Preparation and oxidation resistance of mullite/SiC coating for carbon materials at 1150 ℃

To protect carbon materials from oxidation, mullite/SiC coatings were prepared on graphite by chemical vapor reaction (CVR) and slurry sintering. The XRD analyses show that the phase of the outer-layer coating is composed of SiO2 and mullite, and the inner-layer coating is mainly composed of β-SiC. The anti-oxidation behavior of the coating and the Rockwell hardness (HRB) of the coating after oxidation were investigated. The oxidation test shows that the as-prepared multi-layer coating exhibits excellent antioxidation and thermal shock resistance at high temperature. After oxidation at 1150 ℃ for 109 h and thermal shock cycling between 1150 ℃ and room temperature for 12 times, the mass gain of the coated sample is 0.085%. Meanwhile, the indentation tests also demonstrate that the as-prepared coating has good bonding ability between the layers.

Corrosion resistance of electrodeposited RE-Ni-W-P-SiC composite coating

Immersion experiment results show that corrosion rate of the as deposited RE Ni W P SiC composite coating in HCl solutions increases with the rise of HCl concentration. On the contrary, the corrosion rate of the composite coating after heat treatment decreases with increasing HCl concentration. The corrosion rates of the composite coatings in as deposited state and after heat treatment in H 2SO 4 and H 3PO 4 solutions respectively decrease with the rise of H 2SO 4 and H 3PO 4 concentrations. The corrosion rate of the composite coating as deposited in FeCl 3 solutions decreases with increasing FeCl 3 concentration, while the rate of the composite coating after heat treatment increases with the rise of FeCl 3 concentration. The corrosion rate of 316L stainless steel in the corrosion media of H 2SO 4, HCl, H 3PO 4 and FeCl 3 solutions at different concentrations increases with rising concentration. In addition, the corrosion rate of 316L stainless steel in the corrosion media of H 2SO 4, HCl, H 3PO 4 and FeCl 3 solutions respectively is much greater than that of the RE Ni W P SiC composite coating as deposited and after heat treatment in the same corrosion media. [

Structure and erosion resistance of Ni60A/SiC coatting by laser cladding

The Ni60A and Ni60A/SiC coatings were obtained by laser cladding on 0.45% C steel. The microstructure and hardness of the coatings were studied by SEM and XRD. The erosion resistances of Ni60A and Ni60A/SiC coatings were also investigated. The results show that the structure of different coatings is up to the temperature gradient and solidifying velocity in metal-melting region during laser cladding process. The coatings consist of a cladding layer, in which dendritic crystal and bulky cell-like crystal exist mainly, and a thermo-affected layer. Ni60A/SiC coating has higher microhardness than that of Ni60A coating, which is mainly caused by SiC and complicated phases formed by Ni, Cr, Fe, C and Si. It is obvious from the erosion test that the Ni60A/SiC coating has high erosion resistance.

RESISTANCE BRAZING OF SiC/2024AI COMPOSITE

The resistance brazing of 2024Al reinforced with15 volume percent of Sic particulate was simulated by using a Gleeble - 1500 Tharmal/Mechanical sindator. The results show that too high or too low brazing temperature and pressure result in decrease in shear strength of joint,but brazing time influenc- es it slightly. The action between filler metals and the composite was analyzed by SEM and EPAM. The use of simulation method helped in the design and predication of welding technology,which re- duced the rejection rate as well as the cost of production.

CATHODIC PROCESS AND WEAR RESISTANCE OF ELECTRO-DEPOSITED RE-Ni-W-P-SiC COMPOSITE COATING

Cathodic deposition current density of the composite coatings increases when SiC par-ticles and rare earth (RE) were added in the bath, which is profitable for Ni- W-P alloy to deposit in the cathod, forming Ni-W-P-SiC and RE-Ni-W-P-SiC composite coatings. On the contrary, the addition of PTFE in the bath decreases cathodic deposition current density of the coatings. The current density increases a little when the amount of RE is 7-9g/l; however, the current density increases greatly when the amount of RE is increased to 11-13g/l. Bui ij the amount of RE is raised further, the current density decreases. Hardness and wear resistance of RE-Ni-W-P-SiC composite coating have been studied, and the results show that the hardness and wear resistance of RE-Ni-W-P-SiC composite coating increase with increasing heat treatment tempera-ture, which reach peak values at 400℃; while the hardness and wear resistance of the coating decrease with the rise of heat treated temperature continuously.

