To improve the corrosion resistance of Cf/SiC composites in a water vapor oxygen coupled environment,the bilayer Yb_(2)Si_(2)O_(7)/SiC and tri-layer Yb2Si2O7/(SiCw-Mullite,SM)/SiC environment barrier coatings were de...To improve the corrosion resistance of Cf/SiC composites in a water vapor oxygen coupled environment,the bilayer Yb_(2)Si_(2)O_(7)/SiC and tri-layer Yb2Si2O7/(SiCw-Mullite,SM)/SiC environment barrier coatings were designed and prepared on the surface of Cf/SiC composites by chemical vapor deposition and sol-gel method united with air spraying.Results show that the mass loss of bi-layer Yb_(2)Si_(2)O_(7)/SiC coating coated samples was 17.24×10^(-3) g cm^(-2) after 200 h oxidation at 1673 K,and the average compression strength retention rate was only 79.44% due to the formation of wide penetrating cracks.Comparatively,SiC whiskers in SM middle coating can not only increase the crack propagation resistance of mullite middle coating,but also alleviate the difference of coefficient of thermal expansion between Yb_(2)Si_(2)O_(7) outer coating and mullite middle coating.Therefore,the mass loss of trilayer Yb_(2)Si_(2)O_(7)/SM/SiC coating coated samples was only 2.93×10^(-3) g cm^(-2) after 200 h oxidation at 1673 K,and the average compression strength retention rate was up to 98.79%.展开更多
Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements for environmental barrier coatings used on silicon-bas...Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements for environmental barrier coatings used on silicon-based ceramics.RE2Si2O7(RE=rare earth)has been widely recognized as one of the most promising candidates for environmental barrier coatings due to its good water vapor corrosion resistance.However,the relatively high thermal conductivity and poor resistance to CMAS corrosion have limited its practical application.Inspired by the high entropy effect,in this work,a novel rare earth disilicate(Lu_(_(1/7))Yb_(_(1/7))Sc_(_(1/7))Er_(_(1/7))Y_(_(1/7))Ho_(_(1/7))Dy_(_(1/7)))2Si2O7((7RE_(_(1/7)))2Si2O7)has been designed and synthesized by a solid reaction process.(7RE_(_(1/7)))2Si2O7 showed a low thermal conductivity of 1.81 W·m^(−1)·K^(−1)at 1273 K.Furthermore,the thermal expansion coefficient of(7RE_(_(1/7)))_(2)Si_(2)O_(7)(4.07×10^(−6)℃^(−1)from room temperature(RT)to 1400℃)is close to that of the SiC-based ceramic matrix composites(SiC-CMCs)((4.5–5.5)×10^(−6)℃^(−1)).Additionally,(7RE_(_(1/7)))2Si2O7 exhibited excellent resistance to CMAS corrosion.When exposed to CMAS at 1300℃for 48 h,the reaction layer thickness was 22μm.The improved performance of(7RE_(_(1/7)))2Si2O7 highlights its potential as a promising candidate for thermal/environmental barrier coatings.展开更多
The corrosion behavior of environmental barrier coatings(EBCs)directly affects the service life and stability of ceramic matrix composite(CMC)structural parts in the aero-engines.The silicon carbide(SiC)whisker toughe...The corrosion behavior of environmental barrier coatings(EBCs)directly affects the service life and stability of ceramic matrix composite(CMC)structural parts in the aero-engines.The silicon carbide(SiC)whisker toughening phase and c-AlPO_(4) bonding phase are firstly used to improve the service life of novel tri-layer Yb_(2)Si_(2)O_(7)/mullite/SiC EBCs in the burner rig test.The formation of penetrating cracks in Yb_(2)Si_(2)O_(7)/mullite/SiC coating caused the failure of coating at 1673 K.The SiC whiskers in mullite middle coating significantly inhibited the formation of penetrating