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Papers by satyapal mahade

Thermal spray, Jun 7, 2017

Gadolinium zirconate (GZ) is considered as a promising top coat candidate for high temperature (&... more Gadolinium zirconate (GZ) is considered as a promising top coat candidate for high temperature (>1200 °C) thermal barrier coating (TBC) applications. Suspension plasma spray (SPS) technique has shown the capability to generate a wide range of microstructures which includes the more desirable columnar microstructure. In this study, GZ single layer TBCs were deposited by axial SPS process. The variable parameters include the standoff distance, solid load content of the suspension and input power. The cross section and top surface of the as sprayed TBCs were analyzed by SEM. The phase content in the as sprayed TBCs was analyzed by XRD. The porosity content of the as sprayed TBCs was measured using image analysis. In the SEM analysis, it was observed that a lower solid load content in the suspension favored the formation of a columnar microstructure. Additionally, at lower solid load content, increase in standoff distance resulted in columnar microstructure with high porosity content in the TBC. However, with higher solid content suspension and alteration of input power, only a dense vertical cracked microstructure can be obtained.

Surface and Coatings Technology

Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount o... more Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount of the ferrite (α-Fe) and austenite (γ-Fe) phases as a matrix. Since this steel has a relatively low hardness of 256 HV0.1, an attempt has been made to improve its hardness and wear properties without compromising the corrosion resistance by plasma nitriding and nitrocarburising process. Plasma nitriding and plasma nitrocarburising process was performed with 80% nitrogen and 20% hydrogen gas and 78% nitrogen, 20% hydrogen and 2% acetylene gas respectively at 350, 400, 450 and 500 o C for 4 hours. The temperature played an important role in the distribution of nitrogen and carbon in the original austenite and ferrite phases present in the bulk material. As a result there was an improvement in microhardness and corrosion properties after these treatments. It was observed that plasma nitrocarburising process performed better than plasma nitriding process in improving the corrosion properties...

Surface and Coatings Technology, 2017

Gadolinium zirconate (GZ) is considered as a promising top coat candidate for high temperature TB... more Gadolinium zirconate (GZ) is considered as a promising top coat candidate for high temperature TBC applications. Suspension plasma spray has shown the capability to generate a wide range of microstructures including the desirable columnar microstructure. In this study, two different TBC architectures were deposited using the axial suspension plasma spray. The first variation was a triple layered TBC comprising of thin YSZ base layer beneath a relatively porous GZ intermediate layer and a dense GZ top layer. The second variation was a composite TBC architecture of GZ and YSZ comprising of thin YSZ base layer and GZ + YSZ top layer. Cross sectional SEM analysis of the layered and composite TBCs revealed a columnar microstructure. The porosity content of the deposited TBCs was measured using two methods (Image Analysis and Water Intrusion). The as-sprayed TBCs were exposed at 900°C for 8 h to a corrosive salt environment consisting of a mixture of vanadium pentoxide and sodium sulfate. XRD analysis on the as-corroded TBCs top surface showed the presence of gadolinium vanadate in both the layered and the composite TBCs. SEM/EDS analysis of the top surface and the cross-section of the layered and composite TBCs after hot corrosion test revealed the infiltration of the molten salts through the columnar gaps. The composite TBC showed a lower hot corrosion induced damage compared to the layered TBC where a considerable spallation was observed.

SSRN Electronic Journal, 2021

Surface and Coatings Technology, 2022

Materials Letters, 2017

Yttria stabilized zirconia (YSZ) is susceptible to CMAS (Calcium Magnesium Alumino Silicates) att... more Yttria stabilized zirconia (YSZ) is susceptible to CMAS (Calcium Magnesium Alumino Silicates) attack at high temperatures (>1200°C) which limits its durability. New ceramic materials which can overcome these high temperature challenges are highly desirable. This work investigates the feasibility of depositing two variations of three ceramic layered thermal barrier coatings. The first variation comprised of yttria as the top ceramic layer with gadolinium zirconate (GZ) as the intermediate layer and YSZ as the base layer. The second variation comprised of Yttrium Aluminum Garnet (YAG) as the top layer with gadolinium zirconate as the intermediate layer and YSZ as the base layer. Microstructural analysis of the as sprayed three layered TBCs were performed by SEM/EDS. Columnar microstructures with a relatively dense top layer were obtained in both the variations. The porosity content of the TBCs was measured by water intrusion and image analysis methods. Phase composition of each layer of the as sprayed TBCs was analyzed using XRD. YAG showed an amorphous phase whereas GZ showed a cubic defect fluorite phase and tetragonal phase was observed in YSZ. In the case of yttria, monoclinic and cubic phases were observed.

