保护气氛下反应烧结MoSi_2/Al_2O_3复合陶瓷

以金属Mo粉、Si粉和Al粉为原料,采用反应烧结法制备MoSi_2/Al_2O_3陶瓷复合材料,有效增强其室温韧性和强度,并揭示其电阻率随烧结温度变化规律。利用XRD和SEM分析不同温度烧结后MoSi_2/Al_2O_3复合材料试样的物相组成和微观结构;研究不同烧结温度下试样的力学和电学性能。结果表明:在氩气保护气氛下1 200℃时,MoSi_2/Al_2O_3陶瓷复合材料的各项性能较好,其显气孔率为20.7%,体积密度为4.8g/cm~3,断裂韧性值为9.72MPa·m1/2,电阻率为6.0×10~(-2)Ω·cm。所制备的MoSi_2/Al_2O_3陶瓷复合材料物相结构主要由Al_2O_3包覆MoSi_2形成的连续包覆相组成,组织结构均匀。烧结温度为1 200℃时,MoSi2导电相由弥散分布变成相互连接的网络状分布,且Al_2O_3包覆MoSi_2导电相的包覆层变薄,包裹的MoSi_2颗粒之间易于突破包覆相而互相连通,有助于降低电阻率。     

补加合金成分对铝合金熔体直接氧化生长的影响

为了控制DIMOX工艺中复合材料的生长速度和体积,采用压差法补加合金,使剩余铝合金熔体的成分得到调整并与正在氧化生长的Al₂O₃/Al复合材料层保持连续接触。试验研究了补加合金成分对Al-3Mg-10Si合金氧化生长的影响作用。结果表明:补加纯Al或低Mg、Si含量的铝合金,能够降低合金熔体的含镁量,缩短材料生长前沿合金熔体成分到达Al₂O₃-(Al,Mg)两相区的时间,促进传质过程,加速材料生长,有利于获取较大体积的复合材料。     

SiC颗粒强韧化MoSi2复合材料

通过湿法混料和热压烧结工艺成功地制备了20vo1%SiC_P/MoSi₂复合材料,并测定了其显微组织和力学性能。结果表明:SiC_P/MoSi₂复合材料主要由MoSi₂和SiC颗粒组成,还有少量的Mo₅Si₃,致密度为92.3% 。与MoSi₂相比,其室温抗弯强度提高了30.6%,断裂韧性提高了53%,1200℃的抗压强度提高了44%,1400℃的抗压强度提高了53%;其硬度、弹性模量等性能有较大提高。在Al₂O₃和SiC对磨盘上表现出极其优异的耐磨性能。SiC颗粒对MoSi₂的室温增韧、高温增强效果显著。     

钼网表面MoSi2涂层的制备及其1500℃高温氧化性能

钼网被广泛用作高温催化剂载体,但关于其高温防护涂层的制备及失效机制却鲜有报道.用包埋渗硅方法在钼网表面制备了MoSi2高温抗氧化涂层,并在静态大气环境中开展了1500℃恒温氧化试验.利用X射线衍射仪(XRD)、扫描电镜(SEM)、能谱分析(EDS)等对氧化前后涂层的微观形貌和组织结构进行了表征.结果表明:1500℃氧化2h,MoSi2涂层中的Si元素会发生选择性氧化,在涂层表面形成一层连续的、具有“自愈合”功能的熔融态SiO2保护膜,阻挡氧向基体一侧的扩散,展现出了良好的高温抗氧化性能;高温条件下,涂层中的Si元素会和钼基体发生界面扩散反应生成抗氧化性能差的Mo5Si3,同时MoSi2不断地和氧发生反应生成Mo5Si3和SiO2,当涂层中的MoSi2完全转化为Mo5Si3,涂层将快速氧化失效.     

Composition of alumina films grown on Si at low temperature with catalytic CVD

The X-ray photoelectron spectroscopy (XPS) measurements have been used to reveal the compositions of alumina (Al₂O₃) films formed on Si wafers using tri-methyl aluminium (TMA) and molecular oxygen (O₂) with catalytic chemical vapour deposition (Cat-CVD). The atomic ratio (O/Al) for Al₂O₃ samples formed at substrate temperature of 200-400 °C has been obtained to be 1.4 which is close to stoichiometry. The increase of growth rate at substrate temperatures below 200 °C and above 400 °C can be attributed to formation of aluminum oxides with non-stoichiometry and metallic aluminum incorporated in the films resulting from deficient oxygen. Angle resolved XPS measurements have revealed that the alumina/Si interface with no SiO₂ film has been obtained at substrate temperatures below 200 °C.     

