C/C复合材料大气等离子喷涂mullite/ZrB_2-MoSi_2涂层抗烧蚀性能（英文）

采用大气等离子喷涂技术(APS)在C/C复合材料表面制备了mullite/ZrB_2-MoSi_2双层抗烧蚀涂层。借助XRD、SEM、EDS等分析手段对涂层的组织结构进行研究;基于氧丙烯焰烧蚀试验考察ZrB_2-MoSi_2/mullite复合涂层对C/C复合材料高温耐烧蚀性能的影响。结果表明,在1700和1800℃的氧丙烯焰下烧蚀60s,ZrB_2-MoSi_2/mullite涂层试样的质量烧蚀率分别为3.49×10~(-3)与3.77×10~(-3)g/s。其与单层ZrB_2-MoSi_2涂层试样相比,ZrB_2-MoSi_2/mullite涂层试样展现了出色的抗烧蚀性能。烧蚀过程中形成的硅酸盐玻璃可以作为热障层而减少氧气的进一步渗透,并且还具有自我封填缺陷的能力,使ZrB_2-MoSi_2/mullite涂层表现较好的抗烧蚀性。     

石墨和C/C复合材料表面ZrB2-SiC陶瓷涂层的研究进展

C/C复合材料具有优异的高温力学性能,是航空航天领域最具发展前景的结构材料之一,但在高温含氧环境中的氧化问题严重地限制了其实际应用。涂层技术是提升基体抗氧化能力的有效手段,因ZrB_2-SiC陶瓷涂层具有优异的抗氧化、抗烧蚀、抗热震等性能,非常适合作为C/C复合材料的高温防护涂层。首先,介绍了ZrB_2-SiC陶瓷涂层在氧化和烧蚀过程中组织结构的演变规律,阐明了该涂层的高温防护机理;然后,综述了该涂层的主要制备方法(包埋法、CVD、等离子喷涂)及每种方法的优点与不足,并对不同方法所制备涂层的抗氧化性和抗烧蚀性进行了比较;之后,针对该涂层研究和应用中存在的问题,如涂层致密性差、元素分布不均匀、应用温度范围窄、与基体热匹配性差等,从粉体改性和掺杂改性两方面总结了该涂层的改性研究现状,重点阐述了对ZrB_2-SiC粉末进行喷雾造粒和感应等离子球化处理对于提升等离子喷涂涂层性能的重要意义;最后,从涂层制备、涂层结构设计、涂层改性、涂层性能测试等方面,指出了该涂层体系存在的主要问题和未来的发展方向。     

SiC-Al2O3-SiO2复合陶瓷涂层组织结构及抗烧蚀性能研究

目的提高C/C复合材料的抗氧化性能。方法采用大气等离子喷涂在C/C复合材料表面制备SiC-Al_2O_3-SiO_2(SAS)复合陶瓷涂层,并选用氧-乙炔在1500℃对涂层进行抗氧化烧蚀性能考核。利用XRD、SEM、EDS等检测分析手段,对团聚粉末和球化粉体以及烧蚀前后涂层的成分及组织进行检测。结果经过等离子球化处理后,三种粉体流动性为90 s/50 g左右,粉末松装密度为1 g/cm~3左右。与团聚的SiC-Al_2O_3-SiO_2粉体相比,粉末流动性提升了20%左右,松装密度提高了20%,更加适宜等离子喷涂工艺。采用球化处理SiC-Al_2O_3-SiO_2粉体制备得到的涂层组织明显优于采用团聚粉体制备的涂层,涂层致密区域明显增大,内部缺陷数量和尺寸减少。在1500℃烧蚀600s后,SiC-36%Al_2O_3-4%SiO_2涂层具有最佳的抗烧蚀效果,涂层整体完整,质量烧蚀率为1.62×10~(-4) g/s。结论 SiC-Al_2O_3-SiO_2体系解决了等离子喷涂制备SiC涂层过程中沉积率低、SiC分解的问题。SiC-Al_2O_3_-SiO_2涂层具有良好的抗氧化烧蚀效果,烧蚀过程中SiO_2和Al_2O_3形成的莫来石相具有良好的高温稳定性、抗热震性以及较低的热膨胀率和氧扩散率,可以进一步提高涂层的抗氧化烧蚀效果。     