Surface and Coatings Technology, 2017

7-8 wt% yttria stabilized zirconia (YSZ) is the standard ceramic top coat material used in gas tu... more 7-8 wt% yttria stabilized zirconia (YSZ) is the standard ceramic top coat material used in gas turbines to insulate the underlying metallic substrate. However, at higher temperatures (>1200 ºC), phase stability and sintering becomes an issue for YSZ. At these temperatures, YSZ is also susceptible to CMAS (calcium magnesium alumino silicates) infiltration. New ceramic materials such as pyrochlores have thus been proposed due to their excellent properties such as lower thermal conductivity and better CMAS attack resistance compared to YSZ. However, pyrochlores have inferior thermo mechanical properties compared to YSZ. Therefore, double-layered TBCs with YSZ as the intermediate layer and pyrochlore as the top ceramic layer have been proposed. In this study, double layer TBC comprising gadolinium zirconate (GZ)/YSZ and triple layer TBC (GZdense/GZ/YSZ) comprising relatively denser GZ top layer on GZ/YSZ were deposited by suspension plasma spray. Also, single layer 8YSZ TBC was suspension plasma sprayed to compare its functional performance with the multilayered TBCs. Cross sections and top surface morphology of as sprayed TBCs were analyzed by scanning electron microscopy (SEM). XRD analysis was done to identify phases formed in the top surface of as sprayed TBCs. Porosity measurements were made using water intrusion and image analysis methods. Thermal diffusivity of the as sprayed TBCs was measured using laser flash analysis and thermal conductivity of the TBCs was calculated. The multi-layered GZ/YSZ TBCs were shown to have lower thermal conductivity than the single layer YSZ. The as sprayed TBCs were also subjected to thermal cyclic testing at 1300 ºC. The double and triple layer TBCs had a longer thermal cyclic life compared to YSZ. The thermo cycled samples were analyzed by SEM.

Journal of Thermal Spray Technology, 2016

This study investigates the corrosion resistance of two-layer Gd 2 Zr 2 O 7 /YSZ, three-layer den... more This study investigates the corrosion resistance of two-layer Gd 2 Zr 2 O 7 /YSZ, three-layer dense Gd 2 Zr 2 O 7 / Gd 2 Zr 2 O 7 /YSZ, and a reference single-layer YSZ coating with a similar overall top coat thickness of 300-320 lm. All the coatings were manufactured by suspension plasma spraying resulting in a columnar structure except for the dense layer. Corrosion tests were conducted at 900°C for 8 h using V 2 O 5 and Na 2 SO 4 as corrosive salts at a concentration of approximately 4 mg/cm 2. SEM investigations after the corrosion tests show that Gd 2 Zr 2 O 7-based coatings exhibited lower reactivity with the corrosive salts and the formation of gadolinium vanadate (GdVO 4), accompanied by the phase transformation of zirconia was observed. It is believed that the GdVO 4 formation between the columns reduced the strain tolerance of the coating and also due to the fact that Gd 2 Zr 2 O 7 has a lower fracture toughness value made it more susceptible to corrosion-induced damage. Furthermore, the presence of a relatively dense layer of Gd 2 Zr 2 O 7 on the top did not improve in reducing the corrosion-induced damage. For the reference YSZ coating, the observed corrosion-induced damage was lower probably due to combination of more limited salt penetration, the SPS microstructure and superior fracture toughness of YSZ. Keywords gadolinium zirconate Á hot corrosion Á multilayer thermal barrier coatings Á suspension plasma spraying Á vanadium pentoxide ? sodium sulfate This article is an invited paper selected from presentations at the 2016

