A thermally grown oxide （TGO） layer is formed at the interface of bond coat/top coat. The TGO growth during thermal exposure in air plays an important role in the spallation of the ceramic layer from the bond coat. ...A thermally grown oxide （TGO） layer is formed at the interface of bond coat/top coat. The TGO growth during thermal exposure in air plays an important role in the spallation of the ceramic layer from the bond coat. High temperature oxidation resistance of four types of atmospheric plasma sprayed TBCs was investigated. These coatings were oxidized at 1000 °C for 24, 48 and 120 h in a normal electric furnace under air atmosphere. Microstructural characterization showed that the growth of the TGO layer in nano NiCrAlY/YSZ/nano Al2O3 coating is much lower than in other coatings. Moreover, EDS and XRD analyses revealed the formation of Ni（Cr,Al）2O4 mixed oxides （as spinel） and NiO onto the Al2O3 （TGO） layer. The formation of detrimental mixed oxides （spinels） on the Al2O3 （TGO） layer of nano NiCrAlY/YSZ/nano Al2O3 coating is much lower compared to that of other coatings after 120 h of high temperature oxidation at 1000 °C.展开更多
Thermally grown oxide(TGO)is a critical factor for the service life of thermal barrier coatings(TBC).Numerical simulations of the growth process of TGO have become an effective means of comprehensively understanding t...Thermally grown oxide(TGO)is a critical factor for the service life of thermal barrier coatings(TBC).Numerical simulations of the growth process of TGO have become an effective means of comprehensively understanding the progressive damage of the TBC system.At present,technologies of numerical simulation to TGO growth include two categories:coupled chemical-mechanical methods and mechanical equivalent methods.The former is based on the diffusion analysis of oxidizing elements,which can describe the influence of bond coat(BC)consumption and phase transformation in the growth process of TGO on the mechanical behavior of each layer of TBC,and has high accuracy for the thickness evolution of TGO,but they cannot describe the lateral growth of TGO and the rumpling phenomenon induced.The latter focuses on describing the final stress and strain state after the growth of a specific TGO rather than the complete growth processes of TGO.Based on the measured TGO thickness growth curve,simulations of thickening and lateral growth can be achieved by directly applying anisotropic volumetric strain to oxidized elements and switching elements properties from the BC to the TGO.展开更多
The properties of two different types of thermal barrier coatings （TBCs） were compared to improve the surface characteristics on high temperature components. These TBCs consisted of a duplex TBC and a five-layered f...The properties of two different types of thermal barrier coatings （TBCs） were compared to improve the surface characteristics on high temperature components. These TBCs consisted of a duplex TBC and a five-layered functionally graded TBC. NiCrAIY bond coats were deposited on a number of Inconel-738LC specimens using high velocity oxy-fuel spraying （HVOF） technique. For duplex coating, a group of these specimens were coated with yttria stabilized zirconia （YSZ） using plasma spray technique. Functionally graded NiCrAIY/YSZ coatings were fabricated by plasma spray using co-injection of the two different powders in a single plasma torch. The amount of zirconia in functionally graded coatings were gradually increased from 30 to 100 vol. pct. Microstructural changes, thermally grown oxide （TGO） layer growth and damage initiation of the coatings were investigated as a function of isothermal oxidation test at 970℃. As a complementary test, the performance of the fabricated coatings by the optimum processing conditions was evaluated as a function of intense thermal cycling test at 1100℃. Also the strength of the adhesive coatings of the substrate was also measured. Microstructural characterization was analyzed by scanning electron microscopy （SEM） and optical microscopy whereas phase analysis and chemical composition changes of the coatings and oxides formed during the tests were studied by XRD （X-ray diffraction） and EDS （energy dispersive spectrometer）. The results showed that microstructure and compositions gradually varied in the functionally graded coatings. By comparison of duplex and functionally graded TBCs oxidation behavior （duplex failure after 1700 h and funcitionally graded TECs failure after 2000 h）, thermal shock test and adhesion strength of the coatings, the functionally graded TBC had better performance and more durability.展开更多
In cooling process of Fe-Cr-Al alloy oxidized at 1 300 ℃, the effect of cooling speed and exposure time on oxide spalled area fraction and successive variety of the spalled region were studied by investigating evolve...In cooling process of Fe-Cr-Al alloy oxidized at 1 300 ℃, the effect of cooling speed and exposure time on oxide spalled area fraction and successive variety of the spalled region were studied by investigating evolvement of the thermally grown oxide using in-situ CCD monitoring technique. The results showed that oxide spallation can be restrained by controlling cooling speed and the critical temperature drop of spallation initiation which is closely related to the oxide thickness or exposure time, and the spallation process of a little region may be described in more detail as two routes： from the oxide/substrate interface micro-decohesion, micro-buckles, buckle spreading, buckle crack to spallation and from the interface micro-decohesion, micro-buckles, buckle crack and spallation to the residual oxide decohesion and spallation.展开更多
