SiC/Si-Mo-Cr涂层SiCf/SiC复合材料辐照行为

通过浆料涂刷法(Slurry painting,SP)结合化学气相沉积(Chemical vapor deposition,CVD)，在SiC_f/SiC复合材料表面制备了致密的SiC/Si-Mo-Cr复合涂层。采用拉曼光谱、XRD和SEM研究了Si²⁺离子辐照前后涂层的相组成、结构和形貌，并通过三点弯曲试验评估了辐照前后涂层样品的力学性能。结果表明：SiC_f/SiC复合材料在Si²⁺离子辐照后发生结构损伤，如SiC纤维变得更粗糙，PyC界面膨胀以及SiC基体非晶化；而制备好的涂层可以极大地保护SiC_f/SiC复合材料；因此，内部的纤维、界面和SiC基体在Si²⁺离子辐照中都没有出现损伤。辐照后，SiC_f/SiC复合材料在辐照损伤区的界面脱黏和纤维拔出减少，弯曲断口变平，力学性能下降，弯曲强度保持率为80.49%；与之相比，涂层样品在辐照后的弯曲强度保持率更高，达到84.15%。     

DZ125合金表面Cr-Al-Y涂层抗高温氧化性能及摩擦性能

目的 提高DZ125合金的抗高温氧化性能和耐磨性。方法 采用包埋渗技术在DZ125合金表面制备Cr-Al-Y涂层,分析Cr-Al-Y涂层经高温氧化后的组织结构和相组成,对比研究涂层与基体的摩擦行为。结果Cr-Al-Y涂层具有多层组织结构,经高温氧化100 h后,涂层的平均质量损失量仅为0.85 mg/cm²。由于在高温氧化过程中Cr-Al-Y涂层形成了连续致密的Al₂O₃和Cr₂O₃氧化膜,随着氧化温度的升高,涂层表面的氧化速率增大,导致氧化产物剥落,并出现表面缺陷。Cr-Al-Y涂层的摩擦因数明显低于DZ125基体的摩擦因数,DZ125合金的摩擦因数约为0.45,Cr-Al-Y涂层的摩擦因数约为0.2。在摩擦过程中,DZ125合金发生了犁削磨损和磨粒磨损,涂层表面发生了磨粒磨损。结论 该涂层具有优异的抗高温氧化性能,连续致密的Al₂O₃氧化膜和Cr₂O₃氧化膜能够有效阻挡氧化性气氛与基体直...     

激光辅助热喷涂NiCoCrAlYTa-Cr2O3-Cu-Mo涂层高温静态氧化行为

为探究高温润滑耐磨涂层抗高温氧化行为,采用激光辅助等离子喷涂技术(LPHS)在GH4065A镍基高温合金上制备NiCoCrAlYTa-Cr₂O₃-Cu-Mo涂层,研究了该涂层在(850～1000)℃×220 h的抗高温氧化行为。计算得出氧化激活能约为128.5 kJ·mol^-1,850、900、1000℃氧化速率常数分别为1.44×10^-2、3.61×10^-2、7.71×10^-2 mg²·cm^-4·h^-1。结果表明,850℃×220 h氧化后表面生成Al₂O₃为主的连续致密氧化膜,阻碍涂层内部的进一步氧化;1000℃×220 h氧化后表面生成疏松NiO为主,致密Cr₂O₃·NiO为辅的氧化膜。致密氧化膜的生成阻止了涂层及基体的进一步氧化。     

超音速火焰喷涂NiCoCrAlY/Al2O3复合涂层的抗氧化性能

采用喷雾造粒、化学冶金包覆和固相合金化技术制备了NiCoCrAlY/Al₂O₃复合粉体,并采用超音速火焰喷涂技术制备了NiCoCrAlY/Al₂O₃复合涂层。采用SEM、XRD和马弗炉对该涂层和粉体的显微结构和抗氧化性能进行了研究。结果表明,Al₂O₃颗粒表面均匀致密的包覆着一层NiCoCrAlY合金,NiCoCrAlY/Al₂O₃复合粉体呈球形,颗粒大小均匀。超音速火焰喷涂NiCoCrAlY/Al₂O₃复合涂层与基体结合良好,涂层孔隙率仅为（0.41±0.05）%。涂层抗氧化性能良好,氧化动力学曲线分为3个阶段：大斜率直线阶段,系数较小的抛物线阶段和斜率几乎为零的直线阶段。涂层在850 ℃氧化96 h以后,涂层氧化增重为2.5 mg·cm^-2左右。复合涂层中氧化物膜的形成和Al₂O₃硬质相的加入是涂层抗氧化性能提高的主要原因。     