Self-forming AlOx layer as Cu diffusion barrier on porous low-k film

The copper diffusion barrier properties of an ultrathin self-forming AlO_x layer on a porous low-k film have been investigated. Cu-3 at.% Al alloy films were directly deposited onto porous low-k films by co-sputtering, followed by annealing at various temperatures. Transmission electron microscopy micrographs showed that a ∼ 5 nm layer self-formed at the interface after annealing. X-ray photoelectron spectroscopy analysis showed that this self-formed layer was Al₂O₃. Sharp declines of the Cu and Si concentrations at the interface indicated a lack of interdiffusion between Cu and the porous low-k film for annealing up to 600 °C for 30 min. The leakage currents from Cu(Al)/porous low-k/Si structures were similar to as-deposited films even after a 700 °C, 5 min anneal while a Cu sample without Al doping failed at lower temperatures. Adding small amounts of Al to bulk Cu is an effective way to self-form copper diffusion layer for advanced copper interconnects.     

MoSi2发热元件的微观结构对使用性能的影响

通过对ＭｏＳｉ２发热元件的微观结构分析，探影响使用性能的微观因素。研究发现ＭｏＳｉ２结晶相细小，尤以Ａｌ、Ｓｉ等为主的氧化物组成的玻璃相细等、分布均匀，孔洞少是提高使用性能的必要条件。     

Influence of calcination temperature of kaolin on the structure and properties of final geopolymer

In this paper, the structure of two types of metakaolins from kaolin calcined at 800 and 900 °C, respectively, and the obtained geopolymer were systematically characterized. It was found that calcination temperature had little effect on the environment of silicon atoms but had great effect on that of aluminum ones. ²⁷Al NMR analysis showed that tetrahedral aluminums in the metakaolin from kaolin calcined at 800 and 900 °C were in different environment, of the type AlQ₃(3Si) and AlQ₄(4Si), respectively, leading to different environment of aluminum atoms in the resulted geopolymer. Aluminum atoms in the geopolymer based on metakaolin from kaolin calcined at 800 °C were in the types of tetrahedral and octahedral, and silicon atoms were in the types of tetrahedral Q₄(3Al) together with a small amount of Q₄(0Al). However, geopolymer based on metakaolin from kaolin calcined at 900 °C consisted of Q₄(4Si) unit aluminum and Q₄(3Al) unit silicon. The results revealed that the calcination temperature had a great effect on environment of the aluminum atoms of the metakaolin, thus led to the different structure and properties including mechanical strength and thermal conductivity of the post obtained geopolymer.     

合金元素对 Nb2Mo2Si合金相平衡及Nb2 Nb 5Si 3共晶组织形态的影响

采用电弧熔炼法制备了 Nb220Si210Mo、Nb220Si210Mo23M (M = Cr , Al , Ti) (原子分数) 四种 Nb2Mo2Si基超高温合金。利用 SEM、EDS、XRD等实验技术对铸造合金的相组成与组织形态进行了观察和分析。Nb220Si210Mo 合金由铌固溶体 (Nb SS) 与βNb 5Si 3化合物两相构成 , 其铸造组织包含大量片层状共晶 (Nb SS 2βNb 5Si 3) 组织。少量合金元素 Cr (3 at %) 能够改变 Nb220Si210Mo 合金的相平衡关系 , Nb220Si210Mo23Cr 的铸造组织中不仅存在 Nb SS和βNb 5Si 3 , 而且还出现少量 Cr 2Nb相 ; 而添加合金元素 Al、Ti (3 at %) 并不改变 Nb220Si210Mo 合金的相平衡关系。添加 Cr 使 Nb SS 2 βNb 5Si 3共晶组织失去了平直片层特征 ; Al 有利于共晶组织中片层状共晶形成 ; 添加 Ti使共晶组织呈现羽毛状特征。合金化使 Nb与βNb 5Si 3的晶格常数发生变化 : Nb的晶格常数均变小; Nb220Si210Mo23Cr合金中βNb 5Si 3的 c/ a值减小 , 其它 3种合金中βNb 5Si 3的 c/ a值增大。     

