AlPO4环境障碍涂层材料水氧腐蚀性能研究

采用溶胶凝胶法合成了一种AlPO₄环境障碍涂层材料,测定了其热膨胀系数,在1350℃、50vol% H₂O/50vol%O₂、1.013×10⁵ Pa、气体流速0.085cm/s的水氧耦合环境中研究了其抗水氧腐蚀性能,并利用X射线衍射仪、能谱分析仪和扫描电子显微镜分析了材料组成和微观结构.结果表明,AlPO₄与C/SiC复合材料热膨胀基本匹配,抗水氧腐蚀性能良好.主要存在的问题是AlPO₄分解引起的失重,二氧化硅会加速其分解.     

WO3/Nb2O5掺杂对碲酸盐玻璃热学性质和拉曼光谱特性的影响

报道了钨碲酸盐玻璃系统TeO₂-ZnO-Na₂O-WO₃ 和钨铌碲酸盐玻璃系统TeO₂- ZnO-Na₂O-Nb₂O₅-WO₃抗析晶热稳定性和拉曼光谱特性. 实验研究了掺杂WO₃和Nb₂O₅对碲酸盐玻璃抗析晶热稳定性和拉曼光谱特性的影响, 并分析讨论了掺杂碲酸盐玻璃拉曼谱带展宽机制. 结果表明, 掺杂WO₃和Nb₂O₅较大地提高了碲酸盐玻璃的抗析晶热稳定性, 钨铌碲酸盐玻璃最大抗析晶热稳定性ΔT达154℃. 拉曼光谱研究表明,WO₃和Nb₂O₅的加入使碲酸盐玻璃在921和862cm^-1附近出现特征谱带, 导致拉曼光谱中高频移区从550cm^-1延伸扩展到950cm^-1, 从而有效地拓宽了碲酸盐玻璃的拉曼带宽, 钨铌碲酸盐玻璃最大拉曼光谱半高宽可达355cm^-1. 实验研究表明,钨铌碲酸盐玻璃是宽带拉曼光纤放大器的候选材料之一.     

原位反应法制备Cf/SiC复合材料MoSi2-SiC-Si涂层

以C_f/SiC复合材料为基体, 采用原位反应法制备了MoSi₂-SiC-Si涂层, 借助XRD、扫描电镜及能谱对涂层的结构及组成进行了分析研究, 并考查了其高温抗氧化性能. 结果表明, 涂层总厚度约120μm, 主要由MoSi₂、SiC和Si组成. MoSi₂-SiC-Si涂层具有优异的高温抗氧化性能, 在1500℃静态空气中氧化96h, 涂层试样失重仅1.8%. 涂层试样失重的主要原因是由于氧气通过涂层中的贯穿性裂纹与C_f/SiC复合材料基体发生了反应.     

铌合金表面高温抗氧化涂层

介绍了铌合金表面高温抗氧化涂层的4大体系--耐热合金涂层、铝化物涂层、硅化物涂层和贵金属涂层的组成、特点及制备条件.我国研究人员围绕飞机发动机涡轮叶片和火箭发动机燃烧室及尾气喷管用铌合金的防护进行了大量研究工作,研制的高温抗氧化涂层已经用于49kN推力发动机铌合围裙和姿态控制铌合金喷管.通过研究认为,PVD和传统熔烧工艺相结合的新工艺及纳米涂层技术是今后铌合金表面高温涂层制备的研究方向.     

Cf/SiC复合材料SiC/(ZrB2-SiC/SiC)4涂层的制备及性能研究

以C_f/SiC复合材料为基体, 采用浆料浸涂法和脉冲CVD法制备了SiC/(ZrB₂-SiC/SiC)₄涂层, 借助XRD、扫描电镜及能谱对涂层的结构及组成进行了分析研究, 并初步考查了其高温抗氧化性能. 结果表明, 涂层总厚度约100μm, 主要由ZrB₂-SiC涂层与脉冲CVD SiC涂层交替覆盖而成. 在1500℃空气中氧化25h, 未涂层试样失重明显; 脉冲CVD SiC涂层试样氧化失重率为5.1%; 而SiC/(ZrB₂-SiC/SiC)₄涂层试样出现增重现象, 增重率达2.5%, 表现出优异的抗氧化性能.     