C/C复合材料表面SiC-ZrB_(2)涂层的缺陷修复与抗烧蚀性能EI北大核心CSCD

碳/碳(C/C)复合材料表面涂层在制备与服役过程中易出现裂纹、凹坑和孔洞等缺陷,使涂层失去完整性而极易导致防护失效,目前常用的解决方法为更换整体涂层,成本高、工艺复杂、耗时长,因此快速高效的涂层轻微缺陷修复技术是解决这一难题的有效途径。通过大气等离子焰流在C/C复合材料表面SiC-ZrB_(2)(SZ)涂层表面预先构造缺陷,采用异丙醇以及高温下性能稳定的含硼聚氮硅烷胶粘剂作为修复剂,以SiC-ZrB_(2)粉末作为改性填料,Al_(2)O_(3)作为烧结助剂,对SZ涂层缺陷进行修复,研究修复前后涂层的微观结构演变与烧蚀防护性能。结果表明:经等离子焰流烧蚀后,未修复的SZ涂层试样中心出现圆形凹坑缺陷,裸露出C/C复合材料基底;而对于修复后的涂层试样,修复剂热解生成的SiBCN陶瓷和改性陶瓷填料均匀覆盖于缺陷处,使涂层保持较高完整性,且在氧乙炔烧蚀下生成致密的SiO_(2)玻璃膜可有效阻挡氧扩散,保护C/C复合材料免受机械冲蚀;修复后的涂层试样在氧乙炔焰流下烧蚀60s后线烧蚀率与质量烧蚀率分别为0.65μm/s和-0.28mg/s,相比于未修复涂层试样分别降低了83.54%和129.47%,修复后涂层的抗烧蚀性能得到显著提升。     

Zr-Mo-Si-C四元复合涂层抗氧化烧蚀性能研究

目的提高C/C复合材料高温抗烧蚀性能。方法通过低压等离子喷涂技术,在石墨基体表面制备出Zr-Mo-Si-C四元复合涂层,采用氧-乙炔火焰烧蚀试验对涂层的抗烧蚀性能进行测试,并通过SEM、EDS、XRD分析了烧蚀前后涂层的物相组成和微观形貌,分析了涂层的抗烧蚀机理。结果涂层在1800℃烧蚀60、180、300 s后均保持良好的涂层状态,线烧蚀率分别为1.2×10~(-3)、0.4×10~(-3)、0.3×10~(-3) mm/s。烧蚀300 s后,涂层截面呈现三个区域,分别为表面烧蚀区、阻挡层和未烧蚀区。结论通过添加Mo Si2作为第二相可显著提高ZrC涂层的抗烧蚀性能,涂层在烧蚀过程中形成三个区域,其中表面烧蚀区和阻挡层能够有效地阻隔烧蚀的进行,未烧蚀区发生的烧结致密化进一步提高了涂层的抗氧化烧蚀性能。     

C/C复合材料大气等离子喷涂mullite/ZrB2-MoSi2涂层抗烧蚀性能

采用大气等离子喷涂技术(APS)在C/C复合材料表面制备了mullite/ZrB₂-MoSi₂双层抗烧蚀涂层。借助XRD、SEM、EDS等分析手段对涂层的组织结构进行研究;基于氧丙烯焰烧蚀试验考察ZrB₂-MoSi₂/mullite复合涂层对C/C复合材料高温耐烧蚀性能的影响。结果表明,在1700 °C和1800 °C的氧丙烯焰下烧蚀60 s,ZrB₂-MoSi₂/mullite涂层试样的质量烧蚀率分别为3.49×10_-3 g/s与3.77×10_-3 g/s。其与单层ZrB₂-MoSi₂涂层试样相比,ZrB₂-MoSi₂/mullite涂层试样展现了出色的抗烧蚀性能。烧蚀过程中形成的硅酸盐玻璃可以作为热障层而减少氧气的进一步渗透,并且还具有自我封填缺陷的能力,使ZrB₂-MoSi₂/mullite涂层表现较好的抗烧蚀性。     

