High-temperature stability of yttria-stabilized zirconia thermal barrier coating on niobium alloy—C-103 (original) (raw)
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Materials and Corrosion, 2004
The microstructural change, crack initiation and spallation of a vacuum plasma sprayed (VPS) thermal barrier coating on an INCONEL-738 superalloy substrate were investigated after successive 300 h thermal cycles at 1050 8C. The coating was characterised using Raman spectroscopy, scanning electron microscopy (SEM) energy dispersive X-ray analysis (EDX) and Auger electron spectroscopy (AES). Localised micro-cracks at the yttrium (III) oxide stabilised zirconium (IV) oxide (YSZ) ceramic coating/thermally grown oxide (TGO) interface were observed after 8 cycles. Spallation of the YSZ coating occurred after approximately 21 cycles. Significant amounts of the elements titanium, tantalum and chromium were found within the TGO together with the formation of nickel, cobalt and chromium-rich oxides at this TGO/YSZ interface.
Int. J. Electrochem. …, 2012
Advanced ceramic multilayered coatings are commonly used as protective coatings for engine metal components, where, aerospace gas turbine engines are now designed such that the heat resistant super alloys operate at temperature very close to their melting, so current strategies for performance improvement are centered on thermal barrier coatings. The main focus of this work is to study the effect of different parameters of air plasma spraying technique for various thermal barrier coatings comprised of zirconia stabilized with magnesia top coat and nickel-aluminum bond coat as well as their properties with those obtained using reference techniques. The deviations of the parameters from the optimum conditions are discussed. The investigation shows that: the deviation of the plasma spray parameters from the optimum conditions led to create a poor contact between the bond coat and the Nibase-super alloy substrate, increase of the cracks resulting from the relaxation of residual stresses in the planer direction (open porosity), increase of the voids resulting from poor deformation of partially melted particle (few micrometer void), and present of the un-melted particles. The conclusions of this experimental study are in good agreement with theoretical predictions resulting from a sensitivity analysis reported in a previous study.
Thermal cycle properties of plasma sprayed YSZ/Al2O3thermal barrier coatings
Surface Engineering, 2009
In the present study, yttria partially stabilised zirconia (YSZ)/Al 2 O 3 coatings, which are used for jet engines, gas turbines and diesel engines were coated with thermal barrier coatings to provide high thermal resistance, reduce the metal surface temperatures and increase component durability. The effect of alumina addition from 0 to 80 wt-% on the properties of plasma sprayed YSZ coatings was investigated. The coating comprised of YSZ-Al 2 O 3 (0, 20, 50 and 80 wt-%Al 2 O 3); NiCrAlY bond coat; and AISI 304L stainless steels substrates. Scanning electron microscopy was used to analyse the microstructures of the coated samples. Thermal shock tests were performed over the specimens, at 1000 and 1200uC for 5 min and then forced air quenching for 2 min. The microhardness was investigated depending on the alumina contents. Vickers hardness on cross-section of coatings was observed to increase with the increase in alumina mixing ratio. It was noticed that with increase in Al 2 O 3 content the thermal shock life of the specimens decreased.
Surface Engineering, 2014
The purpose of this work is the evaluation and comparison of plasma sprayed nanostructured 7 wt-% yttria stabilised zirconia (t-7YSZ) with two different sizes and 15YSZ coating with cubic phase (c-15YSZ). To this end, two kinds of 7YSZ nanogranules consisting of agglomerated nanosized particles (40-50 and 90-100 nm respectively) and 15YSZ were plasma sprayed on nickel based superalloy substrates with NiCrAlY as the bond coat. The thermal shock behaviours of all as sprayed thermal barrier coatings (TBCs) were investigated at 1000uC. The results indicated that the thermal cycling lifetime of nanostructured 7YSZ TBCs was longer than that of the nanostructured 15YSZ TBCs due to higher fracture toughness. Moreover, 7YSZ TBC with smaller particle size (labelled as non-commercial 7YSZ) shows better thermal shock resistance than 7YSZ TBC with bigger particle size (labelled as commercial 7YSZ) due to lower elastic modulus and residual stress.
Thermo-mechanical evaluation of plasma sprayed YSZ-based multi-layered thermal barrier coatings
International Journal of Computational Materials Science and Surface Engineering, 2019
The multi-layered YSZ, NiCoCrAlY, Cr2O3 and Al2O3 coatings of varying thickness (200 µm-400 µm) have been investigated for thermal barrier coating (TBC) application. Plasma spray technique has been utilised on piston crown to optimise the thermal fatigue life in view to reduce the heat losses. Four types of TBC overlay each with a 100 µm NiCrAlY bond coat were deposited on the A336 aluminium alloy substrate cut out of the diesel engine piston. The phase composition of coatings before and after the thermal shock testing was analysed by XRD and the lattice strain analysis was performed by Williamson-Hall analysis. It was observed that among the considered multi-layered coating configurations, those with 300 µm YSZ and 200 µm Cr2O3 top coat exhibited acceptable thermal shock resistance as the specimens sustain up to 298 and 325 thermal cycles respectively. The microstructural analysis suggested against the formation of any major deformity or structural changes at the higher temperature as investigated by thermal shock experiment.
