Yttria Partially Stabilized Zirconia Research Articles

Modification effect of Mg(OH)2–2Al(OH)3 composite gels on Y-PSZ ceramics

A Mg(OH)2–2Al(OH)3 composite gel, synthesized via the sol-gel method, served as a modifier in the preparation of modified yttria partially stabilized zirconia (Y-PSZ) ceramics. The volume density, apparent porosity, compressive strength, thermal shock resistance, phase composition, and microstructure of the ceramics were systematically characterized. The findings reveal that, upon sintering, the Mg(OH)2–2Al(OH)3 composite gel decomposes into MgO–Al2O3 powder, which in turn in-situ generates a MgAl2O4 spinel reinforcing phase, characterized by its uniform size and distribution. The presence of this MgAl2O4 spinel applies compressive stress to the adjacent zirconia grains, effectively inhibiting their abnormal growth. By occupying the grain boundaries and establishing a mosaic structure, the compressive strength and thermal shock resistance of the Y-PSZ ceramics are significantly enhanced. Notably, an increase in the composite gel quantity correlates with a reduction in both volume density and apparent porosity of the Y-PSZ samples, whereas the compressive strength initially rises before diminishing, and the thermal shock resistance markedly improves. When the amount of Mg(OH)2–2Al(OH)3 composite gel introduced reaches 9 %, the comprehensive performance of the modified Y-PSZ ceramics is optimized. At this point, its compressive strength is increased by 1.26 times compared to the unmodified Y-PSZ ceramics, reaching 732 MPa; moreover, after undergoing 60 thermal shocks, its residual strength retention rate still remains as high as 59.15 %.

Influence Of Low-Temperature Degradation On Phase Transformation And Biaxial Flexural Strength On Different High-Translucent 4Y-PSZ, 5Y-PSZ, 6Y-PSZ Monolithic Zirconia

Objective: This study aimed to investigate the effect of low-temperature degradation (LTD) in phase transformation and biaxial flexural strength of high-translucent yttria partially stabilized zirconia (Y-PSZ) and yttria tetragonal zirconia polycrystalline (3-YTZP).
 Methods: A total of 120 new high-translucent 3-YTZP (NMS) and Y – PSZ (KST, KUT, NQ3MS) zirconia disc specimens were manufactured according to ISO 6872 for biaxial flexural strength (14 mm., 1.2 ± 0.02 mm). The specimens from each type of material were divided into 3 subgroups (n:30) according to the LTD in an autoclave at 134 C0 at 2 bar (n:10) (at 5, 20 hour (h)). Specimens without LTD served as the control. Data of the monoclinic phase changes (Xm) and flexural strength were analyzed using two-way ANOVA followed by post hoc MannWhitney U test. Weibull statistics were used to analyze strength reliability.
 Results: LTD increased the monoclinic content significantly for NMS and slightly for the KST group. A monoclinic phase was not detected for KUT and NQ3MS groups. The biaxial flexural strength of the NMS group was affected significantly and decreased with an increase in the 20 h aging. For flexural strength values, there was no significant difference in aging times for each of the KST, KUT, and NQ3MS groups. Weibull analysis showed the highest characteristic strength for NMS (1412.9), KST (750.1), NQ3MS(790.5) and KUT (615.2) groups. The Weibull modulus (m) increased in the NMS, KUT, and NQ3MS groups compared with the control group and decreased in the KST group.
 Conclusion: LTD caused a significant decrease in the biaxial flexural strength results of the NMS group but did not significantly affect the KST, KUT, and NQ3MS groups’ values.

Crystallographic and Topographic Analysis of Ultra-Translucent Zirconia After Various Surface Treatments