Journal of Thermal Spray Technology, 2016

7-8 wt.% Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material ... more 7-8 wt.% Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used by the gas turbines industry due to its excellent thermal and thermo-mechanical properties up to 1200°C. The need for improvement in gas turbine efficiency has led to an increase in the turbine inlet gas temperature. However, above 1200°C, YSZ has issues such as poor sintering resistance, poor phase stability and susceptibility to calcium magnesium alumino silicates (CMAS) degradation. Gadolinium zirconate (GZ) is considered as one of the promising top coat candidates for TBC applications at high temperatures ([1200°C) due to its low thermal conductivity, good sintering resistance and CMAS attack resistance. Single-layer 8YSZ, double-layer GZ/YSZ and triplelayer GZdense/GZ/YSZ TBCs were deposited by suspension plasma spray (SPS) process. Microstructural analysis was carried out by scanning electron microscopy (SEM). A columnar microstructure was observed in the single-, double-and triple-layer TBCs. Phase analysis of the assprayed TBCs was carried out using XRD (x-ray diffraction) where a tetragonal prime phase of zirconia in the single-layer YSZ TBC and a cubic defect fluorite phase of GZ in the double and triple-layer TBCs was observed. Porosity measurements of the as-sprayed TBCs were made by water intrusion method and image analysis method. The as-sprayed GZ-based multi-layered TBCs were subjected to erosion test at room temperature, and their erosion resistance was compared with single-layer 8YSZ. It was shown that the erosion resistance of 8YSZ single-layer TBC was higher than GZ-based multi-layered TBCs. Among the multi-layered TBCs, triple-layer TBC was slightly better than double layer in terms of erosion resistance. The eroded TBCs were cold-mounted and analyzed by SEM. Keywords columnar microstructure Á erosion test Á gadolinium zirconate Á multi-layered thermal barrier coating Á suspension plasma spray Á yttria-stabilized zirconia This article is an invited paper selected from presentations at the

International Journal of Applied Ceramic Technology, 2016

Efficiency of a gas turbine can be increased by increasing the operating temperature. Yttria-stab... more Efficiency of a gas turbine can be increased by increasing the operating temperature. Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used in gas turbine applications. However, above 1200°C, YSZ undergoes significant sintering and CMAS (calcium magnesium alumino silicate) infiltration. New ceramic materials of rare earth zirconate composition such as gadolinium zirconate (GZ) are promising candidates for thermal barrier coating applications (TBC) above 1200°C. Suspension plasma spray of single-layer YSZ, double-layer GZ/YSZ, and a triple-layer TBC comprising denser GZ on top of GZ/YSZ TBC was attempted. The overall coating thickness in all three TBCs was kept the same. Isothermal oxidation performance of the three TBCs along with bare substrate and bond-coated substrate was investigated for time intervals of 10 h, 50 h, and 100 h at 1150°C in air environment. Weight gain/loss analysis was carried out by sensitive weighing balance. Microstructural analysis was carried out using scanning electron microscopy (SEM). As-sprayed single-layer YSZ and double-layer GZ/YSZ showed columnar microstructure, whereas the denser layer in the triple-layer TBC was not columnar. Phase analysis of the top surface of as-sprayed TBCs was carried out using XRD. Porosity measurements were made by water intrusion method. In the weight gain analysis and SEM analysis, multilayered TBCs showed lower weight gain and lower TGO thickness compared to single-layer YSZ.

Surface and Coatings Technology, 2015

Per Nylén, Thermal conductivity and thermal cyclic fatigue of multilayered Gd 2 Zr 2 O 7 /YSZ the... more Per Nylén, Thermal conductivity and thermal cyclic fatigue of multilayered Gd 2 Zr 2 O 7 /YSZ thermal barrier coatings processed by suspension plasma spray, Surface & Coatings Technology (2015),