Preparation and Thermal Shock Resistance of Mullite and Corundum Co-bonded SiC Ceramics for Solar Thermal Storage

Mullite and corundum co-bonded SiC-based composite ceramics(SiC-mullite-Al2O3)were prepared by using SiC,calcined bauxite and kaolin via pressureless carbon-buried sintering.The low-cost SiC-based composite ceramics designed in this study are expected to be used as thermal storage materials in solar thermal power generation based on the high density and excellent thermal shock resistance.The influences of calcined bauxite addition and sintering temperature on the microstructures,phase compositions,and physical properties of the samples were investigated.Results demonstrated that the introduction of calcined bauxite containing two bonding phases greatly reduced the lowest sintering temperature to 1400℃.The SiC-mullite Al2O3 composite with 40 wt%calcined bauxite sintered at 1500℃exhibited optimum performance.The density and bending strength were 2.27 g·cm^-3 and 77.05 MPa.The bending strength increased by 24.58%and no cracks were observed after 30 thermal shock cycles,while general clay would reduce the thermal shock resistance of SiC.The SiC-mullite-Al2O3 composites with satisfied performance are expected to be used as thermal storage materials in solar thermal power generation systems.

FRACTURE RESISTANCE OF 3D-C/SiC COMPOSITES AT 1300℃

Based on the energy conservation, the elastic energy linked to the compliance change, non-elastic energy dissipated by irreversible deformation and the resistance for crack propagation were quantitatively characterized by evaluation the load/load point displacement curves tested by three points bend experiment with single notch beam at 1300℃. The cracks length was determined by compliance calibration curves. It is shown by experimental results that the compliance of 3D-C/SiC composites changes with the cracks can be described by third order polynomial. The variation of crack advancing resistance with non-dimensional equivalent crack length presents a convex curve. The crack advancing resistance increases firstly and then decreases with the non-dimensional equivalent crack length, finally is in comparatively low level. The maximum values of crack advancing resistance are 269.73kJ/m2 for non-dimensional equivalent crack length of 0.318 and original notch length of 0.35mm, and 138.65kJ/m2 for non-dimensional equivalent crack length of 0.381 and original notch length of 2.06mm, respectively.

In-situ Synthesis and Oxidation Resistance of Sialon/SiC Composite Ceramics Applied as Solar Absorber

Sialon/SiC composites were synthesized in situ from SiC,α-Si_(3)N_(4),AlN,calcined bauxite,quartz and Y_(2)O_(3) via layered buried sintering at different temperatures (1 540-1 640 ℃).The results showed that the O’-sialon/SiC sample with 60 wt% silicon carbide sintered at 1 600 ℃ exhibited excellent mechanical properties,with apparent porosity of 16.01%,bulk density of 2.06 g·cm^(-3),bending strength of 52.63 MPa,and thermal expansion coefficient of 5.83×10-6 ℃^(-1).The oxide film formed on the surface was linked closely to O’-sialon,so the oxide film was not easily broken.After 100 h oxidization,the sample surface was smoother and denser,with oxidation weight gain rate 23.6 mg/cm^(2) and oxidation rate constant 2.0 mg^(2)·cm^(-4)·h^(-1).Therefore,the sample had the excellent high-temperature oxidation resistance.It was confirmed that the in-situ sialon/SiC composites could be a promising candidate for solar absorber owing to its high-temperature oxidation resistance.

316L不锈钢掺杂SiC环状同轴送粉TIG熔覆层组织结构与性能

TIG熔覆是经济高效的表面修复方法,与传统的预置粉末法相比,同轴送粉法具有优良的适应性,但是试验研究相对较少.自主设计制造了环状同轴送粉TIG熔覆焊枪,与管状同轴送粉TIG熔覆焊枪相比,制造的熔覆层不存在熄弧位置凹坑、焊缝不够平直以及焊缝熔宽不一致等问题,而且具有更高的熔覆效率.结果表明,采用优化的焊接热输入、送粉量和SiC含量参数匹配,在316L不锈钢表面进行环状同轴送粉TIG熔覆,获得了外观优良的单层单道熔覆层、单层多道熔覆层.对熔覆层进行显微硬度测量、微观组织及元素成分分析、宏观电化学腐蚀试验、微区电化学腐蚀试验以及耐磨性能测试,并与母材进行了比对,环状同轴送粉TIG熔覆导入的SiC粉末有效地提升了熔覆层的耐蚀性与耐磨性.

