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Journal of Materials Science & Technology 2012年第6期28卷 488-494页

作者： JieXie Xiaohui Wang yanchun zhou Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Graduate School Of Chinese Academy of Sciences Beijing 100039China Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials&Processing TechnologyBeijing 100076China

Titanate nanowires prepared by hydrothermal treatment of Ti02 in NaOH solution have attracted intensive attentions, but the formation mechanism is still under debate. Herein, we report an in-depth study on the formation mechanism through investigating the hydrothermal behavior of various Ti-containing precursors in basic solutions, including Ti, TiN, TiO2, Ti2SnC and Ti2AIN. Based on the results by means of X-ray diffraction （XRD）, transmission electron microscopy （TEM） and Raman spectroscopy, it is demonstrated that the crystal structure of the hydrothermal products is irrespective to the structure of the precursors or the types of basic solution （NaOH or KOH） in use. Alkali ions play an important role in the formation of titanate nanowires. The formation mechanism of the resultant titanate nanowires was proposed to be dissolution-crystallization mechanism.

关键词： Titanate nanowire Hydrothermal treatment Ti-containing precursors Formation mechanism

Secrets of high thermal emission of transition metal disilicides TMSi_(2)(TM=Ta,Mo)

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Journal of Materials Science & Technology 2021年第30期89卷 114-121页

作者： Huimin Xiang Fuzhi Dai yanchun zhou Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials and Processing TechnologyBeijing 100076China

TMSi_(2)(TM=Ta,Mo)are extensively used as thermal emissivity agents in high emission coatings due to their well-known"high"emissivity in infrared ***,there is a paucity of the high temperature(HT)emissivity property of these two ***,room temperature(RT)spectrometer measurements have demonstrated that the emittance in infrared range of two silicides was considerably ***,providing critical HT data and satisfactory elucidation on the emission incompatibility of TMSi_(2)is eagerly *** this contribution,combining first principles calculations and Drude model,the reflectance spectra of TMSi_(2)were predicted at both RT and *** with spectrometer measurements,the intrinsic emittance of silicides was relatively low in the entire investigated *** explain the incompatible emission behavior,two simplified models including the majority of high emissivity coating,SiO_(2),were ***,with SiO_(2)considered in simulations,no matter covered on the surface or blended in the composites,the emittance of the TMSi_(2)enhanced *** theoretical results demonstrate the non-negligible significance of oxides on the high temperature performance of silicides and provide the guidelines for improving the emission performance of silicides and searching for potential high emissivity agents.

关键词： Disilicide Optical properties Thermal emission First-principles calculations Drude model

Effects of Vacuum Ultraviolet Radiation on Atomic Oxygen Erosion of Polysiloxane/SiO_2 Hybrid Coatings

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Journal of Materials Science & Technology 2009年第4期25卷 483-488页

作者： Longfei Hu Meishuan Li yanchun zhou Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China Graduate Schoolof Chinese Academy of Sciences Beijing 100039 China

Polysiloxane/SiO2 hybrid coatings have been prepared on Kapton films by a sol-gel process. The erosion resistance of polysiloxane/Si02 （20 wt pct） coating was evaluated by exposure tests of vacuum ultraviolet radiation （VUV） and atomic oxygen beam （AO） in a ground-based simulation facility. The experimental results indicate that this coating exhibits better AO resistance than pure polysiloxane coating. The erosion yield （Ey） of the polysiloxane/Si02 （20 wt pct） hybrid coating is about 10-27 cm3/atom, being one or two orders of magnitude lower than that of polysiloxane. VUV radiation can affect the erosion process greatly. Under simultaneous AO and VUV exposure, the value of Ey of the polysiloxane/5iO2 （20 wt pct） hybrid coating increases by 3g% compared with that under single AO exposure.