Journal of Alloys and Compounds, 2016

8 wt% yttria stabilized zirconia (8YSZ) is the standard ceramic top coat material used in thermal... more 8 wt% yttria stabilized zirconia (8YSZ) is the standard ceramic top coat material used in thermal barrier coatings (TBCs) due to its excellent thermo-physical and thermo-mechanical properties. However, above 1200°C, YSZ has issues such as susceptibility to CMAS (Calcium Magnesium Alumino Silicates) attack and enhanced sintering which could lead to catastrophic failure of the TBC. Pyrochlores of rare earth zirconate composition such as gadolinium zirconate have shown to be resistant to CMAS attack and at the same time possess several other attractive properties. However, poor thermal cycling life of single layer gadolinium zirconate (GZ) TBC compared to single layer YSZ has been reported. Therefore, a double layered GZ/YSZ TBC with YSZ as the intermediate coating and GZ as the top coat and a single layer 8YSZ were deposited by the axial suspension plasma spray process. Additionally, a triple layer TBC (GZdense/GZ/YSZ) comprising of denser GZ coating on top of GZ/YSZ TBC was deposited. SEM analysis revealed a columnar microstructure in the single, double and triple layer TBCs. XRD analysis confirmed the presence of tetragonal prime and defect fluorite phases in the top surface of YSZ and GZ based as sprayed TBCs respectively. The single layer YSZ and GZ/YSZ multi-layered TBCs were subjected to thermal cyclic fatigue (TCF) testing at 1100°C and 1200°C. The triple layer TBC showed a higher thermal cyclic life at both the temperatures compared to the single and double layer TBCs. The failed TBCs at 1100°C were analyzed by SEM/EDS and image analysis. It was found that the failure modes in single layer YSZ and GZ based TBCs were different.

Surface and Coatings Technology

Yttria stabilized zirconia (8YSZ) is the standard ceramic material for thermal barrier coating (T... more Yttria stabilized zirconia (8YSZ) is the standard ceramic material for thermal barrier coating (TBC)applications. However, above 1200o C, it has limitations such as poor sintering resistance & ...

Thermal barrier coatings (TBCs) play a vital role in allowing the gas turbine engines to operate ... more Thermal barrier coatings (TBCs) play a vital role in allowing the gas turbine engines to operate at high temperatures. With higher operating temperatures (>1200°C), the standard TBC material, 7- ...

Yttria stabilized zirconia (YSZ) is the state of the art ceramic top coat material used for TBC a... more Yttria stabilized zirconia (YSZ) is the state of the art ceramic top coat material used for TBC applications. The desire to achieve a higher engine efficiency of agas turbine engine by increasing t ...

Thermal spray, Jun 7, 2017

Gadolinium zirconate (GZ) is considered as a promising top coat candidate for high temperature (&... more Gadolinium zirconate (GZ) is considered as a promising top coat candidate for high temperature (>1200 °C) thermal barrier coating (TBC) applications. Suspension plasma spray (SPS) technique has shown the capability to generate a wide range of microstructures which includes the more desirable columnar microstructure. In this study, GZ single layer TBCs were deposited by axial SPS process. The variable parameters include the standoff distance, solid load content of the suspension and input power. The cross section and top surface of the as sprayed TBCs were analyzed by SEM. The phase content in the as sprayed TBCs was analyzed by XRD. The porosity content of the as sprayed TBCs was measured using image analysis. In the SEM analysis, it was observed that a lower solid load content in the suspension favored the formation of a columnar microstructure. Additionally, at lower solid load content, increase in standoff distance resulted in columnar microstructure with high porosity content in the TBC. However, with higher solid content suspension and alteration of input power, only a dense vertical cracked microstructure can be obtained.

Surface and Coatings Technology

Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount o... more Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount of the ferrite (α-Fe) and austenite (γ-Fe) phases as a matrix. Since this steel has a relatively low hardness of 256 HV0.1, an attempt has been made to improve its hardness and wear properties without compromising the corrosion resistance by plasma nitriding and nitrocarburising process. Plasma nitriding and plasma nitrocarburising process was performed with 80% nitrogen and 20% hydrogen gas and 78% nitrogen, 20% hydrogen and 2% acetylene gas respectively at 350, 400, 450 and 500 o C for 4 hours. The temperature played an important role in the distribution of nitrogen and carbon in the original austenite and ferrite phases present in the bulk material. As a result there was an improvement in microhardness and corrosion properties after these treatments. It was observed that plasma nitrocarburising process performed better than plasma nitriding process in improving the corrosion properties...