Growth of permanganate conversion coating on 2024-Al alloy

The growth of permanganate conversion coating on aluminum 2024-T3 alloy has been studied by characterizing, with scanning Auger microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy, the coatings formed by immersion of the alloy in the coating bath (containing KMnO₄ and Na₂B₄O₇, pH 9.1) for different periods of time and at different temperatures. At room temperature, during the first 1-5 min of immersion, MnO₂ deposits are formed only on the second-phase intermetallic particles (of Al-Cu-Mg and Al-Cu-Fe-Mn types), but the coating starts to develop on the Al matrix surface after 5-10 min. The coating slows down and stops after about 150 min, with a thinner deposit over the alloy matrix. The process is accelerated at higher temperatures, for example at 68 °C it self-limits after about 3 min. The electrochemical growth process appears to follow that established for the chromate conversion coatings, although XPS does not detect significant MnO₄⁻ incorporation into the permanganate coatings.     

A new filler metal with low contents of Cu for high strength aluminum alloy brazed joints

The effect of Cu with low contents of 10, 12, 15 wt.% on the microstructure and melting point of Al–Si–Cu–Ni alloy has been investigated. Results showed that low-melting-point properties of Al–Si–Cu–Ni alloys with low contents of Cu were attributed to disappearance of Al–Si binary eutectic reaction and introduction of Al–Si–Cu–Ni quaternary reaction. With raising Cu content from 10 to 15 wt.%, the amount of complex eutectic phases formed during low temperature reactions (Al–Cu, Al–Si–Cu and Al–Si–Cu–Ni alloy reactions) increased and the melting temperature of Al–Si–Cu–Ni filler metals declined. Brazing of 6061 aluminum alloy with Al–10Si–15Cu–4Ni (all in wt.%) filler metal of a melting temperature range from 519.3 to 540.2 °C has been carried out successfully at 570 °C. Sound joints can be obtained with Al–10Si–15Cu–4Ni filler metal when brazed at 570 °C for holding time of 60 min or more, and achieved high shear strength up to 144.4 MPa.     

Preparation and Characterization of Multilayered Al/Fe-Mo-Si-B Alloy with Nanostructure

The bulk multilayered Al/Fe-Mo-Si-B alloy with nanostructure was prepared by annealing the alternate layers consisting of metal Al and amorphous (Fe0.99,Mo0.01)78 Si9B13 alloy ribbons for 30 min at 873 K under pressure of 3~5.5 GPa. The structures and grain sizes of the Fe-MoSi-B nanocrystalline alloy were measured and analyzed. It was found that the pressure could restrain the growth of the grains and influence the formation of phases. The dependence of grain sizes for α-Fe(Mo,Si) and Fe2B on pressure was given. The morphologies of Al/Fe-Mo-SiB nanocrystalline alloy intedeces were observed by SEM. Two intedecial phases formed at various pressures were established by TEM and EDAX, and an unknown Fe-rich one with nanostructure was also observed. The dependence of the intedecial phases on pressure and its formation and growth mechanism were discussed     

Spray deposition of an iron aluminide

High velocity oxyfuel (HVOF) spray forming of an iron aluminide [Fe–12.5 Al–2.93 Ni–0.02 B (wt%), containing 300 p.p.m. oxygen], followed by heat treatment for 24 h at 500°C, 18 h at 600°C and 20 min at 800°C, and multipass hot rolling at 800°C has been studied. Three different thicknesses (0.43, 0.93 and 1.33 mm) of sprayed deposit were produced by spraying for different times (approximately 10, 20 and 30 min). The spray-deposited layers exhibited some oxide and some porosity. This porosity was reduced by heat treatment. The as deposited layer had a high degree of B2 order, and a B2 antiphase domain size of 4.5 nm. On hot rolling this material to a reduction of 38%, it was found to be more susceptible to edge cracking than similar material processed by an ingot–extrusion–hot rolling route. In heat treatment, the aluminide-sprayed layer formed a non-protective Fe2O3 oxide, rather than the usual Al2O3 that forms on the binary alloy. This is attributable to the Ni content of the iron aluminide powder employed. © 1998 Kluwer Academic Publishers     

