Novel MoAlB composites reinforced with 5–15 vol% SiC have been firstly prepared and characterized in the present study. The SiC reinforcement is stable with MoAlB at a sintering temperature of 1200 ℃ in Ar. The 5 vo...Novel MoAlB composites reinforced with 5–15 vol% SiC have been firstly prepared and characterized in the present study. The SiC reinforcement is stable with MoAlB at a sintering temperature of 1200 ℃ in Ar. The 5 vol% SiC/MoAlB composite exhibited improved mechanical properties and enhanced oxidation resistance. A flexural strength of 380 MPa and a Vickers hardness of 12.7 GPa were achieved and increased by 24% and 51%, respectively, as compared with those for MoAlB, indicating the enhanced strengthening effect of SiC. Cyclic oxidation tests at 1200 and 1300 ℃ for 10 h in air showed that the 5 vol% SiC/MoAlB composite has better oxidation resistance than MoAlB due to the formation of a dense and continuous scale composed of Al_(2)O_(3) and SiO_(2), which prevents the oxygen inward diffusion and the evaporation of oxides. We expect that the general strategy of second phase reinforcing for materials will help to widen the applications of MoAlB composites.展开更多
MoAlB as a typical member of MAB phases has attracted much-growing attention due to its unique properties.However,the low production of MoAlB powders limits its further development and potential applications.In the pr...MoAlB as a typical member of MAB phases has attracted much-growing attention due to its unique properties.However,the low production of MoAlB powders limits its further development and potential applications.In the present work,the ultra-fast preparation of high-purity MoAlB powders in a few seconds is achieved by self-propagating high-temperature synthesis(SHS)using a raw powder mixture at an atomic ratio of Mo:Al:B=1:1.3:1.SHS reaction mechanism is obtained by analyzing the corresponding composition changes of starting materials.Furthermore,the thermodynamic prediction for the SHS reaction is consistent with the present experiments,where the preparation of MoAlB also conforms to two common self-propagating conditions of the SHS.The enthalpy vs.temperature curve shows that the adiabatic temperature of the reaction decreases with the amount of excuse Al increasing but increases when pre-heating the reactants.Also,this thermodynamic calculation provides a new idea for the preparation of other MAB phases by the SHS.展开更多
In the context of the fifth-generation(5G)smart era,the demand for electromagnetic wave(EMW)-absorbing materials has become increasingly prominent,so it is necessary to explore promising candidate materials.This work ...In the context of the fifth-generation(5G)smart era,the demand for electromagnetic wave(EMW)-absorbing materials has become increasingly prominent,so it is necessary to explore promising candidate materials.This work focuses on the exploration of the material absorbing properties of a MoAlB MAB(MAB represents a promising group of alternatives,where M stands for a transition metal,A typically denotes Al,and B is boron)phase system.First,the first-principles calculations were performed to reveal the unique crystal and layered structure of the MoAlB ceramics and to predict their potential for use as an EMW absorption material.Subsequently,a series of MoAlB ceramics were synthesized at temperatures ranging from 800 to 1300℃,and the influence of temperature on the phase compositions and microstructures of the obtained MoAlB ceramics was characterized and analyzed.Finally,the practical EMW absorption performance of the prepared MoAlB ceramics was evaluated via a combination of experiments and radar cross-sectional calculations.The MoAlB sample synthesized at 900℃ exhibits superior EMW absorption performance,achieving an impressive minimum reflection loss(RL)of−50.33 dB.The unique layered structure and good electrical conductivity of the MoAlB samples are the main reasons for their enhanced wave absorption performance,which provides interfacial polarization and multiple dielectric loss mechanisms.Therefore,this study not only contributes to the understanding of the preparation of MoAlB materials but also provides potential guidance for their utilization in the realm of electromagnetic wave absorption.展开更多
基金This work was supported by the National Natural Science Foundation of China(No.51772020)Beijing Government Funds for the Constructive Project of Central Universities.