晶须增强氮化硅陶瓷自生复合材料

本文提出了两种制备氮化硅陶瓷自生复合材料的方法:以氟化钙为添加剂,对硅坯体直接进行氮化;经预氮化后的反应烧结氮化硅多孔体,在含酚醛树脂和硅酸乙酯的无水乙醇溶液中浸渍处理后,再经过高温热处理,分别可得到以β-Si₃N₄和β-SiC晶须增强的氮化硅陶瓷复合材料。同时,还对生长条件对晶须的形态,以及自生晶须对氮化硅陶瓷力学性能的影响进行了探讨。     

纳米TiO2/Sb2O5涂层的光生阴极保护研究

采用溶胶凝胶法在304不锈钢表面制备了纳米TiO₂/Sb₂O₅叠层涂层. 用扫描电子显微镜（SEM）、X射线衍射（XRD）、X射线光电子能谱(XPS)对涂层表面形貌、晶体结构以及组成进行表征. 采用电化学方法研究涂层的光电化学性能与光生阴极保护特性. 结果表明,所制备的纳米TiO₂/Sb₂O₅叠层涂层表面连续、均匀、致密;XRD分析表明纳米TiO₂为锐钛矿型;XPS分析表明纳米涂层表面与内层均由Ti、Sb、O、C四种元素组成;稳定电位与极化曲线测试表明,在3%NaCl溶液中,纳米TiO₂/Sb₂O₅叠层涂层的光电化学性能低于纯纳米TiO₂涂层,但纳米TiO₂/Sb₂O₅涂层经紫外光照1h,停止紫外光照后的延时阴极保护作用可达4h. 通过研究分析,提出了一种新的纳米叠层涂层光生阴极保护作用机理.     

铌上熔盐涂覆NbSi2

Nb是航空应用中很具潜力的材料.但由于铌的氧化膜不具保护性,在600K的大气中就会被氧化,使其应用受到了限制.研究证明,金属间的铝化物或硅化物涂层中的Al2O3或SiO2层可阻止氧的侵入.要得到铝化物或硅化物涂层,热浸是最简单的涂覆方法,Kumon等人曾采用热浸法在Nb上得到了氧化铝膜.但由于Nb-Si体系的最低熔点达到了1668K,要在铌上涂覆硅化铌涂层,使其形成具有保护作用的SiO2层,很难直接通过热浸实现.综合考虑各种沉积方法,认为熔盐涂覆在铌上沉积硅化物比较理想.     

低压沉积温度对MoSi2涂层微观结构与性能影响

以SiCl₄和H₂为原料,采用低压化学气相沉积（LPCVD）渗硅法在Mo基体表面原位反应制备了MoSi₂涂层,研究了沉积温度对MoSi₂涂层微观形貌、物相组成、沉积速率、涂层的硬度、涂层与基体结合强度的影响. 研究结果表明：在1100~1200℃下制备的涂层结构致密,由单一MoSi₂组成,沉积速率、涂层的硬度以及与基体的结合强度均表现为増加的趋势;当沉积温度高于1200℃,涂层出现开裂现象,由游离Si和MoSi₂两相组成,涂层沉积速率、硬度和结合强度均出现下降的趋势. 1100℃以下沉积的主要控制步骤为Si与Mo反应,而1100℃以上Si在涂层中的扩散对沉积过程起控制作用.     

C/C复合材料MoSi2-Mo5Si3/SiC涂层的制备及组织结构

采用化学气相反应法和料浆刷涂反应法, 在C/C复合材料表面制备了MoSi₂-Mo₅Si₃/SiC复合涂层, 借助X射线衍射仪、扫描电镜及能谱等分析手段, 对涂层的形成、组织结构进行了研究, 并初步考察了涂层的高温抗氧化性能. 结果表明: 制备的复合涂层厚度为400μm左右, 主要由β-SiC、MoSi₂及少量的Mo₅Si₃组成. 1350℃等温氧化10h后, 复合涂层试样的氧化失重率只有1.21%, 明显低于C/C复合材料SiC单涂层试样, 其高温抗氧化性能得到明显的提高. 因此, 与C/C复合材料SiC单涂层相比, 经封填改性制得的复合涂层结构更致密, 具有良好的高温抗氧化性能.     