W-SiC-C/C复合材料制备及等离子烧蚀性能

目的提高C/C复合材料在超高温下的抗烧蚀性能。方法采用化学气相沉积法,在C/C复合材料表面制备SiC过渡层,然后以惰性气体保护等离子喷涂工艺在带有SiC过渡层的C/C材料表面制备W涂层,研究所制备的W-SiC-C/C复合材料的微观形貌与结构特征。以200 kW超大功率等离子焰流,考核W-SiC-C/C材料的抗烧蚀性能,并与无涂层防护的C/C材料进行对比分析。结果W涂层主要为层状的柱状晶结构。W涂层与SiC过渡层、过渡层与基体界面呈镶嵌结构,结合良好。SiC过渡层阻止了W、C元素相互迁移与反应。在驻点压力为4.5 MPa、温度约5000 K、热流密度为36 MW/m²的烧蚀条件下,当烧蚀时间小于10 s时,涂层对C/C材料起到了较好的保护作用,W涂层发生氧化烧蚀,基体未发现烧蚀,平均线烧蚀率为0.0523 mm/s;当烧蚀时间超过15 s后,涂层防护作用基本失效,基体C/C材料发生烧蚀现象。结论以W涂层、SiC过渡层为防护的C/C复合材料,能够适用于短时间超高温的烧蚀环境,如固体火箭发动机等。W涂层的熔融吸热、氧化耗氧以及SiC过渡层的氧化熔融缓解涂层热应力和氧扩散阻碍的联合作用,提高了C/C材料的抗烧蚀性能。     

一种新型的SiC-ZrB_2涂层包覆C/C复合材料的制备及烧蚀性能（英文）

利用两步工艺结合泥浆烧结法和化学气相反应法在C/C复合材料表面制备了一种新型的SiC-ZrB_2涂层。SiC-ZrB_2涂层由分散的ZrB_2相和连续的SiC相组成,涂层与C/C复合材料基体结合较好。与C/C复合材料相比,SiC-ZrB_2涂层包覆C/C复合材料试样具有更好的抗烧蚀性能。SiO_2-ZrO_2陶瓷层的阻氧作用、气态氧化产物的散热以及ZrO_2的钉扎作用是涂层试样具有良好抗烧蚀性能的主要原因。     

等离子喷涂制备C/C复合材料SiC涂层的驻点烧蚀性能

目的在C/C复合材料表面制备SiC涂层,提高C/C复合材料抗烧蚀性能。方法采用真空等离子喷涂技术在C/C复合材料表面制备纯Si涂层,在惰性气氛保护下对涂层高温热处理,纯Si涂层与C元素在高温下反应,原位生成SiC涂层。利用电弧加热器在不同烧蚀温度下,分别考核涂层的驻点烧蚀性能,并采用OM、SEM、EDS和XRD等对烧蚀前后的微观形貌和物相成分进行分析。结果在C/C复合材料表面制备了致密的SiC涂层,涂层中没有明显的裂纹存在,并在涂层下方产生较深的渗透区域,深度超过涂层厚度。制备的SiC涂层在1400℃下烧蚀50 s,涂层完整,具有良好的驻点烧蚀性能;在1600℃和1650℃下烧蚀50 s,涂层部分剥落,C/C复合材料基体产生烧蚀。结论 SiC涂层在高温下氧化成Si O2玻璃态膜,并覆盖在C/C复合材料表面,对基体具有良好的保护作用。随着烧蚀温度的提高,在超音速气流的冲刷下,由于热膨胀系数不匹配和SiC主动氧化的原因,涂层在烧蚀面边缘出现剥落,且剥落现象越来越严重,涂层失去对C/C基体的保护作用,烧蚀性能下降。     

超音速大气等离子喷涂TiB_2-SiC涂层的抗氧化性及耐熔盐腐蚀性能（英文）

采用超音速大气等离子喷涂制备全包覆TiB_2-SiC涂层,研究了TiB_2-SiC涂层在400和800℃的氧化性能,并探究其氧化机理。对TiB_2-SiC涂层在900℃下的抗铝熔盐腐蚀性能进行研究,并探讨其耐熔盐腐蚀机理。结果表明,超音速大气等离子喷涂制备的TiB_2-SiC涂层具有良好的抗氧化性,在400℃的氧化速率常数为1.92×10~(-5) mg~2·cm~(-4)·s~(-1),在800℃的氧化速率常数为1.82×10~(-4) mg~2·cm~(-4)·s~(-1)。超音速大气等离子喷涂制备的TiB_2-SiC涂层在900℃下具有良好的抗熔盐腐蚀性能,熔盐腐蚀后TiB_2-SiC涂层都保持致密结构,未发生涂层的开裂及剥落。     

Corrosion characterisation of alumina-magnesium metal matrix composites

Alumina magnesium metal matrix composites are a precious alternative for aerospace and automotive applications because of their high stiffness-to-weight ratio. A considerable deal of investigations had been devoted to their processing and mechanical properties, while the corrosion behaviour is still uncertain. In this study, the corrosion behaviour of Al₂O₃ fibres strengthened magnesium AS41 composite, in aqueous solutions containing various concentrations of NaCl at different pH values, was studied and compared with the behaviour of pure AS41 magnesium matrix alloy using electrochemical techniques, hydrogen evolution test, optical microscopy, and scanning electron microscopy (SEM) coupled with EDX and WDX capabilities. The results showed that the corrosion behaviour of the composite was comparable to its pure matrix alloy, yet a reduction in the corrosion resistance was observed in the composite at higher chloride concentrations. The corrosion mechanism involved, as well as the corrosion characteristics, was extensively discussed in terms of the effect of Al₂O₃ fibres. Also, an appropriate model describing the corrosion mechanism was proposed.     