Influence of TiC additions on the oxidation behaviour of Si3N4-based ceramics

The oxidation behaviour in air of Si3N4 ceramics containing Y2O3 and Al2O3 as sintering aids, with and without a dispersion of TiC particles, has been studied between 1200 and 1400 °C. The influence of TiC additions on the oxidation kinetics is discussed in comparison with the results obtained for the Si3N4–Y2O3–Al2O3 reference material. However, in all cases and within the experimental temperature range, the oxidation kinetics were observed to be of a parabolic type. The microstructure of the oxide scales formed, which has been characterized by scanning and transmission electron microscopy, was observed to depend on the oxidation temperature and the initial composition of the material. © 1998 Chapman & Hall     

Investigation of thermal stability of Mo thin-films as the buffer layer and various Cu metallization as interconnection materials for thin film transistor-liquid crystal display applications

Cu/Mo/Si multi-layer structures were fabricated to investigate diffusion behaviors and thermal stability between Cu and Mo. Physical vapor deposition (PVD), chemical vapor deposition, electroplating and electrolessplating were used to grow 100 nm thick Cu films as interconnection materials, and radio-frequency sputtering system was introduced to grow 37.5 nm thick Mo films as a buffer layer. All Cu/Mo/Si multi-layer specimens were annealed at 350 to 700 °C for 30 min. When the annealing temperature was over 600 °C, the Cu diffused through Mo into Si, and the Cu₃Si phase and Mo-Si intermetallic compounds formed at the Mo/Si interface. The diffusion mechanism is the grain boundary diffusion. The results indicate that Cu film deposited by PVD had best crystallinity, lower roughness, large adhesive energy and resistivity. The values of the resistivity, diffusion activity energy and large adhesive energy are 5.47 μΩ-cm, 0.948 eV and 2.46 N/m, respectively.     

Formation and thermal stability of aluminium nanoparticles synthesized via yttrium ion implantation into sapphire

Yttrium ion implantation of 1 1 2 3 alumina resulted in the formation of metallic aluminium–yttrium, face centred cubic (a0=0.41 nm) spherical nanocrystals ( 12 nm in diameter) embedded in an amorphous matrix. A fluence of 5×1016Y+/cm2 implanted at ambient temperature and accelerating energies of 150 or 170 keV yielded this result. Crystalline nanoparticles were not present in the amorphous matrix for implantations done with identical conditions but lower energy (100 keV). Substrates implanted at 150 keV were annealed in laboratory air for times ranging from 20 to 90 min and temperatures ranging from 1000 to 1400°C. A clear progression of morphologies resulted from these annealing treatments. A 1000°C, 90 min anneal produced 13% recrystallization of the amorphous region and induced the formation of crystallites of a metastable Y–Al alloy. An 1100°C, 90 min anneal demonstrated 40% recrystallization of the amorphous region, accompanied by the formation of partially aligned internal grains of Y2O3. Electron diffraction shows that the Y–Al alloy crystallites which formed in the 1000°C anneal are also present at 1100°C. A highest temperature anneal of 1400°C, 60 min induced essentially complete recrystallization of the amorphous phase, the dissolution of the metastable Y–Al alloy, the retention of the internal yttria grains, and the formation of partially oriented external grains of yttria resulting from the segregation of yttrium to the substrate surface.     

MOSi2材料的强韧化研究进展

综述了近年来MoSi2材料的强韧化研究进展,主要包括复合化Si3 N4、ZrO2、SiC、TiC、La2O3、多种增强体和合金元素Al、Re、Nb对MoSi2性能的影响及强韧化机理,并展望了MoSi2材料的强韧化发展趋势.     

