High temperature oxidation behavior of the bond coat layer is a critical factor that controls the failure mechanism of thermal barrier coatings（TBCs）.Previous work reveald that TBCs with cryomilled NiCrAlY bond coat...High temperature oxidation behavior of the bond coat layer is a critical factor that controls the failure mechanism of thermal barrier coatings（TBCs）.Previous work reveald that TBCs with cryomilled NiCrAlY bond coats exhibited an improved oxidation behavior compared to equivalent TBCs with conventional bond coats.The cryomilled NiCrAlY bond coats contributed to a slower growth rate of thermally grown oxides（TGO） with a final thinner thickness and enhanced homogeneity in TGO composition.To better understand the improved oxidation behavior,a mechanistic investigation based on diffusion theory and quantum mechanics is performed to elucidate the role of aluminum diffusion in the oxidation behavior and how the microstructural features of the cryomilled NiCrAlY bond coats,i e,the creation of a thermally stable,uniform distribution of ultrafine Al-rich oxide dispersoids,affect the diffusion kinetics of Al and the migration of free electrons.It is revealed that these Al-rich oxide dispersoids result in a uniform diffusion of Al and slow migration of free electrons within the NiCrAlY bond coat,consequently leading to the improved oxidation behavior.展开更多
In this paper, the diffusion behavior between MgO and Fe2O3（the main iron oxide in pellets） is investigated using a diffusion couple method. In addition, the distribution regulation of MgO in MgO-bearing pellets is ...In this paper, the diffusion behavior between MgO and Fe2O3（the main iron oxide in pellets） is investigated using a diffusion couple method. In addition, the distribution regulation of MgO in MgO-bearing pellets is analyzed via pelletizing experiments. The results illustrate that MgO is prone to diffuse into Fe2O3 in the form of solid solution; the diffusion rate considered here is 13.64 μm·min^（-1）. Most MgO content distributes in the iron phase instead of the slag phase. The MF phase {（Mg（1-x）Fex）O·Fe2O3, x ≤ 1} is generated in the MgO-bearing pellets. However, the distribution of MgO in the radial direction of the pellets is inconsistent. The solid solution portion of MgO in the MF phase is larger in the outer layer of the pellets than in the inner layer. In this work, the approximate chemical composition of the MF phase in the outer layer of the pellets is {（Mg（0.35-0.77）·Fe（0.65-0.23）） O·Fe2O3} and in the inner layer is {（Mg（0.13-0.45）·Fe（0.87-0.55））O·Fe2O3}.展开更多
The behaviors of lead zirconate titanate （PZT） deposited as the dielectric for high-voltage devices are investigated experimentally and theoretically. The devices demonstrate not only high breakdown voltages above 3...The behaviors of lead zirconate titanate （PZT） deposited as the dielectric for high-voltage devices are investigated experimentally and theoretically. The devices demonstrate not only high breakdown voltages above 350 V, but also excellent memory behaviors. A drain current–gate voltage （ID-VG） memory window of about 2.2 V is obtained at the sweep voltages of ±10 V for the 350-V laterally diffused metal oxide semiconductor （LDMOS）. The retention time of about 270 s is recorded for the LDMOS through a controlled ID-VG measurement. The LDMOS with memory behaviors has potential to be applied in future power conversion circuits to boost the performance of the energy conversion system.展开更多
Experiments on the solid-state reaction between iron ore particles and MgO were performed to investigate the coating mechanism of MgO on the iron ore particles＇ surface during fluidized bed reduction. MgO powders and...Experiments on the solid-state reaction between iron ore particles and MgO were performed to investigate the coating mechanism of MgO on the iron ore particles＇ surface during fluidized bed reduction. MgO powders and iron ore particles were mixed and compressed into briquettes and, subsequently, roasted at different temperatures and for different time periods. A Mg-containing layer was observed on the outer edge of the iron ore particles when the roasting temperature was greater than 1173 K. The concentration of Fe in the Mg-containing layer was evenly distributed and was approximately 10wt%, regardless of the temperature change. Boundary layers of Mg and Fe were observed outside of the iron ore particles. The change in concentration of Fe in the boundary layers was simulated using a gas–solid diffusion model, and the diffusion coefficients of Fe and Mg in these layers at different temperatures were calculated. The diffusion activation energies of Fe and Mg in the boundary layers in these experiments were evaluated to be approximately 176 and 172 k J/mol, respectively.展开更多