SiC改性提升聚酰亚胺薄膜直流耐电晕性能的机理

传统聚酰亚胺(PI)薄膜应用到更高电压等级设备中,易产生电晕放电甚至绝缘失效。为提升聚酰亚胺薄膜耐电晕能力,实验采取碳化硅(SiC)作为增强相对PI基体相进行改性,探究SiC改性对复合薄膜耐电晕特性的影响机理。实验结果表明,随着SiC含量增加,SiC/PI复合薄膜出现非线性电导特性并逐渐增强,其同步提升的浅深陷阱密度比与载流子迁移率促进了表面电荷消散速率的增加。同时,SiC提升了15 kV直流电压下薄膜的沿面闪络和击穿时间,其中质量分数25%SiC/PI复合薄膜较纯PI膜分别提升了416.28%和298.39%。这是因为增强的非线性电导率和表面电荷消散速率,有利于空间和表面电荷运输,减少电场畸变,从而提升复合薄膜的耐电晕能力。对电晕损伤薄膜的无损区、圆状白斑区和白色堆积区进行形貌观测,发现SiC颗粒会在等离子体碰撞下形成放电阻挡层,有效减少电晕对基体相的侵蚀,延长了复合薄膜的耐电晕时间。最后发现质量分数15%SiC/PI复合薄膜为综合耐电晕与力学特性下的最优选择。

国产SiC功率模块热阻测试方法研究

为解决国产SiC功率模块的热阻不能准确测试的问题,开展了非开关式电学法在线测量模块热阻的研究。提出模块热阻测试方案,设计搭建模块热阻测试平台,结合器件结构特点和工艺特点,研究获得适用于模块的热阻测试方法,并选用两款典型SiC功率模块进行了验证,验证了测试结果的准确性。

High-performance 4H-SiC junction barrier Schottky diodes with double resistive termination extensions

4H-SiC junction barrier Schottky （JBS） diodes with a high-temperature annealed resistive termination extension （HARTE） are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 mΩ·cm^2 with a total active area of 2.46× 10 ^-3 cm^2. Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7 V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250 ℃ in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9× 10^-5 A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure.

浆料浸渍辅助PIP工艺制备C/HfC-SiC复合材料的微观结构及性能研究

针对高速飞行器对于防热/承载一体化超高温陶瓷基复合材料的迫切需求,以及现有反应型HfC先驱体存在的成本高、效率低和致密效果差等不足,本研究将HfC亚微米粉体配制成稳定的陶瓷浆料,利用浆料加压浸渍辅助先驱体浸渍裂解(PIP)工艺制备了HfC基体均匀分布的C/HfC-SiC复合材料,探讨了HfC含量对于复合材料微观结构、力学与烧蚀性能的影响。结果表明,当HfC实际体积分数为13.1%~20.3%时,复合材料密度为2.20~2.58 g·cm^(-3),开孔率约为5%。通过单层碳布加压浸渍陶瓷浆料,HfC颗粒能够分散到纤维束内部,且在复合材料中分布比较均匀。提高HfC含量会降低复合材料纤维含量,其力学性能也呈现出降低趋势。当HfC体积分数为20.3%时,复合材料的密度、拉伸强度和断裂韧性分别为2.58 g·cm^(-3)、147 MPa和9.3 MPa·m^(1/2);经氧乙炔焰烧蚀60 s后,复合材料的线烧蚀率和质量烧蚀率分别为0.0062 mm/s和0.005 g/s,烧蚀过程中形成的熔融相Hf_(x)Si_(y)O_(z)能覆盖在材料表面,起到良好的保护作用。

