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Xinghong Zhang - One of the best experts on this subject based on the ideXlab platform.
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evaluations of cooling rate and initial temperature on Thermal Shock behavior of zrb2 sic ceramic
Journal of Alloys and Compounds, 2018Co-Authors: Anzhe Wang, Dongyang Zhang, Cheng Fang, Ping Hu, Xinghong ZhangAbstract:Abstract The effects of cooling rate and initial temperature on Thermal Shock behavior of ZrB2-SiC ceramic were studied by water spraying method with a thermocouple real-time temperature acquisition technique for the first time. It was shown that the cooling rate could be adjusted by changing the water flow rate, and the fracture behavior strongly depended on both the cooling rate and initial temperature. When the extreme value of cooling rate was constant, the decrease of initial temperature would lead to the increase of Thermal stress, accompanied by a more serious damage of material, which was mainly because of the nonlinear relationship between Thermal expansion coefficient and temperature.
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Thermal Shock behavior of zrb2 based sharp leading edges evaluated by a novel water spraying method
Ceramics International, 2018Co-Authors: Anzhe Wang, Xinghong Zhang, Dongyang Zhang, Cheng FangAbstract:Abstract Reliable evaluation of the Thermal Shock behavior of complex-shaped components is very important for ultra-high temperature ceramics. Unfortunately progress in this field is hampered by a lack of available experimental methods. Here, a novel water spraying method is proposed to investigate the Thermal Shock behavior of ZrB 2 -based sharp leading edges (SLEs). Results indicated that the introduction of graphite flakes significantly improved the Thermal Shock resistance of ZrB 2 -SiC (ZS) SLEs. However, owing to the anisotropies of microstructure and Thermal conductivity of ZrB 2 -SiC-G (ZSG) ceramic, the Thermal Shock resistance and the failure mode of ZSG SLEs were sensitive to the sampling orientation, which also were remarkably influenced by the size and/or shape of SLEs, leading to the variability of critical failure temperature from 750 °C to 375 °C and crack patterns from deflection to wave-shaped.
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electrostatic assembly preparation of high toughness zirconium diboride based ceramic composites with enhanced Thermal Shock resistance performance
ACS Applied Materials & Interfaces, 2016Co-Authors: Baoxi Zhang, Changqing Hong, Xinghong Zhang, Jia Zhang, Pingan HuAbstract:The central problem of using ceramic as a structural material is its brittleness, which associated with rigid covalent or ionic bonds. Whiskers or fibers of strong ceramics such as silicon carbide (SiC) or silicon nitride (Si3N4) are widely embedded in a ceramic matrix to improve the strength and toughness. The incorporation of these insulating fillers can impede the Thermal flow in ceramic matrix, thus decrease its Thermal Shock resistance that is required in some practical applications. Here we demonstrate that the toughness and Thermal Shock resistance of zirconium diboride (ZrB2)/SiC composites can be improved simultaneously by introducing graphene into composites via electrostatic assembly and subsequent sintering treatment. The incorporated graphene creates weak interfaces of grain boundaries (GBs) and optimal Thermal conductance paths inside composites. In comparison to pristine ZrB2–SiC composites, the toughness of (2.0%) ZrB2–SiC/graphene composites exhibited a 61% increasing (from 4.3 to 6.93 MP...
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effect of graphite flake on microstructure as well as mechanical properties and Thermal Shock resistance of zrb2 sic matrix ultrahigh temperature ceramics
Journal of Alloys and Compounds, 2009Co-Authors: Zhi Wang, Xinghong Zhang, Sai Wang, Changqing HongAbstract:Abstract ZrB2–20vol.%SiC containing the various volume fractions of graphite flake (ZSG) composites were investigated to determine the effect of graphite content on the microstructure as well as the mechanical properties and Thermal Shock resistance. The results revealed that the flexural strength generally decreased as the graphite volume fractions increased. Compared with the fracture toughness of about 4.5 MPa m1/2 for the ZrB2–SiC composites, the toughness of the ZSG composites is essentially higher than that of the ZrB2–SiC composites due to their lower strength relative to the ZrB2–SiC composites. The toughening mechanisms, such as the crack deflection and bridging, were related to the Thermal residual stresses, and the Thermal residual stresses in interfaces were calculated using Hsueh's formula. Moreover, the critical crack size that represents Thermal Shock resistance was calculated using the Griffith criterion. It was found that the Thermal Shock resistance was improved with the increasing graphite volume fractions.