Nb2O5/TiO2微弧氧化复合膜层微观组织和高温性能的研究

为了研究Ti6Al4V钛合金微弧氧化膜层的抗高温氧化性能,在硅酸钠电解液中添加纳米铌(Nb)颗粒制备了Nb₂O₅/TiO₂复合膜层。采用扫描电子显微镜(SEM)和X射线衍射仪(XRD)分析膜层的微观结构和相组成。结果表明：随着纳米Nb浓度增加,膜层表面微孔直径增大、数量减小,膜层中Nb元素含量逐渐增加至5at%,膜层厚度由42.28μm增加至55.48μm;膜层由锐钛矿型TiO₂、金红石型TiO₂、Al₂TiO₅、Nb₂O₅及Nb-Ti化合物组成,金红石型TiO₂峰值和Nb₂O₅峰值逐渐上升;试样增重由基体10.25 mg/cm²降低至Nb浓度为6 g/L制备膜层的2.281 mg/cm²,平均氧化速率由2.8472×10^-5 mg·cm^-2     

镍基单晶高温合金N5及其纳米晶涂层在900℃下O2和O2+20%H2O气氛中的氧化行为

以镍基单晶高温合金N5为基体,采用磁控溅射技术在基体表面沉积与其成分相同的纳米晶涂层,并对比研究合金及其纳米晶涂层在900℃下O₂和O₂+20%(体积分数) H₂O气氛中的氧化行为。结果表明,水蒸气加快了合金和涂层的氧化速率,促进合金表面氧化膜的剥落,并且影响了氧化膜的组成和结构。在O₂和O₂+H₂O环境中,合金表面氧化膜都由外层NiO、中间层NiAl₂O₄和内层Al₂O₃组成;但在O₂+H₂O环境中,合金氧化速率较大,外层氧化膜发生剥落。纳米晶涂层显著提高了合金的抗高温氧化性能,在O₂气氛中表面形成Al₂O₃,而在O₂+H₂O气氛中表面氧化膜主要为NiAl₂O₄。同时,纳米...     

NiCrAlY/Al-Al2O3/Ti2AlNb高温抗氧化和力学性能研究

采用电弧离子镀技水在NiCrAlY涂层与O相Ti₂AlNb合金之间沉积不同Al:Al₂O₃比例的Al-Al₂O₃薄膜作为扩散阻挡层.研究了900℃下恒温氧化500 h后NiCrAlY/Al-Al₂O₃/Ti₂AlNb体系中Al-Al₂O₃层阻挡合金元素互扩散的行为,以及对涂层氧化动力学曲线的影响.结果表明,没有添加扩散阻挡层的NiCrAlY/Ti₂AlNb体系,涂层和基体之间的元素互扩散十分严重,涂层丧失抗氧化能力;而添加扩散阻挡层的材料体系,涂层和基体之间的元素互扩散受到抑制,涂层的长期抗高温氧化性能得到提高.对于3Al-Al₂O₃,1Al-Al₂O₃和0Al-Al₂O₃ 3种扩散阻挡层,综合比较材料体系的抗氧化性能、阻挡层阻挡涂层和基体元素互扩散能力、以及涂层和基体之间结合力,当1Al-Al₂O₃薄膜作为扩散阻挡层时,材料性能最优异.同时,本文利用扩散阻挡系数简洁定量地表示出不同Al:Al₂O₃比例阻挡层的阻挡扩散能力.     