关键词： Atomic oxygen Vacuum ultraviolet radiation Erosion yield Hybrid coating

Electronic structure,bonding characteristics,and mechanical behaviors of a new family of Si-containing damage-tolerant MAB phases M_(5)SiB_(2)(M=IVB-VIB transition metals)

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Journal of Advanced Ceramics 2022年第10期11卷 1626-1640页

作者： Na NI Hanchao ZHANG yanchun zhou School of Mechanical Engineering Shanghai Jiao Tong UniversityShanghai 200240China Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials&Processing TechnologyBeijing 100076China

MAB phases are layered ternary compounds with alternative stacking of transition metal boride layers and group A element *** now,most of the investigated MAB phases are concentrated on compounds with Al as the A element *** this work,the family of M_(5)SiB_(2)(M=IVB-VIB transition metals)compounds with silicon as interlayers were investigated by density functional theory(DFT)methods as potential MAB phases for high-temperature *** from the known Mo5SiB2,the electronic structure,bonding characteristics,and mechanical behaviors were systematically investigated and *** the composition of M_(5)SiB_(2) does not follow the general formula of experimentally reported(MB)_(2z)A_(x)(MB_(2))_(y)(z=1,2;x=1,2;y=0,1,2),their layered structure and anisotropic bonding characteristics are similar to other known MAB phases,which justifies their classification as new members of this material *** a result of the higher bulk modulus and lower shear modulus,Mo_(5)SiB_(2) has a Pugh’s ratio of 0.53,which is much lower than the common MAB *** was found that the stability and mechanical properties of M_(5)SiB_(2) compounds depend on their valence electron concentrations(VECs),and an optimum VEC exists as the criteria for *** hypothesized Zr and Hf containing compounds,i.e.,Zr_(5)SiB_(2) and Hf_(5)SiB_(2),which are more interesting in terms of high-temperature oxidation/ablation resistance,were found to be unfortunately *** cope with this problem,a new stable solid solution(Zr_(0.6)Mo_(0.4))_(5)SiB_(2) was designed based on VEC tuning to demonstrate a promising approach for developing new MAB phases with desirable compositions.

关键词： borides MAB phases density functional theory(DFT) thermodynamic stability electronic structure mechanical properties

Synthesis,Microstructure,and Property of Cr_2AlC

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Journal of Materials Science & Technology 2007年第6期23卷 I0001-I0002,721-746页

作者： Zhijun LIN yanchun zhou Meishuan LI Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China Graduate School of Chinese Academy of Sciences Beijing 100049 China

Cr2AlC is an unusual layered ternary ceramic that combines the merits of both metals and ceramics. The salient properties of Cr2AlC are strongly related to its bonding characteristics and microstructures. Synthesis, microstructure, and property of Cr2AlC are reviewed in this paper. First, theoretical calculations and physical properties are introduced. Then, the processing of Cr2AlC ceramic in both bulk form and thin films and their basic mechanical properties are summarized. Atomic-scale characterizations of Cr2AlC, as well as the microstructural relationships among Cr2AlC, AlCr5, and AlCr2 were achieved using a series of transmission electron microscopy （TEM） techniques. Moreover, high-temperature oxidation and hot corrosion behaviors of Cr2AlC were investigated by means of thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and TEM. Mechanism of the excellent high-temperature corrosion resistance of Cr2AlC is discussed based on systematic microstructural analyses. Finally, concise conclusions are drawn.

关键词： Cr2AlC First principles calculation Synthesis TEM High-temperature oxidation Hot corrosion

TEM Investigations on Layered Ternary Ceramics

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Journal of Materials Science & Technology 2007年第2期23卷 I0001-I0002,145-165页

作者： Zhijun LIN Meishuan LI yanchun zhou Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China Graduate School of Chinese Academy of Sciences Beijing 100039 China

Layered ternary ceramics represent a new class of solids that combine the merits of both metals and *** unique properties are strongly related to their layered crystal structures and microstructures. The combination of atomic-resolution Z-contrast scanning transmission electron microscopy （STEM） and transmission electron microscopy （TEM）, selected area electron diffraction （SAED）, convergent beam electron diffraction （CBED） represents a powerful method to link microstructures of materials to macroscopic properties, allowing layered ternary ceramics to be investigated in an unprecedented detail. Vicrostructural information obtained using TEM is useful in understanding the formation mechanism, layered stacking characteristics, and defect structures for layered ternary ceramics down to atomic-scale level; and thus provides insight into understanding the ＂Processing-Structure-Property＂ relationship of layered ternary ceramics. Transmission electron microscopic characterizations of layered ternary ceramics in Ti-Si-C, Ti-Al-C, Cr-Al-C, Zr-Al-C, Ta-Al-C and Ti-Al-N systems are reviewed.