文摘Novel MoAlB composites reinforced with 5–15 vol% SiC have been firstly prepared and characterized in the present study. The SiC reinforcement is stable with MoAlB at a sintering temperature of 1200 ℃ in Ar. The 5 vol% SiC/MoAlB composite exhibited improved mechanical properties and enhanced oxidation resistance. A flexural strength of 380 MPa and a Vickers hardness of 12.7 GPa were achieved and increased by 24% and 51%, respectively, as compared with those for MoAlB, indicating the enhanced strengthening effect of SiC. Cyclic oxidation tests at 1200 and 1300 ℃ for 10 h in air showed that the 5 vol% SiC/MoAlB composite has better oxidation resistance than MoAlB due to the formation of a dense and continuous scale composed of Al_(2)O_(3) and SiO_(2), which prevents the oxygen inward diffusion and the evaporation of oxides. We expect that the general strategy of second phase reinforcing for materials will help to widen the applications of MoAlB composites.
基金supported by the National Natural Science Foundation of China(Grant No.51972080)the National Key R&D Program of China(Grant No.2018YFA0702802)Shenzhen Science and Technology Program.
文摘MoAlB as a typical member of MAB phases has attracted much-growing attention due to its unique properties.However,the low production of MoAlB powders limits its further development and potential applications.In the present work,the ultra-fast preparation of high-purity MoAlB powders in a few seconds is achieved by self-propagating high-temperature synthesis(SHS)using a raw powder mixture at an atomic ratio of Mo:Al:B=1:1.3:1.SHS reaction mechanism is obtained by analyzing the corresponding composition changes of starting materials.Furthermore,the thermodynamic prediction for the SHS reaction is consistent with the present experiments,where the preparation of MoAlB also conforms to two common self-propagating conditions of the SHS.The enthalpy vs.temperature curve shows that the adiabatic temperature of the reaction decreases with the amount of excuse Al increasing but increases when pre-heating the reactants.Also,this thermodynamic calculation provides a new idea for the preparation of other MAB phases by the SHS.
基金the Joint Fund of R&D Program of Henan Province(No.222301420002)the Outstanding Youth Fund of Henan Province(No.242300421009)+3 种基金the National Natural Science Foundation of China(No.U21A2064)the Scientific and Technological Innovation Talents in Colleges and Universities in Henan Province(No.22HASTIT001)the Henan Province Key Research Project for Higher Education Institutions(No.23B430017)Bingbing Fan thanks the China Scholarship Council(CSC,No.202207045028)for an academic visitor scholarship,and Wei Li is grateful for the financial support from the Technical University of Darmstadt.
文摘In the context of the fifth-generation(5G)smart era,the demand for electromagnetic wave(EMW)-absorbing materials has become increasingly prominent,so it is necessary to explore promising candidate materials.This work focuses on the exploration of the material absorbing properties of a MoAlB MAB(MAB represents a promising group of alternatives,where M stands for a transition metal,A typically denotes Al,and B is boron)phase system.First,the first-principles calculations were performed to reveal the unique crystal and layered structure of the MoAlB ceramics and to predict their potential for use as an EMW absorption material.Subsequently,a series of MoAlB ceramics were synthesized at temperatures ranging from 800 to 1300℃,and the influence of temperature on the phase compositions and microstructures of the obtained MoAlB ceramics was characterized and analyzed.Finally,the practical EMW absorption performance of the prepared MoAlB ceramics was evaluated via a combination of experiments and radar cross-sectional calculations.The MoAlB sample synthesized at 900℃ exhibits superior EMW absorption performance,achieving an impressive minimum reflection loss(RL)of−50.33 dB.The unique layered structure and good electrical conductivity of the MoAlB samples are the main reasons for their enhanced wave absorption performance,which provides interfacial polarization and multiple dielectric loss mechanisms.Therefore,this study not only contributes to the understanding of the preparation of MoAlB materials but also provides potential guidance for their utilization in the realm of electromagnetic wave absorption.