TiAl合金表面热障涂层的高温抗氧化性能研究

利用大气等离子喷涂技术(APS)在TiAl合金基体表面制备TiAl₃/Al₂O₃-13TiO₂纳米热障涂层。采用SEM、EDS和XRD技术分析纳米热障涂层在氧化前后的微观组织及相组成,并对其在950℃下的抗氧化性能进行测试。结果表明,TiAl合金表面制备TiAl₃/Al₂O₃-13TiO₂纳米热障涂层后高温抗氧化性能显著提高,氧化动力学曲线呈对数变化规律,950℃高温氧化时,氧化速率常数为3.7×10^-3 mg²·cm⁴/s。在高温氧化过程中,TiAl₃粘结层与TiAl合金基体之间发生元素扩散,TiAl合金基体与粘结层之间界面消失。在陶瓷层与粘结层之间形成均匀连续的热生长氧化物层(TGO),在TiAl₃粘结层完全降解为TiAl₂相和三元Ti-Al-O化合物后,TGO对陶瓷层和粘结层仍...     

Nb-Hf合金表面Si-Ti-Cr硅化物涂层在恒温氧化和热震中的高温抗氧化性能（英文）

为了提高Nb-Hf合金的高温抗氧化性能,采用浆料烧结和高温渗透制备了Si-Ti-Cr硅化物涂层。分析了Si-Ti-Cr硅化物包覆的Nb-Hf合金样品在恒温氧化和高温热震条件下的抗氧化性能,揭示了Si-Ti-Cr涂层高温恒温氧化和高温热震条件下的失效机理。结果表明,在1800℃恒温氧化5 h条件下,涂层的增重为7 mg/cm²;在1700℃热震循环50周次和恒温氧化5 h条件下,涂层的最大增重为1.8mg/cm²。硅化物涂层在1800℃恒温氧化环境下和1700℃热震/恒温氧化环境下具有优异的抗氧化性能。     

不同工艺下镁合金MAO/GO/SA复合涂层的耐蚀性

为提高AZ91D镁合金基体的耐蚀性，采用微弧氧化、电沉积和自组装工艺在AZ91D镁合金表面制备了微弧氧化/氧化石墨烯/硬脂酸(MAO/GO/SA)复合涂层。通过SEM对复合涂层的微观组织结构进行了分析，利用电化学阻抗谱、极化曲线测试了复合涂层的耐蚀性能。结果表明，最佳电沉积电压为4 V,此时，MAO/GO复合涂层的电荷转移电阻(R_ct)为4.41×10⁵Ω·cm²,腐蚀电流密度(J_corr)为3.88×10^-7 A/cm²。醇水比为7∶3时，MAO/GO/SA复合涂层的R_ct值为3.07×10⁶Ω·cm²,J_corr为3.02×10^-8 A/cm²,达到超疏水状态，涂层耐蚀性最好。     

Electrochemical performance of SrF2-coated LiMn2O4 cathode material for Li-ion batteries

SrF2-coated LiMn2O4 powders with excellent electrochemical performance were synthesized. The electrochemical performance of SrF2-coated LiMn2O4 electrodes was studied as function of the level of SrF2 coating. With increasing the amount of the coated-SrF2 to 2.0% （molar fraction）, the discharge capacity of LiMn2O4 decreases slightly, but the cycleability of LiMn2O4 at elevated temperature is improved obviously. In view of discharge capacity and cycleability, the 2.0% （molar fraction） coated sample shows optimum cathodic behaviors. When being cycled at 55 ℃, as-repared LiMn2O4 remains only 79% of its initial capacity after 20 cycles, whereas the 2.0% （molar fraction） coated sample shows initial discharge capacity of 108 mA-h/g, and 97% initial capacity retention.     

等离子喷涂La2(Zr0.7Ce0.3)2O7热障涂层的抗热震性能

采用等离子喷涂制备了La₂(Zr_0.7Ce_0.3)₂O₇（LZ7C3）热障涂层,并对涂层的微观组织、相结构、成分、相稳定性、涂层热导率以及抗热震性能进行了研究.结果表明,LZ7C3涂层由单相烧绿石结构物质组成,高温稳定性较好;涂层的热导率较块材下降约20%,这是由于涂层具有较高的孔隙率所致:涂层在不同温度范围的热震寿命和失效机制不同,在室温至约1000℃间的热震寿命为116 cyc,涂层失效方式以片状剥落为主:在室温至1100℃间的热震寿命为53 cyc,涂层失效方式为片状剥落和层状撕裂;在室温至1200℃间的热震寿命为3 cyc,涂层失效方式以层状撕裂为主.     

