Effect of layer thickness on thermal shock behavior in double-layer micro- and nano-structured ceramic top coat APS TBCs

The performance of thermal barrier coatings with the double-layer top coat in thermal shock condition has been investigated. Used powders to produce coatings are as follows: Yttria Stabilized Zirconia (YSZ, Y), Ceria-Yttria Stabilized Zirconium Oxide (CSZ, C) and nano-structured YSZ (YSZ-N, YN). The samples were classified into four double-layer families, including Y-C, YN-C, Y-YN and YN-Y. At the end of each cycle, samples were photographed, and the surface and edge damage were determined. Furthermore, scanning electron microscope (SEM) Images and energy-dispersive spectrometer (EDS) analysis of sample's cross-section were taken before and after the test. After collecting experiment's data, the effects of various factors on the outputs were checked. The results showed that Y-YN, YN-Y and YN-C families, have the best performance, respectively. Moreover, it was found that using YSZ-N as the top layer, reduces the thickness of TGO, and it has a great effect on performance and the amount of damage.     

Hot corrosion and thermal shock resistance of Dense-CYSZ/YSZ bilayer thermal barrier coatings systems applied onto Ni-base superalloy

Bilayer thermal barriers coatings of Dense Ceria-Yttria-Stabilized Zirconia (D-CYSZ)/Yttria-Stabilized Zirconia (YSZ) were deposited onto Inconel 625 using atmospheric plasma spray (APS). The thickness of the d-CYSZ layer varied (0, 50, 100, and 150 μm), but the total thickness of the system was kept at 300 μm. The thermo-mechanical resistance of the multilayer system was evaluated through thermal shock tests, in which the bilayer systems evaluated exceeded 500 cycles with percentages of delamination of the coating below 20 % of the exposed area and showed higher thermomechanical resistance than a conventional YSZ system. Hot corrosion (HC) resistance of the bilayer system was evaluated using a salt mixture of 32 wt.% Na₂SO₄ and 68 wt.% V₂O₅ at 900 °C. The systems with a d-CYSZ layer showed higher resistance to HC, exhibiting fewer changes into the microstructure and presence of the monoclinic phase despite the presence of vertical cracks in the microstructure.     

Thermal shock resistance of rare-earth doped in-situ SiAlON reinforced h-BN matrix ceramics under vacuum thermal cycling

In-situ SiAlON reinforced BN-matrix ceramics were prepared by hot pressing sintering, and the effects of different rare earth oxides on the thermal shock resistance of the materials were investigated. The effects of rare earth oxides on the phase composition, microstructure, bending strength, thermal properties and thermal shock resistance of the composites were studied. The results show that the phase composition and bending strength of ceramics with different rare earth oxides had no obvious change. However, the influence on the thermal expansion coefficient of the material was notable. The thermal expansion coefficient of the ceramics with CeO₂ increased by 24.6% compared with Sm₂O₃ in the test temperature range. After 50 cycles of thermal shock at Δt = 1150 °C, the residual strength of ceramics with CeO₂ was down to 157.1 MPa, decreased by 40.6% compared with the one tested in room temperature. And the Sm₂O₃-added ceramics reduced by 34.7%–167.1 MPa after thermal shock. The decrease of the residual strength of ceramics is mainly caused by the internal stress generated by the mismatch between the growth of quartz and SiAlON phase in the matrix and the thermal expansion coefficient of the matrix. However, no macro cracks were observed on the surface of the samples after thermal shock.     

Heat treatment effect on coating shock resistance of thermal barrier coating system with different types of bond coat

The effect of heat treatment, growth of the TGO layer, oxidation of bond coat, and the impact of the presence of two bond coats on the TBC's thermal shock resistance has been investigated experimentally. TGO oxide layers were created with two-time heat treatment of 12 and 24 h at 1000. Then the thermal shock test was performed on the APS/APS and HVOF/APS/APS samples. The results show that the use of two BCs and the presence of a thin TGO layer has a good effect on TBC performance. The presence of two BC layers increased the shock resistance by an average of 37.2%. 12 h heat treatment caused a 14.0% and 17.4% shock resistance increase in samples with the HVOF/APS/APS layer and APS/APS layer, respectively. 24 h heat treatment decreased the samples' performance by 6.7% and 10.2% for samples with two BC and one BC, respectively.     