As a nondestructive testing technique,terahertz time-domain spectroscopy technology is commonly used to measure the thickness of ceramic coat in thermal barrier coatings(TBCs).However,the invisibility of ceramic/therm...As a nondestructive testing technique,terahertz time-domain spectroscopy technology is commonly used to measure the thickness of ceramic coat in thermal barrier coatings(TBCs).However,the invisibility of ceramic/thermally grown oxide(TGO)reflective wave leads to the measurement failure of natural growth TGO whose thickness is below 10μm in TBCs.To detect and monitor TGO in the emergence stage,a time of flight(TOF)improved TGO thickness measurement method is proposed.A simulative investigation on propagation characteristics of terahertz shows the linear relationship between TGO thickness and phase shift of feature wave.The accurate TOF increment could be acquired from wavelet soft threshold and cross-correlation function with negative effect reduction of environmental noise and system oscillation.Thus,the TGO thickness could be obtained efficiently from the TOF increment of the monitor area with different heating times.The averaged error of 1.61μm in experimental results demonstrates the highly accurate and robust measurement of the proposed method,making it attractive for condition monitoring and life prediction of TBCs.展开更多
Thermally Grown Oxide（TGO） is a dominating component in controlling the effectiveness of thermal barrier coating.During the growth of TGO,whether we could homogeneously distribute Al atom on the TGO and the intermed...Thermally Grown Oxide（TGO） is a dominating component in controlling the effectiveness of thermal barrier coating.During the growth of TGO,whether we could homogeneously distribute Al atom on the TGO and the intermediate metal layer will be the key factor in forming TGO with continuous,uniform and single-ingredient（Al2O3）.In this experiment,we bombarded particles on to the metallic bound layer.We studied the influence of supersonic particle bombardment on the diffusion of Al.We hope to control the growth of TGO by monitoring the diffusion of Al.Thermal barrier coating（TBC）,which consists of a NiCoCrAlY bond coat and a ZrO2-8Y2O3（wt.%） topcoat（TC）,is fabricated on the nickel-base superalloy by air plasma spray（APS）.NiCoCrAlY bond coat is treated by supersonic fine particles bombarding（SFPB）.The morphology,oxidation behavior of TBC and phase are characterized by scanning electron microscope（SEM） equipped with an energy dispersive spectromrter（EDS） and X-ray diffractometer（XRD）.The influence of supersonic fine particles bombarding technique on the service life of thermal barrier coating is studied.The results show that SFPB technique improves the flaw of excessive surface undulation in the as-sprayed bond coat.A continuous,uniform and single-ingredient（Al2O3） TGO can quickly form in the SFPB TBC during high temperature oxidation process.The thickening of TGO is relatively slow.These will effectively suppress the formation of other non-protective oxides.Therefore,SFPB technique reduces the growth stress level generated by the continuous growth of TGO,and also avoids the stress concentration induced by formation of the large particle spinal oxide.Thermal barrier coating still remains well after 350 thermal cycles.The service life of TBC is improved.The proposed research provides theoretical basis and technical references to further improve and enhance the SFPB technique.展开更多
基金financed by Institutional Scholarship provided by Universiti Teknologi Malaysia and the Ministry of Higher Education of Malaysiathe Ministry of Higher Education of Malaysia and Universiti Teknologi Malaysia (UTM) for providing research facilities and financial support under the grant Q.J130000.2524.02H55
文摘A thermally grown oxide （TGO） layer is formed at the interface of bond coat/top coat. The TGO growth during thermal exposure in air plays an important role in the spallation of the ceramic layer from the bond coat. High temperature oxidation resistance of four types of atmospheric plasma sprayed TBCs was investigated. These coatings were oxidized at 1000 °C for 24, 48 and 120 h in a normal electric furnace under air atmosphere. Microstructural characterization showed that the growth of the TGO layer in nano NiCrAlY/YSZ/nano Al2O3 coating is much lower than in other coatings. Moreover, EDS and XRD analyses revealed the formation of Ni（Cr,Al）2O4 mixed oxides （as spinel） and NiO onto the Al2O3 （TGO） layer. The formation of detrimental mixed oxides （spinels） on the Al2O3 （TGO） layer of nano NiCrAlY/YSZ/nano Al2O3 coating is much lower compared to that of other coatings after 120 h of high temperature oxidation at 1000 °C.