Effects of modification on performance of natural graphite coated by SiO2 for anode of lithium ion batteries

A stable silicon dioxide film was coated on the surface of natural graphite anode by sol-gel method with Si（OCH2CH3）4, and effects of modification on performance of natural graphite were investigated. The structure and properties of graphite samples were determined by X-ray diffi＇actometry（XRD）, scanning electron microscopy（SEM）, energy-dispersive X-ray spectroscopy（EDS） and electrochemical measurements. The modified graphite shows mainly the layer structure, and silicon dioxide film is amorphous. Compared with the pure natural graphite, the modified graphite exhibits the higher specific capacity of 366 mA-h/g. After 40 charge-discharge cycles, the capacity retention ratio of the modified graphite reaches 99.55%, while that of natural graphite is only 83.04%. The results indicate that the surface modification of natural graphite by SiO2 is effective for improving the electrochemical performance of the natural graphite anode for lithium ion batteries.     

氩弧熔覆原位合成TiC-TiB2复合抗氧化涂层

为了提高石墨电极的高温抗氧化性能,以钛粉和B₄C粉为原料,采用氩弧熔覆技术在石墨电极表面原位反应合成TiC-TiB₂复合涂层. 利用X射线衍射分析、蔡司电子显微镜和扫描电子显微镜对涂层的组织形貌和物相组成进行了分析,利用间歇法测试了TiC-TiB₂复合涂层的高温抗氧化性能. 结果表明,熔覆层由花瓣状的TiC颗粒和棒状的TiB₂颗粒组成,熔覆层与石墨基体热匹配性好,表面无裂纹和气孔等缺陷,且熔覆层具有良好的抗高温氧化性能,1 300℃高温氧化6 h,氧化增重率为0.546 mg/mm2·h-1.     

Formation of zirconium diboride (ZrB2) by room temperature mechanochemical reaction between ZrO2, B2O3 and Mg

A mixture of magnesium, boric oxide and zirconium dioxide were mechanically milled under argon for up to 15 h in a laboratory scale ball mill. X-ray diffraction showed that there was an increasing conversion of ZrO₂ to ZrB₂ with milling time with >98% reaction after 15 h. Differential thermal analysis revealed there were multiple, overlapping reactions all of which seemed to be formation of ZrB₂. The energy evolved decreased with milling time and the sample after 15 h milling showed no thermal reaction. After milling, separation of the ZrB₂ from the coproduct MgO was easily achieved by a mild acid leaching leaving essentially pure ZrB₂ with a crystallite size of 75 nm.     

Effects of laser shock processing,solid solution and aging,and cryogenic treatments on microstructure and thermal fatigue performance of ZCuAl10Fe3Mn2 alloy

The materials used in variable temperature conditions are required to have excellent thermal fatigue performance. The effects of laser shock processing (LSP), solid solution and aging treatment (T6), and cryogenic treatment (CT) on both microstructure and thermal fatigue performance of ZCuAl₁₀Fe₃Mn₂ alloys were studied. Microstructure and crack morphology were then examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The result showed that, after being subjected to the combination treatment of T6+CT+LSP, the optimal mechanical properties and thermal fatigue performance were obtained for the ZCuAl₁₀Fe₃Mn₂ alloy with the tensile strength, hardness, and elongation of 720 MPa, 300.16 HB, and 16%, respectively, and the thermal fatigue life could reach 7,100 cycles when the crack length was 0.1 mm. Moreover, the ZCuAl₁₀Fe₃Mn₂ after combination treatment shows high resistance to oxidation, good adhesion between the matrix and grain boundaries, and dramatically reduced growth rate of crack. During thermal fatigue testing, under the combined action of thermal and alternating stresses, the microstructure around the sample notch oxidized and became loose and porous, which then converted to micro-cracks. Fatigue crack expanded along the grain boundary in the early stage. In the later stage, under the cyclic stress accumulation, the oxidized microstructure separated from the matrix, and the fatigue crack expanded in both intergranular and transgranular ways. The main crack was thick, and the path was meandering.     