The aim of the present study was to analyze the effects of 4 different surface treatments, on the crystallographic characteristics of Ultra-Translucent Zirconia. Fully sintered zirconia specimens of highly translucent yttria partially stabilized zirconia (Y-PSZ) (KATANA UTML) were divided into four experimental groups and a control group (n=10). Each group received one of the following surface treatments: sandblasting with 50µm alumina particles (Al₂O₃), sandblasting with 110µm alumina particles, and grinding with a rotary high-speed turbine with and without water irrigation. For each sample, x-ray diffraction was carried out to analyze peak intensity, calculate the crystallite size, and detect the presence of compressive and tensile stress. Surface roughness was measured on all specimens using a standard scanning profilometer. Additionally, scanning electron microscopy (SEM) was performed to qualitatively analyze the surfaces of the specimens. Statistical analysis included repeated measures analysis of variance and post hoc Tukey test (p≤0.05). The control group exhibited the highest crystallite size (323nm). All surface treatments led to a reduction in the crystallite size, with the most significant reduction observed in the groups subjected to sandblasting with 110µm alumina particles and high-speed grinding with irrigation. Sandblasting with 50µm alumina particles resulted in less transformation of the crystallite size. A general tendency of the diffraction peaks to shift to a lower angle can be observed in the experimental groups, indicating the presence of compressive stress on the samples. Profilometry revealed higher roughness in the ground samples (6,14µm and 6,57µm) compared to the sandblasted groups (2,93µm and 2,02µm). The crystal domain size showed a tendency to decrease after the surface treatments. Sandblasted samples, as well as ground samples without irrigation, exhibited compressive stress. Sandblasted samples had lower surface roughness compared to the ground samples. Sandblasting with 50µm alumina particles caused the least decrease in crystallite size.

Evaluating laser surface melting of NiCrAlY-APS coating and its effect on high-temperature oxidation behavior of NiCrAlY/YSZ thermal barrier coating before and after surface melting

This research study was conducted to investigate the laser melting parameters of NiCrAlY-APS coating. High-temperature oxidation was investigated using yttria partially stabilized zirconia (YSZ) ceramic coating. Also, the oxidation behavior of the TBC coating was investigated and studied before to and after laser surface melting of the NiCrAlY coating. Microstructural characterization was done using a scanning electron microscope (SEM), elemental analysis by energy dispersive spectroscopy (EDS), and phase analysis by X-ray diffraction (XRD). Surface melting was then performed in the power range of 150–300 W and scanning speed of 2–6 mm s−1. Surface melting was also conducted on the coating using two strategies: single-pass and multi-pass. The obtained results showed that the average melting depth and thickness reduction were directly related to the laser power, while they had an inverse relation with the laser scanning speed. Furthermore, multi-pass surface melting parameters reduced porosity to less than 0.1 %. Roughness measurements also showed a decrease in the coating's surface hardness after surface melting, as compared to the APS coating. The structure consisted of oriented columnar dendrites after melting the laser. The adhesion strength of the TBC coating and laser surface melting coating was at 41 MPa and 53 MPa, respectively. After 200 h of oxidation in the G1504 sample, the TGO layer's growth was decreased; due to the growth of a single oxide layer, it had better oxidation resistance in comparison to the other sample.

A Comparison of Failure Loads for Polycrystalline Zirconia Ceramics with Varying Amounts of Yttria, Glass-Ceramics and Polymers in Two Different Test Conditions.

It is unclear how zirconia dental crowns with different yttria compositions will perform clinically, and how they will compare with crowns made of glass-ceramics and polymers. The present objective was to determine failure loads of crowns and discs made of glass ceramics or polymers as compared to yttria-partially stabilized zirconia (Y-PSZ) crowns and discs with varying yttria concentrations. Crowns of zirconia (Cercon XT, Katana UTML, BruxZir Anterior), glass ceramic (Celtra press, IPS e.max press, Lisi press), and polymeric materials (Trilor, Juvora, Pekkton) were fabricated and cemented to epoxy abutments. The total number of specimens was 135 for crowns and 135 for discs (n = 15 specimens per material type and design). A universal testing machine was used to perform compressive loading of crowns/discs to failure with a steel piston along the longitudinal axis of the abutments. Energy dispersive spectroscopy (EDS) was used to identify the yttria concentration for each zirconia brand. The data were analyzed using generalized linear models and regression analyses. The results revealed significant differences (p < 0.05) in mean failure loads for different crown materials: Trilor (6811 ± 960 N) > Juvora (5215 ± 151 N) > Cercon (4260 ± 520 N) = BruxZir (4186 ± 269 N) = e.max (3981 ± 384 N) > Katana (3195 ± 350 N) = Lisi (3173 ± 234 N) = Pekkton (3105 ± 398 N) > Celtra (2696 ± 393 N). The general linear model revealed significant differences (p < 0.05) in mean failure loads when comparing the different materials for the discs, i.e., Trilor (5456 ± 1748 N) > Juvora (4274 ± 869 N) > Pekkton (3771 ± 294 N) > Katana (2859 ± 527 N) > Cercon (2319 ± 342 N) = BuxZir (2250 ± 515 N) = e.max (2303 ± 721 N) = Lisi (2333 ± 535 N) > Celtra (1965 ± 659 N). EDS showed that the zirconia materials contained yttria at different concentrations (BruxZir = 5Y-PSZ, Cercon = 4Y-PSZ, Katana = 3Y-PSZ). The yttria concentration had a significant effect on the failure load of the Katana (3Y-PSZ) crowns, which revealed lower failure loads than the Cercon (4Y-PSZ) and BruxZir (5Y-PSZ) crowns, whose failure loads were comparable or higher than e.max glass ceramic. The failure load of the trilayer disc specimens did not correlate with the failure load of the respective crown specimens for the zirconia, glass-ceramic and polymeric materials.

