先驱体转化法制备SiBNC陶瓷

以三氯化硼、甲基氢二氯硅烷、六甲基二硅氮烷为起始原料,通过共缩合路径合成了SiBNC陶瓷先驱体-聚硼硅氮烷(PBSZ),将PBSZ直接在氮气气氛中高温热解可得SiBNC陶瓷.通过元素分析、XPS、NMR、FTIR和XRD等对所得先驱体及相应陶瓷的组成、结构和高温结晶性能进行了表征.结果表明,先驱体的骨架结构为-Si-N-B-,其中,B、N以硼氮六环形式存在,而C则以Si-CH3形式存在;该先驱体在1000℃下的陶瓷产率为63%,所得SiBNC陶瓷主要由Si3N4、BN、SiC等相组成,具有很好的热稳定性能,在1700℃时能够保持非晶态,在1850℃时部分结晶,且其在1500～1850℃间失重仅为3.8%左右.     

含锆聚硼硅氮烷的合成与表征

通过二氯二茂化锆(Zr(Cp)_2Cl_2)与液态聚硼硅氮烷(LPBS)反应制备了含锆聚硼硅氮烷(PBS-Zr),随着Zr(Cp)2Cl2投料比的增加,PBS-Zr的分子量明显增大,且出现了高分子量部分,陶瓷产率达到56%(质量分数)。红外光谱显示了含锆聚硼硅氮烷中N-H、Si-H等活性键明显减少。XPS谱图显示了PBS-Zr与Zr(Cp)_2Cl_2中Zr原子化学结构的差异。通过29SiMASNMR分析表明,陶瓷产物中Si元素主要以SiN3C、SiN42种结构存在。XRD分析显示,陶瓷产物在1200℃以下保持无定形状态,1600℃出现了Zr_2CN和Si3_N_4等微晶结构,但继续升温到1800℃,这2种微晶都发生了分解,转化为ZrB_2和SiC结晶相。     

SiBNC陶瓷的制备与高温行为研究

本文通过六甲基二硅氮烷与二氯甲基硅烷和三氯化硼共聚缩合的方法,合成了SiBNC陶瓷先驱体。通过FT-IR与XPS对先驱体的化学组成与结构进行了表征,平面B-N单元与Si-N单元的随机排列形成了以–Si-N-B-为骨架的理想先驱体结构。先驱体在氮气气氛下加热到800°C后转化成多元的SiBNC陶瓷,1000°C裂解后的陶瓷产率为50.1wt%。在氮气气氛下,得到的SiBNC陶瓷在1700°C下保持无定形,在1800°C下形成Si3N4 结晶。但在氩气气氛中,得到的SiBNC陶瓷在1800°C形成明显的β-SiC 与BNC2结晶。     

聚甲基硅倍半氧烷气凝胶的制备及相分离控制研究

以甲基三甲氧基硅烷(methyltrimethoxysilane, MTMS)为先驱体、二甲基亚砜(dimethylsulfoxide, DMSO)为溶剂,采用溶胶—凝胶法和超临界干燥技术制备了聚甲基硅倍半氧烷(polymethylsilsesquioxane, PMSQ)气凝胶。通过改变碱性催化剂氨水和DMSO的相对含量用量,获得了PMSQ凝胶时间的变化规律。PMSQ气凝胶具有典型的纳米多孔结构。凝胶时间随氨水用量的增加而缩短,随DMSO用量的增加而延长。DMSO含量越多,溶胶粘度变化越缓慢;氨水含量越多,粘度变化越快。不可水解基团–CH₃的存在将引起短链或环状Si–O–Si结构,造成颗粒团聚,产生沉淀,引起相分离。控制凝胶时间与相分离时间的关系,可获得均匀凝胶。     

TiZrNiCu钎焊Si3N4-MoSi2复合陶瓷与Nb接头组织与力学性能

采用高温活性钎料TiZrNiCu对Si₃N₄-MoSi₂复合陶瓷和金属Nb进行真空钎焊试验,研究了其典型界面组织组成及形成机理,分析了钎焊温度和保温时间对钎焊接头界面组织及力学性能的影响规律。结果表明,接头典型界面结构为Nb/β-Ti/(Ti. Zr)₂(Cu, Ni)+β-Ti+(Ti, Zr)₅Si₃/TiN+(Ti, Zr)₅Si₃+MoSi₂/Si₃N₄-MoSi₂。钎焊温度和保温时间主要通过控制Si₃N₄-MoSi₂复合陶瓷母材中Si原子向钎料中扩散程度,来影响钎缝中(Ti, Zr)₅Si₃化合物的数量及分布,进而影响钎焊接头的抗剪强度。在920 ℃/10 min的工艺参数下,Si₃N₄-MoSi₂/Nb接头的室温抗剪强度最高达到112 MPa,选择最优参数条件下的Nb/Si₃N₄-MoSi₂钎焊接头在500 ℃和600 ℃条件下进行高温剪切实验,其高温抗剪强度分别达到123 MPa和131 MPa。     