Effect of NiO and/or TiO2 mullite formation and microstructure from gels

Polymeric and colloidal gels with a constant molar ratio of (Al+Ni and/or Ti)/Si=3/1 and various (Al/Ni and/or Ti) ratios (up to 21.42 mol% NiO+TiO2) were prepared and used to study the effect of the precursor chemical homogeneity on mullite formation processes and the resulting microstructure. Both kinds of gel precursors were preheated at 750°C for 3 h in order to obtain appropriate gel-derived glasses for further thermal processing. After annealing for several time periods at temperatures between 750 and 1500°C, differences in crystallization pathways were observed. Polymeric gels crystallized Al–Si and NiAl2O4 spinels from the amorphous form at temperatures in the range between 900 and 1000°C, depending on the amount of aluminium substitution. Mullite formation was initiated at temperatures between 1100 and 1200°C, except for the higher substituted 3:2 mullite in which it was produced at 1000°C. In constrast, -Al2O3 and NiAl2O4 spinel were the first crystalline phases identified at 750°C in specimens from colloidal gels, whereas mullite was formed at temperatures higher than 1200°C. In specimens with high substitution, mullite was observed at lower temperatures. Although the sequences of reaction from either kind of gel were rather different, mainly at low temperatures (as could be inferred from the chemical homogeneity attained in both gel-derived glasses), the final set of crystalline phases after long annealing at 1400°C was quite similar. Differences in the microstructure of specimens from either type of gel precursor after annealing at 1400°C concerned the size of mullite particles and the presence of secondary phases in specimens derived from colloidal precursors. © 1998 Kluwer Academic Publishers     

Microstructure of hot dip coated Fe–Si steels

Hot dipping is a coating technique pre-eminently used in industry to galvanize machine parts or steel sheets for constructional applications. However, other hot dipping applications have been developed in order to have a positive effect on specific material properties. For instance, in Fe–Si electrical steels, a Si/Al rich top layer is applied and followed by diffusion annealing to increase the electrical resistivity of the material and consequently, lower the power losses. Hot dipped aluminised mild steels have been developed with increased corrosion resistance for high temperature applications by the development of a dense Al₂O₃ layer. Regardless of the type of steel coated and the intended application, after the interaction between the molten Al and the solid material, three constituents are formed: Fe₂Al₅, FeAl₃ and an Al-rich alloy. The structural morphology, which can negatively affect the wear resistance and the thermal stability, also appears to be highly dependent on the chemical composition of the base material. To study thermo-mechanical and compositional effects on the coating behavior after hot dipping, cold rolling with different reductions was performed on different Fe–Si materials. It was demonstrated that hardness differences between the layers caused crack formation inside the Fe₂Al₅ layer during subsequent deformation. The present work reports the results obtained on materials that were hot dipped in a hypo-eutectic Al + 1 wt.% Si bath. The bath was used to coat Fe–Si steel substrates with variable silicon content with dipping times ranging from 1 to 20 s. Before dipping, the samples were heated to 700 °C and subsequently immersed in the liquid bath at temperatures of 710 °C, 720 °C and 740 °C. To further evaluate the interactions between Al, Si and Fe, a diffusion annealing treatment at 1000 °C was performed. The main diffusing elements during this treatment are Al and Fe, although small variations in Si content are also observed. At a certain distance from the surface, voids were observed, which most probably can be related to the Kirkendall effect. A characterization of the formed intermetallics was performed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD) and Electron Backscatter diffraction (EBSD).     

Solid state synthesis and properties of monoclinic celsian

Monoclinic celsian of Ba0.75Sr0.25Al2Si2O8 (BSAS-1) and Ba0.85Sr0.15Al2Si2O8 (BSAS-2) compositions have been synthesized from metal carbonates and oxides by solid state reaction. A mixture of BaCO3, SrCO3, Al2O3, and SiO2 powders was precalcined at 900–940 °C to decompose the carbonates followed by hot pressing at 1300 °C. The hot pressed BSAS-1 material was almost fully dense and contained the monoclinic celsian phase, with complete absence of the undesirable hexacelsian as indicated by X-ray diffraction. In contrast, a small fraction of hexacelsian was still present in hot pressed BSAS-2. However, on further heat treatment at 1200 °C for 24 h, the hexacelsian phase was completely eliminated. The average linear thermal expansion coefficients of BSAS-1 and BSAS-2 compositions, having the monoclinic celsian phase, were measured to be 5.28 × 10–6 °C–1 and 5.15 × 10–6 °C–1, respectively, from room temperature to 1200°C. The hot-pressed BSAS-1 celsian showed room temperature flexural strength of 131 MPa, elastic modulus of 96 GPa and was stable in air up to temperatures as high as 1500 °C.