60%SiCp/2009铝基复合材料表面等离子体电解氧化膜的生长和表征

在硅酸盐溶液中采用等离子体电解氧化技术在60%SiCP(体积分数)/2009铝基复合材料表面制备陶瓷膜。研究氧化膜的显微组织、成分、润湿性及其耐腐蚀性能,探讨SiC颗粒表面火花放电的产生机理。结果表明,来自硅酸盐溶液的不溶性化合物(SiO_(2))使SiC颗粒表面产生火花放电,Al-Si-O化合物中的缺陷为SiC颗粒表面放电电流的传导提供优先路径。1200s时铝基复合材料表面形成5.5μm厚的均匀膜层,膜层的表面自由能在40s时达到最大值37.10 m J/cm^(2),并在1200 s时下降到25.95 m J/cm^(2)。此外,等离子体电解氧化处理可以显著提高复合材料的耐蚀性。

CeO_(2)/MoSi_(2)改性ZrB_(2)-SiC陶瓷的烧结性能及耐烧蚀性能

无压烧结ZrB_(2)-SiC陶瓷可制备复杂形状构件,但致密化难且耐烧蚀性能有待提高,因此亟需研究能够改善陶瓷致密化的有效烧结助剂。本文采用CeO_(2)和MoSi_(2)为烧结助剂,在1850℃无压烧结1 h条件下制备了ZrB_(2)-SiC陶瓷,研究了CeO_(2)和MoSi_(2)对ZrB_(2)-SiC陶瓷烧结性能和耐烧蚀性能的影响。结果表明,当5%(体积分数)的烧结助剂中CeO_(2)和MoSi_(2)体积比为1∶1时,ZrB_(2)-SiC陶瓷的烧结性能、耐烧蚀性能最佳。烧结助剂在烧结过程中形成Ce-Mo液相,陶瓷颗粒在液相的表面张力下重排和传质,Ce-Mo液相促进陶瓷颗粒在毛细力下形成烧结颈,填充于陶瓷颗粒的间隙中,并在降低陶瓷晶粒的晶界能时促进致密化进程,最终获得无压烧结密度为5.02 g/cm^(3)、相对密度为89.71%、维氏硬度为14.04 GPa的ZrB_(2)-SiC陶瓷。相对于未添加烧结助剂时,实际密度提高了53%,维氏硬度提高了43%。在烧蚀过程中,烧结助剂适量补充SiO_(2)后可促进黏度适宜的玻璃相自愈合,并提高ZrO_(2)的稳定性,使ZrB_(2)-SiC陶瓷具有最好的耐烧蚀性能,此时ZrB_(2)-SiC陶瓷质量烧蚀率为-1.62 mg/s,线烧蚀率为0.33μm/s。

SiC纳米线对大气等离子喷涂硅涂层性能的影响

为提升C/SiC复合材料表面Si涂层的韧性及其与C/SiC复合材料的结合强度,首先以10 mm×10 mm×10 mm的C/SiC复合材料作为基体,在基体表面生成约20μm厚的SiC纳米线(SiCnws)多孔层;再用大气等离子体喷涂法分别将生长SiCnws的基体和未生长SiCnws的基体喷涂约30、60、90μm厚的Si涂层。研究SiCnws对涂层试样的结合强度和抗氧化性的影响,并借助XRD、SEM、TEM和EDS对所制备的SiCnws和SiCnws/Si涂层进行物相组成、显微结构的分析。结果表明:1)制备的SiCnws形状平直,表面光滑,取向随机,直径为100~200 nm,是沿[111]晶向择优生长的β-SiC;2)SiCnws引入到Si涂层后,SiCnws/Si涂层试样的结合强度均比相应的Si涂层试样的高,说明SiCnws增强了Si涂层与C/SiC复合材料的结合;3)从室温至1400℃经历12次热震循环后,SiCnws/Si涂层试样的质量损失率比相应Si涂层试样的低20.7%~37.2%,说明SiCnws能有效缓解热应力,抑制裂纹的形成和扩展,降低裂纹尺寸和数量,提高涂层的抗氧化性。