Thermo-physical properties of as deposited and aged thermal barrier coatings (TBC) for gas turbines: State-of-the art and advanced TBCs

In the perspective of fuelling the future generations of gas turbines by hydrogen rich syngas, the evaluation of the effect of a higher water vapour content into the flue gases on the TBC used, or potentially usable, is a need. For this purpose YPSZ APS TBC with two different microstructures have been exposed for 500?h at different temperatures in the range 1000?°C–1250?°C either in air and air +20% vol. H₂O. The comparison between the different testing conditions has been performed in terms of sintering kinetics and phase stability, as evaluated by thermal diffusivity measurements and Synchrotron X-Rays diffraction, respectively. Furthermore the characterisation of thermal properties of two innovative TBCs (GZO-YPSZ and YAG) potentially able to withstand the CMAS attack and erosive environments, respectively, has been carried out.No clear evidence of a different behaviour of TBC has been observed, at least in the considered aging time and temperature range.     

Microstructural evaluation and thermal oxidation behaviors of YSZ/NiCoCrAlYTa coatings deposited by different thermal techniques

In this paper, two coating techniques, the high velocity oxy-fuel (HVOF) and air plasma spray (APS) techniques, were used to deposit a bond coat of NiCoCrAlYTa on the Inconel 625 substrate, followed by applying a topcoat of yttria-stabilized zirconia (YSZ). The samples were preoxidized in an argon-controlled furnace at a temperature of 1000 °C for 12 and 24 h to characterize the microstructure of a thermally grown oxide (TGO) using the two coating techniques. The most suitable preoxidized samples were further tested for isothermal oxidation at 1000 °C for up to 120 h, and a hot corrosion test was performed at 1000 °C for up to 52 h or until spalling occurred. As-sprayed and oxidized samples prepared with different coating techniques were evaluated in terms of their microstructure using different characterization methods, such as field emission scanning electron microscopy (FESEM), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) equipped with energy dispersive X-ray and X-ray diffraction (XRD) analyses. In addition, the mechanical properties of these samples were evaluated using adhesion tests. The results show that the YSZ/NiCoCrAlYTa coating applied with the HVOF technique forms a more thin and continuous layer of TGO than that obtained when applying a YSZ/NiCoCrAlYTa coating using the APS technique, indicating that a severe brittle oxidation interface exists between the two layers. The results also indicate that the mechanical strength obtained from the adhesion test of the coated samples is observably affected by the oxidation behaviors obtained with the different deposition techniques chosen.     

Investigating the effect of andalusite on mechanical strength and thermal shock resistance of cordierite-spodumene composite ceramics

For increasing working stability of cordierite-spodumene composite ceramics for solar heat transmission pipeline, andalusite was utilized as modified additive to improve mechanical strength and thermal shock resistance of the composite ceramics. The effects of andalusite on densification, mechanical strength, thermal stability, phase composition and microstructure were studied. The experiment results showed that andalusite significantly influenced bending strength and thermal shock resistance of the composite ceramics. Especially, specimen B1 with 5 wt% andalusite sintered at 1400 °C achieved the best performances. The linear shrinkage, water absorption, apparent porosity, bulk density and bending strength were 5.62%, 0.02%, 0.06%, 2.19 g cm^?3 and 104.94 MPa, respectively. After 30 thermal shock cycles (wind cooling from 1100 °C to room temperature), the residual strength of the specimen increased to 110.65 MPa, accompanying with ?5.44% strength loss rate. The XRD and SEM analysis illustrated that mullite grains with short rod-like shape could prevent crack growth of inter-granular fracture to enhance bending strength of the specimens. Furthermore, the generation of β-spodumene grains with low thermal expansion coefficient after thermal shock improved thermal shock resistance of the composite ceramics. It is considered that the cordierite-spodumene composite ceramics with high densification, good mechanical strength and excellent thermal stability can be a potential material for high temperature thermal transmission pipeline in solar thermal power generation.     