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microstructure and Thermal Shock behavior of zrb2 sic graphite composite
Materials Chemistry and Physics, 2009Co-Authors: Zhi Wang, Changqing Hong, Xinghong ZhangAbstract:Abstract A water-quenching technique was adopted to evaluate the Thermal Shock behavior of hot-pressed ZrB 2 –SiC and ZrB 2 –SiC–graphite composites in an air atmosphere. The strength retention of the two kinds of composites was measured after varying temperature (Δ T c ) up to 1000 °C. Monolithic ZrB 2 –SiC showed rapidly drop in flexural strength above Δ T of 400 °C, however the critical Thermal Shock temperature difference (Δ T c ) is enhanced by adding graphite, and the ZrB 2 –SiC–graphite composite showed a higher retained strengths up to 1000 °C. The main reasons for a great improvement of Thermal Shock resistance (TSR) were also discussed and analyzed.
Hossein Jamali - One of the best experts on this subject based on the ideXlab platform.
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the influence of laser treatment on Thermal Shock resistance of plasma sprayed nanostructured yttria stabilized zirconia Thermal barrier coatings
Ceramics International, 2014Co-Authors: Reza Ghasemi, Reza Mozafarinia, Reza Shojarazavi, Hossein JamaliAbstract:Abstract The main goal of this paper was to evaluate the effects of laser glazing on the microstructure and Thermal Shock resistance of nanostructured Thermal barrier coatings (TBCs). To this end, nanostructured yttria stabilized zirconia (YSZ) top coat and NiCrAlY bond coat were deposited on Inconel 738LC substrate by air plasma spraying (APS). The Nd:YAG pulsed laser was used for laser treatment of top coat surface. The Thermal Shock behavior of plasma-sprayed and laser-glazed coatings was investigated by quenching the samples in cold water from 1000 °C. The microstructure and phase composition of the coatings were characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Energy dispersive spectroscopy (EDS) was used to analyze the interface diffusion behavior of the bond coat elements. The results of SEM revealed that the laser glazing process reduced the surface roughness, eliminated the porosity of the surface and produced network cracks perpendicular to the surface. XRD results also indicated that both as-sprayed and laser glazed coatings consisted of non-transformable (T′) phase. Thermal Shock test results showed that the lifetimes of the plasma-sprayed TBCs were almost doubled by laser glazing. Continuous network of segmented cracks perpendicular to the surface produced by laser glazing improved the strain accommodation and recognized it as the main enhancement mechanism for TBC life extension.
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comparison of Thermal Shock resistances of plasma sprayed nanostructured and conventional yttria stabilized zirconia Thermal barrier coatings
Ceramics International, 2012Co-Authors: Hossein Jamali, Reza Mozafarinia, Reza Shoja Razavi, Raheleh AhmadipidaniAbstract:Abstract The main goal of the current study is evaluation and comparison of Thermal Shock behavior of plasma-sprayed nanostructured and conventional yttria stabilized zirconia (YSZ) Thermal barrier coatings (TBCs). To this end, the nanostructured and conventional YSZ coatings were deposited by atmospheric plasma spraying (APS) on NiCoCrAlY-coated Inconel 738LC substrates. The Thermal Shock test was administered by quenching the samples in cold water of temperature 20–25 °C from 950 °C. In order to characterize elastic modulus of plasma-sprayed coatings, the Knoop indentation method was employed. Microstructural evaluation, elemental analysis, and phase analysis were performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffractometry (XRD) respectively. The results revealed that failures of both nanostructured and conventional TBCs were due to the spallation of ceramic top coat. Thermal stresses caused by mismatch of Thermal expansion coefficients between the ceramic top coat and the underlying metallic components were recognized as the major factor of TBC failure. However, the nanostructured TBC, due to bimodal unique microstructure, presented an average Thermal cycling lifetime that was approximately 1.5 times higher than that of the conventional TBC.