Si元素对Ti-Cu-Zr-Ni基非晶钎料微观组织和性能的影响

采用电弧熔炼和快冷甩带工艺制备了(Ti_0.46Cu_0.14Zr_0.27Ni_0.13)_1-xSi_x非晶钎料,研究了添加一定量的Si对钎料非晶形成能力的影响。结果表明,当Si的含量达到0.5%时钎料的非晶形成能力最强,钎料的润湿面积为3.06 cm₂,过冷液相区宽度(?T_x)?T_x=56 ℃,约化玻璃转变温度(T_rg)T_rg=0.5387,液相线温度为949 ℃。以此非晶合金作为钎料对SiC和TC4进行真空钎焊,所得钎焊接头剪切强度为80 MPa。Si元素的加入显著提高了钎料的非晶形成能力。     

L12型Al3Sc基金属间化合物有序化行为和力学性能的第一性原理计算

本文采用亚晶格模型,辅助以第一性原理总能计算,研究了L1₂型Al₃Sc基金属间化合物中元素的占位有序化行为和力学性能。结果表明：Al₃Sc合金呈现完全有序化,其中Al占据3c亚晶格位置,Sc占据1a亚晶格位置；L1₂-Al₃(Sc_0.75M_0.25)金属间化合物(M=Y、Ti、Zr和Hf)也呈现完全有序化,第三组元M均只占据1a亚晶格位置,这些元素的占位行为均不受温度的影响。L1₂-Al₃(Sc_0.75M_0.25)金属间化合物均满足力学稳定性条件。M为Y时,L1₂-Al₃(Sc_0.75M_0.25)金属间化合物的剪切模量、体弹模量和杨氏模量和硬度下降；M为Ti、Zr或Hf时,随着原子半径增大,剪切模量、体弹模量、杨氏模量和硬度逐渐降低,其中Ti的加入可使L1₂-Al₃(Sc_0.75M_0.25)金属间化合物的塑性和韧性达到最好。     

铒元素对锆基合金的非晶形成能力及力学性能的影响

以海绵锆为原料,采用水冷铜坩埚熔炼和铜模吸铸法制备了直径为3 mm、成分为(Zr_0.55Cu_0.3Al_0.1Ni_0.05)_100-xEr_x (x=0,0.5,1,2,3,4,5)的锆基块体合金,通过对比不同铒含量海绵锆基合金的组织结构与性能,研究了铒元素对其非晶形成能力、热稳定性和力学性能的影响。结果表明：以海绵锆为原料时,锆基合金的非晶形成能力和力学性能明显下降。x=0时,无法制备成锆基非晶合金;添加Er元素后,海绵锆基合金的非晶形成能力和力学性能显著提高,具有非晶态结构;x=2时,海绵锆基非晶合金的力学性能最优,抗压强度σ_bc为2142.5 MPa,室温下塑性应变ε_p为10.01%。与高纯锆制备的同直径(Zr_0.55Cu_0.3Al_0.1Ni_0.05)₉₈Er₂非晶合金相比,其抗压强度恢复97.63%,室温塑性恢复69.95%。添加铒元素有利于改善和提高海绵锆基合金的非晶形成能力和力学性能,为低成本制备锆基非晶合金提供一种新思路。     

