Effect of Na<sub>2</sub>SO<sub>4</sub>-V<sub>2</sub>O<sub>5</sub> Mixture on Y<sub>2</sub>O<sub>3</sub> Stabilized ZrO<sub>2</sub> Thermal Barrier Coatings Exposed at High Temperature
0
Citation
12
Reference
10
Related Paper
Abstract:
Yttria stabilized zirconia thermal barrier coating (TBC) along with CoNiCrAlY bondcoat was deposited using air plasma spray on Inconel-X750 superalloy. The coated samples were exposed at 9500C in a mixture of Na 2 SO 4 and V 2 O 5 . The exposed specimens were investigated using XRD and SEM. The formation of spinel and perovskite structures was revealed at the interface of topcoat and the bondcoat. XRD analyses of the samples confirmed phase transformation of the tetragonal zirconia into monoclinic zirconia and yttrium vanadate.Keywords:
Monoclinic crystal system
Tetragonal crystal system
Ceramic thermal barrier coatings (TBCs) have been used for decades to extend the life of combustors and high temperature turbine stationary and rotating components to increase the operating temperature and in turn the performance of gas turbines or diesel engines can be increased. At present, thermal barrier coatings (TBCs) of Y2O3 partially stabilized ZrO2 (YSZ) films are widely used. In recent years ceramic compositions useful in thermal barrier coatings having reduced thermal conductivity are being explored to further increasing the operating temperature of gas turbines and improve the engine efficiency. In the present study, a comparison of the properties of state-of-the art 8wt% yttria stabilized zirconia (YSZ) and lanthana doped YSZ plasma sprayed coatings is presented. Plasma sprayable powders were prepared in the laboratory by a single step precipitation method and characterized. Both the powders had good flowability. These powders were plasma sprayed at identical critical plasma spray parameters. The coatings were characterized for phase, microstructure and thermal conductivity. Both the powders and coatings exhibited tetragonal form of zirconia and no traces of lanthana were observed. Both the coatings exhibited similar porosity levels. Microstructure of the coatings revealed porous coating with good adhesion of the bondcoat with the topcoat. Plasma sprayed 8wt% YSZ and lanthana doped YSZ exhibited thermal conductivity values of 0.88 and 0.67 W m−1 K−1 respectively which is lower than that reported in literature. This study shows that lanthana doping in YSZ helps in lowering the thermal conductivity and hence this coating may be a potential candidate for TBC application.
Cite
Citations (0)
Thermal barrier coatings (TBCs), which protect metallic components from high-temperature environments, have been widely applied to the fields of high-temperature and corrosion-resistant structural parts such as gas turbine engines, diesel engines, and power generation systems. Yttria-stabilized zirconia (YSZ) is one of the most widely used materials for TBCs owing to its excellent shock resistance, low-thermal conductivity, and relatively high coefficient of thermal expansion. In this paper the properties of YSZ and the recent developments of YSZ-TBCs are reviewed. The failure mechanism of YSZ-TBCs and corresponding methods for lengthening the lifetime of YSZ-TBCs are discussed. The advantages of graded thermal barrier coatings and the problems in processing are elucidated.
Thermal shock
Cite
Citations (179)
Inconel
Temperature cycling
Zirconate
Thermal shock
Cite
Citations (73)
Cite
Citations (47)
Cite
Citations (6)
The spinel growth induces undulation of the thermal growth oxide layer and decreases the service life of plasma-sprayed thermal barrier coatings. An analytical model is introduced to investigate the effect of spinel growth on the delamination of thermal barrier coating. The analytical results show that the number per unit area and the growth rate of spinel have significant influence on the delamination of thermal barrier coating. The stiffer and thicker thermal barrier coating is more easily to delaminate from the bond coat due to the existence of spinels. The effect of spinel on the delamination cannot be neglected. How to reduce the growth rate and the number of spinel is a key problem to prolong the service life of thermal barrier coatings.
Delamination
Barrier layer
Cite
Citations (5)
ABSTRACT An investigation of the zirconia‐spinel system, ZrO 2 ‐MgAl 2 O 4 , was made, using the criteria of thermal expansion, density, and microstructure. The samples were fired for six hours at 1650°C. No stable compounds or solid solutions were formed. An unstable solid solution, possibly based on a zirconia‐spinel compound, was formed, however, apparently extending from pure spinel to 30 mol. % of zirconia. The solid solution gradually decomposed on repeated heating to 1300°C., and the system ultimately behaved as a series of simple aggregates of zirconia and spinel. The zirconia transformation took place at 1110°C. throughont the system. On cooling, the transformation temperature was lowered by the presence of spinel from 990°C. for the zirconia‐rich samples to fi30°C. at the spinel end of the system.
Cite
Citations (5)
Inconel
Isothermal process
Cite
Citations (5)
Performance enhancement of gas turbines is a main issue for the aircraft industry. Over many years, a large part of the effort has been focused on the development of more insulating Thermal Barrier Coatings (TBCs). In this study, Yttria Stabilized Zirconia (YSZ) columnar structures are processed by Suspension Plasma Spraying (SPS). These structures have already demonstrated abilities to get improved thermal lifetime, similarly to standard YSZ TBCs performed by EB-PVD. Thermal diffusivity measurements coupled with differential scanning calorimetry analysis are performed from room temperature up to 1100 °C, first, on HastelloyX substrates and then, on bilayers including a SPS YSZ coating. Results show an effective thermal conductivity for YSZ performed by SPS lower than 1 W.m-1K-1 whereas EB- PVD YSZ coatings exhibit a value of 1.5 W.m-1K-1.
Suspension
Cite
Citations (4)