Strength and residual stresses of functionally graded Al2O3/ZrO2 discs prepared by electrophoretic deposition

Biaxial strength testing of functionally graded Al₂O₃/ZrO₂ discs revealed that the strength of such discs, prepared by electrophoretic deposition, was almost doubled from 288 MPa for pure Al₂O₃ to 513 MPa for the graded discs; this was due to the compressive surface residual thermal stresses in the Al₂O₃ surface layer caused by the graded compositional profile. The surface compressive stress measured by means of X-ray diffraction was compared with the analytically calculated stress distribution in the graded component.     

Synthesis and characterization of 0.3 Vf TiC–Ti3SiC2 and 0.3 Vf SiC–Ti3SiC2 composites

In this work, two composite compositions—one with 30% (v/v) SiC, the other with 30% (v/v) TiC, balance Ti₃SiC₂—were synthesized and characterized. Fully dense samples were fabricated by hot isostatically pressing Ti, SiC and C powders for 8 h at 1500 or 1600 °C and a pressure of 200 MPa. Both TiC and SiC lower grain boundary mobility in Ti₃SiC₂. Coarsening of the SiC particles was also observed. At comparable grain sizes, all composites tested were weaker in flexure than the unreinforced Ti₃SiC₂ matrix, with the reduction in strength being the worst for the SiC composites. This reduction in strength is most probably due to thermal expansion mismatches between the matrix and reinforcement phases. The composite samples were exceptionally damage tolerant; in one case a 100 N Vickers indentation (in a 1.5-mm thick bar) did not reduce the flexural strength as compared to an unindented or as-fabricated samples. The same is true for thermal shock resistance; quenching samples from 1400 °C in room temperature water, resulted in strength reductions that were 12% at best and 50% at worst. In the 25–1000 °C temperature range, the thermal expansion coefficients of the two composites were indistinguishable at 8.2×10⁻⁶ K⁻¹. The Vickers hardness values depended on load; at 100 N, the hardnesses were ≈15 GPa; at 300 N, they asymptote to 7–8 GPa. For the most part, very few cracks emanate from the corners of the Vickers indents even at loads as high as 500 N. In the few cases where cracks did initiate, fracture toughness values were crudely estimated to lie in the 5–7.5 MPa √m range.     

ZrO2–SiO2 gradient multilayer oxidation protective coating for SiC coated carbon/carbon composites

In order to eliminate the mismatch of thermal expansion coefficient between the ZrO₂ outer layer and the internal bonding SiC layer, ZrO₂–SiO₂ composition-gradient transition layers were prepared by a sol–gel technique using tetraethoxysilane (TEOS) and zirconyl chloride as source materials. Energy dispersive spectroscopy (EDS) analysis displays that the gradient composition ZrO₂–SiO₂ outer coating could be obtained by immersing the SiC precoated carbon/carbon (C/C) composites into the gradient composition zirconia-silica sols (ZS sol) in turn. Oxidation test shows that, after 10 h oxidation in air at 1773 K, the weight loss of the gradient ZrO₂–SiO₂ coating coated SiC-C/C is only 1.97%.     

In-situ high temperature X-ray diffraction study of Ni/Al2O3 interface reactions

In-situ experiments on the Ni/Al₂O₃ interface reaction were carried out with a high temperature X-ray diffractometer capable of measuring the X-ray diffraction pattern in 1–2 s using an imaging plate. The kinetic formation processes of the interface reaction layer were measured by short-period exposure experiments with a high temperature X-ray diffractometer. NiAl₂O₄ was formed at the Ni/Al₂O₃ interface from 1468 K to 1673 K in air. The formation of NiAl₂O₄ obeyed the parabolic rate law. The value of the activation energy suggests that the diffusion of Al through NiAl₂O₄ controls the rate of formation. The results of thermal expansion coefficient measurements suggest that when a sample is cooled to room temperature, the magnitude of the stress on the Al₂O₃ owing to NiAl₂O₄ is smaller than that caused by NiO.