cracks in Yb_(2)Si_(2)O_(7)/mullite/SiC coating,and efficiently prevented the oxidation of carbon fiber reinforced silicon carbide(C_(f)/SiC)samples for 360-min thermal cycles(24 times)with a weight loss of 6.19×10^(−3) g·cm^(−2).Although c-AlPO_(4) particles further improved the service life of SiC_(w)-mullite(SM)coating,the overflow of PO_(x) gas aggravated the formation and expansion of cracks in the Yb_(2)Si_(2)O_(7) outer coating,and caused the service life of overall Yb_(2)Si_(2)O_(7)/c-AlPO_(4)-SiC_(w)-mullite(ASM)/SiC coating to be slightly lower than that of Yb_(2)Si_(2)O_(7)/SM/SiC coating.This study guides the design of modified tri-layer EBCs with long service life in high-temperature and high-speed gas environment.展开更多
A series of h-BN based composites with Yb_4Si_2O_7N_2 as a secondary phase were successfully synthesized by an in situ reaction hot pressing method. It was found that the relative density and room-temperature mechanic...A series of h-BN based composites with Yb_4Si_2O_7N_2 as a secondary phase were successfully synthesized by an in situ reaction hot pressing method. It was found that the relative density and room-temperature mechanical properties monotonically increased with increasing the content of Yb_4Si_2O_7N_2 from 20 to 50 vol%. When 50 vol% Yb_4Si_2O_7N_2 was introduced, the relative density of the composite reached 98.75%, and its flexural strength, compressive strength, fracture toughness, and hardness reached 338±10 MPa, 803±49 MPa, 2.06±0.06 MPa·m1/2, and 2.69±0.10 GPa, respectively. The strengthening effect of Yb_4Si_2O_7N_2 was mainly attributed to its high modulus and high hardness. Fine microstructure was also advantageous to strength and could lead to more tortuous crack propagation paths and then improve the fracture toughness of the composites simultaneously. Meanwhile, the composites maintained good machinability.展开更多
基金This work was funded by the National Natural Science Foundation of China(Grant No.52102122 and 52075555)Natural Science Foundation of Hunan Province(Grant No.2021JJ10057 and Grant No.2020JJ4116)the National Defense Basic Scientific Research Program of China(fund from National Key Laboratory of Science and Technology on Highstrength Structural Materials,Central South University,Changsha 410083,China)。
文摘To improve the corrosion resistance of Cf/SiC composites in a water vapor oxygen coupled environment,the bilayer Yb_(2)Si_(2)O_(7)/SiC and tri-layer Yb2Si2O7/(SiCw-Mullite,SM)/SiC environment barrier coatings were designed and prepared on the surface of Cf/SiC composites by chemical vapor deposition and sol-gel method united with air spraying.Results show that the mass loss of bi-layer Yb_(2)Si_(2)O_(7)/SiC coating coated samples was 17.24×10^(-3) g cm^(-2) after 200 h oxidation at 1673 K,and the average compression strength retention rate was only 79.44% due to the formation of wide penetrating cracks.Comparatively,SiC whiskers in SM middle coating can not only increase the crack propagation resistance of mullite middle coating,but also alleviate the difference of coefficient of thermal expansion between Yb_(2)Si_(2)O_(7) outer coating and mullite middle coating.Therefore,the mass loss of trilayer Yb_(2)Si_(2)O_(7)/SM/SiC coating coated samples was only 2.93×10^(-3) g cm^(-2) after 200 h oxidation at 1673 K,and the average compression strength retention rate was up to 98.79%.
基金the National Key R&D Program of China(No.2022YFE0121200)the National Natural Science Foundation of China(Nos.52371052 and 52073029).
