The mechanical and thermal properties of Y_(4)Al_(2)O_(9)were predicted using a combination of first-principles and chemical bond theory(CBT)calculations.Density functional theory(DFT)computations were performed for t...The mechanical and thermal properties of Y_(4)Al_(2)O_(9)were predicted using a combination of first-principles and chemical bond theory(CBT)calculations.Density functional theory(DFT)computations were performed for the structural,mechanical,and thermal properties,and the results were confirmed by chemical bond theory.Based on the calculated equilibrium crystal structure,heterogeneous bonding nature has been revealed,i.e.,Al-O bonds are stronger than Y-O bonds.Low second-order elastic constants c44,c55,and c66 demonstrate the low shear deformation resistance.Low G/B ratio suggests that Y_(4)Al_(2)O_(9)is a damage tolerant ceramic.Y_(4)Al_(2)O_(9)shows anisotropy in elastic behavior based on the discussion of direction dependence of Young’s modulus.The hardness is predicted to be 10.2 GPa from calculated elastic moduli.The thermal expansion coefficient(TEC)calculated by chemical bond theory is 7.51×10^(-6)K^(-1).In addition,the minimum thermal conductivity of Y_(4)Al_(2)O_(9)is estimated to be 1.13 W·m^(-1)·K^(-1),and the thermal conductivity decreases with temperature as 1305.6/T.展开更多
In our previous work,anisotropic chemical bonding,low shear deformation resistance,damage tolerance ability,low thermal conductivity,and moderate thermal expansion coefficient of Y_(4)Al_(2)O_(9)(YAM)were predicted.In...In our previous work,anisotropic chemical bonding,low shear deformation resistance,damage tolerance ability,low thermal conductivity,and moderate thermal expansion coefficient of Y_(4)Al_(2)O_(9)(YAM)were predicted.In this work,phase-pure YAM powders were synthesized by solid-state reaction between Y2O3 and Al_(2)O_(3)and bulk YAM ceramics were prepared by hot-pressing method.Lattice parameters and a new set of X-ray powder diffraction data were obtained by Rietveld refinement.The mechanical and thermal properties of dense YAM ceramics were investigated.The measured elastic moduli are close to the theoretical predicted values and the stiffness can be maintained up to 1400℃.The flexural strength and fracture toughness are 252.1±7.3 MPa and 3.36±0.20 MPa·m^(1/2),respectively.Damage tolerance of YAM was also experimentally proved.The measured average linear thermal expansion coefficient(TEC)of YAM is 7.37×10^(-6)K^(-1),which is very close to the theoretical predicted value.Using high-temperature X-ray diffraction(XRD)analysis,volumetric TEC is determined(23.37±1.61)×10^(-6)K^(-1)and the anisotropic TEC areaa=7.34×10^(-6)K^(-1),ab=7.54×10^(-6)K^(-1),andac=7.61×10^(-6)K^(-1).展开更多
基金supported by the National Outstanding Young Scientist Foundation for Y.C.Zhou under Grant No.59925208the National Natural Science Foundation of China under Grant Nos.50832008 and U1435206.
文摘The mechanical and thermal properties of Y_(4)Al_(2)O_(9)were predicted using a combination of first-principles and chemical bond theory(CBT)calculations.Density functional theory(DFT)computations were performed for the structural,mechanical,and thermal properties,and the results were confirmed by chemical bond theory.Based on the calculated equilibrium crystal structure,heterogeneous bonding nature has been revealed,i.e.,Al-O bonds are stronger than Y-O bonds.Low second-order elastic constants c44,c55,and c66 demonstrate the low shear deformation resistance.Low G/B ratio suggests that Y_(4)Al_(2)O_(9)is a damage tolerant ceramic.Y_(4)Al_(2)O_(9)shows anisotropy in elastic behavior based on the discussion of direction dependence of Young’s modulus.The hardness is predicted to be 10.2 GPa from calculated elastic moduli.The thermal expansion coefficient(TEC)calculated by chemical bond theory is 7.51×10^(-6)K^(-1).In addition,the minimum thermal conductivity of Y_(4)Al_(2)O_(9)is estimated to be 1.13 W·m^(-1)·K^(-1),and the thermal conductivity decreases with temperature as 1305.6/T.
基金supported by the National Outstanding Young Scientist Foundation for Y.C.Zhou under Grant No.59925208the National Natural Science Foundation of China under Grant Nos.50832008 and U1435206.
文摘In our previous work,anisotropic chemical bonding,low shear deformation resistance,damage tolerance ability,low thermal conductivity,and moderate thermal expansion coefficient of Y_(4)Al_(2)O_(9)(YAM)were predicted.In this work,phase-pure YAM powders were synthesized by solid-state reaction between Y2O3 and Al_(2)O_(3)and bulk YAM ceramics were prepared by hot-pressing method.Lattice parameters and a new set of X-ray powder diffraction data were obtained by Rietveld refinement.The mechanical and thermal properties of dense YAM ceramics were investigated.The measured elastic moduli are close to the theoretical predicted values and the stiffness can be maintained up to 1400℃.The flexural strength and fracture toughness are 252.1±7.3 MPa and 3.36±0.20 MPa·m^(1/2),respectively.Damage tolerance of YAM was also experimentally proved.The measured average linear thermal expansion coefficient(TEC)of YAM is 7.37×10^(-6)K^(-1),which is very close to the theoretical predicted value.Using high-temperature X-ray diffraction(XRD)analysis,volumetric TEC is determined(23.37±1.61)×10^(-6)K^(-1)and the anisotropic TEC areaa=7.34×10^(-6)K^(-1),ab=7.54×10^(-6)K^(-1),andac=7.61×10^(-6)K^(-1).
