Synthesis,spheroidization and spray deposition of lanthanum zirconate using thermal plasma process

During the last decade, research efforts were devoted to the development and manufacturing of ceramic thermal barrier coatings (TBCs) on turbine parts because the traditional turbine materials have reached the limits of their temperature capabilities. TBCs have been widely used in hot-section metal components in gas turbines either to increase the inlet temperature with a consequent improvement of the efficiency or to reduce the requirements of the cooling air. There are several ceramics that have been evaluated as TBC materials, and lanthanum zirconate (LZ) is one of the most promising among them. The properties namely high-melting point, phase stability up to its melting point, low thermal conductivity, low sintering ability and oxygen-non transparent make the LZ a potential TBC material for high-temperature applications. However, the production methods used to synthesise LZ are highly time consuming and the powder is not commercially available. Hence, in this investigation an attempt was made to synthesise, spheroidize and spray deposit LZ material using thermal plasma process. This paper illustrates the effectiveness of thermal plasma as a major materials processing technique. Suitable characterization techniques have been used to study the material modifications after respective plasma processing exposures.     

等离子喷涂Ag-SnO2涂层的微观结构和性能

采用等离子喷涂技术在铜基体表面制备了Ag-SnO2涂层,应用XRD和SEM对涂层的相结构和微观组织进行了表征,通过拉伸和硬度实验测定了涂层的力学性能,并采用电弧侵蚀实验测试了涂层的耐电弧侵蚀性能。结果表明,所得涂层结构均匀致密,涂层内纳米级SnO2颗粒均匀分布在银基体中;涂层的力学性能和电弧侵蚀性能与块体合金接近;电弧侵蚀试验后,涂层表面阴极斑点分散,烧蚀轻微,表明所制备的Ag-SnO2涂层具有良好的耐电弧侵蚀特性。     

大气等离子喷涂锆酸镧热障涂层

利用自制的稀土元素复合掺杂锆酸镧热喷涂粉末,采用大气等离子喷涂技术,在镍基高温合金表面制备La1.6Nd0.4Ce1.0Zr1.0O7(LNCZ)热障涂层,研究了喷涂参数对涂层沉积率、显微结构、结合强度及抗热震性能的影响。结果表明,增大喷涂功率,降低送粉速率可以有效地提高涂层的沉积率,但对涂层结合和抗热震性能不利。减小喷涂距离不仅提高沉积率,还有利于获得孔径细小、孔隙率适中的层状组织结构,该结构对提高涂层的抗热震性能极为有利。采用DH-1080大气等离子喷涂设备制备LNCZ涂层较好的喷涂条件为:功率40 kW,喷涂距离9 cm,送粉速率12 g/min。     

石墨粒径对反应等离子喷涂TiCN涂层性能的影响

以不同粒径的石墨粉为碳源,采用等离子喷涂的方法制备TiCN涂层。对涂层中的物相、显微硬度、组织形貌进行分析与比较。结果表明,随着石墨粉粒径的减小,涂层中的主相由TiC0.2N0.8变为TiC0.7N0.3,并且石墨粉粒径减小到5μm时涂层中氧化物的含量少,涂层致密,硬度高。     

等离子喷涂氧化锆涂层及激光重熔涂层的摩擦磨损性能

采用等离子喷涂制备了常规氧化锆涂层和纳米氧化锆涂层,并对制备的纳米氧化锆涂层进行了激光重熔处理,系统地研究了3种氧化锆涂层(常规、纳米和激光重熔涂层)在常温和高温下的摩擦磨损性能.结果表明,纳米氧化锆涂层耐磨性能明显优于常规氧化锆涂层,而激光重熔处理后的纳米氧化锆涂层在常温和高温下,都表现出最低的摩擦系数和最好的耐磨性能.这3种涂层的表面粗糙程度、涂层孔隙率和裂纹状况明显不同,从而表现出不同的摩擦磨损特性;说明纳米粉末等离子喷涂结合激光重熔技术是提高氧化锆涂层性能的有效方法.     

Effect of substrate surface temperature on the microstructure and ionic conductivity of lanthanum silicate coatings deposited by plasma spraying

Apatite-type lanthanum silicate shows a high ionic conductivity and low activation energy at intermediate temperature (600-800 °C) compared with Yttria stabilized Zirconia (YSZ). In addition, its excellent stability in a wide oxygen partial pressure range meets the requirement for the electrolyte. Thus it is a potential candidate for intermediate temperature solid oxide fuel cell (IT-SOFC) electrolytes. Moreover, atmospheric plasma spraying is expected to be a promising alternative to other costly or low-deposition rate electrolyte processing methods. However, the amorphous phase and pores existing in the plasma sprayed coatings might impair the stability and the higher ionic conductivity of lanthanum silicate. The present work investigated the effect of substrate surface temperature from 545 °C to 900 °C on the microstructure and ionic conductivity of the lanthanum silicate coating. The crystallinity of as-deposited coatings increased with the increase of substrate surface temperature, whereas the porosity showed a contrary tendency. Ionic conductivity increased about four times with increasing substrate surface temperature, which is related to the low porosity and high crystallinity of coatings. Increasing the substrate surface temperature during plasma spraying is a feasible method to increase ionic conductivity of the lanthanum silicate coatings by reducing the porosity and enhancing the crystallinity.     