Alkali corrosion resistant coatings for Si3N4 ceramics

The use of ceramic oxide coatings on silicon nitride is one method to improve its alkali corrosion resistance. Four oxide coatings, including (Ca_0.6, Mg_0.4) Zr₄(PO₄)₆ (CMZP), zirconia, mullite and alumina, were examined. These coatings were applied on Si₃N₄ using both sol–gel and dip coating techniques. The coated and uncoated samples were exposed to sodium molten-salt and sodium-containing atmospheres at 1000 °C for 50 h. The weight loss of all the coated samples was less than that of the uncoated Si₃N₄ with CMZP-coated samples exhibiting the smallest weight loss. There was no decrease in the flexural strength of Si₃N₄ after coating with zirconia and CMZP, and a decrease in strength after coating with either mullite or alumina. After alkali exposure, the strength of the CMZP and zirconia coated samples were significantly higher than those of the mullite-coated, alumina-coated, and uncoated Si₃N₄. The observed behaviour is explained in terms of the microstructure and protection mechanisms. This revised version was published online in November 2006 with corrections to the Cover Date.     

多孔氮化硅表面封孔增强涂层研究

以CaO-SiO2-B2O3体系作为α-Si3N4的结合剂和助烧剂,采用溶胶-凝胶法在多孔氮化硅表面制备了防潮增强涂层.采用X射线衍射(XRD)方法对涂层进行了相结构分析;用扫描电子显微镜(SEM)观察了涂层的微观形貌;用阿基米德法测量了封孔前后基体的密度、吸水率和显气孔率;分别在SANS电子式材料实验机和1MHz LCR测试仪上测量了封孔前后材料的抗弯强度、介电常数和介电损耗.结果表明:封孔防潮处理使基体吸水率下降了90.99%～96.97%,强度提高了9%～22%,而对多孔体的密度、介电常数和介电损耗影响很小.     

Oxidation protection of porous reaction-bonded silicon nitride

Oxidation kinetics of both as-fabricated and coated reaction-bonded silicon nitride (RBSN) were studied at 900 and 1000°C with thermogravimetry. Uncoated RBSN exhibited internal oxidation and parabolic kinetics. An amorphous Si-C-0 coating provided the greatest degree of protection to oxygen, with a small linear weight loss observed. Linear weight gains were measured on samples with an amorphous Si-N-C coating. Chemically vapour deposited (CVD) Si₃N₄ coated RBSN exhibited parabolic kinetics, and the coating cracked severely. A continuous-SiC-fibre-reinforced RBSN composite was also coated with the Si-C-O material, but no substantial oxidation protection was observed.     

等离子喷涂制备HA/ZrO2复合涂层

采用等离子喷涂技术,在Ｔｉ－６Ａｌ－４Ｖ基体上成功地制备了羟基磷灰石／氧化锆（ＨＡ／ＺｒＯ２）复合涂层,对涂层的微观结构,相组成和结合强度进行了研究,并以模拟体液试验评估涂层的生物活性,结果表明,复合涂层较有较为微观结构,ＨＡ／ＺｒＯ２复合涂层的结合强度明显高于ＨＡ涂层,ＨＡ／６０ｗｔ％ＺｒＯ２涂层的结合强度高达２８．５ＭＰａ,为ＨＡ涂层的２．２倍,复合涂层在模拟体液中浸泡一段时间后,表面覆盖一层     

Pulse electrodeposition and corrosion properties of Ni–Si3N4 nanocomposite coatings

The development of modern technology requires metallic materials with better surface properties. In the present investigation; Si₃N₄-reinforced nickel nanocomposite coatings were deposited on a mild steel substrate using pulse current electrodeposition process employing a nickel acetate bath. Surface morphology, composition, microstructure and crystal orientation of Ni and Ni–Si₃N₄ nanocomposite coatings were investigated by scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction analysis, respectively. The effect of incorporation of Si₃N₄ particles in the Ni nanocomposite coating on the micro hardness, corrosion behaviour has been evaluated. Smooth composite deposits containing well-distributed silicon nitride particles were obtained and the crystal grains on the surface of Ni–Si₃N₄ composite coating are compact. The crystallite structure was face centred cubic (fcc) for electrodeposited nickel and Ni–Si₃N₄ nanocomposite coatings. The micro hardness of the composite coatings (720 HV) was higher than that of pure nickel (310 HV) due to dispersion-strengthening and matrix grain refining and increased with the increase of incorporated Si₃N₄ particle content. The corrosion potential (E _corr) in the case of Ni–Si₃N₄ nanocomposite had shown a negative shift, confirming the cathodic protective nature of the coating.     