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improving the Thermal Shock resistance of plasma sprayed cysz Thermal barrier coatings by laser surface modification
Optics and Lasers in Engineering, 2012Co-Authors: Raheleh Ahmadipidani, Reza Mozafarinia, Reza Shojarazavi, Hossein JamaliAbstract:Abstract In this study, substrates of Inconel 738 LC superalloy coupons were first sprayed with a NiCoCrAlY bondcoat and then with a ceria and yttria stabilized zirconia (CYSZ) topcoat by air plasma spraying (APS). After that, the plasma sprayed CYSZ Thermal barrier coatings (TBCs) were treated using a pulsed Nd:YAG laser. The effects of laser glazing on the microstructure and Thermal Shock resistance of the coatings were evaluated. Thermal Shock test was administered by holding specimens at 950 °C for 5 min and then water quenching. More than 20% of the spalled region of the surface of the topcoat was adopted as the criterion for the failure of samples. The microstructures of both the as processed and the tested TBCs were investigated using scanning electron microscope (SEM). The phases of the coatings were analyzed with X-ray diffractometry (XRD). XRD analysis revealed that both as sprayed and laser glazed topcoats consisted of nonequilibrium tetragonal (T′) phase. The results showed that the life times of the as sprayed TBCs were enhanced around fourfold by the formation of a continuous network of segmented cracks perpendicular to the surface and the increase in strain accommodation.
Liang Wang - One of the best experts on this subject based on the ideXlab platform.
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what is the suitable segmentation crack density for atmospheric plasma sprayed thick Thermal barrier coatings with the improved Thermal Shock resistance
Applied Surface Science, 2018Co-Authors: Liang Wang, X H Zhong, Jinxing Ni, Junwei Yang, Feng Shao, Y WangAbstract:Abstract The optimization and control of the segmentation crack density (Ds) for the thick Thermal barrier coatings (TTBCs) with the improved Thermal Shock resistance has been performed via finite element modeling. The simulation results based on the current property parameters of each layer of the TTBCs fabricated by atmospheric plasma spraying (APS) are well consistent with the experimental results of Thermal Shock test. The investigation results indicate that too large or too low Ds will be not beneficial to the improvement of the Thermal Shock resistance of the TTBCs. The Ds must be located at a suitable range, and this paper has revealed the objective law quantitatively. Based on our simulation and experimental results, the appropriate segmentation crack density is in the range of 2.38–4.76 cracks/mm which will be beneficial to improve the Thermal Shock resistance ability. It has been found that the as-sprayed TTBCs exhibited superior Thermal Shock resistance when the segmentation crack density is about 4 mm−1. The stress intensity factor (KI) and energy release rate (J integration) will increase with the increasing of segmentation crack length. The existence of segmentation crack will improve the strain tolerance of TTBCs. The strain tolerance has been characterized by Ds and segmentation crack length quantitatively. The failure mechanism of APS-TTBCs can be attributed to the propagation of segmentation crack at the top-coat of the TTBCs, formation and propagation of the horizontal crack at the top-coat/TGO (Thermally grown oxide) interface. The propagation rate of the main segmentation crack has been calculated and the life prediction model of the TTBCs during Thermal cycle has been established. The possible methods which can prolong the service life of the TTBCs have also been proposed.