Failure behaviour of EB-PVD YSZ thermal barrier coatings under simulated aero-engine operating conditions

Thermal shock test simulating aero-engine operating conditions was carried out on electron beam physical vapor deposition (EB-PVD) yttria partially stabilized zirconia (YSZ) thermal barrier coatings (TBCs) using advanced multi factor coupling test equipment. Phase composition, thermally grown oxide (TGO) residual stress, surface morphology and cross-sectional microstructure evolution in coatings were systematically studied. Based on XRD results, coatings possessed tetragonal phase structure without any further transformation during testing. After 5000 cycles, the thickness of TGO gradually increased from 0.3 to 2 μm. TGO residual compressive stress also gradually increased and then drastically dropped when the coating spalled. Horizontal cracks first initiated from TGO/bond coat (BC) interface, then arose from top coat (TC)/TGO interface and finally coalesced through TGO to cause delamination. Repeated thermal shock and gas impact conditions promoted the emergence of vertical cracks in ceramic top coat. Once communicated with transverse delaminations, cracks eventually led to spalling failure of the coating system. The contribution to spallation failure was mainly from thermal stress as a result of thermal expansion mismatch between the coating and the substrate. In turn, elastic stress induced by high speed impact of gas and TGO growth stress promoted initiation and propagation of coating cracks.

A Study on Long-Term Oxidation and Thermal Shock Performance of Nanostructured YSZ/NiCrAlY TBC with a Less Dense Bond Coat.

This paper focused on studying the performance of a nanostructured thermal barrier coating (TBC) system deposited by APS, which had a bond coat with inter-lamellar porosities that resulted during the manufacturing process. The higher porosity level of the bond coat was studied as a possible way to keep the thickness of the TGO under control, as it is distributed on a higher surface, thereby reducing the chance of top-coat (TC) spallation during long-term oxidation and high-temperature thermal shock. The TBC system consisted of nanostructured yttria partially stabilized zirconia (YSZ) as a top coat and a conventional NiCrAlY bond coat. Inter-lamellar porosities ensured the development of a TGO distributed on a higher surface without affecting the overall coating performance. Based on long-term isothermal oxidation tests performed at 1150 °C, the inter-lamellar pores do not affect the high resistance of nanostructured TBCs in case of long-term iso-thermal oxidation at 1150 °C. The ceramic layer withstands the high-temperature exposure for 800 h of maintaining without showing major exfoliation. Fine cracks were discovered in the ceramic coating after 400 h of isothermal oxidation, and larger cracks were found after 800 h of exposure. An increase in both ceramic and bond-coat compaction was observed after prolonged high-temperature exposure, and this was sustained by the higher adhesion strength. Moreover, in extreme conditions, under high-temperature thermal shock cycles, the TBC withstands for 1242 cycles at 1200 °C and 555 cycles at 1250 °C.