SLM成形AlSi10Mg合金及SiC/AlSi10Mg复合材料的耐蚀和耐磨性能

利用SLM成形制备SiC/AlSi10Mg复合材料,采用XRD,SEM,EDS,EBSD,电化学方法和摩擦磨损实验分析其物相特征、微观组织和耐蚀、耐磨性能,并与SLM成形AlSi10Mg合金进行对比。结果表明:在3.5%(质量分数)NaCl溶液中,SLM成形SiC/AlSi10Mg试样的腐蚀电流密度(2.0827μA/cm^(2))小于SLM成形AlSi10Mg试样的腐蚀电流密度(3.389μA/cm^(2)),同时SLM成形SiC/AlSi10Mg试样表面钝化膜的厚度(7.1 nm)大于AlSi10Mg试样表面钝化膜的厚度(1.9 nm),说明SLM成形SiC/AlSi10Mg试样耐蚀性能更优。究其原因为,SiC加入后引起晶粒细化、大角度晶界比例增多及铝基体连续性破坏,进而导致腐蚀速率减缓,耐蚀性能增强。此外,与SLM成形AlSi10Mg合金的硬度(103.58±7.41)HV_(0.2)相比,SLM成形SiC/AlSi10Mg复合材料的硬度(207.68±16.02)HV_(0.2)大约是前者的2倍,硬度明显提高,耐磨性能增强;SLM成形AlSi10Mg和SiC/AlSi10Mg的磨损机制均以磨料磨损和氧化磨损为主。

原位自生SiC晶须对原料预氧化SiC耐磨材料显微结构和性能的影响

以Si粉、活性炭、预氧化的SiC颗粒为原料,于埋炭条件下经1500℃保温3h烧制后,制备出了原位自生SiC晶须复合SiC耐磨材料,并研究了SiC晶须对原料预氧化SiC耐磨材料性能的影响,并分析了这些性能和显微结构间的关系。结果表明,原位自生SiC晶须可提高SiC耐磨材料的致密度和力学性能,并在Si粉和活性炭共同添加量为12 wt.%时改善效果较佳,对应试样的抗冲击强度和硬度分别为29.91 kJ·m^(-2)和98(HRB),磨耗比为4.49。这是因为原位自生的SiC晶须充填在SiC颗粒间的孔隙中,形成了均匀的网络结构,且其伴生的SiO_(2)和SiC原料预氧化的产物SiO_(2),均可与α-Al_(2)O_(3)添加剂反应生成莫来石,增强了晶须与基体间的结合力。当SiC耐磨材料受到外力作用时,这些与基体结合较好的SiC晶须,可通过拔出、裂纹的偏转和桥联等途径改善SiC耐磨材料的力学性能。

Corrosion Resistance of Ceramic Materials in Metallic Neodymium and NdF_3-LiF-Nd_2O_3 System

Corrosion resistant properties of Si3N4-SiC and TiB2 at high temperature were studied. The experiments were carried out in metallic neodymium and NdF3-LiF-Nd2O3 system, respectively. Corrosion temperature was 1100 ℃ and the holding time of corrosion experiments was 24 h. Corrosion products were analyzed by XRD and SEM, and corrosion behavior and corrosion mechanism of the experiments were studied. The results showed that Si3N4-SiC was corroded seriously in the above-mentioned two systems. A few of compounds were found on the surface of Si3N4-SiC, and surface structure of the Si3N4-SiC samples was loosened. The corrosion resistance of TiB2 was better than that of Si3N4-SiC. Oxidation resistance of TiB2 at high temperature should be enhanced.

喷涂-烧结法制备SiC涂层及抗冲蚀性能的研究

为了提高低密度C/C复合材料的抗冲蚀性能,使用喷涂-烧结法在其表面制备了均匀完整的SiC涂层,研究了反应原材料中蔗糖、葡萄糖、活性炭、磷粉四种碳源对SiC涂层的物相组成、微观形貌以及抗冲蚀性能的影响。结果表明:碳源种类对涂层中的物相组成产生影响,蔗糖和葡萄糖作为碳源时涂层均以单一的SiC物相存在,在10次冲蚀性能测试后涂层仍完整覆盖基体表面,冲蚀损失率分别为1.288%和1.144%,可能是由于残碳现象的改善以及大体积SiC颗粒的生成使冲蚀粒子发生了回弹作用,导致抗冲蚀性能提升。