Researching for interphase materials that can protect SiC fibers from oxygen and water vapor attacks has become one of the most important issues for the applications of SiC_f/SiC composites in high-temperature combust...Researching for interphase materials that can protect SiC fibers from oxygen and water vapor attacks has become one of the most important issues for the applications of SiC_f/SiC composites in high-temperature combustion environment. However, such kinds of interphase materials are not available yet. Herein,we report theoretically predicted properties of two promising interphase materials Y_5Si_3 C and Y_3Si_2C_2.Although crystallizing in different structures, they share the common features of layered structure,anisotropic chemical bonding, anisotropic electrical and mechanical properties, and low shear deformation resistance. The bulk moduli for Y_5Si_3C and Y_3Si_2C_2 are 78 and 93 GPa, respectively; while their shear moduli are 52 and 50GPa, respectively. The maximum to minimum Young's modulus ratios are1.44 for Y_5Si_3C and 3.27 for Y_3Si_2C_2. Based on the low shear deformation resistance and low Pugh's ratios(G/B = 0.666 forY_5Si_3C and 0.537 for Y_3Si_2C_2; G: shear modulus; B: bulk modulus), they are predicted as damage tolerant and soft ceramics with predicted Vickers hardness of 9.6 and 6.9 GPa, respectively.The cleavage plane and possible slip systems are(000 l) and(0001)[1120] and(1010)[0001] forY_5Si_3C,and those for Y_3Si_2C_2 are {h00} and(010)[101]. Since the oxidation products are water-vapor resistant Y2 Si2 O7, Y2 SiO5 and/or Y_2 O_3 upon oxidation, and the volume expansions are ca 140% and ca 26% for Y_5Si_3C and Y_3Si_2C_2, they are expected to seal the interfacial cracks in SiC_f/SiC composites. The unique combination of easy cleavage, low shear deformation resistance, volume expansions upon oxidation, and the resistance of the oxidation products to water vapor attack warrant them promising as interphase materials of SiC_f/SiC composites for water-vapor laden environment applications.展开更多
The substitution of TiO_(2)for SiO_(2)in Y_(2)O_(3)-Li_(2)O-Al_(2)O_(3)-SiO_(2)(YLAS)glass-ceramics significantly altered their crystallization behavior and properties.Introducing TiO_(2)reduced the glass transition t...The substitution of TiO_(2)for SiO_(2)in Y_(2)O_(3)-Li_(2)O-Al_(2)O_(3)-SiO_(2)(YLAS)glass-ceramics significantly altered their crystallization behavior and properties.Introducing TiO_(2)reduced the glass transition temperature while increasing the crystallization peak temperature and lowering activation energy,which facilitated crystallization.The crystal growth shifted from three-dimensional to two-dimensional,and the primary phases transitioned from Al_(9.83)Zr_(0.17)and Y_(2)Si_(2)O_(7)to Y_(4.67)(SiO_(4))_(3)O,though crystal morphology remained unchanged.Grain size increased with higher crystallization temperatures.Mechanically,Vickers hardness slightly decreased(from 796 to 784 Hv),while bending strength improved(from 141 to 146 MPa),suggesting that TiO_(2)enhanced toughness without compromising structural integrity.The strength of the glass can be further improved through two-step ion exchange,but excessive crystallization can lead to cracks on the glass surface due to excessive surface compressive stress,resulting in a decrease in bending strength.These findings provide critical insights for optimizing YLAS glass-ceramics for advanced applications.展开更多
基金supported financially by the National Natural Science Foundation of China (Nos. U1435206 and 51672064)the Beijing Municipal Science & Technology Commission (No. D161100002416001)
文摘Researching for interphase materials that can protect SiC fibers from oxygen and water vapor attacks has become one of the most important issues for the applications of SiC_f/SiC composites in high-temperature combustion environment. However, such kinds of interphase materials are not available yet. Herein,we report theoretically predicted properties of two promising interphase materials Y_5Si_3 C and Y_3Si_2C_2.Although crystallizing in different structures, they share the common features of layered structure,anisotropic chemical bonding, anisotropic electrical and mechanical properties, and low shear deformation resistance. The bulk moduli for Y_5Si_3C and Y_3Si_2C_2 are 78 and 93 GPa, respectively; while their shear moduli are 52 and 50GPa, respectively. The maximum to minimum Young's modulus ratios are1.44 for Y_5Si_3C and 3.27 for Y_3Si_2C_2. Based on the low shear deformation resistance and low Pugh's ratios(G/B = 0.666 forY_5Si_3C and 0.537 for Y_3Si_2C_2; G: shear modulus; B: bulk modulus), they are predicted as damage tolerant and soft ceramics with predicted Vickers hardness of 9.6 and 6.9 GPa, respectively.The cleavage plane and possible slip systems are(000 l) and(0001)[1120] and(1010)[0001] forY_5Si_3C,and those for Y_3Si_2C_2 are {h00} and(010)[101]. Since the oxidation products are water-vapor resistant Y2 Si2 O7, Y2 SiO5 and/or Y_2 O_3 upon oxidation, and the volume expansions are ca 140% and ca 26% for Y_5Si_3C and Y_3Si_2C_2, they are expected to seal the interfacial cracks in SiC_f/SiC composites. The unique combination of easy cleavage, low shear deformation resistance, volume expansions upon oxidation, and the resistance of the oxidation products to water vapor attack warrant them promising as interphase materials of SiC_f/SiC composites for water-vapor laden environment applications.
基金Funded by the China Building Material Federation Projects(Nos.20221JBGS06-19 and 2023JBGS02-01)。
文摘The substitution of TiO_(2)for SiO_(2)in Y_(2)O_(3)-Li_(2)O-Al_(2)O_(3)-SiO_(2)(YLAS)glass-ceramics significantly altered their crystallization behavior and properties.Introducing TiO_(2)reduced the glass transition temperature while increasing the crystallization peak temperature and lowering activation energy,which facilitated crystallization.The crystal growth shifted from three-dimensional to two-dimensional,and the primary phases transitioned from Al_(9.83)Zr_(0.17)and Y_(2)Si_(2)O_(7)to Y_(4.67)(SiO_(4))_(3)O,though crystal morphology remained unchanged.Grain size increased with higher crystallization temperatures.Mechanically,Vickers hardness slightly decreased(from 796 to 784 Hv),while bending strength improved(from 141 to 146 MPa),suggesting that TiO_(2)enhanced toughness without compromising structural integrity.The strength of the glass can be further improved through two-step ion exchange,but excessive crystallization can lead to cracks on the glass surface due to excessive surface compressive stress,resulting in a decrease in bending strength.These findings provide critical insights for optimizing YLAS glass-ceramics for advanced applications.