基金supported by Major Special Projects of Gansu Province,China(No.21ZD4WA017)University Industry Transformation Promotion Project of Gansu Province,China(No.2020C-11)+1 种基金the Program of“Science and Technology International Cooperation Demonstrative Base of Metal Surface Engineering along the Silk Road”,China(No.2017D01003)the National Natural Science Foundation of China(No.51901093)。
基金supported by the National Natural Science Foundation of China(Grant No.51905510)National Science and Technology Major Project(J2019-IV-0003-0070).
文摘Thermally grown oxide(TGO)is a critical factor for the service life of thermal barrier coatings(TBC).Numerical simulations of the growth process of TGO have become an effective means of comprehensively understanding the progressive damage of the TBC system.At present,technologies of numerical simulation to TGO growth include two categories:coupled chemical-mechanical methods and mechanical equivalent methods.The former is based on the diffusion analysis of oxidizing elements,which can describe the influence of bond coat(BC)consumption and phase transformation in the growth process of TGO on the mechanical behavior of each layer of TBC,and has high accuracy for the thickness evolution of TGO,but they cannot describe the lateral growth of TGO and the rumpling phenomenon induced.The latter focuses on describing the final stress and strain state after the growth of a specific TGO rather than the complete growth processes of TGO.Based on the measured TGO thickness growth curve,simulations of thickening and lateral growth can be achieved by directly applying anisotropic volumetric strain to oxidized elements and switching elements properties from the BC to the TGO.
文摘The properties of two different types of thermal barrier coatings （TBCs） were compared to improve the surface characteristics on high temperature components. These TBCs consisted of a duplex TBC and a five-layered functionally graded TBC. NiCrAIY bond coats were deposited on a number of Inconel-738LC specimens using high velocity oxy-fuel spraying （HVOF） technique. For duplex coating, a group of these specimens were coated with yttria stabilized zirconia （YSZ） using plasma spray technique. Functionally graded NiCrAIY/YSZ coatings were fabricated by plasma spray using co-injection of the two different powders in a single plasma torch. The amount of zirconia in functionally graded coatings were gradually increased from 30 to 100 vol. pct. Microstructural changes, thermally grown oxide （TGO） layer growth and damage initiation of the coatings were investigated as a function of isothermal oxidation test at 970℃. As a complementary test, the performance of the fabricated coatings by the optimum processing conditions was evaluated as a function of intense thermal cycling test at 1100℃. Also the strength of the adhesive coatings of the substrate was also measured. Microstructural characterization was analyzed by scanning electron microscopy （SEM） and optical microscopy whereas phase analysis and chemical composition changes of the coatings and oxides formed during the tests were studied by XRD （X-ray diffraction） and EDS （energy dispersive spectrometer）. The results showed that microstructure and compositions gradually varied in the functionally graded coatings. By comparison of duplex and functionally graded TBCs oxidation behavior （duplex failure after 1700 h and funcitionally graded TECs failure after 2000 h）, thermal shock test and adhesion strength of the coatings, the functionally graded TBC had better performance and more durability.