Surface and Coatings Technology, 2017

Gadolinium zirconate (GZ) is considered as a promising top coat candidate for high temperature TB... more Gadolinium zirconate (GZ) is considered as a promising top coat candidate for high temperature TBC applications. Suspension plasma spray has shown the capability to generate a wide range of microstructures including the desirable columnar microstructure. In this study, two different TBC architectures were deposited using the axial suspension plasma spray. The first variation was a triple layered TBC comprising of thin YSZ base layer beneath a relatively porous GZ intermediate layer and a dense GZ top layer. The second variation was a composite TBC architecture of GZ and YSZ comprising of thin YSZ base layer and GZ + YSZ top layer. Cross sectional SEM analysis of the layered and composite TBCs revealed a columnar microstructure. The porosity content of the deposited TBCs was measured using two methods (Image Analysis and Water Intrusion). The as-sprayed TBCs were exposed at 900°C for 8 h to a corrosive salt environment consisting of a mixture of vanadium pentoxide and sodium sulfate. XRD analysis on the as-corroded TBCs top surface showed the presence of gadolinium vanadate in both the layered and the composite TBCs. SEM/EDS analysis of the top surface and the cross-section of the layered and composite TBCs after hot corrosion test revealed the infiltration of the molten salts through the columnar gaps. The composite TBC showed a lower hot corrosion induced damage compared to the layered TBC where a considerable spallation was observed.

SSRN Electronic Journal, 2021

Surface and Coatings Technology, 2022

Materials Letters, 2017

Yttria stabilized zirconia (YSZ) is susceptible to CMAS (Calcium Magnesium Alumino Silicates) att... more Yttria stabilized zirconia (YSZ) is susceptible to CMAS (Calcium Magnesium Alumino Silicates) attack at high temperatures (>1200°C) which limits its durability. New ceramic materials which can overcome these high temperature challenges are highly desirable. This work investigates the feasibility of depositing two variations of three ceramic layered thermal barrier coatings. The first variation comprised of yttria as the top ceramic layer with gadolinium zirconate (GZ) as the intermediate layer and YSZ as the base layer. The second variation comprised of Yttrium Aluminum Garnet (YAG) as the top layer with gadolinium zirconate as the intermediate layer and YSZ as the base layer. Microstructural analysis of the as sprayed three layered TBCs were performed by SEM/EDS. Columnar microstructures with a relatively dense top layer were obtained in both the variations. The porosity content of the TBCs was measured by water intrusion and image analysis methods. Phase composition of each layer of the as sprayed TBCs was analyzed using XRD. YAG showed an amorphous phase whereas GZ showed a cubic defect fluorite phase and tetragonal phase was observed in YSZ. In the case of yttria, monoclinic and cubic phases were observed.

Surface and Coatings Technology, 2017

7-8 wt% yttria stabilized zirconia (YSZ) is the standard ceramic top coat material used in gas tu... more 7-8 wt% yttria stabilized zirconia (YSZ) is the standard ceramic top coat material used in gas turbines to insulate the underlying metallic substrate. However, at higher temperatures (>1200 ºC), phase stability and sintering becomes an issue for YSZ. At these temperatures, YSZ is also susceptible to CMAS (calcium magnesium alumino silicates) infiltration. New ceramic materials such as pyrochlores have thus been proposed due to their excellent properties such as lower thermal conductivity and better CMAS attack resistance compared to YSZ. However, pyrochlores have inferior thermo mechanical properties compared to YSZ. Therefore, double-layered TBCs with YSZ as the intermediate layer and pyrochlore as the top ceramic layer have been proposed. In this study, double layer TBC comprising gadolinium zirconate (GZ)/YSZ and triple layer TBC (GZdense/GZ/YSZ) comprising relatively denser GZ top layer on GZ/YSZ were deposited by suspension plasma spray. Also, single layer 8YSZ TBC was suspension plasma sprayed to compare its functional performance with the multilayered TBCs. Cross sections and top surface morphology of as sprayed TBCs were analyzed by scanning electron microscopy (SEM). XRD analysis was done to identify phases formed in the top surface of as sprayed TBCs. Porosity measurements were made using water intrusion and image analysis methods. Thermal diffusivity of the as sprayed TBCs was measured using laser flash analysis and thermal conductivity of the TBCs was calculated. The multi-layered GZ/YSZ TBCs were shown to have lower thermal conductivity than the single layer YSZ. The as sprayed TBCs were also subjected to thermal cyclic testing at 1300 ºC. The double and triple layer TBCs had a longer thermal cyclic life compared to YSZ. The thermo cycled samples were analyzed by SEM.