ZrC增强激光熔覆CoCrNi合金熔覆层的组织及性能

本研究采用激光熔覆技术,在低碳钢表面制备了ZrC增强的CoCrNi合金涂层。研究了ZrC的不同分数(0, 1, 3, 5 wt.%)对CoCrNi基中熵合金涂层组织、硬度和耐磨性的影响。利用X射线衍射仪、扫描电镜和能谱仪分析了涂层的相组成及微观组织结构,并采用显微硬度和摩擦磨损试验对样品的硬度和耐磨性进行了测试。结果表明：熔覆层与基体形成了良好的冶金结合,没有出现明显的裂纹和及空洞等缺陷。不含ZrC的CoCrNi中熵合金涂层由单相FCC结构组成,随着涂层中ZrC的加入,涂层中的物相组成变为了FCC+ ZrC_0.7+Cr₂₃C₆+ZrO₂。涂层的晶粒得到了明显细化,实现了晶界强化、固溶强化和弥散强化(Orowan)的共同作用,形成的碳化物Cr₂₃C₆相与FCC固溶体结合形成共晶碳化物,起到了协同强化作用,有效地提高了涂层的硬度和耐磨性。然而ZrC中的Zr与空气中的杂质O结合生成的ZrO₂也对涂层的性能产生了不利影响,主要是因为ZrO₂的存在会导致涂层中颗粒分布不均匀加剧,弱化弥散强化的作用。所以当ZrC较少时,涂层的性能并未得到较好的提升,但是当涂层中ZrC含量增加到5wt.%时,涂层中析出了较多的强化相ZrC0.7能够有效的提高材料的性能,该涂层的最大硬度为651±15 HV_0.1,摩擦系数为0.161,相较于不含ZrC的涂层均有较大的提升。     

Aurivillius型钛酸铋钠的低温合成及电性能研究

以分析纯的Bi(NO₃)₃.5H₂O、Ti(C₄H₉O)₄和CH₃COONa?3H₂O为反应起始原料,通过两次水热法制备Aurivillius型钛酸铋钠(Na_0.5Bi_4.5Ti₄O₁₅,NBT),采用XRD和SEM研究两次水热条件所合成粉体的晶相组成和形貌,并测量了所得陶瓷的显微结构和电性能。研究表明,水热法所得纳米粉体由粒径～1.0μm、平均厚度<100nm的片状颗粒堆积而成,且各元素之比非常接近于NBT的化学计量比。NBT纳米粉体的合成温度低至260~270℃,是已公开报道文献中的最低温度。与传统固相烧结法所得NBT陶瓷相比较,用该水热粉体所得陶瓷具有非常相近的居里温度(≈674℃),且瓷体致密、细晶(<2μm),高温介电性能获得明显改善。     

Microstructure and mechanical properties of ZrB2–SiC ultrahigh temperature ceramic composite joint using TiZrNiCu filler metal

Abstract

ZrB₂–SiC ceramic composite was brazed by using TiZrNiCu active filler metal. The microstructure and interfacial phenomena of the joints were analysed by means of SEM, energy dispersive X-ray spectroscopy and X-ray diffraction. The joining effect was evaluated by shear strength. The results showed that the reaction products of the ZrB₂–SiC ceramic composite joint were TiC, ZrC, Ti₅Si₃, Zr₂Si, Zr(s,s) and (Ti, Zr)₂ (Ni, Cu), and the microstructure was separately ZrB₂–SiC/Zr(s,s)/Ti₅Si₃+Zr₂Si+TiC+ZrC+(Ti,Zr)₂(Ni,Cu)/Zr(s,s)/ZrB₂–SiC. A conceptual interface evolution model was established to explain the interface evolution mechanism. The maximum shear strength of the brazed joints was 143·5 MPa at the brazing temperature T of 920°C and the holding time t of 10 min.     

Structure, morphology and electrical properties of sputtered Zr-Si-N thin films: From solid solution to nanocomposite

DC reactive magnetron co-sputtering was used for the deposition of Zr-Si-N thin films. Si content (C_Si) was varied by changing the power applied on the Si target, whereas that on Zr target was kept constant. Three series of samples have been deposited at various substrate temperatures: room temperature, 240 °C and 440 °C. The evolution of morphology, crystalline structure, grain size and lattice constant has been investigated by X-ray diffraction analyses. Nanohardness, stress and resistivity measurements provide complementary information, which validate the proposed 3-step model for the film formation of the Zr-Si-N system deposited by reactive magnetron co-sputtering. For low Si content the Si atoms substitute the Zr atoms in the ZrN lattice. Above the solubility limit, a nanocomposite film containing ZrN:Si nanocrystallites and amorphous SiN_y is formed. Further increase of Si content results in a reduction of grain size (D), while the thickness of the SiN_y layer at the crystallite surface remains constant. The increasing amount of the SiN_y amorphous phase in the films is realized by increasing the surface to volume ratio of the crystallites. In this concentration range, the size of the crystallites in the Zr-Si-N films decreases according to the relationship C_Si ∼ 1 / D. With increasing substrate temperature, the solubility limit of Si in ZrN decreases whereas the films' global nitruration (C_N / (C_Si + C_Zr)) increases. The concentration dependence of the electrical resistivity is interpreted in terms of the variation of the SiN_y layer thickness.     