Journal of the European Ceramic Society, 2007
Widely used in turbines for propulsion and power generation, thermal barrier coatings (TBCs) increase the efficiency of turbine engines by allowing them to work at higher temperatures, due to their thermal insulating properties. Typically TBC systems consist of a metallic bondcoat (BC) and a ceramic topcoat (TC). Previous research has revealed that ceramic TCs possess an amplitude-dependent mechanical behaviour and that they can be used as damping treatments, due to their good damping properties. The microstructure and the properties of ceramic TCs vary significantly depending on the employed deposition technique. This work investigates the differences in the mechanical behaviour of yttria-stabilised zirconia (YSZ with 8 wt% yttria) TC deposited by atmospheric plasma spraying (APS) and electron beam-physical vapour deposition (EB-PVD), by means of tests run with the amplitude dependent damping (ADD) test rig and of scanning electron microscopy (SEM) analysis.
Journal of Thermal Spray Technology, 2018
Gas-turbine engines are widely used in transportation, energy and defense industries. The increasing demand for more efficient gas turbines requires higher turbine operating temperatures. For more than 40 years, yttria-stabilized zirconia (YSZ) has been the dominant thermal barrier coating (TBC) due to its outstanding material properties. However, the practical use of YSZbased TBCs is limited to approximately 1200°C. Developing new, higher temperature TBCs has proven challenging to satisfy the multiple property requirements of a durable TBC. In this study, an advanced TBC has been developed by using the solution precursor plasma spray (SPPS) process that generates unique engineered microstructures with the higher temperature yttrium aluminum garnet (YAG) to produce a TBC that can meet and exceed the major performance standards of state-of-the-art air plasma sprayed YSZ, including: phase stability, sintering resistance, CMAS resistance, thermal cycle durability, thermal conductivity and erosion resistance. The temperature improvement for hot section gas turbine materials (superalloys & TBCs) has been at the rate of about 50°C per decade over the last 50 years. In contrast, SPPS YAG TBCs offer the near-term potential of a[200°C improvement in temperature capability.
Archives of Civil and Mechanical Engineering
Yttrium-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are indispensable elements of present-day turbine propulsion systems. The ones deposited with atmospheric plasma spraying (APS) are characterized by required low thermal conductivity, but they are unable to survive frequent thermomechanical loading and therefore their application is limited to parts remaining stationary. Expanding capability of TBCs is sought in various areas, but the one realized through modification of most proliferated apparatus used for plasma spraying (PS) (from radial to axial injection) and substituting micrometric powders with the nano-structured suspension needs least changes in the industry established procedures and offers the highest property improvement. The present experiment covered the deposition of ZrO2-8Y2O3 YSZ TBC using both atmospheric and suspension PS processes. They were performed with commercial micrometric and nano-structured YSZ (8% Y2O3) powders. The coatings morphology and...
Surface and Coatings Technology, 1999
Advanced ceramic multilayered coatings are commonly used as protective coatings for engine metal components to improve performance, e.g. thermal barrier coatings ( TBCs). Zirconia-based TBCs were produced by plasma spraying process and characterized in terms of microstructure, porosity, elastic modulus, adherence and residual stresses. In this contribution the residual stresses in multilayered coatings applied on Ni based superalloys for use as thermal barrier coatings were studied both by numerical modelling and experimental stress measurement. The thermal residual stresses generated during the spraying process of duplex TBCs were simulated by using an heat transfer finite element program and an elasto-plastic biaxial stress model. The TBC system was subjected to different thermal cycling conditions (maximum temperature, heating up and cooling down rates, dwell time at maximum temperature, etc.). The stress distribution within the TBC was also modelled after thermal cycling. The stress state in the as-deposited and in thermally cycled coatings was verified using an X-ray diffraction technique. The measurements were in good agreement with the residual stress modelled calculations. It was observed that the residual stresses were dependent on the thermal history of the TBC (as-deposited and thermally cycled). It is proposed that thermal cycling allowed the stresses to relax by microcracking and creep mechanisms at high temperature such that on cooling down to room temperature, an in-plane biaxial compressive stress will arise on the zirconia top coating due to the difference on the coefficients of thermal expansion between the metallic substrate and ceramic coating material.
Advances in Materials Science and Engineering : An International Journal (MSEJ), 2016
Thermal Barrier Coatings (TBCs), routinely prepared from Ceramic based compositions (typically 8%Y2O3-ZrO2or 8YSZ) are being engineered to protect the metallic components from degradation in applications like gas turbines, jet and automotive engines. With a goal of finding improved TBC materials a wide variety of ceramics are being researched worldwide. Before physically preparing the TBCs of uncommon compositions in the laboratory, their suitability to perform can be predicted. Limited accessibility to detailed and realistic information on the influence of newer compositions (other than 8YSZ) on TBCs warrants methods to obtain this information.