Al_(2)O_(3)is extensively utilized as an oxidant barrier in aeroengines and gas turbines at elevated temperatures,and smallangle grain boundaries significantly reduce its oxygen permeation.However,experimentally obser...Al_(2)O_(3)is extensively utilized as an oxidant barrier in aeroengines and gas turbines at elevated temperatures,and smallangle grain boundaries significantly reduce its oxygen permeation.However,experimentally observing and regulating these small-angle grain boundaries poses considerable challenges.In this study,we search for these small-angle Al_(2)O_(3)grain boundaries via first-principles calculations.We identify two families of ultralow-oxygen-diffusion grain boundaries,namely,Gb(xxx)/(001)and Gb(xxx)/(110),whose diffusion rates are 2 to 4 orders of magnitude lower than those of conventional grain boundaries.On the basis of these findings,we summarize and analyze the influence mechanisms and relative importance of various factors affecting grain boundary permeation.Our results indicate that,in addition to the grain boundary angle,the average bond length and band gap play primary roles in impeding oxidant transport.Finally,the[0001]selective nucleation growth of alumina was achieved by stepwise sintering,and ultralow-oxygen-diffusion Gb(104)/(110)was successfully prepared,which was consistent with the simulation results.These findings provide valuable insights for the design of ultralow-oxygen-diffusion Al_(2)O_(3)grain boundaries,thereby significantly enhancing the oxidation resistance of aluminum-containing superalloys.展开更多
基金Funded by the U.S.Office of Naval Research(ONR)(No.N00014-06-1-0506)
文摘High temperature oxidation behavior of the bond coat layer is a critical factor that controls the failure mechanism of thermal barrier coatings（TBCs）.Previous work reveald that TBCs with cryomilled NiCrAlY bond coats exhibited an improved oxidation behavior compared to equivalent TBCs with conventional bond coats.The cryomilled NiCrAlY bond coats contributed to a slower growth rate of thermally grown oxides（TGO） with a final thinner thickness and enhanced homogeneity in TGO composition.To better understand the improved oxidation behavior,a mechanistic investigation based on diffusion theory and quantum mechanics is performed to elucidate the role of aluminum diffusion in the oxidation behavior and how the microstructural features of the cryomilled NiCrAlY bond coats,i e,the creation of a thermally stable,uniform distribution of ultrafine Al-rich oxide dispersoids,affect the diffusion kinetics of Al and the migration of free electrons.It is revealed that these Al-rich oxide dispersoids result in a uniform diffusion of Al and slow migration of free electrons within the NiCrAlY bond coat,consequently leading to the improved oxidation behavior.
基金the financial support of China Postdoctoral Science Foundation (No.2016M591445)Postdoctoral Science Foundation of NEU China (No.20160302)National Natural Science Foundation of China (No.51604069)
文摘In this paper, the diffusion behavior between MgO and Fe2O3（the main iron oxide in pellets） is investigated using a diffusion couple method. In addition, the distribution regulation of MgO in MgO-bearing pellets is analyzed via pelletizing experiments. The results illustrate that MgO is prone to diffuse into Fe2O3 in the form of solid solution; the diffusion rate considered here is 13.64 μm·min^（-1）. Most MgO content distributes in the iron phase instead of the slag phase. The MF phase {（Mg（1-x）Fex）O·Fe2O3, x ≤ 1} is generated in the MgO-bearing pellets. However, the distribution of MgO in the radial direction of the pellets is inconsistent. The solid solution portion of MgO in the MF phase is larger in the outer layer of the pellets than in the inner layer. In this work, the approximate chemical composition of the MF phase in the outer layer of the pellets is {（Mg（0.35-0.77）·Fe（0.65-0.23）） O·Fe2O3} and in the inner layer is {（Mg（0.13-0.45）·Fe（0.87-0.55））O·Fe2O3}.
