Improvement for Ti3SiC2/Cu joint brazed using composite fillers with abnormal expansion ceramic particulates

Reducing the residual stresses and improving the mechanical strength of large-scale ceramic/metal brazing joints is an important problem that must be solved for its practical engineering application. Using composite filler with solid-state phase transformation ceramic particulates, it is theoretically feasible to relieve the residual stress and improve the mechanical properties of ceramic/metal brazed joints. In this study, Cu mesh, Ag–28Cu–2Ti (wt.%), and yttria-stabilized zirconia (0.6 mol.% YSZ solid-state phase transformation ceramic particulates) composite power fillers were used in the brazing of Ti₃SiC₂ ceramic and pure copper. The microstructure of joints and YSZ particulates in the interface was investigated and confirmed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), scanning transmission electron microscopy (STEM), and transmission electron microscopy (TEM). In addition, the effect of YSZ particulates content on the mechanical properties of joints was investigated and evaluated by the shear strength. The results show that the interfacial phases were mainly Ti₅Si₃, TiC, Ti_xCu, Ag (s, s), Cu (s, s), and YSZ particulates. Moreover, most of YSZ particulates undergo the solid-state phase transformation from tetragonal zirconia (t-ZrO₂) to monoclinic zirconia (m-ZrO₂) during the cooling process of brazing. The abnormal volume expansion of the solid-state phase transformation reduced the thermal mismatch between Ti₃SiC₂ ceramic and filler, thereby reducing the residual stress in the interface of joint. When using composite filler with 6 wt.% YSZ particulates, the shear strength of Ti₃SiC₂/Cu joint reached the maximum. The maximum average shear strength of the joints was 80.2 MPa, which was about 103.6% more than the joint without YSZ particulates.     

Nano-scale surface of ZrO2 ceramics achieved efficiently by peanut-shaped and heart-shaped SiO2 abrasives through chemical mechanical polishing

Zirconia ceramics are regarded as the best development target for 5G mobile phone rear covers. However, it is necessary and urgent to improve the surface quality and processing efficiency of zirconia ceramics. Non-spherical silica abrasives were prepared by the KH550 induction method and were used in chemical mechanical polishing (CMP) of zirconia ceramics for the first time. While achieving low surface roughness of 1.9 nm, it has an efficient polishing rate of 0.31 μm/h which is superior to conventional abrasives. Silica particles are peanut-shaped and heart-shaped in the scanning electron microscopy image, and its distinctive morphology provides the possibility of its excellent polishing performance. X-ray photoelectron spectroscopy analysis shows that during the CMP process, silica abrasives and zirconia ceramic undergo a solid phase chemical reaction to form ZrSiO₄. At the same time, the contact wear model established in combination with the coefficient of friction indicates that the two-dimensional surface contact mode of non-spherical silica abrasives on the surface of zirconia ceramics greatly improves its mechanical effect.     

Crystal defects and phase transitions of nanocrystalline yttria-stabilised zirconia induced by high-energy ball milling

Yttria-stabilised zirconia (YSZ) is a promising electrolyte for SOFCs and gas sensors. In this study, the particle size of a co-precipitated 5 mol% yttria-stabilised zirconia (5 YSZ) powder was refined from 10.47 μm to 130 nm via high-energy ball milling to improve its sinterability and ionic conductivity. The ball milling process increased the specific surface area of the 5 YSZ powder from approximately 11 to 22 m² g^?1. The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) results indicated that the 5 YSZ crystallites decomposed into irregular shapes with the evolution of point, linear, and planar defects. An increase in the milling duration increased the number of oxygen defects in the 5 YSZ powder, as revealed by the X-ray photoelectron spectroscopy results. The tetragonal-to-monoclinic phase transformation occurring in the powder was investigated by X-ray diffraction, Raman spectroscopy, HRTEM, and selected-area electron diffraction pattern analyses. The ball-milled powders could be easily densified, but the presence of too many crystal defects and the large fraction of the m-ZrO₂ phase were detrimental to the further densification of the 5 YSZ powders. In spite of the high sintering temperature (1500 °C) used in this study, the maximum relative density of 99.67% could be achieved for the powder ball-milled for 60 min at the rotor speed of 1500 rpm. Moreover, the ionic conductivity of 5 YSZ was improved significantly from 20.6 to 36.2 mS cm^?1 (850 °C) after the high-energy ball milling process.     