Reaction behavior and formation mechanism of ZrC and ZrB2 in the Cu–Zr–B4C system

In this work, the formation mechanism of ZrC and ZrB₂ in the Cu–Zr–B₄C system was studied by differential scanning calorimeter and X-ray diffraction. Moreover, the effect of heating rate on the reaction behavior was also investigated. The results revealed that the heating rate did hardly influence the reaction process and product in the range of 10–30 °C/min. The formation mechanism of ZrC and ZrB₂ in the Cu–Zr–B₄C system could be ascribed to the solid-state reaction between Zr and B₄C particles, and the replacement reactions of B₄C with the Cu–Zr liquid and copper zirconium compounds. The addition of Cu in the Cu–Zr–B₄C reactants can change the phase evolution route via producing various Cu–Zr intermediate phases and promote the formation of ZrC and ZrB₂.     

低压化学气相沉积制备ZrC涂层：原位溴化工艺

本研究设计了一种溴化装置,用于合成并稳定控制ZrBr4蒸汽的流量。采用低压化学沉积技术,以Zr-Br2-C3H6-H2-Ar为体系,1200°C在石墨基底上制备了ZrC涂层。研究了气体组分(源气C/Zr比)对ZrC涂层微观形貌及生长机制的影响。源气C/Zr比为1.5时,涂层的沉积过程为由表面反应机制为主,ZrC涂层较为疏松。源气C/Zr比为0.5~1时,扩散动力学是涂层的主要生长机制,所制备的ZrC涂层具有致密均匀ZrC涂层,并沿(200)晶面择优取向。同时,源气C/Zr比为0.5时,制备的ZrC涂层无自由碳存在并具有近化学计量比。     

In situ fabrication of ZrC powder obtained by self-propagating high-temperature synthesis from Al-Zr-C elemental powders

The in situ synthesis of ZrC powder utilizing self-propagating high-temperature synthesis (SHS) reaction that occurred in the compact consisting of Al, Zr and C powders was investigated. The result shows when Al contents were 0-40 wt.% SHS reaction proceeded favorably. The as-products display a uniform distribution of ZrC particles with the sizes ranging from 8 μm at Al free to 50 nm at 40 wt.% Al. The temperature curve, coupled with the quenched treatment, indicates that the Al-Zr reaction to form ZrAl₃ initiated and then C reacted with ZrAl₃ to form the more stable ZrC phase. It also proves that the mechanism of reaction-precipitation should be responsible for the formation of ZrC in this system. Al has been playing an important role in determining the formation of ZrC, not only as a diluent to inhibit the ZrC grains from coarsening, but also as an intermediate reactant to participate in the total reaction.     

Interdiffusion and reaction between Zr and Al alloys from 425° to 625 °C

Zirconium has recently garnered attention for use as a diffusion barrier between U–Mo nuclear fuels and Al cladding alloys. Interdiffusion and reactions between Zr and Al, Al-2 wt.% Si, Al-5 wt.% Si or AA6061 were investigated using solid-to-solid diffusion couples annealed in the temperature range of 425° to 625 °C. In the binary Al and Zr system, the Al₃Zr and Al₂Zr phases were identified, and the activation energy for the growth of the Al₃Zr phase was determined to be 347 kJ/mol. Negligible diffusional interactions were observed for diffusion couples between Zr vs. Al-2 wt.% Si, Al-5 wt.% Si and AA6061 annealed at or below 475 °C. In diffusion couples with the binary Al–Si alloys at 560 °C, a significant variation in the development of the phase constituents was observed including the thick τ₁ (Al₅SiZr₂) with Si content up to 12 at.%, and thin layers of (Si,Al)₂Zr, (Al,Si)₃Zr, Al₃SiZr₂ and Al₂Zr phases. The use of AA6061 as a terminal alloy resulted in the development of both τ₁ (Al₅SiZr₂) and (Al,Si)₃Zr phases with a very thin layer of (Al,Si)₂Zr. At 560 °C, with increasing Si content in the Al–Si alloy, an increase in the overall rate of diffusional interaction was observed; however, the diffusional interaction of Zr in contact with multicomponent AA6061 with 0.4–0.8 wt.% Si was most rapid.     