Degradation and failure of a novel double-layer LC/YSZ thermal barrier coating in a burner rig corrosion test

ABSTRACT Thermal barrier coatings (TBCs) are susceptible to corrosion by molten calcium-magnesium-aluminium-silicate (CMAS) during high temperature service. The microstructural evolution and thermal cycling lives of double-layer La2Ce2O7 (LC)/yttria partially stabilised zirconia (YSZ) and single-layer YSZ coatings were comparatively studied by a burner rig corrosion test. The results suggest that the thermal cycling life of double-layer LC/YSZ coating is approximately 80% longer than that of single-layer YSZ counterpart. The CMAS penetrated into the whole YSZ coating, which remarkably accelerated the spallation failure of the coating. However, due to the superior CMAS resistance of the LC layer, the failure of the double-layer LC/YSZ coating was mainly caused by the sintering of the LC layer, which resulted in a large in-plane stress and initiation of cracks. These cracks propagated, branched and deflected along the LC/YSZ interface, ultimately leading to the spallation of the LC layer.

Comparative investigation on the hot corrosion failure of YSZ and GdYb-YSZ double-ceramic-layer thermal barrier coatings under Na2SO4+V2O5 molten salts

The 5.2Gd2O3-5.6Yb2O3-9.5Y2O3 co-doped ZrO2 (GdYb-YSZ) double-ceramic-layer (DCL) thermal barrier coatings (TBCs) were prepared by atmospheric plasma spraying (APS) in this work. Hot corrosion behavior and failure mechanism of the APS GdYb-YSZ DCL and single-layer yttria partially stabilized zirconia (YSZ) TBCs under the Na2SO4+V2O5 molten salts were comparably investigated. The YSZ coating suffered from severe breakage after the hot corrosion test due to its poor corrosion resistance and easy infiltration by molten salts. In contrast, GdYb-YSZ DCL coating exhibited a better resistance to crack propagation and a significantly longer corrosion lifetime than the YSZ coating, which was attributed to the protective effect of the upper GdYb-YSZ layer. On the one hand, the superior phase stability of the GdYb-YSZ DCL coating could slow down the generation speed of phase transformation stress. On the other hand, the higher corrosion reaction rate of the upper GdYb-YSZ layer could suppress the further infiltration of molten salts into the inner TBCs, which improved the structural integrity of TBCs in corrosive environments.

Significantly toughened PZT-based piezoelectric ceramics simultaneously keeping excellent electrical properties via incorporating trace amount of yttria-partially-stabilized zirconia

Piezoelectric ceramics are prone to cracking during functioning due to the repetitively applied high stress. Hence, toughened ceramics with robust microstructures are highly desired for resisting the potential cracks. Toughening of Lead Zirconium Titanate (PZT) based piezoelectric ceramics with high d33·g33 for ignition applications is investigated in this work. Yttria-partially-stabilized zirconia (YPSZ) particles were incorporated into the PZT-based piezoelectric ceramics via conventional solid state reaction. Measurements of mechanical properties of as-sintered ceramics indicate that incorporation of an appropriate amount of YPSZ significantly improves the fracture toughness of PZT-based ceramics by 38.7%, meanwhile the piezoelectric coefficient still remains at a high level with a decrease of less than 7%. When doping 0.5 wt% YPSZ, the optimal comprehensive properties can be obtained as follows: fracture toughness KIC = 1.41 MPa·m1/2, Vickers hardness HV = 4.60 GPa, piezoelectric coefficient d33 = 462 pC/N, planar electromechanical coupling factor kp = 60.1%, and dielectric constant ε33T/ε0 = 1750. This successful toughening mechanism paves a way in developing functional ceramics simultaneously possessing superior fracture toughness and electrical properties via doping an appropriate content of YPSZ submicron particles.

Mechanical Properties Durability of Sc2O3-Y2O3 Co-Stabilized ZrO2 Thermal Barrier Materials for High Temperature Application

The poor phase stability of conventional 6–8 wt.% yttria-partially stabilized zirconia (YSZ) results in the formation of detrimental cracks in thermal barrier coatings (TBCs) as well as the decrease of fracture toughness, limiting its long-term application above 1200 °C. Here, we try to prove that a higher t′-phase stability is the prerequisite for the mechanical properties durability of ZrO2-based TBC materials. Compared with YSZ ceramic, 7.0 mol.% Sc2O3 and 0.5 mol.% Y2O3 co-stabilized ZrO2 (ScYSZ) shows a superior t′ phase stability at 1300 °C. In addition, the fracture toughness of ScYSZ is nearly stable after being annealed at 1300 °C for 0–40 h, while the value of YSZ gradually declines during the aging process. The stable fracture toughness of ScYSZ is closely related to its prominent t′ phase stability. The elastic modulus of ScYSZ is nearly unchanged and lower than that of YSZ. The excellent stability of the phase structure and mechanical properties makes ScYSZ a great potential material for next generation high-temperature TBCs.