基金the National Basic Research Program of China(Grant No.50772019)the National Natural Science Foundation of China(Grant No.61204084)
文摘The behaviors of lead zirconate titanate （PZT） deposited as the dielectric for high-voltage devices are investigated experimentally and theoretically. The devices demonstrate not only high breakdown voltages above 350 V, but also excellent memory behaviors. A drain current–gate voltage （ID-VG） memory window of about 2.2 V is obtained at the sweep voltages of ±10 V for the 350-V laterally diffused metal oxide semiconductor （LDMOS）. The retention time of about 270 s is recorded for the LDMOS through a controlled ID-VG measurement. The LDMOS with memory behaviors has potential to be applied in future power conversion circuits to boost the performance of the energy conversion system.
基金supported by the Fundamental Research Funds for the Central Universities (FRF-TP-15-009A2)the Project Funded by China Postdoctoral Science Foundation (2015M570931)+1 种基金the National Natural Science Fund Project of China (91534121)the National Major Scientific Instruments Special Plan (2011YQ12003907)
文摘Experiments on the solid-state reaction between iron ore particles and MgO were performed to investigate the coating mechanism of MgO on the iron ore particles＇ surface during fluidized bed reduction. MgO powders and iron ore particles were mixed and compressed into briquettes and, subsequently, roasted at different temperatures and for different time periods. A Mg-containing layer was observed on the outer edge of the iron ore particles when the roasting temperature was greater than 1173 K. The concentration of Fe in the Mg-containing layer was evenly distributed and was approximately 10wt%, regardless of the temperature change. Boundary layers of Mg and Fe were observed outside of the iron ore particles. The change in concentration of Fe in the boundary layers was simulated using a gas–solid diffusion model, and the diffusion coefficients of Fe and Mg in these layers at different temperatures were calculated. The diffusion activation energies of Fe and Mg in the boundary layers in these experiments were evaluated to be approximately 176 and 172 k J/mol, respectively.
基金supported by the National Key R&D Program of China(No.2024YFB3715200)the National Natural Science Foundation of China(Nos.52401109 and U22A20110).
文摘Al_(2)O_(3)is extensively utilized as an oxidant barrier in aeroengines and gas turbines at elevated temperatures,and smallangle grain boundaries significantly reduce its oxygen permeation.However,experimentally observing and regulating these small-angle grain boundaries poses considerable challenges.In this study,we search for these small-angle Al_(2)O_(3)grain boundaries via first-principles calculations.We identify two families of ultralow-oxygen-diffusion grain boundaries,namely,Gb(xxx)/(001)and Gb(xxx)/(110),whose diffusion rates are 2 to 4 orders of magnitude lower than those of conventional grain boundaries.On the basis of these findings,we summarize and analyze the influence mechanisms and relative importance of various factors affecting grain boundary permeation.Our results indicate that,in addition to the grain boundary angle,the average bond length and band gap play primary roles in impeding oxidant transport.Finally,the[0001]selective nucleation growth of alumina was achieved by stepwise sintering,and ultralow-oxygen-diffusion Gb(104)/(110)was successfully prepared,which was consistent with the simulation results.These findings provide valuable insights for the design of ultralow-oxygen-diffusion Al_(2)O_(3)grain boundaries,thereby significantly enhancing the oxidation resistance of aluminum-containing superalloys.
基金supported by the National Natural Science Foundation of China(52222112,52101151)Shenzhen Science and Technology Program(SGDX20210823104002016,JCYJ20220531095217039)Hong Kong Research Grant Council(RGC,C1020-21G,C1017-21G)。