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Thermal Shock behaviors of ysz thick Thermal barrier coatings fabricated by suspension and atmospheric plasma spraying
Surface & Coatings Technology, 2014Co-Authors: Yuexing Zhao, Liang Wang, Dachuan Li, Xinghua Zhong, Huayu Zhao, Fang ShaoAbstract:Abstract Thick Thermal barrier coating (TTBC) having segmentation-crack structure is favorable to its durability under severe Thermal Shock conditions. The present study reports the results of a comparative study on the Thermal Shock behavior of yttria-stabilized zirconia (YSZ) TTBCs with the segmentation-crack structure fabricated using axial suspension plasma spraying (ASPS) and atmospheric plasma spraying (APS) processes, respectively. The evolution of the microstructures, the phase composition and the failure behavior of both TTBCs before and after the Thermal Shock tests were investigated. Microstructure analysis showed that both the APS and ASPS coatings possessed typical segmentation cracks in the through-thickness direction, the measured segmentation crack densities ( Ds ) of the APS and ASPS YSZ top coat were about 2.5 cracks mm − 1 and 4 cracks mm − 1 , respectively. The microstructure analysis also showed an evenly spaced horizontal crack structure for the ASPS coating instead of the large columnar and eliminated splats boundaries structure for the APS coating. During Thermal Shock cycling, the spallation life of the ASPS TTBCs was improved by a factor of about 2 compared with that of APS coatings. Failure of the APS coatings is due to the fringe segments spallation, but in addition to the fringe segments spallation, a different center segment pull-out spallation can also be detected in the ASPS coatings.
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Thermal Shock behavior of toughened gadolinium zirconate ysz double ceramic layered Thermal barrier coating
Journal of Alloys and Compounds, 2014Co-Authors: Xinghua Zhong, Liang Wang, Huayu Zhao, Fang Shao, Xiaming Zhou, Chenguang Liu, Kai Yang, Shunya Tao, Chuanxia DingAbstract:Abstract Double-ceramic-layered (DCL) Thermal barrier coating system comprising of toughened Gadolinium zirconate (Gd 2 Zr 2 O 7 , GZ) as the top ceramic layer and 4.5 mol% Y 2 O 3 partially-stabilized ZrO 2 (4.5YSZ) as the bottom ceramic layer was fabricated by plasma spraying and Thermal Shock behavior of the DCL coating was investigated. The GZ top ceramic layer was toughened by addition of nanostructured 3 mol% Y 2 O 3 partially-stabilized ZrO 2 (3YSZ) to improve fracture toughness of the matrix. The Thermal Shock resistance of the DCL coating was enhanced significantly compared to that of single-ceramic-layered (SCL) GZ-3YSZ composite coating, which is believed to be primarily attributed to the two factors: (i) the increase in fracture toughness of the top ceramic layer by incorporating nanostructured YSZ particles and (ii) the improvement in strain tolerance through the utilization of 4.5YSZ as the bottom ceramic layer. In addition, the failure mechanisms are mainly attributed to the still low fracture toughness of the top ceramic layer and oxidation of the bond-coat.
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finite element simulation of stress distribution and development in 8ysz and double ceramic layer la2zr2o7 8ysz Thermal barrier coatings during Thermal Shock
Applied Surface Science, 2012Co-Authors: Liang Wang, Y Wang, Wei Zhang, C H WangAbstract:Abstract In this paper, the Thermal stress of the double-ceramic-layer (DCL) La2Zr2O7/8YSZ Thermal barrier coatings (TBCs) fabricated by atmospheric plasma spraying (APS) during Thermal Shock has been calculated. The residual stress of the coating after being sprayed has been regarded as the initial condition of the first Thermal cycle. The characteristic of the stress development during the Thermal cycle has been discussed, and the influence of the defects on the failure mode during the Thermal cycle has also been discussed systematically. Finite element simulation results show that there exist higher radial Thermal Shock stresses on the ceramic layer surface of these two coatings. There also exist higher Thermal stress gradient at the interface between the ceramic layer and the metallic layer. Higher Thermal stress in 8YSZ/NiCoCrAlY coating lead to the decrease of Thermal Shock property as compared to that of LZ/8YSZ/NiCoCrAlY coating. The addition of LZ ceramic layer can increase the insulation temperature, impede the oxygen transferring to the bond coating and can also reduce the Thermal stress. Considering from the aspects of Thermal insulation ability and the Thermal Shock resistance ability, DCL type LZ/8YSZ TBCs is a more promising coating material compared with the single-ceramic-layer (SCL) type 8YSZ TBCs for the application.