Investigating the thermal,mechanical and thermal cyclic properties of plasma-sprayed Al2O3-7YSZ/7YSZ double ceramic layer TBCs

Double ceramic layer (DCL) TBCs consisting of a top 20 wt.% Al₂O₃-7YSZ layer and a bottom 7YSZ layer were desirably designed to achieve preferable performance while the thermal, mechanical and thermal cyclic properties were comprehensively investigated. Compared to the conventional 7YSZ TBCs, the thermal insulation properties of the DCL coating were significantly improved due to the increased oxygen vacancy concentration induced by Al₂O₃ addition while the thickness of the thermally grown oxides was diminished by the decreased oxygen diffusion rate. Furthermore, the improved fracture toughness of the DCL coating also prolonged the thermal cyclic life.     

The effects of thermoplastic poly(olefin) (TPO) morphology on subsequent paintability and thermal shock performance

Adhesion to thermoplastic olefin (TPO) substrates is strongly influenced by the type and amount of solvent contained within paint applied. Morphological changes in the TPO substrate are accomplished in the presence of solvent from the topcoat and vary depending upon paint bake times and temperatures. These morphological changes at and near the surface of TPO affect not only the paint adhesion to the substrate but also the cohesive integrity of the painted plastic composite. This paper attempts to delineate the influence of paint and paint processes on the adhesion/cohesion and mechanical properties of coated TPO parts, in particular, the performance of 2K topcoated TPO substrates under thermal shock conditions. It was found that the most important attribute contributing to thermal shock resistance of painted TPO parts was the bake temperature of the topcoat. A temperature of 250 °F in either the adhesion promoter bake or the topcoat bake is necessary to afford acceptable thermal shock performance. It is postulated that the rearrangement of poly(propylene) crystallites at the uppermost surface of the TPO under a 250 °F bake accounts for the increased cohesive strength of the painted composite.     

Microstructure and mechanical properties of plasma-sprayed LaMgA111O19 thick ceramic coatings

In the research, the effect of different critical plasma spray parameters (CPSP) on the microstructure and mechanical properties of plasma-sprayed LMA coatings with thickness of 797 μm were investigated. As a result, the porosity of coatings was increased from 12.14% to 24.88% with the decrease of CPSP from 1.20 to 0.86, while bonding strength of coatings was obviously reduced from 15.98 ± 0.36 MPa to 4.87 ± 0.7 MPa. Relatively, Young's modulus and hardness of the coatings exhibited a decreasing tendency with the decrease of CPSP. When the CPSP was decreased from 1.20 to 0.97, the residual compressive stress of coating surface varied from ?162.10 ± 12.13 MPa to ?93.49 ± 3.28 MPa, and that obtained from cross-section was decreased from ?116.02 ± 5.92 MPa to ?70.68 ± 3.99 MPa. Meanwhile, the fracture toughness of coating was improved from 0.62 ± 0.05MPa?m^1/2 to 1.34 ± 0.05 MPa?m^1/2, which was higher than that of cross-section of coating. The microstructure and mechanical properties of LMA thick coatings were strongly dependent on the CPSP.     

Microstructure, mechanical properties and thermal shock resistance of plasma sprayed nanostructured zirconia coatings

Nanostructured yttria stabilized zirconia (YSZ) coatings were deposited by Atmospheric Plasma Spraying (APS). X-ray diffraction (XRD) was used to investigate their phase composition, while scanning electron microscopy (SEM) was employed to examine their microstructure. The coatings showed a unique and complex microstructure composed of well-melted splats with columnar crystal structure, partially melted areas, which resembled the morphology of the powder feedstock, and equiaxed grains. Vickers microhardness of nanostructured zirconia coatings was similar to that of the conventional ones and strongly depended on the indentation load. Otherwise, a higher thermal shock resistance was found. This effect was addressed to the retention of nanostructured areas in coating microstructure and to the corresponding high porosity.     

