness of both the coated substrates were higher than that of the bare substrate. Cr3C2-25NiCr and NiCrMoNb coating bond strength was 38.9 MPa and 42.5 MPa. Thermogravimetric analysis showed the parabolic rate law of oxidation for all the substrates in both environments. In the molten salt environment, all the substrates exhibited higher weight gain compared to the air oxidation environment. In both environmental conditions, the uncoated X8CrNiMoVNb16-13 alloy exhibited higher weight gain than the coated substrates. The formation of Cr2O3, NiO and spinel oxide NiCr2O4 offers good resistance to corrosion to all the substrates in both the environmental condition. However, the presence of Mo and Nb significantly accelerated the corrosion of the substrate, thereby increasing the weight of the NiCrMoNb substrate. It is observed that Cr3C2-25NiCr and NiCrMoNb coating over the X8CrNiMoVNb16-13 substrate significantly protected the substrate against the hot corrosion than the bare alloy exposed to similar environmental conditions.

HOT CORROSION OF YTTRIUM STABILIZED ZIRCONIA COATINGS DEPOSITED BY AIR PLASMA SPRAY ON A NICKEL-BASED SUPERALLOY

2016 ◽  
Vol 24 (06) ◽  
pp. 1750084
Author(s):  
N. DIAZ VALLEJO ◽  
O. SANCHEZ ◽  
J. C. CAICEDO ◽  
W. APERADOR ◽  
G. ZAMBRANO
Keyword(s):  
Hot Corrosion ◽  
Electrochemical Impedance ◽  
Xrd Analysis ◽  
Inconel 625 ◽  
Quantitative Phase Analysis ◽  
Microstructural Development ◽  
Air Plasma ◽  
Stabilized Zirconia ◽  
Nickel Based Superalloy ◽  
Fitting Procedure

In this research, the electrochemical impedance spectroscopy (EIS) and Tafel analysis were utilized to study the hot corrosion performance at 700[Formula: see text]C of air plasma-sprayed (APS) yttria-stabilized zirconia (YSZ) coatings with a NiCrAlY bond coat grown by high velocity oxygen fuel spraying (HVOF), deposited on an INCONEL 625 substrate, in contact with corrosive solids salts as vanadium pentoxide V2O5 and sodium sulfate Na2SO4. The EIS data were interpreted based on proposed equivalent electrical circuits using a suitable fitting procedure performed with Echem AnalystTM Software. Phase transformations and microstructural development were examined using X-ray diffraction (XRD), with Rietveld refinement for quantitative phase analysis, scanning electron microscopy (SEM) was used to determinate the coating morphology and corrosion products. The XRD analysis indicated that the reaction between sodium vanadate (NaVO[Formula: see text] and yttrium oxide (Y2O[Formula: see text] produces yttrium vanadate (YVO[Formula: see text] and leads to the transformation from tetragonal to monoclinic zirconia phase.

scholarly journals Characterization of ceramic layers for thermal barriers coatings

2019 ◽  
Vol 1 (1) ◽  
pp. 29-31
Keyword(s):  
High Temperature ◽  
Bond Coat ◽  
Thermal Protection ◽  
Decisive Role ◽  
Thermally Grown Oxide ◽  
Air Plasma ◽  
Operation Conditions ◽  
Bond Layer ◽  
Critical Issues ◽  
Size And Morphology

Thermal barrier coatings (TBC) represent the most effective system to protect structural components from damage caused by high temperature and corrosive/erosive environments. Yttria-stabilized zirconia (YSZ) is among the most studied ceramics for such applications. The adherence of the ceramic layer to the metallic object needing thermal protection is one of the critical issues in real operation conditions at high temperature or under thermal shocks. A bond coat is necessary to ensure the adherence of the YSZ top coat to the substrate. In our work, Y, Ta doped NiCrAl compounds bond coat obtained by air plasma spray (APS – Fig. 1) and high velocity air fuel (HVAF) have been subjected to increasing temperature thermal treatments (700 – 1 300 oC/5 h). The system behavior under thermal stress has been investigated by microstructural methods including XRD, SEM and TEM. The TEM/STEM results (Fig. 2) show the oxidation resistance of the HVAF vs APS deposited bond coats. Spurious Y-Ta-O structures have been evidenced which otherwise failed to be observed by conventional XRD/SEM-EDS (Fig. 3). The identified microphases which appear at the high temperature represent the nucleation point for the layer of thermally grown oxide (TGO) with a decisive role in the delaminating process at high temperature. We show that in the APS-deposited bond coat the TGO was distributed in the whole mass of the bond coat, while in the HVAF-deposited bond coat the TGO is pushed toward its outer surface. Formation of TGO is initiated both at the ceramic-bond layer interface and into the pores existing inside the bond layer. The size and morphology of the pores inside the deposited layers depend on the deposition method (ex: APS or HVAF). Fracture occurs at the YSZ/TGO interface. Below fracture, the TGO to bond coat transition is abrupt (~ 5 – 10 µm). Diffuse Al2O3 can be observed in TGO/BC region (2), which segregates at the BC/substrate interface (3); TGO does not built in a compact oxidation barrier layer. Ta, Y, Ti segregations form into the top coat, bond coat and substrate.