Changqing Hong - One of the best experts on this subject based on the ideXlab platform.
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electrostatic assembly preparation of high toughness zirconium diboride based ceramic composites with enhanced Thermal Shock resistance performance
ACS Applied Materials & Interfaces, 2016Co-Authors: Baoxi Zhang, Changqing Hong, Xinghong Zhang, Jia Zhang, Pingan HuAbstract:The central problem of using ceramic as a structural material is its brittleness, which associated with rigid covalent or ionic bonds. Whiskers or fibers of strong ceramics such as silicon carbide (SiC) or silicon nitride (Si3N4) are widely embedded in a ceramic matrix to improve the strength and toughness. The incorporation of these insulating fillers can impede the Thermal flow in ceramic matrix, thus decrease its Thermal Shock resistance that is required in some practical applications. Here we demonstrate that the toughness and Thermal Shock resistance of zirconium diboride (ZrB2)/SiC composites can be improved simultaneously by introducing graphene into composites via electrostatic assembly and subsequent sintering treatment. The incorporated graphene creates weak interfaces of grain boundaries (GBs) and optimal Thermal conductance paths inside composites. In comparison to pristine ZrB2–SiC composites, the toughness of (2.0%) ZrB2–SiC/graphene composites exhibited a 61% increasing (from 4.3 to 6.93 MP...
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mechanical properties and Thermal Shock resistance of zrb2 sic ceramic toughened with graphite flake and sic whiskers
Scripta Materialia, 2009Co-Authors: Xi Zhang, Zhi Wang, Changqing HongAbstract:ZrB 2 –20 vol.% SiC ceramic containing 10 vol.% graphite flake and 10 vol.% SiC whiskers (ZSGS) was fabricated by hot pressing. The mechanical properties and Thermal Shock resistance of the ZSGS ceramic were investigated. The results revealed that Thermal Shock resistance and fracture toughness were significantly improved, whereas slight degradation was attained in the flexural strength of the ZSGS ceramic. Furthermore, the effect of the Thermal conductivity, toughness and strength on the Thermal Shock resistance of the ZSGS ceramic was also investigated and discussed.
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effect of graphite flake on microstructure as well as mechanical properties and Thermal Shock resistance of zrb2 sic matrix ultrahigh temperature ceramics
Journal of Alloys and Compounds, 2009Co-Authors: Zhi Wang, Xinghong Zhang, Sai Wang, Changqing HongAbstract:Abstract ZrB2–20vol.%SiC containing the various volume fractions of graphite flake (ZSG) composites were investigated to determine the effect of graphite content on the microstructure as well as the mechanical properties and Thermal Shock resistance. The results revealed that the flexural strength generally decreased as the graphite volume fractions increased. Compared with the fracture toughness of about 4.5 MPa m1/2 for the ZrB2–SiC composites, the toughness of the ZSG composites is essentially higher than that of the ZrB2–SiC composites due to their lower strength relative to the ZrB2–SiC composites. The toughening mechanisms, such as the crack deflection and bridging, were related to the Thermal residual stresses, and the Thermal residual stresses in interfaces were calculated using Hsueh's formula. Moreover, the critical crack size that represents Thermal Shock resistance was calculated using the Griffith criterion. It was found that the Thermal Shock resistance was improved with the increasing graphite volume fractions.