Enhanced mechanical properties,thermal shock resistance and ablation resistance of Si2BC3N ceramics with nano ZrB2 addition

The mechanical properties, thermal shock resistance, and ablation resistance of nano ZrB₂ modified Si₂BC₃N ceramics were investigated. The results show that ZrB₂ stimulated microstructure evolution obviously. Therefore, the maximum strength and fracture toughness reach 559.6 MPa and 6.77 MPa·m^1/2, which are improved by 61.0% and 29.4%, respectively. Furthermore, the residual strengths of 10 wt% ZrB₂ containing composites tested at 1000 ℃ retain 363.6 MPa, which is much higher than 97.7 MPa of pristine Si₂BC₃N ceramics. Besides, the ablation resistance of ZrB₂ modified Si₂BC₃N ceramics at 3000 ℃ is enhanced remarkably and the linear and mass ablation rates of ZrB₂-10 are only 0.009 mm/s and 1.91 mg/s, respectively. The ablation in the ultra-high temperature zone is totally dominated by the ZrB₂ component, and the thermochemical erosion is determined by the oxidation resistance of ZrB₂ in the thermal affected zone.     

Failure mechanism of a (Ni,Pt)Al/EB-PVD 8YSZ deposited on substrate with different curvature signs in thermal shock test

A thermal shock test was conducted on an 8 wt% Y₂O₃ stabilized ZrO₂ electron beam-physical vapor deposited (EB-PVD 8YSZ) thermal barrier coating with a (Ni, Pt)Al bond coating on the substrate with different curvature signs. The microstructural evolution and durability have been characterized. The microstructure of the top ceramic layer is strongly dependent on the substrate geometry. The results of the thermal shock test indicated that the sample with a positive curvature exhibits mixed mode spalling by the linking of cracks at TBC/TGO interface and TGO/BC interface. Spallation occurs primarily at the TGO/BC interface and inside the bond coats near to the surface of bond coats in planar samples. The spalling occurs principally at the TGO/BC interface in specimens with a negative curvature. The failure mechanism is elucidated integrate with stress analysis.     

Impact of thermal shock cycles on mechanical properties and microstructure of lithium disilicate dental glass-ceramic

In the present paper, we report results on the impact of thermal shock cycles on mechanical properties and microstructure of lithium disilicate dental glass-ceramic relevant to the production process. A distinct reduction of the bending strength is observed after suffering more than five thermal shock cycles. The crystal, morphological and atomic structural characteristics before and after the thermal shock were detected by X-ray diffraction, infrared spectroscopy and field-emission scanning electron microscopy. Furthermore, theoretical calculations, based on density functional theory, were performed on models for the distorted and undistorted lithium disilicate crystal lattices. We show that the morphological and mechanical changes can be attributed primarily to the distortion of the Si-O-Si structural unit of the lithium disilicate glass-ceramic.     

Effects of two silane surface modifications with different functional groups on the thermal conductivity and mechanical properties of UV-cured composites with high ceramic filler loading

With rapid technological advancements, efficient thermal management is becoming increasingly important to sustain the stable operation of electronic devices. In this study, aluminum nitride (AlN) fillers with various acrylate monomers were subjected to two types of silane surface treatments to prepare composites with a high loading of AlN filler (65 wt%). The acrylates—isobornyl acrylate (IBOA), 1,4-butanediol diacrylate (BDDA), and trimethylolpropane triacrylate (TMPTA)—were mixed with bisphenol A ethoxylate dimethacrylate (Bis-EMA) as an oligomer, and phenylbis (2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) as a photo-initiator in different proportions to obtain resin matrices. Pristine AlN and AlN functionalized with APTES and MPS were used as fillers. The effect of the acrylate functional group in silanes on the thermal and mechanical properties of the acrylate resin was explored. The thermal conductivities of the IBOA/AlN/APTES and IBOA/AlN/TMPTA composites with a high loading of the filler functionalized with APTES and MPS were 1.34 and 1.57 W/(m?K), respectively, 4.15 and 5.28 times higher than that of the composite with neat resin. The enhanced filler–matrix compatibility increased the tensile strength of the composites. The findings highlighted that silane functionalization of AlN can enhance the thermal conductivity and mechanical properties of the composite.     