基金Item Sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars
文摘In cooling process of Fe-Cr-Al alloy oxidized at 1 300 ℃, the effect of cooling speed and exposure time on oxide spalled area fraction and successive variety of the spalled region were studied by investigating evolvement of the thermally grown oxide using in-situ CCD monitoring technique. The results showed that oxide spallation can be restrained by controlling cooling speed and the critical temperature drop of spallation initiation which is closely related to the oxide thickness or exposure time, and the spallation process of a little region may be described in more detail as two routes： from the oxide/substrate interface micro-decohesion, micro-buckles, buckle spreading, buckle crack to spallation and from the interface micro-decohesion, micro-buckles, buckle crack and spallation to the residual oxide decohesion and spallation.
基金the National Natural Science Foundation of China(Grant Nos.52275096,51905102)the Fujian Provincial Science and Technology Project,China(Grant No.2019I0004)+2 种基金the State Key Laboratory of Mechanical Systems and Vibration,China(Grant No.MSV-2018-07)the Shanghai Natural Sciences Fund,China(Grant No.18ZR1414200)the China Postdoctoral Science Foundation(Grant No.2019M662226).
文摘As a nondestructive testing technique,terahertz time-domain spectroscopy technology is commonly used to measure the thickness of ceramic coat in thermal barrier coatings(TBCs).However,the invisibility of ceramic/thermally grown oxide(TGO)reflective wave leads to the measurement failure of natural growth TGO whose thickness is below 10μm in TBCs.To detect and monitor TGO in the emergence stage,a time of flight(TOF)improved TGO thickness measurement method is proposed.A simulative investigation on propagation characteristics of terahertz shows the linear relationship between TGO thickness and phase shift of feature wave.The accurate TOF increment could be acquired from wavelet soft threshold and cross-correlation function with negative effect reduction of environmental noise and system oscillation.Thus,the TGO thickness could be obtained efficiently from the TOF increment of the monitor area with different heating times.The averaged error of 1.61μm in experimental results demonstrates the highly accurate and robust measurement of the proposed method,making it attractive for condition monitoring and life prediction of TBCs.
基金supported by National Natural Science Foundation of China (Grant No. 50575220)
文摘Thermally Grown Oxide（TGO） is a dominating component in controlling the effectiveness of thermal barrier coating.During the growth of TGO,whether we could homogeneously distribute Al atom on the TGO and the intermediate metal layer will be the key factor in forming TGO with continuous,uniform and single-ingredient（Al2O3）.In this experiment,we bombarded particles on to the metallic bound layer.We studied the influence of supersonic particle bombardment on the diffusion of Al.We hope to control the growth of TGO by monitoring the diffusion of Al.Thermal barrier coating（TBC）,which consists of a NiCoCrAlY bond coat and a ZrO2-8Y2O3（wt.%） topcoat（TC）,is fabricated on the nickel-base superalloy by air plasma spray（APS）.NiCoCrAlY bond coat is treated by supersonic fine particles bombarding（SFPB）.The morphology,oxidation behavior of TBC and phase are characterized by scanning electron microscope（SEM） equipped with an energy dispersive spectromrter（EDS） and X-ray diffractometer（XRD）.The influence of supersonic fine particles bombarding technique on the service life of thermal barrier coating is studied.The results show that SFPB technique improves the flaw of excessive surface undulation in the as-sprayed bond coat.A continuous,uniform and single-ingredient（Al2O3） TGO can quickly form in the SFPB TBC during high temperature oxidation process.The thickening of TGO is relatively slow.These will effectively suppress the formation of other non-protective oxides.Therefore,SFPB technique reduces the growth stress level generated by the continuous growth of TGO,and also avoids the stress concentration induced by formation of the large particle spinal oxide.Thermal barrier coating still remains well after 350 thermal cycles.The service life of TBC is improved.The proposed research provides theoretical basis and technical references to further improve and enhance the SFPB technique.