文摘Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements for environmental barrier coatings used on silicon-based ceramics.RE2Si2O7(RE=rare earth)has been widely recognized as one of the most promising candidates for environmental barrier coatings due to its good water vapor corrosion resistance.However,the relatively high thermal conductivity and poor resistance to CMAS corrosion have limited its practical application.Inspired by the high entropy effect,in this work,a novel rare earth disilicate(Lu_(_(1/7))Yb_(_(1/7))Sc_(_(1/7))Er_(_(1/7))Y_(_(1/7))Ho_(_(1/7))Dy_(_(1/7)))2Si2O7((7RE_(_(1/7)))2Si2O7)has been designed and synthesized by a solid reaction process.(7RE_(_(1/7)))2Si2O7 showed a low thermal conductivity of 1.81 W·m^(−1)·K^(−1)at 1273 K.Furthermore,the thermal expansion coefficient of(7RE_(_(1/7)))_(2)Si_(2)O_(7)(4.07×10^(−6)℃^(−1)from room temperature(RT)to 1400℃)is close to that of the SiC-based ceramic matrix composites(SiC-CMCs)((4.5–5.5)×10^(−6)℃^(−1)).Additionally,(7RE_(_(1/7)))2Si2O7 exhibited excellent resistance to CMAS corrosion.When exposed to CMAS at 1300℃for 48 h,the reaction layer thickness was 22μm.The improved performance of(7RE_(_(1/7)))2Si2O7 highlights its potential as a promising candidate for thermal/environmental barrier coatings.
基金funded by the National Key R&D Program of China(Grant Nos.2021YFB3703800 and 2021YFB3703802)National Natural Science Foundation of China(Grant No.52102122)+1 种基金National Key Laboratory of Science and Technology on High-strength Structural Materials,Central South University(Grant No.SYSJJ2021LWS01)China Postdoctoral Science Foundation(Grant No.2022M711540).
文摘The corrosion behavior of environmental barrier coatings(EBCs)directly affects the service life and stability of ceramic matrix composite(CMC)structural parts in the aero-engines.The silicon carbide(SiC)whisker toughening phase and c-AlPO_(4) bonding phase are firstly used to improve the service life of novel tri-layer Yb_(2)Si_(2)O_(7)/mullite/SiC EBCs in the burner rig test.The formation of penetrating cracks in Yb_(2)Si_(2)O_(7)/mullite/SiC coating caused the failure of coating at 1673 K.The SiC whiskers in mullite middle coating significantly inhibited the formation of penetrating cracks in Yb_(2)Si_(2)O_(7)/mullite/SiC coating,and efficiently prevented the oxidation of carbon fiber reinforced silicon carbide(C_(f)/SiC)samples for 360-min thermal cycles(24 times)with a weight loss of 6.19×10^(−3) g·cm^(−2).Although c-AlPO_(4) particles further improved the service life of SiC_(w)-mullite(SM)coating,the overflow of PO_(x) gas aggravated the formation and expansion of cracks in the Yb_(2)Si_(2)O_(7) outer coating,and caused the service life of overall Yb_(2)Si_(2)O_(7)/c-AlPO_(4)-SiC_(w)-mullite(ASM)/SiC coating to be slightly lower than that of Yb_(2)Si_(2)O_(7)/SM/SiC coating.This study guides the design of modified tri-layer EBCs with long service life in high-temperature and high-speed gas environment.
基金supported by the National Natural Science Foundation of China under Grant Nos.50802099 and 51072201
文摘A series of h-BN based composites with Yb_4Si_2O_7N_2 as a secondary phase were successfully synthesized by an in situ reaction hot pressing method. It was found that the relative density and room-temperature mechanical properties monotonically increased with increasing the content of Yb_4Si_2O_7N_2 from 20 to 50 vol%. When 50 vol% Yb_4Si_2O_7N_2 was introduced, the relative density of the composite reached 98.75%, and its flexural strength, compressive strength, fracture toughness, and hardness reached 338±10 MPa, 803±49 MPa, 2.06±0.06 MPa·m1/2, and 2.69±0.10 GPa, respectively. The strengthening effect of Yb_4Si_2O_7N_2 was mainly attributed to its high modulus and high hardness. Fine microstructure was also advantageous to strength and could lead to more tortuous crack propagation paths and then improve the fracture toughness of the composites simultaneously. Meanwhile, the composites maintained good machinability.