Phase stability and microstructure evolution of MgO-ZrO2 and MgO-6YSZ ceramic fibers

In this work, MgO-ZrO₂ and MgO-6YSZ ceramic fibers were prepared with sol-gel method via electrospinning. Polymorph stability and microstructure evolution of zirconia fibers were fully characterized by X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, and Scanning electron microscope. The results indicated that tetragonal zirconia for MgO-ZrO₂ was obtained and cubic zirconia could be fully stabilized for MgO-6YSZ with MgO molar fractions varying from 0.1 to 0.5 at 800°C. Monoclinic phase appeared with MgO molar fractions even up to 0.5 for MgO-ZrO₂ system and partially or fully stabilized zirconia could be achieved for MgO-6YSZ at 1000°C and 1200°C. Grain size was gradually decreased with increasing of MgO content at 800°C both for MgO-ZrO₂ and MgO-6YSZ ceramic fibers. The grain size of both systems increased with MgO molar fractions varying from 0.1 to 0.2 and then decreased at higher contents at 1000°C and 1200°C. A discussion on relationship among MgO state and the phase stability and grain size was presented. This work shows surface excess and solid solution of MgO predominantly controlled the phase stability and microstructure evolution of zirconia fibers.     

Reactive flash sintering: MgO and α-Al2O3 transform and sinter into single-phase polycrystals of MgAl2O4

We show that flash experiments with three phase mixed-powders of yttria-stabilized zirconia (8YSZ), MgO, and α-Al₂O₃ not only produce polycrystals of high density, but also the transformation of magnesia and alumina into single-phase spinel. The presence of zirconia facilitates the onset of the flash. The sintering experiments in the laboratory were extended to live experiments at the National Synchrotron Light Source II at Brookhaven National Laboratory in order to measure the time-dependent evolution of single-phase spinel. The phase transformation occurred in <3 seconds during Stage II. Later, during Stage III the cubic zirconia transformed partly into the monoclinic phase, which reverted back to the cubic phase when the flash was extinguished by turning off the current to the specimen. The results underpin a recent report on the synthesis of single-phase bismuth ferrite from constituent oxides in reactive flash experiments, raising the specter of flash as a method for synthesis as well as sintering of complex oxide ceramics. The role of zirconia in catalyzing the flash in the present study is discussed.     

Mechanical properties and thermal conductivities of 3YSZ-toughened fully stabilized HfO2 ceramics

In this work, the 3 mol% yttria stabilized zirconia (3YSZ) composed of tetragonal phase has been introduced into the 10 mol% Er₂O₃ stabilized cubic hafnia (10ErSH) matrix to improve its fracture toughness. The effects of the addition of 3YSZ on the phase composition, microstructure, mechanical properties and thermal conductivities of the 10ErSH have been investigated. The results showed that all the 3YSZ-toughened 10ErSH samples were composed of cubic phase and a little (<10 mol%) monoclinic phase. The introduced tetragonal phase of 3YSZ fully disappeared even when the volume fraction of 3YSZ reached 50%, indicating that the phase transformation occurred during 1500 °C. The fracture toughness for the sample with 50% 3YSZ was improved by 60% compared with the pure 10ErSH ceramics owing to the sub-mico/micro hybrid structure, which changed the crack propagation mode and consumed part of the crack extension energy. Additionally, the thermal conductivity slightly decreased due to the mass and radius misfits induced by substitution atoms (Zr⁴⁺, Er³⁺ and Y³⁺). Considering the improved mechanical and thermal properties, the 3YSZ-toughened 10ErSH ceramics may be alternative TBC materials.     

Synthesis and characterization of highly ordered mesoporous YSZ by tri-block copolymer

A highly ordered mesoporous yttria-stabilized zirconia (YSZ) has been successfully prepared by evaporation-induced self-assembly method (EISA) using tri-block copolymer Pluronic F127 as a structure-directing agent and inorganic chlorides as precursors in a non-aqueous medium. The characterization of the mesoporous YSZ materials was carried out by using small angle X-ray diffraction (SAXRD), transmission electron microscopy (TEM) and N₂ adsorption/desorption. The well ordered mesoporous YSZ is thermally stable up to 600^°C with an average pore size of 5.4 nm and specific surface area of 90 m²/g. The walls of mesoporous YSZ are composed of ～6.5 nm nano-crystalline domains.     