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microstructure and Thermal Shock behavior of zrb2 sic graphite composite
Materials Chemistry and Physics, 2009Co-Authors: Zhi Wang, Changqing Hong, Xinghong ZhangAbstract:Abstract A water-quenching technique was adopted to evaluate the Thermal Shock behavior of hot-pressed ZrB 2 –SiC and ZrB 2 –SiC–graphite composites in an air atmosphere. The strength retention of the two kinds of composites was measured after varying temperature (Δ T c ) up to 1000 °C. Monolithic ZrB 2 –SiC showed rapidly drop in flexural strength above Δ T of 400 °C, however the critical Thermal Shock temperature difference (Δ T c ) is enhanced by adding graphite, and the ZrB 2 –SiC–graphite composite showed a higher retained strengths up to 1000 °C. The main reasons for a great improvement of Thermal Shock resistance (TSR) were also discussed and analyzed.
Raheleh Ahmadipidani - One of the best experts on this subject based on the ideXlab platform.
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comparison of Thermal Shock resistances of plasma sprayed nanostructured and conventional yttria stabilized zirconia Thermal barrier coatings
Ceramics International, 2012Co-Authors: Hossein Jamali, Reza Mozafarinia, Reza Shoja Razavi, Raheleh AhmadipidaniAbstract:Abstract The main goal of the current study is evaluation and comparison of Thermal Shock behavior of plasma-sprayed nanostructured and conventional yttria stabilized zirconia (YSZ) Thermal barrier coatings (TBCs). To this end, the nanostructured and conventional YSZ coatings were deposited by atmospheric plasma spraying (APS) on NiCoCrAlY-coated Inconel 738LC substrates. The Thermal Shock test was administered by quenching the samples in cold water of temperature 20–25 °C from 950 °C. In order to characterize elastic modulus of plasma-sprayed coatings, the Knoop indentation method was employed. Microstructural evaluation, elemental analysis, and phase analysis were performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffractometry (XRD) respectively. The results revealed that failures of both nanostructured and conventional TBCs were due to the spallation of ceramic top coat. Thermal stresses caused by mismatch of Thermal expansion coefficients between the ceramic top coat and the underlying metallic components were recognized as the major factor of TBC failure. However, the nanostructured TBC, due to bimodal unique microstructure, presented an average Thermal cycling lifetime that was approximately 1.5 times higher than that of the conventional TBC.
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improving the Thermal Shock resistance of plasma sprayed cysz Thermal barrier coatings by laser surface modification
Optics and Lasers in Engineering, 2012Co-Authors: Raheleh Ahmadipidani, Reza Mozafarinia, Reza Shojarazavi, Hossein JamaliAbstract:Abstract In this study, substrates of Inconel 738 LC superalloy coupons were first sprayed with a NiCoCrAlY bondcoat and then with a ceria and yttria stabilized zirconia (CYSZ) topcoat by air plasma spraying (APS). After that, the plasma sprayed CYSZ Thermal barrier coatings (TBCs) were treated using a pulsed Nd:YAG laser. The effects of laser glazing on the microstructure and Thermal Shock resistance of the coatings were evaluated. Thermal Shock test was administered by holding specimens at 950 °C for 5 min and then water quenching. More than 20% of the spalled region of the surface of the topcoat was adopted as the criterion for the failure of samples. The microstructures of both the as processed and the tested TBCs were investigated using scanning electron microscope (SEM). The phases of the coatings were analyzed with X-ray diffractometry (XRD). XRD analysis revealed that both as sprayed and laser glazed topcoats consisted of nonequilibrium tetragonal (T′) phase. The results showed that the life times of the as sprayed TBCs were enhanced around fourfold by the formation of a continuous network of segmented cracks perpendicular to the surface and the increase in strain accommodation.