Thermal explosion synthesis of ZrC particles and their mechanism of formation from Al–Zr–C elemental powders

ZrC particles were fabricated by thermal explosion (TE) from mixture of Al, Zr and C elemental powders. Without the addition of Al, the synthesized ZrC particles had irregular shape of ~ 4.0 μm in average. Increasing Al content up to 30 wt.%, however, refined significantly them down to < 0.2 μm with regularly square morphology. The Al effect of reaction mechanism promoted the ZrC formation as diluents in the course of TE, which was clarified using differential thermal analysis and X-ray diffraction technique. The melting of Al favored the reaction with Zr to generate ZrAl₃, and then the dissolution of C into the Al–Zr liquid resulted in precipitation of ZrC. Meanwhile, the exothermic effect prompted C atoms dissolving into Zr–Al liquid and eventually led to precipitation of ZrC out of the supersaturated liquid. The Al addition inhibited particle growth, but also promoted the TE reaction.     

Pyrolysis mechanism of ZrC precursor and fabrication of C/C-ZrC composites by precursor infiltration and pyrolysis

C/C-ZrC composites were prepared by precursor infiltration and pyrolysis using the organic zirconium as precursor. The conversion mechanisms of the precursors such as the thermal behavior, structural evolution, phase composition, microstructure, composition of the precursors and products were analyzed by thermal gravimetric analyzer, Fourier transform infrared spectrometer, X-ray diffraction and scanning electron microscope. The results indicate that the ZrC precursor transforms to inorganic ZrO₂ from room temperature to 1200 °C, then reduces to ZrC at 1600 °C through the carbothermal reduction reaction. The microstructure of the C/C-ZrC composites was also investigated. The composites exhibit an interesting structure, a coating composed of ZrC ceramic covers the exterior of the composite, and the ZrC ceramic is embedded in the pores of the matrix inside the composite.     

Role of C: Zr stoichiometry in the formation of a nanocrystalline structure and magnetic properties in Fe87-x Zr13Cx films

X-ray diffraction analysis was used to study the structure of as-sputtered and annealed Fe-13 at. % Zr-C films, which were produced by reactive magnetron sputtering and characterized by stoichiometric and nonstoichiometric (with respect to ZrC) at. % C to at. % Zr ratios. A special packet of programs was used to resolve wide reflections observed in X-ray diffraction patterns of the films. The as-sputtered films of all compositions were found to be amorphous in terms of X-ray diffraction. The thermal stability of the amorphous phase increases as the C: Zr ratio in the films departs from the stoichiometric ratio (1: 1) characteristic of the monocarbide ZrC. Annealing leads to the formation of a mixed (amorphous + nanocrystalline) structure. Depending on the carbon content and annealing temperature, the phase composition of the films is represented by different combinations of phases, such as bcc α-Fe (the basis phase), fcc ZrC, monoclinic Fe₂C, monoclinic Fe_2.5C, orthorhombic Fe₃C, and Fe₂₃Zr₆. After annealing at 550°C, the best magnetic properties are characteristic of the films having the stoichiometric composition with respect to ZrC (at. % C: at. % Zr ～ 1).     

X-ray photoelectron spectroscopy analysis of zirconium nitride-like films prepared on Si(100) substrates by ion beam assisted deposition

Thin zirconium nitride films were prepared on Si(100) substrates at room temperature by ion beam assisted deposition with a 2 keV nitrogen ion beam. Arrival rate ratios ARR(N/Zr) used were 0.19, 0.39, 0.92, and 1.86. The chemical composition and bonding structure of the films were analyzed with X-ray photoelectron spectroscopy (XPS). Deconvolution results for Zr 3d, Zr 3p_3/2, N 1s, O 1s, and C 1s XPS spectra indicated self-consistently the presence of metal Zr⁰, nitride ZrN, oxide ZrO₂, oxynitride Zr₂N₂O, and carbide ZrC phases, and the amounts of these compounds were influenced by ARR(N/Zr). The chemical composition ratio N/Zr in the film increased with increasing ARR(N/Zr) until ARR(N/Zr) reached 0.92, reflecting the high reactivity of nitrogen in the ion beam, and stayed almost constant for ARR(N/Zr) ≥ 1, the excess nitrogen being rejected from the growing film. A considerable incorporation of contaminant oxygen and carbon into the depositing film was attributed to the getter effect of zirconium.