Solution combustion synthesis of calcia-magnesia-aluminosilicate powder and its interaction with yttria-stabilized zirconia and co-doped yttria-stabilized zirconia

Thermal Barrier Coatings (TBCs) play a significant role in improving the efficiency of gas turbines by increasing their operating temperatures. The TBCs in advanced turbine engines are prone to silicate particles attack while operating at high temperatures. The silicate particles impinge on the hot TBC surfaces and melt to form calcia-magnesia-aluminosilicate (CMAS) glass deposits leading to coating premature failure. Fine powder of CMAS with the composition matching the desert sand has been synthesized by solution combustion technique. The present study also demonstrates the preparation of flowable yttria-stabilized zirconia (YSZ) and cluster paired YSZ (YSZ-Ln₂O₃, Ln = Dy and Gd) powders by single-step solution combustion technique. The as-synthesized powders have been plasma sprayed and the interaction of the free standing TBCs with CMAS at high-temperatures (1200 °C, 1270 °C and 1340 °C for 24 h) has been investigated. X-ray diffraction analysis of CMAS attacked TBCs revealed a reduction in phase transformation of tetragonal to monoclinic zirconia for YSZ-Ln₂O₃ (m-ZrO₂: 44%) coatings than YSZ (m-ZrO₂: 67%). The field emission scanning electron microscopic images show improved CMAS resistance for YSZ-Ln₂O₃ coatings than YSZ coatings.     

Study on the interaction between SiO2 and ZrO2 in the chemical mechanical polishing of zirconia ceramic with colloidal silica

Colloidal silica is usually used for the chemical mechanical polishing of zirconia ceramic wafer in industry, but the process is often optimized only through experience without a precise understanding of the polishing mechanism. There are still many theoretical and technical issues, especially the material removal mechanism and the effect of polishing on the phase transformation, have not been studied in depth. In this study, the effect of the abrasive concentration, polishing pressure and slurry pH on the material removal rate was analyzed. It is found that the removal rate tends to be stable when the concentration exceeds 30 wt%; the influence of pressure on the polishing rate conforms to the Preston formula. When the pH of the slurry is 6, the removal rate is the highest, but polishing under acidic conditions will leave corrosion pits due to the dissolution of the stabilizer. Through X-ray photoelectron spectroscopy analysis of the residue on the wafer surface, it was found that Si-O-Zr bonds were formed, but it was uncertain whether the residue was zirconium silicate. Through X-ray diffraction analysis, it is found that polishing will not affect the crystal structure of zirconia. The Zr-O-Si bond formed by tribochemical action on the ceramic surface prevents the deep migration of surface hydroxyl groups. At the same time, kinetic factors will cause internal hydroxyl groups to transfer to the surface for recovery oxygen vacancies, thereby stabilizing the tetragonal phase.     

Synthesis and characterization of highly ordered mesoporous YSZ by tri-block copolymer

A highly ordered mesoporous yttria-stabilized zirconia (YSZ) has been successfully prepared by evaporation-induced self-assembly method (EISA) using tri-block copolymer Pluronic F127 as a structure-directing agent and inorganic chlorides as precursors in a non-aqueous medium. The characterization of the mesoporous YSZ materials was carried out by using small angle X-ray diffraction (SAXRD), transmission electron microscopy (TEM) and N₂ adsorption/desorption. The well ordered mesoporous YSZ is thermally stable up to 600^∘C with an average pore size of 5.4 nm and specific surface area of 90 m²/g. The walls of mesoporous YSZ are composed of ∼6.5 nm nano-crystalline domains.     