Surrogate model for energy release rate and structure optimization of double-ceramic-layers thermal barrier coatings system

The finite element (FE) model is established based on the microstructure of the double-ceramic-layer thermal barrier coating system (DCL-TBCs). Different structural parameters are sampled by Latin hypercube Sampling method to construct corresponding models. The energy release rates of the interfacial crack, which is between lanthanum zirconate (LZ) layer and yttria-partially stabilized zirconia (YSZ) layer of DCL-TBCs, are calculated by numerical simulation during cooling and a dataset is created according to the results. On the basis of the dataset, a surrogate model is constructed to predict the maximum energy release rate during cooling by the extreme random forest algorithm, and the prediction accuracy of the surrogate model is verified by testing dataset. The thicknesses and porosities of the LZ and YSZ layers of DCL-TBCs, and the length of the interfacial crack are set as input variables, and the maximum energy release rate during cooling process is set as output variables of the surrogate model. Using the surrogate model and the particle swarm optimization (PSO) method, the LZ and YSZ layers with different combination of thicknesses is optimized to minimize the energy release rate of the interfacial crack of DCL-TBCs.

Influence of high-speed sintering protocols on translucency, mechanical properties, microstructure, crystallography, and low-temperature degradation of highly translucent zirconia

ObjectivesImpacts of high-speed sintering on the optical and mechanical properties, microstructure, crystallography, and low-temperature degradation of commercial yttria-partially stabilized zirconia (Y-PSZ) were investigated. MethodsFive commercial Y-PSZ products (KATANA HT, KATANA STML, KATANA UTML, Zpex 4, and Zpex Smile) were investigated. Specimens were sintered following speed-sintering (~90 min) and conventional-sintering protocols (~7 h), and a group of KATANA STML was super-speed-sintered (18 min). Dimensions of the zirconia specimens after sintering were 14.5 mm (diameter) and 1.2 mm (thickness). Translucency was assessed using a colorimeter. Biaxial flexural strength was measured using a universal testing machine, followed by Weibull analysis. Scanning electron microscopy was used for microstructure assessments. X-ray diffraction was used to analyze the crystallography before and after hydrothermal aging. Low-temperature degradation (LTD) tests were performed at 134 °C under 2–3 bar water vapor in an autoclave. ResultsThe translucency and flexural strength were not affected significantly by the sintering programs (p > 0.05). The conventionally sintered KATANA STML and speed-sintered Zpex 4 presented the highest and lowest Weibull modulus, respectively. The conventionally-sintered Y-PSZ had a larger average grain size and smaller fraction of fine grains than those of the speed-sintered specimens. The fractographic analysis of the speed- and conventionally sintered Y-PSZ yielded comparable results. The speed-sintered Y-PSZ exhibited a lower c-ZrO2 content than that of conventionally-sintered Y-PSZ, except for KATANA HT and KATANA STML. LTD tests indicated that some of the speed and conventionally-sintered Y-PSZ exhibited similar monoclinic volume fractions. SignificanceSpeed-sintering programs are acceptable for Y-PSZ zirconia.

The analyses of frictional losses and thermal stresses in a diesel engine piston coated with different thicknesses of thermal barrier films using co-simulation method

This study comparatively presents the thermal and mechanical effects of different Thermal Barrier Coatings (TBCs) and their thicknesses on the performance of aluminum diesel engine piston by combining Finite Element Analyses (FEA) and Artificial Neural Network (ANN) methods. The piston structure of MWM TbRHS 518S indirect injection six-cylinder diesel engine was modeled. The clustered TBCs (NiCrAlY–Gd2Zr2O7, NiCrAlY–MgO-ZrO2, NiCrAl–Yttria Partially Stabilized Zirconia (YPSZ), and NiCrAlY–La2Zr2O7) were implemented to the related surface of aluminum alloy piston and then static, thermal, and transient structural FEA were conducted for each model. Based on both of the temperature and equivalent stress distributions, NiCrAlY–Gd2Zr2O7 coated model displayed the best performance. Additionally, the effects of top coating thicknesses of TBCs were investigated in the range of 0.1–1.0 mm with 0.1 mm increments in FEAs. The thermally effective top coating thickness was predicted as 0.95 mm for the selected TBC using ANN method. Then the effects of coating thickness on frictional performance were revealed by generating transient structural FE models and utilizing stribeck diagram. The uncoated and 0.95 mm NiCrAlY–Gd2Zr2O7 coated models were adjusted as transient and the related crank angle – dependent in-cylinder combustion pressure data was implemented. The friction force was reduced by at least 15% in NiCrAlY–Gd2Zr2O7 coated model.