Microstructural,mechanical, and thermal properties of microwave-sintered KLS-1 lunar regolith simulant

KLS-1 Lunar regolith simulant was microwave sintered to explore its potential applicability in future lunar construction. The effects of sintering temperature on linear shrinkage, density, porosity, and microstructural, mechanical, and thermal properties were investigated. As the sintering temperature increased, linear shrinkage and density increased and porosity decreased. Structural evolution in the sintered samples was characterized by scanning electron microscopy and X-ray diffraction. Unconfined compressive strength testing showed that mechanical strength increased significantly with increasing sintering temperature, with 1120 °C giving the highest strength of 37.0 ± 4.8 MPa. The sintered samples exhibited a coefficient of thermal expansion of approximately 5 × 10⁻⁶ °C⁻¹, which was well-maintained even after cyclic temperature stress between −100 and 200 °C. Therefore, this microwave processing appears promising for the fabrication of building material with sufficient mechanical strength and thermal durability for lunar construction.     

Influence of beta-to-alpha quartz transition on residual stresses of a feldspar glass matrix composite: A relationship with catastrophic fracture due to thermal shock

A wide range of porcelain-based materials is composed of quartz crystalline particles dispersed in a homogeneous glassy phase. During the cooling stage these composites are subjected to stresses related to the transition from β to α quartz at 573 °C. This work studies, numerically and experimentally, the influence of the cooling rate, the quantity, and the size of the quartz crystalline particles on the stresses suffered by the material throughout the cooling process. This procedure allows calculating the instantaneous profile of stresses through the cross-section specimen during the whole cooling stage. For this, a dense glass matrix from sodium feldspar was prepared. The results reveal that the evolution of the stress profile is strongly affected by the cooling rate. The evolution of the tension state in the sample during the cooling can help to understand the catastrophic fracture suffered during the β to α quartz transition related to thermal shock.     

Preparation of closed-pore MgO-MgFe2O4 aggregates with low thermal conductivity and high mechanical properties

MgO-MgFe₂O₄ refractory aggregates with high closed porosity were fabricated using MgO agglomerates and Mg(OH)₂ with introducing Fe₂O₃ additive. The evolutions of pores and microstructure and their relationship with the properties of the specimens were studied. The addition of Fe₂O₃ obviously promoted the MgO grain growth and conversion of large open pores into small closed pores, attributing to the formation of cationic vacancies and intergranular MgFe₂O₄ bonding phase. Owing to the presence of closed pores and networks of intergranular MgFe₂O₄, both thermal insulation and strength were enhanced significantly. Besides, the formed closed pores and MgFe₂O₄ phase could accommodate thermal stress and induce transgranular fracture and crack deflection, therefore effectively improving the thermal shock resistance. The specimen with 15 wt% Fe₂O₃ showed a apparent/closed porosity of 0.7%/10.1%, median pore diameter of 4.37 µm, thermal conductivity of 9.3 W/(m·K) (500 °C), flexural strength of 143.5 MPa, and residual flexural strength of 24.1 MPa after thermal shock.     

Fabrication and mechanical properties of metal matrix composite with homogeneously dispersed ceramic particles

Titanium carbide (TiC) particles were coated with nickel (Ni) to increase their compatibility with a metal matrix, leading to an improvement in the dispersibility of TiC particles in the molten matrix. TiC particles were dispersed into a basic aqueous solution of pH 12, and then nickel nitrate (Ni(NO₃)₂), as a Ni precursor, was added to the TiC suspension. The interaction between the TiC particles and the Ni precursor is driven by the attractive force between the Ni cations and the TiC particles with negative charge. An inoculant (ferrosilicon), which has been used in the foundry industry to improve crystal growth of graphite, was used as a core particle. The Ni-treated TiC particles were coated onto the surface of the inoculant using an inorganic binder converted into its glass phase by sol–gel reactions. The reinforcement particles prepared through the dual-coating process were then injected into the molten matrix based on iron at 1500 °C. The crystal phase of the graphite is more finely and shortly grown in the reinforced metal matrix than in that without the reinforcement particles. This means that the reinforcement particles are homogeneously and uniformly dispersed into the matrix without any aggregation of particles, implying that the mechanical properties of the reinforced matrix would be greater than those of a non-reinforced matrix. Consequently, metal matrix composites with reasonable properties can be fabricated successfully using the reinforcement particles prepared by the dual-coating process.