Evaluation of biphasic calcium phosphate/nanosized 3YSZ composites as toughened materials for bone substitution

In this research, biphasic calcium phosphate (BCP), comprising 70 wt% of beta tricalcium phosphate and 30 wt% of hydroxyapatite, was mixed with different amounts of 3 mol% yttria-stabilized zirconia (3YSZ) and sintered at 1200 °C to produce toughened bone substitutes. The fracture toughness (K_Ic) of the obtained bodies was determined using the indentation-strength fracture method. Scanning electron microscopy and energy dispersive X-ray spectroscopy analysis were utilized to study the microstructure of the samples. The phase composition of the samples was also determined using X-ray diffraction technique. In order to investigate the cell supporting ability of the samples, G-292 cells were cultured on them and cell morphology was evaluated after 48 h. Based on the results, the maximum fracture toughness and compressive strength values (i.e., 2.11 MPa m^0.5 and 150 MPa, respectively) were obtained for the sample containing 3 vol% of 3YSZ. The obtained fracture toughness value was approximately two times higher than that of the original BCP (1.07 MPa m^0.5) and also was comparable with that of the cortical human bone. The following mechanisms for the improved K_Ic of the β-tricalcium phosphate were determined: Grain bridging of 3YSZ particles during crack growth resistance, formation of microcracks on the tip of the larger cracks, absorbing crack extension energy due to the volume expansion during 3YSZ tetragonal-monoclinic transformation and crack deflection by the presence of 3YSZ particles. Also, 3YSZ additive encourages transformation of HA phase into β-TCP during sintering BCP. Finally, based on the cell studies, the samples exhibited an adequate cell attachment and a good cell spreading condition.     

Effect of zirconia content on mechanical and thermal properties of mullite–zirconia composite

Abstract

Mullite–zirconia composites were prepared by adding various zirconia contents in the mullite ranging from 0 to 30 wt-% and sintering at 1400–1600°C for 2 h. The phase composition examined by X-ray diffraction showed that mullite was the major phase combined with developed t-ZrO₂ and m-ZrO₂ phase as a function of zirconia content, especially at 1600°C, wherein m-ZrO₂ predominated. Density increased when the zirconia content and sintering temperature were increased ranging from 2·2 to 3·53 g cm^?3. The morphology of mullite grain showed elongated grains, whereas dispersed zirconia showed equiaxed and intergranular grains. Flexural strength was continuously improved by adding zirconia during the sintering temperature ranging from 1400 to 1500°C, whereas flexural strength was initially improved up to 5 wt-% of zirconia addition and deteriorated with more than 5 wt-% of zirconia content during sintering between 1550 and 1600°C. The maximum strength, 190 MPa, was obtained when sintering mullite with 30 wt-% of zirconia content at 1500°C. The degradation of strength at high sintering temperature may be a result from more occurrence of m-ZrO₂ phase. Thermal expansion of sintered specimens indicated linear change and hysteresis loop change. The hysteresis loop obtained with increased zirconia content resulted in the t–m phase transformation. Martensitic start temperature M_s was determined to be 530°C for 15 wt-% zirconia sintered at 1500°C, implying that the t–m phase transformation occurred.     

Tailoring the O2 reduction activity on hydrangea-like La0.5Sr0.5MnO3 cathode film fabricated via atmospheric pressure plasma jet process

An atmospheric-pressure plasma jet (APPJ) is applied to prepare porous perovskite materials, particularly of lanthanum strontium manganite La_0.5Sr_0.5MnO₃ (LSM551) oxide powder and film. LSM nano powder around 50.0?nm is obtained, and characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscope. A spherical morphology with hydrangea-like shape is observed as associates to the pure tetragonal phase. LSM film is deposited onto yttria-stabilized zirconia (YSZ) electrolyte-support substrate as cathode layer for the operation in a solid oxide fuel cell at 600–900?°C operating temperatures. A series of symmetrical cells possessing high exchange current density of 30.12?mA/cm² at 800?°C. The prepared samples are assessed as an object to discover the diffusion mechanism of oxygen pathways for LSM/YSZ system based on the microstructural (particles size, and porosities) and electrochemical (kinetic and impedance) data. The mechanism of oxygen pathways is directly associated with the triple phase boundary lengthiness, in which the surface and bulk pathways occurring in APPJ-prepared LSM layer on YSZ lead to an increasing in activity of oxygen reduction reaction. Moreover, a fabrication of desirable ternary metal oxide, LSM, with highly porous structure via an advance-innovative APPJ preparation is outlined.     