关键词： Layered ternary ceramics MAX phase TEM STEM Interfacial structure

Theoretical Investigation on Mechanical and Thermal Properties of a Promising Thermal Barrier Material:Yb_3Al_5O_(12)

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Journal of Materials Science & Technology 2014年第7期30卷 631-638页

作者： yanchun zhou Huimin Xiang Zhihai Feng Science and Technology of Advanced Functional Composite Laboratory Aerospace Research Institute of Materials and Processing Technology

An investigation on the mechanical and thermal properties of Yb3Al5O12 is conducted by a combination of first- principles calculations and chemical bond theory calculation. Density functional theory （DFT） computations were performed for the structural, mechanical, and thermal properties, and the results are confirmed by chemical bond theory. Based on the calculated equilibrium crystal structure, heterogeneous bonding nature is revealed. The full set of elastic constants and mechanical properties of Yb3Al5O12 are presented for the first time. The thermal expansion coefficient of Yb3Al5O12 is calculated to be 7.5 × 10^-6 K-1 by chemical bond theory. In addition, the minimum thermal conductivity of Yb3Al5O12 is estimated to be 1.22 W m-t K-1, and the origin of such low thermal conductivity is discussed. Our theoretical results highlight the potential of Yb3Al5O12 as a prospective thermal barrier coating material.

关键词： Thermal barrier coating Ytterbium aluminum garnet First principles calculations Chemical bond theory

In-situ Synthesis of Ti_3AlC2/TiC-Al_2O_3 Composite from TiO_2-Al-C System

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Journal of Materials Science & Technology 2006年第4期22卷 455-458页

作者： Jixin CHEN Jialin LI yanchun zhou Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China

Ti3AlC2/TiC-Al2O3 composite was synthesized by a combustion reaction in TiO2-Al-C system. The effect of the compositions in raw materials on the products was investigated. Ti3AlC2/TiC-Al2O3 composite was obtained at the molar ratio of TiO2：Al：C=3.0：5.0～5.1：1.8～2.0. The reaction path for the 3TiO2-5Al- 2C system was proposed. Al3Ti, Ti203, TiO, and 6-Al2O3 are found to be transitional phases. Finally, Ti3AlC2/TiC-Al2O3 composite forms at～900℃ of furnace temperature. The measured Vickers hardness, fracture toughness, and flexural strength of the nearly dense sample from 3TiO2-5Al-2C are 13.3±1.1 GPa, 5.8±0.3 MPa.m^1/2, and 466±39 MPa, respectively.

关键词： Ti3AlC2 TiC Al2O3 TiO2-Al-C Reaction path

Y_5Si_3C and Y_3Si_2C_2: Theoretically predicted MAX phase like damage tolerant ceramics and promising interphase materials for SiC_f/SiC composites

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Journal of Materials Science & Technology 2019年第3期35卷 313-322页

作者： yanchun zhou Huimin Xiang Fu-Zhi Dai Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials & Processing Technology

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_*** 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, *** 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.

关键词： Y5Si3C Y3Si2C2 Interphase material Damage tolerant ceramics Electronic structure

General Trends in Electronic Structure, Stability, Chemical Bonding and Mechanical Properties of Ultrahigh Temperature Ceramics TMB_2(TM=transition metal)

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Journal of Materials Science & Technology 2015年第3期31卷 285-294页

作者： yanchun zhou Huimin Xiang Zhihai Feng Zhongping Li Science and Technology on Advance Functional Composite Laboratory Aerospace Research Institute of Materials & Processing Technology

The electronic structure, stability, chemical bonding and mechanical properties of 3d, 4d and 5d transition metal diboride TMB2 were investigated using first-principles calculations based on density functional theory. All the primary chemical bonds, i.e., metallic, ionic and covalent have contributions to the bonding of TMB2. The number of valence electrons of transition metals or the valence electron concentration(VEC) of TMB2 has strong effects on the lattice parameters, stability and mechanical properties of TMB2. Both lattice constants a and c decrease with VEC, but c decreases faster than a, which is attributed to the enhanced TM de B p(sp2) bonding. Bulk modulus B of TMB2 increases continuously with VEC due to the enhanced TM de B p(sp2) and TM dd bonding. Shear modulus G increases with VEC,reaching a maximum at VEC=3.33, and then decreases with further increase of VEC. YB2 and Mn B2 have low Young’s modulus and are predicted to have good thermal shock resistance. According to Pugh’s criterion(G/B < 0.571), Mn B2, Mo B2 and WB2are predicted as ductile or damage tolerant ultrahigh temperature ceramics(UHTCs).

关键词： Ultrahigh temperature ceramics Transition metal di