Journal of Thermal Spray Technology, 2016

This study investigates the corrosion resistance of two-layer Gd 2 Zr 2 O 7 /YSZ, three-layer den... more This study investigates the corrosion resistance of two-layer Gd 2 Zr 2 O 7 /YSZ, three-layer dense Gd 2 Zr 2 O 7 / Gd 2 Zr 2 O 7 /YSZ, and a reference single-layer YSZ coating with a similar overall top coat thickness of 300-320 lm. All the coatings were manufactured by suspension plasma spraying resulting in a columnar structure except for the dense layer. Corrosion tests were conducted at 900°C for 8 h using V 2 O 5 and Na 2 SO 4 as corrosive salts at a concentration of approximately 4 mg/cm 2. SEM investigations after the corrosion tests show that Gd 2 Zr 2 O 7-based coatings exhibited lower reactivity with the corrosive salts and the formation of gadolinium vanadate (GdVO 4), accompanied by the phase transformation of zirconia was observed. It is believed that the GdVO 4 formation between the columns reduced the strain tolerance of the coating and also due to the fact that Gd 2 Zr 2 O 7 has a lower fracture toughness value made it more susceptible to corrosion-induced damage. Furthermore, the presence of a relatively dense layer of Gd 2 Zr 2 O 7 on the top did not improve in reducing the corrosion-induced damage. For the reference YSZ coating, the observed corrosion-induced damage was lower probably due to combination of more limited salt penetration, the SPS microstructure and superior fracture toughness of YSZ. Keywords gadolinium zirconate Á hot corrosion Á multilayer thermal barrier coatings Á suspension plasma spraying Á vanadium pentoxide ? sodium sulfate This article is an invited paper selected from presentations at the 2016

Journal of Thermal Spray Technology, 2016

7-8 wt.% Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material ... more 7-8 wt.% Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used by the gas turbines industry due to its excellent thermal and thermo-mechanical properties up to 1200°C. The need for improvement in gas turbine efficiency has led to an increase in the turbine inlet gas temperature. However, above 1200°C, YSZ has issues such as poor sintering resistance, poor phase stability and susceptibility to calcium magnesium alumino silicates (CMAS) degradation. Gadolinium zirconate (GZ) is considered as one of the promising top coat candidates for TBC applications at high temperatures ([1200°C) due to its low thermal conductivity, good sintering resistance and CMAS attack resistance. Single-layer 8YSZ, double-layer GZ/YSZ and triplelayer GZdense/GZ/YSZ TBCs were deposited by suspension plasma spray (SPS) process. Microstructural analysis was carried out by scanning electron microscopy (SEM). A columnar microstructure was observed in the single-, double-and triple-layer TBCs. Phase analysis of the assprayed TBCs was carried out using XRD (x-ray diffraction) where a tetragonal prime phase of zirconia in the single-layer YSZ TBC and a cubic defect fluorite phase of GZ in the double and triple-layer TBCs was observed. Porosity measurements of the as-sprayed TBCs were made by water intrusion method and image analysis method. The as-sprayed GZ-based multi-layered TBCs were subjected to erosion test at room temperature, and their erosion resistance was compared with single-layer 8YSZ. It was shown that the erosion resistance of 8YSZ single-layer TBC was higher than GZ-based multi-layered TBCs. Among the multi-layered TBCs, triple-layer TBC was slightly better than double layer in terms of erosion resistance. The eroded TBCs were cold-mounted and analyzed by SEM. Keywords columnar microstructure Á erosion test Á gadolinium zirconate Á multi-layered thermal barrier coating Á suspension plasma spray Á yttria-stabilized zirconia This article is an invited paper selected from presentations at the