Comparison of hot corrosion behaviors of plasma-sprayed nanostructured and conventional YSZ thermal barrier coatings exposure to molten vanadium pentoxide and sodium sulfate

The purpose of the current study was evaluation and comparison of hot corrosion behaviors of plasma-sprayed conventional and nanostructured yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs). Hot corrosion studies were performed on the surface of coatings in the presence of a molten mixture of V₂O₅+Na₂SO₄ at 1000 °C for 30 h. Results indicated that the hot corrosion mechanisms of conventional and nanostructured YSZ coatings were similar. The reaction between corrosive salt and Y₂O₃ produced YVO₄, leaching Y₂O₃ from YSZ and causing the detrimental phase transformation of zirconia from tetragonal to monoclinic. The nanostructured coating, as compared to its conventional counterpart, in spite of a further reaction with the corrosive salt, showed a higher degradation resistance during the hot corrosion test due to increased compliance capabilities resulting from the presence of an extra source of porosity associated with the nano-zones.     

Phase Evolution in Yttria-Stabilized Zirconia Thermal Barrier Coatings Studied by Rietveld Refinement of X-Ray Powder Diffraction Patterns

One failure mechanism of thermal barrier coatings composed of yttria-stabilized zirconia (YSZ) has been proposed to be caused, in part, by the transformation of the tetragonal phase of YSZ into its monoclinic phase. Normally, studies of phase evolution are performed by X-ray diffraction (XRD) and by evaluating the intensities of a few diffraction peaks for each phase. However, this method misses some important information that can be obtained with the Rietveld method. Using Rietveld's refinement of XRD patterns, we observed, upon annealing of YSZ coatings, an increase of cubic phase content, a reduction in as-deposited tetragonal phase content, and the appearance of a new tetragonal phase having a lower yttria content that coexists with the as-deposited tetragonal phase of YSZ.     

Synthesis and characteristics of nanocrystalline YSZ powder by polyethylene glycol assisted coprecipitation combined with azeotropic-distillation process and its electrical conductivity

Nanoscale 8 mol% yttria stabilized zirconia (YSZ) powders were prepared by polyethylene glycol (PEG-1540) assisted coprecipitation coupling with azeotropic distillation drying process. The role of PEG and azeotropic-distillation on the morphology and particle size of YSZ was studied. Thermogravimetry and X-ray diffraction results showed that azeotropic-distillation could reduce the formation temperature of YSZ phase. X-ray patterns of the YSZ powders revealed that the crystallite size of the powders increases with increasing calcination temperature, which is consistent with transmission electron microscopy observations. The sintering behavior and the ionic conductivity of the pellets prepared from YSZ powders calcined at 800 °C were also studied. At sintering temperatures ≥1400 °C, more than 99% of the relative density was obtained. The alternating-current impedance spectroscopy results showed that the YSZ pellet sintered at 1450 °C has ionic conductivity of 0.0726 S cm⁻¹ at 800 °C in air. The present work results have indicated that the PEG assisted coprecipitation combined with azeotropic-distillation drying process is an alternative method to synthesize yttria stabilized zirconia powders with a high sinterability and a good ionic conductivity.     

Effect of waste-derived MA spinel on sintering and stabilization behavior of partially stabilized double phase zirconia

Cubic-stabilized zirconia ceramic composites have been synthesized by conventional sintering, starting from commercial m-ZrO₂, Y₂O₃, and waste-derived magnesium aluminate spinel (MA) powders. In this work, the effect of sintering temperature and MA content on stabilization and densification properties of YSZ have been duly considered. MA-free YSZ0 composite sintered at 1600°C-1700°C revealed m- and t-ZrO₂ dual-phase structure where its m-ZrO₂ was partially stabilized upon temperature rising into tetragonal phase by Y³⁺ diffusion inside zirconia structure. YSZ10-50 composites containing 10-50 wt% MA demonstrated dissimilar behavior where their m-ZrO₂ was transformed and stabilized into a cubic form by diffusion of Y³⁺, Mg⁺², and Al⁺³ inside zirconia lattice. Furthermore, densification of YSZ10-50 powder mixtures by conventional sintering at 1600°C for 2 hours resulted in fully dense compacts with micrometer-sized grains. The outcomes indicate that MA has a significant effect on m-ZrO₂ stabilization into the cubic phase structure at room temperature. In this respect, this study offers huge potentials for developing fully stabilized c-ZrO₂ ceramics that could be possibly used as industrial ceramics for structural applications of harsh chemical and thermal environmental conditions.     