The Effect of the Aluminide Coating on the Thermal Properties and Oxidation Resistance of Inconel 625 Ni-Base Superalloy

2015 ◽  
Vol 227 ◽  
pp. 313-316 ◽  
Author(s):  
Maryana Zagula-Yavorska ◽  
Jan Sieniawski ◽  
Ryszard Filip ◽  
Marcin Drajewicz
Keyword(s):  
Thermal Diffusivity ◽  
Outer Layer ◽  
Aluminide Coating ◽  
Diffusion Coating ◽  
Chemical Vapor ◽  
Deposition Process ◽  
Optical Microscope ◽  
Coated Sample ◽  
Inconel 625 ◽  
Base Superalloy

An investigation was conducted to synthesize βNiAl coating on the nickel based superalloy Inconel 625 in the low activity chemical vapor deposition process (CVD). The deposition was carried out for 8 hours at 1050°C using the BPXpro3252 IonBond company equipment. Surface morphology and cross-section microstructure of the diffusion coating were studied and compared using an optical microscope, an X-ray diffractometer and a scanning electron microscope (SEM) equipped with an energy dispersive spectroscope. It was found that 29 μm thick aluminide coating consisted of two layers: an outer one and the inner interdiffusion one. The outer layer consisted of the βNiAl phase. The inner one consisted of the βNiAl phase with chromium, molybdenum and niobium carbides (M23C6 and MC type) inclusions. Outer layer hardness was about 564 HV0.002 while interdiffusion layer hardness was about 725 HV0.002. Thermal diffusivity of Inconel 625 superalloy with and without coating was measured using a NETZSCH model 427 laser flash diffusivity apparatus. The thermal diffusivity measurements were conducted in the argon atmosphere at the temperature interval 20 - 1200 oC. Thermal diffusivity of the uncoated Inconel 625 Ni-base superalloy at the room temperature is about 2 mm2/s, while for the coated superalloy thermal diffusivity is about 2.8 mm2/s. The increase of the temperature from 20 to 1200 oC leads to the increase of the thermal diffusivity of the coated sample from 2.8 to 5.6 mm2/s. Cyclic oxidation tests for both coated and uncoated superalloys were performed at 1100°C for 1000 h in the air atmosphere. The aluminized samples exhibited a small mass increase and the α-Al2O3 scale was formed during the oxidation test.

Effect of Pre-Weld Heat Treatment Temperatures on TIG Welded Microstructures on Nickel Base Superalloy, GTD-111

2015 ◽  
Vol 658 ◽  
pp. 14-18
Author(s):  
Tanaporn Rojhirunsakool ◽  
Duangkwan Thongpian ◽  
Nutthita Chuankrerkkul ◽  
Panyawat Wangyao
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Heat Treatment Temperature ◽  
Treatment Temperature ◽  
Tig Welding ◽  
Nickel Base Superalloy ◽  
Nickel Base ◽  
Base Superalloy ◽  
Weld Heat

Nickel-base superalloys have been used as high temperature materials in land-base gas turbine application. When subjected to long term, high temperature service, large crack propagation was observed. Typical refurbishment method of these turbines is carried out by using TIG welding followed by post-weld standard heat treatment. However, new crack initiation is found in the heat-affected zone after TIG welding. Pre-weld heat treatment has been discovered to improves final γ + γ’ microstructure. This study focuses on the effect of pre-weld heat treatment temperature on final γ + γ’ microstructure. Seven different conditions of pre-weld heat treatment temperature were investigated. Scanning electron microscopy studies were carried out after pre-weld and post-weld heat treatments to compare the γ + γ’ microstructure and capture microcracks. The best pre-weld heat treatment temperature produces uniform distribution of finely dispersed γ’ precipitates in the γ matrix without post-weld crack.

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