A Review on Thermal Barrier Coatings

To protect the hot parts of the engine turbines, thermal barrier coatings (TBCs) are exceedingly applied. TBC decrease the temperature of the turbines during operation and hence enhanced the engine performance. Recently, researchers have concentrated on developing and processing TBCs for turbine parts. Promote the thermal barrier coatings will authorize the gas turbines to serve at elevated temperatures. TBCs mostly consists of 2 layers, the bond coat, and the topcoat. The top-coat is mainly composed of ceramic materials that possess low thermal conductivity properties and its main job is to protect the metallic parts from high temperatures. Apparent attempts are being carried out to figure new materials having beneficial fulfillments. To defeat the yttria partially stabilized zirconia (YSZ) troubles, pyrochlore rare-earth zirconate ceramics (A2B2O7) have been suggested as most of them are refractory and thermally stable. Hexaaluminates are another suggestion that meets the current requirements of TBCs. The present review summarizes and reviews the novel advance of the materials suitable for Thermal Barrier Coatings, their selection criteria, and their processing techniques.

Understanding the influence of microstructure on hot corrosion and erosion behavior of suspension plasma sprayed thermal barrier coatings

Thermal barrier coatings (TBCs) are bilayer systems comprising a 7–8 wt% yttria partially stabilized zirconia (YSZ) top coat deposited over a metallic bond coat. Suspension plasma spraying (SPS) is an advanced and attractive top coat processing technique due to its capability to yield a variety of microstructures, including the desired columnar microstructure for enhanced strain tolerance and durability. This work attempts to investigate the desirable microstructural features in an SPS processed TBCs to mitigate hot corrosion and minimize erosion related losses that are often responsible for coating degradation. SPS processed TBCs were deposited utilizing three different spray conditions to obtain distinct microstructural features (column density, interpass [IP] porosity bands, column width), porosity content, and mechanical properties. Apart from comprehensive characterization utilizing SEM, XRD and micro-indentation tests, the as-deposited TBCs were subjected to hot-corrosion tests in the presence of vanadium pentoxide and sodium sulfate as corrosive salts. Post-corrosion analysis revealed complete infiltration of the molten salts in all the investigated TBCs. However, the delamination cracks generated due to the infiltrated corrosive species were minimal in case of TBCs with higher fracture toughness. The differences in microstructure and mechanical properties also led to differences in erosion performance, with TBCs possessing minimal total porosity content and high fracture toughness best resisting erosion related damage. Post-erosion analysis revealed that the TBCs with higher fracture toughness and micro-hardness showed superior erosion resistance. Based on the erosion and corrosion results and subsequent post-mortem of failed specimens, plausible damage mechanisms are proposed. Findings from this work provide new insights on developing damage tolerant TBCs microstructures with enhanced durability when exposed to erosion and hot corrosion environments. • SPS TBCs with varying columnar microstructural features and mechanical properties were deposited. • Influence of parameters (suspension feed rate, spray distance, etc.) on microstructural features in SPS TBCs examined. • Desirable microstructural features were identified to minimize erosion and hot corrosion.

Microchanneling on bio-inert dental ceramic using dry pulsed laser ablation and liquid supported pulsed laser ablation approach

As the rate of heat energy transferred in yttria-partially stabilized zirconia (Y-PSZ) is very slow, it entraps the high temperature at localised region in laser microchanneling process eventually causes thermic damages which results in geometrical howlers and poor channel quality. Present work justifies, experimental inquisitions and microstructural with an aid of EDS analysis to determine the potentiality of laser ablation processes under D-PLA and LS-PLA approach. However, microchannels processed by D-PLA approach exhibit critical issues like, generation of thermal stress, frequent formation of cracks, re-deposition of eroded material and HAZ; to address these issues, a novel technique of underwater nanosecond laser micro machining was adopted. The phenomena behind the formation of channels in LS-PLA are unalike to that in D-PLA. The objective of this research is to discuss those phenomena during the study of influencing parameters over dimensional veracity of microchannels with an aid of surface integrity. In accession to that, multi-objective desirability based optimization using PSO algorithm (MOPSO) was applied to obtain the desired values of microchannel characteristics.