Detection of breakaway oxidation with Acoustic Emission during titanium oxide scale growth

Extensive in-situ analysis of high temperature breakaway oxidation of titanium metal has been performed using the Acoustic Emission (AE) technique. Depending on temperature and oxidising atmosphere, different model cases were examined: with breakaway (900 °C/O₂), without breakaway (750 °C/O₂ and 900 °C/H₂O). Two specific population of AE hits were observed before and after breakaway. Contrary to the pre-breakaway population, the post-breakaway population exhibited low AE activity characterised by high values of energy. A critical energy value of E = 3 fJ was determined as a frontier between signals resulting from oxide parabolic growth and signals resulting from rapid linear growth.     

Microstructure of the Fe-based hardfacing layers reinforced by TiC-VC-Mo2C particles

In this study, the hardfacing alloys with different measures of ferrotitanium (Fe-Ti), ferrovanadium (Fe-V), ferromolybdenum (Fe-Mo) and graphite were deposited on AISI 1020 steel substrates by shielded manual arc welding (SMAW). Fe-based hardfacing layers reinforced by carbide particles were produced. The thermodynamic analysis for carbide and effect of the carbide forming elements on the properties of hardfacing layers were also discussed. The experimental results showed that TiC-VC-Mo₂C carbides could be synthesized by metallurgic reaction during SMAW process. Carbides with particle sizes in the range 1-3 μm are uniformly dispersed in the matrix. The hardfacing layer with good cracking resistance and high hardness could be obtained when the amounts of graphite, Fe-Ti, Fe-V and Fe-Mo were controlled within a range of 8-10%, 12-15%, 10-12% and 2-4%, respectively.     

Crevice corrosion initiation and propagation on Alloy-22 under galvanically-coupled and galvanostatic conditions

The initiation and propagation of crevice corrosion on the Ni–Cr–Mo Alloy-22 has been studied in concentrated chloride solutions under galvanically-coupled and galvanostatic conditions. Under galvanically-coupled natural corrosion conditions crevice corrosion initiated but propagation was limited by repassivation. This was attributed to the slow kinetics of oxygen reduction on passive surfaces external to the crevice. Under galvanostatic conditions a potential more positive than 200 mV_Ag/AgCl and an applied current greater than 5 μA were required to stabilize propagation. A minimum critical current density to establish active sites within the crevice was estimated to be around 250 μA cm⁻².     

Corrosion behavior of three iron-based model alloys in reducing atmospheres containing HCl and H2S at 600 °C

The corrosion of three Fe-xCr alloys (x = 8, 12, 18 wt.%) was examined at 600 °C in reducing atmospheres containing HCl and H₂S with two different H₂S contents and compared with the behavior of the same materials in H₂S-free H₂-CO₂ and H₂-HCl-CO₂ mixtures producing similar oxygen and chlorine pressures. Exposure to the low-H₂S gas mixture had only a reduced effect on the behavior of Fe-8Cr and Fe-18Cr, but increased significantly the corrosion rate of Fe-12Cr. Increasing the H₂S level accelerated the corrosion of all the alloys, but particularly that of Fe-18Cr. In both cases only minor amounts of sulfur and chlorine were present close to the alloy/scale interface. An increase of the Cr content reduced the corrosion rate in both H₂S gas mixtures, especially in the range 8-12 wt.% Cr, due to a larger volume fraction of Cr₂O₃ in the scale. The results have been discussed on the basis of the thermodynamic stability diagrams of the Fe-O-Cl-S and Cr-O-Cl-S systems.     

The effect of pre-corrosion and steel microstructure on inhibitor performance in CO2 corrosion

The importance of chemical composition and microstructure on CO₂ corrosion of carbon and low alloy steels has been widely recognized, still contradictory results can be found in the literature. The aim of this work is to assess the relationship between microstructure, surface condition and inhibitor efficiency in CO₂ corrosion. A C-Mn steel with two different microstructures was tested in a deoxygenated 5% wt. NaCl solution saturated with CO₂ at 40 °C, pH 6. A commercial imidazoline-based inhibitor was added after different pre-corrosion periods. The results obtained showed that pre-corrosion decreases the inhibitor efficiency, but that its impact is microstructure dependent.     