Study on tribological behavior of electrodeposited Cu–Si3N4 composite coatings

Cu–Si₃N₄ composite coatings were prepared by electrolysis from a copper sulphate solution containing dispersed Si₃N₄ particles of 0.4 or 1 μm mean size. Wear behavior of Cu–Si₃N₄ composite and pure copper coatings were evaluated using a pin-on-disc test machine under dry condition sliding. Effects of current density and particle concentration on the incorporation percentage of Si₃N₄, the preferred orientation of copper crystallites, the microstructure, the microhardness and the wear resistance of the coatings were determined. Si₃N₄ particles in the copper matrix resulted in the production of composite deposits with smaller grain sizes and led to change the preferred orientation growth from [1 0 0] to [1 1 0]. It was proved that the presence of Si₃N₄ particles decreases the wear loss and the friction coefficient of the coating. According to the results, the friction coefficient decreased dramatically from 0.52 to 0.26 for pure copper coatings to 0.16–0.24 for Cu–Si₃N₄ composite coatings. In addition, fluctuation of friction coefficient values for Cu–Si₃N₄ composite coating was lower compared with the pure copper coating. The wear properties of Cu–Si₃N₄ composite coatings were shown to depend on the weight fraction, the size and the distribution of co-deposited particles.     

溶胶-凝胶法制备纳米Si3N4(Y2O3)粉末的研究

本文以硅溶胶、尿素和炭黑为原料，采用溶胶－凝胶碳热氮化法在１５００℃、２ｈ条件下制得粒径为５０－８０ｎｍ的Ｓｉ３Ｎ４纳米粉末。比较了由硅溶胶与尿素经氨解合成的前驱体和硅溶胶二种不同起始物料的反应活性，研究了氮化条件对合成反应的影响。结果表明：氨解前驱体使硅溶胶中的结构水排除，有助于加快反应速率，提高产物氮含量。本文同时以Ｙ（ＮＯ３）３为添加剂，在溶液状态与硅源混合，合成了Ｓｉ３Ｎ４－Ｙ２Ｏ３纳米复     

Analysis of coating interlayer between silicon nitride cutting tools and titanium carbide and titanium nitride coatings

Silicon nitride (Si₃N₄) cutting tools exhibit excellent thermal stability and wear resistance in the high-speed machining of cast irons, but show poor chemical wear resistance in the machining of steel. Conventional chemical vapour deposition (CVD) coating of Si₃N₄ tools has not been very successful because of thermal expansion mismatch between coatings and the substrate. This problem was overcome by developing a CVD process to tailor the interface for titanium carbide (TiC) and titanium nitride (TiN) coatings. Computer modelling of the CVD process was done to predict which phases would form at the interface, and the results compared with analyses of the interface. Three Si₃N₄ compositions were considered, including pure Si₃N₄, Si₃N₄ with a glass phase binder, and Si₃N₄ + TiC composite with a glass phase binder. Results of machining tests on coated tools show that the formation of an interlayer provides superior wear resistance and tool life in the machining of steel as compared to uncoated and conventionally coated Si₃N₄ tools.     

新型层状化合物Ti2AlC在酸性溶液中的腐蚀行为

热压烧结得到高纯致密的Ti₂AlC块体.将Ti₂AlC在浓的和稀的HNO₃、HCl及H₂SO₄溶液中浸泡,得到试样的腐蚀速率及腐蚀类型.电化学方法测量试样在三种稀溶液中的腐蚀电位和腐蚀电流及动电位极化曲线.浸泡腐蚀实验发现,Ti₂AlC在酸中的腐蚀类型由点腐蚀发展到晶间腐蚀最后为剥蚀,腐蚀速率随着浸泡时间的延长而不断增大.其中在浓HNO₃中腐蚀速率最大,稀HCl的腐蚀速率最小.除H₂SO₄外,Ti₂AlC在浓酸溶液中的腐蚀率均大于其稀溶液.电化学实验表明,在稀HNO₃中自腐蚀电流最小,自腐蚀电位最大.稀H₂SO₄自腐蚀电流最大.在三种稀溶液中均出现钝化,其中稀H₂SO₄维钝区间最宽.     

Effects of SiC coating on ablation resistance of carbon fibre reinforced BN–Si3N4 matrix composite

Abstract

A SiC coating was prepared on the surface of a carbon fibre reinforced BN–Si₃N₄ composite by chemical vapour deposition. The coating was characterised by SEM and XRD, and the ablation behaviours of the coated and uncoated composites were investigated and compared. The coating is mainly amorphous SiC and quite compact; the ablated area of the composite is reduced considerably by the coating and the coated composite presents a lower linear ablation rate of 21˙4% and a lower mass ablation rate of 51˙6%. The SiC coating covers over the pores on the surface of the ablative composite, which prevents the flame from spreading to other regions and from penetrating the inside of the composite. As a result, both the chemical erosion and the mechanical denudation are restrained and the ablation resistance of the composite is improved.