International Journal of Applied Ceramic Technology, 2016

Efficiency of a gas turbine can be increased by increasing the operating temperature. Yttria-stab... more Efficiency of a gas turbine can be increased by increasing the operating temperature. Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used in gas turbine applications. However, above 1200°C, YSZ undergoes significant sintering and CMAS (calcium magnesium alumino silicate) infiltration. New ceramic materials of rare earth zirconate composition such as gadolinium zirconate (GZ) are promising candidates for thermal barrier coating applications (TBC) above 1200°C. Suspension plasma spray of single-layer YSZ, double-layer GZ/YSZ, and a triple-layer TBC comprising denser GZ on top of GZ/YSZ TBC was attempted. The overall coating thickness in all three TBCs was kept the same. Isothermal oxidation performance of the three TBCs along with bare substrate and bond-coated substrate was investigated for time intervals of 10 h, 50 h, and 100 h at 1150°C in air environment. Weight gain/loss analysis was carried out by sensitive weighing balance. Microstructural analysis was carried out using scanning electron microscopy (SEM). As-sprayed single-layer YSZ and double-layer GZ/YSZ showed columnar microstructure, whereas the denser layer in the triple-layer TBC was not columnar. Phase analysis of the top surface of as-sprayed TBCs was carried out using XRD. Porosity measurements were made by water intrusion method. In the weight gain analysis and SEM analysis, multilayered TBCs showed lower weight gain and lower TGO thickness compared to single-layer YSZ.

Surface and Coatings Technology, 2015

Per Nylén, Thermal conductivity and thermal cyclic fatigue of multilayered Gd 2 Zr 2 O 7 /YSZ the... more Per Nylén, Thermal conductivity and thermal cyclic fatigue of multilayered Gd 2 Zr 2 O 7 /YSZ thermal barrier coatings processed by suspension plasma spray, Surface & Coatings Technology (2015),

Journal of Alloys and Compounds, 2016

8 wt% yttria stabilized zirconia (8YSZ) is the standard ceramic top coat material used in thermal... more 8 wt% yttria stabilized zirconia (8YSZ) is the standard ceramic top coat material used in thermal barrier coatings (TBCs) due to its excellent thermo-physical and thermo-mechanical properties. However, above 1200°C, YSZ has issues such as susceptibility to CMAS (Calcium Magnesium Alumino Silicates) attack and enhanced sintering which could lead to catastrophic failure of the TBC. Pyrochlores of rare earth zirconate composition such as gadolinium zirconate have shown to be resistant to CMAS attack and at the same time possess several other attractive properties. However, poor thermal cycling life of single layer gadolinium zirconate (GZ) TBC compared to single layer YSZ has been reported. Therefore, a double layered GZ/YSZ TBC with YSZ as the intermediate coating and GZ as the top coat and a single layer 8YSZ were deposited by the axial suspension plasma spray process. Additionally, a triple layer TBC (GZdense/GZ/YSZ) comprising of denser GZ coating on top of GZ/YSZ TBC was deposited. SEM analysis revealed a columnar microstructure in the single, double and triple layer TBCs. XRD analysis confirmed the presence of tetragonal prime and defect fluorite phases in the top surface of YSZ and GZ based as sprayed TBCs respectively. The single layer YSZ and GZ/YSZ multi-layered TBCs were subjected to thermal cyclic fatigue (TCF) testing at 1100°C and 1200°C. The triple layer TBC showed a higher thermal cyclic life at both the temperatures compared to the single and double layer TBCs. The failed TBCs at 1100°C were analyzed by SEM/EDS and image analysis. It was found that the failure modes in single layer YSZ and GZ based TBCs were different.

Surface and Coatings Technology

Yttria stabilized zirconia (8YSZ) is the standard ceramic material for thermal barrier coating (T... more Yttria stabilized zirconia (8YSZ) is the standard ceramic material for thermal barrier coating (TBC)applications. However, above 1200o C, it has limitations such as poor sintering resistance & ...

Thermal barrier coatings (TBCs) play a vital role in allowing the gas turbine engines to operate ... more Thermal barrier coatings (TBCs) play a vital role in allowing the gas turbine engines to operate at high temperatures. With higher operating temperatures (>1200°C), the standard TBC material, 7- ...

Yttria stabilized zirconia (YSZ) is the state of the art ceramic top coat material used for TBC a... more Yttria stabilized zirconia (YSZ) is the state of the art ceramic top coat material used for TBC applications. The desire to achieve a higher engine efficiency of agas turbine engine by increasing t ...