Ni添加对直接乙醇燃料电池Pt基催化剂催化性能的影响

本文通过水热法制备出孔径分布范围3.1~4.2nm,比表面积为174.72m₂/g的CeO₂作为助催化剂,以碳纳米管为载体,采用微波辅助乙二醇法制备PtNiCeO₂/C催化剂,探究Ni添加对Pt基催化剂电催化性能的影响。利用X射线衍射仪(XRD)、比表面积及孔径分析仪(BET)、扫描电镜(SEM)和电子能谱(EDAX)对所制备的CeO₂及催化剂进行微观表征,利用电化学工作站对所制备的催化剂进行电化学性能测试。结果表明,添加CeO₂且催化剂中Pt与Ni的比例为5:1时,制备的催化剂电催化性能最优,其电化学活性表面积为90.41m₂/g,对乙醇催化氧化的峰电流密度值为837.67A/g,1100s的稳态电流密度值为178.33A/g,说明添加一定量的Ni,可提高催化剂的抗中毒能力和电催化性能。     

Mechanical properties and fracture of Al–15 vol.-%B4C based metal matrix composites

The present work was performed on three aluminium metal matrix composites (MMCs) containing 15 vol.-%B₄C particles. The matrix in two of these materials is pure aluminium, whereas the matrix of the third material was an experimental 6063 aluminium alloy. All composites were homogenised at elevated temperatures for 48 h before being quenched in warm water. The quenched samples were aged in the range of 25–400°C for 10 h, at each temperature. Hardness and tensile tests performed on the aged MMCs show that the presence of Zr (with or without Ti) resulted in a noticeable hardening due to the precipitation of a Zr rich phase. Maximum strengthening was obtained from the 6063 based MMC due to the precipitation of Mg₂Si phase particles. The present technique used to produce the MMCs examined proved capable of manufacturing composites with a uniform distribution of B₄C in the matrix with a strong degree of matrix/particle bonding. When the MMC samples were deformed to failure, the B₄C was fractured transgranularly without debonding from the matrix. The addition of Zr and Ti resulted in the formation of protective layers around the B₄C particles that were retained after fracture; these protective layers were not affected by the B₄C particle size (0·15–20 μm). Stacking faults were commonly observed in fractured Al 6063/B₄C/15p samples. The precipitation of zirconium–titanium compounds during aging contributed to the composite strength.     

The influence of the conditions of the ZrO2 passive film formation on its properties in 1 M NaOH

In this paper, results of the potentiodynamic-potentiostatic formation of a homogeneous, passive films of ZrO₂ onto a Zr electrode in 1 M NaOH solution at different potentials (2.0, 4.0, 6.0 and 8.0 V vs. SCE) are presented. The properties of such films were investigated by EIS measurements at different potentials. After fitting the EIS spectra by an appropriate equivalent circuit, the capacitance (C_pf) and resistance (R_pf) of these films were determined. All films were found to become insulators at the potentials equal and/or more positive than 2.0 V, with their thicknesses increasing linearly with the potential from about 7 nm at 2.0 V to about 20 nm at 8.0 V. In the potential range 0.8 V < E < 2.0 V a transition from a semiconducting to insulating behaviour has been recorded for all films (except for the one formed at 2.0 V). The donor densities (N_sc) for all films, as well as their flat band potentials (E_fb) and their thicknesses of the space charge layer (d_sc), were determined from the corresponding Mott-Schottky plots (MS) recorded in the potential range (0.0 V < E < 0.8 V), where all films behaved as n-type semiconductors.     

Co_6W_6C化合物的热力学研究

以高纯钨、钴、碳粉为原料,在真空条件下制备获得物相纯净的Co_6W_6C化合物,对Co_6W_6C进行系列实验测定并结合计算得出了其相关的热力学参数。结果表明:在原料粉中碳含量为0.98%~1.06%(质量分数)、真空反应温度为1000℃、保温时间为1 h的条件下,可制备获得物相纯净的Co_6W_6C。结合其等压热容及1173 K下氧化反应的反应焓测定结果,通过计算获得了Co_6W_6C的标准摩尔熵(S_m~Θ)、标准摩尔生成焓(Δ_fH_m~Θ)等热力学参数以及其等压热容(C_p)、焓(H)、熵(S)和吉布斯自由能(G)等基础热力学参量随温度变化的函数关系。