Thermal cycling of EB-PVD TBCs based on YSZ ceramic coat and diffusion aluminide bond coat

The objective of this research was to optimize the surface morphology and element compositional distribution of the bond coat by adjusting the hydrogen flow, and to fabricate the 6–8 wt% yttria partially stabilized zirconia (YSZ) ceramic topcoat via EB-PVD. The interfacial stability and spalling failure behavior of thermal barrier coatings (TBCs) were evaluated by cyclic oxidation test at 1373 K. The results show that with the increment of hydrogen flow, the X-ray diffraction peak belonging to the β phase tends to be obvious and the high temperature oxidation resistance becomes correspondingly excellent. There are no microcracks, spalling, peeling, edge warping and cloud spatter on the ceramic coating surface. The cross section of the ceramic layer exhibits a typical columnar grain microstructure. The columnar crystal grows evenly perpendicular to the interface between the ceramic and bonding layers. Although it has been exposed to long-term thermal exposure, the ceramic coat has densified and sintered locally, and the grain boundary between the columnar grains is basically disappeared, the ceramic coat surface still has the typical columnar crystal “cauliflower” shape. Lots of transverse cracks and voids have been found at the interface of the bond coat and TGO layer, and within a dozen micrometers approach the bond coat surface. Internal fracture has occurred in the bonding layer and bridging structures have been developed due to internal oxidation in the bond coat.

Effects of surface roughness on CMAS corrosion behavior for thermal barrier coating applications

Calcium-magnesium-alumina-silicate (CMAS) corrosion is an important cause for thermal barrier coating (TBC) failure, which has attracted increased attentions. In this study, some thermal barrier coating (TBC) materials including YSZ (yttria partially stabilized zirconia), GdPO4, and LaPO4 were prepared into bulks, and the effects of their surface roughness on wettability and spreading characteristics of molten CMAS were investigated. As-fabricated and polished bulks with different surface roughness were exposed to CMAS corrosion at 1250 °C for 1 and 4 h, following by macro and micro observations. Results revealed that compared with the as-fabricated bulks, molten CMAS on the polished samples had lower wettability and a smaller spreading area, mainly attributable to the reduced capillary force to drive the melt spreading. Meanwhile, GdPO4 and LaPO4 bulks exhibited lower CMAS wettability than YSZ bulk. It is thus considered that reducing the surface roughness is beneficial to CMAS corrosion resistance of TBCs.

Preparation and thermal stability investigation of Al2O3–mullite–ZrO2–SiC composite ceramics for solar thermal transmission pipelines

To obtain composite ceramics with excellent thermal shock resistance and satisfactory high−temperature service performance for solar thermal transmission pipelines, SiC additive was incorporated into Al2O3−mullite−ZrO2 composite ceramics through a pressureless sintering process. The effect of the SiC additive on thermal shock resistance was studied. Also, the variations in the microstructure and physical properties during thermal cycles at 1300 °C were discussed. The results showed that both thermal shock resistance and thermal cycling performance could be improved by adding 20 wt% SiC. In particular, the sample with 50 wt% Al2O3, 35 wt% Coal Series Kaolin (CSK), 15 wt% partially yttria−stabilized zirconia (PSZ), and 20 wt% SiC additional (denoted as sample A2) exhibited the best overall performance after firing at 1600 °C. Furthermore, the bending strength of sample A2 increased to 124.58 MPa, with an increasing rate of 13.63% after 30 thermal shock cycles. The increase in thermal conductivity and the formation of mullite were the factors behind the enhancement of thermal shock resistance. During the thermal cycles, the oxidation of SiC particles was favorable as it increased the microstructure densification and also facilitated the generation of mullite, which endowed the composite ceramics with a self−reinforcing performance.