Fabrication and characterization of 8YSZ ceramic based abradable seal coatings by atmospheric plasma spraying

8 wt% yttria-stabilized zirconia (8YSZ) powders are fabricated as high-temperature based materials via a solid-state reaction method and ground into spheres in this paper. Following that, 4 wt% Nickle (Ni), 4 wt% Hexagonal Boron Nitride (hBN) and 4 wt% PHB (Polyphenyl ester) are added to 8YSZ for getting 8YSZ ceramic-based abradable seal powders (8YSZ CAS_p). Then, the 8YSZ CAS_p are sprayed on the stainless steel substrate with a NiCoCrAlY transition layer by an atmospheric plasma spraying (APS) technology. The phase structure, surface morphology and the cross-section topography of the fabricated are analyzed, the indentation hardness and nano-indentation test are conducted. The experiments of 8YSZ ceramic-based abradable seal coatings (8YSZ CAS_c) show that the deposition efficiency and porosity are respectively 78.5% and 21.8%, the bond strength is 4.6 MPa, the cycle number of thermal shock resistance is 37 times, those parameters prove that the fabricated 8YSZ CAS_c are promising abradable seal coatings.     

Phase stability,thermo-physical properties and thermal cycling behavior of plasma-sprayed CTZ,CTZ/YSZ thermal barrier coatings

ZrO₂ co-stabilized by CeO₂ and TiO₂ with stable, nontransformable tetragonal phase has attracted much attention as a potential material for thermal barrier coatings (TBCs) applied at temperatures >?1200?°C. In this study, ZrO₂ co-stabilized by 15?mol% CeO₂ and 5?mol% TiO₂ (CTZ) and CTZ/YSZ (zirconia stabilized by 7.4?wt% Y₂O₃) double-ceramic-layer TBCs were respectively deposited by atmospheric plasma spraying. The microstructures, phase stability and thermo-physical properties of the CTZ coating were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric-differential scanning calorimeter (TG-DSC), laser pulses and dilatometry. Results showed that the CTZ coating with single tetragonal phase was more stable than the YSZ coating during isothermal heat-treatment at 1300?°C. The CTZ coating had a lower thermal conductivity than that of YSZ coating, decreasing from 0.89?W?m^?1 K^?1 to 0.76?W?m^?1 K^?1 with increasing temperature from room temperature to 1000?°C. The thermal expansion coefficients were in the range of 8.98?×?10^?6 K^?1 – 9.88 ×10^?6 K^?1. Samples were also thermally cycled at 1000?°C and 1100?°C. Failure of the TBCs was mainly a result of the thermal expansion mismatch between CTZ coating and superallloy substrate, the severe coating sintering and the reduction-oxidation of cerium oxide. The thermal durability of the TBCs at 1000?°C can be effectively enhanced by using a YSZ buffer layer, while the thermal cycling life of CTZ/YSZ double-ceramic-layer TBCs at 1100?°C was still unsatisfying. The thermal shock resistance of the CTZ coating should be improved; otherwise the promising properties of CTZ could not be transferred to a well-functioning coating.     

Low–thermal–conductivity and high–toughness CeO2–Gd2O3 co–stabilized zirconia ceramic for potential thermal barrier coating applications

Yttria partially stabilized zirconia (～4.0?mol% Y₂O₃–ZrO₂, 4YSZ) has been widely employed as thermal barrier coatings (TBCs) to protect the high–temperature components of gas–turbine engines. The phase stability problem existing in the conventional 4YSZ has limited it to application below 1200?°C. Here we report an excellent zirconia system co–doped with 16?mol% CeO₂ and 4?mol% Gd₂O₃ (16Ce–4Gd) presenting nontransformable feature up to 1500?°C, in which no detrimental monoclinic (m) ZrO₂ phase formed on partitioning. It also exhibits a high fracture toughness of ～46?J m^?2 and shows high sintering resistance. Besides, the thermal conductivity and thermal expansion coefficient of 16Ce–4Gd are more competent for TBCs applications as compared to the 4YSZ. The combination of properties suggests that the 16Ce–4Gd system could be of potential use as a thermal barrier coating at 1500?°C.