Effects of Y2O3 addition on the phase evolution and thermophysical properties of lanthanum zirconate

Lanthanum zirconate (La₂Zr₂O₇, LZ) powders with the addition of various Y₂O₃ contents for potential thermal barrier coatings (TBCs) application were synthesized by solid-state reaction. The structure evolution, sintering-resistance and thermophysical properties of the synthesized powders and sintered ceramics were systematically studied. X-ray diffraction (XRD) results indicate that LZ containing 3–12 wt.% Y₂O₃ mainly keeps a pyrochlore-type structure, and two new phases of LaYO₃ and Y_0.18Zr_0.82O_1.91 are also detected. Raman spectra confirm that the higher the Y₂O₃ content, the easier is the formation of LaYO₃. With the increase of Y₂O₃ content, the linear thermal expansion coefficients (TEC) of different La₂O₃–ZrO₂–Y₂O₃ ceramics may gradually decrease. Additionally, LZ ceramics doped with 3 wt.% Y₂O₃ have the lowest relative density and the highest sintering-resistance among all samples, implying that it is the best candidate for TBCs among those samples in this investigation.     

等离子喷涂制备铁基非晶涂层及其耐磨性

采用等离子喷涂的方法制备铁基非晶涂层,并对不同喷涂功率制备涂层的组织和耐磨性进行了分析。结果表明,3种功率制备涂层表面致密、孔隙率低,且具有较高的热稳定性、硬度和耐磨性。当喷涂功率为30 k W时,涂层非晶程度高;喷涂功率为35和40 k W时,涂层中有Fe2B和Mo6Co6C晶相出现,随喷涂功率增加,涂层硬度和摩擦因数升高,35 k W制备涂层的耐磨性最好。     

Effects of deposition conditions on composition and thermal cycling life of lanthanum zirconate coatings

Lanthanum zirconate (La₂Zr₂O₇, LZ) coatings were prepared under four different deposition conditions by electron beam-physical vapor deposition (EB-PVD). The composition, crystal structure, surface and cross-sectional morphology, cyclic oxidation behavior of these coatings were studied. Elemental analysis indicates that the coating composition has partially deviated from the stoichiometry of pyrochlore, and the existence of excess La₂O₃ is also observed. The deviation could be reduced by properly controlling the electron beam current or by changing the ingot composition. Meanwhile, when the electron beam current was 500 - 600 mA, the thermal cycling life of the coating is superior to other coatings.     

热喷涂制备非晶合金涂层的研究状况

非晶合金是一种极具发展潜力的新兴金属材料.用热喷涂方法制备非晶合金涂层是将非晶推向工程应用的有效方法.从分析非晶合金及其制备特性入手,阐述了非晶合金热喷涂涂层的特性及目前制备非晶合金涂层的两类热喷涂技术路线,展望了热喷涂制备非晶合金涂层未来的发展趋势.     

等离子喷涂梯度热障涂层的抗热震性能

对比研究了等离子喷涂梯度热障涂层与双层热障涂层,试验中梯度热障涂层选用不同比例的NiCoCrAlY与ZrO₂-8%Y₂O₃复合粉末作为梯度过渡层材料,并对两种结构的热障涂层进行了抗热震性能试验。抗热震试验结果表明,梯度热障涂层的抗热震寿命明显高于双层热障涂层的抗热震寿命。     

热喷涂制备纳米涂层的研究现状与展望

从分析纳米粉末用于纳米表面工程所具有的特性入手，阐述了目前纳米粉末制备方法、热喷涂纳米涂层的种类、制备纳米涂层的热喷涂方法。总结了目前用热喷涂制备纳米涂层所面临的难题及现有的解决措施。展望了热喷涂作为纳米表面工程的关键和最有希望的技术，在未来制备纳米涂层方面的发展。     

大气等离子喷涂和超音速火焰喷涂WC-Ni涂层组织结构和性能的对比研究

采用大气等离子喷涂和超音速火焰喷涂技术在不同工艺参数下制备WC-Ni涂层。涂层的相结构和显微组织结构分别采用X射线衍射(XRD)和扫描电镜(SEM)进行表征。涂层的显微硬度、弹性模量和断裂韧性采用显微维氏硬度计进行表征。采用销盘磨损试验对涂层的磨损性能进行表征。结果表明,较大功率下等离子喷涂的涂层较致密,WC相脱碳程度较大。超音速火焰喷涂距离较小时,制备的涂层较致密,脱碳分解程度较小。相比等离子喷涂技术,超音速火焰喷涂制备的涂层中WC相的分解更少,涂层组织结构相对致密,力学性能相对较高,耐磨粒磨损性能较好。致密度相近,但脱碳程度较小的涂层耐磨性能较好。     

电弧喷涂铝基涂层耐腐蚀性能

采用铝带制作粉芯线材,电弧喷涂方法制备铝基涂层.试验对比研究了铝基涂层、Fe-Al涂层和45CT涂层的抗氧化和耐腐蚀性能,以及铝基涂层、Fe-Al涂层和A304不锈钢的耐硫化氢腐蚀性能.试验结果表明,电弧喷涂铝基粉芯线材制备的涂层在650℃高温下具有优良的抗高温氧化性能;在涂盐和硫化氢耐腐蚀环境下,由于铝基涂层的硫化腐蚀反应仅发生在涂层表面,腐蚀层很薄,涂层内部几乎没有受到影响,因此铝基涂层具有优良的耐腐蚀性能.     

爆炸喷涂WC-Co/CoMoCrSi复合涂层的组织与性能

为了提高CoMoCrSi涂层的结合强度和力学性能,采用爆炸喷涂技术制备了WC-12Co涂层作为过渡层的WC-Co/CoMoCrSi复合涂层,借助SEM和EDS等手段分析了涂层截面组织形貌和化学元素组成,采用显微硬度计、万能拉伸机及销盘式摩擦磨损试验机等研究了涂层的力学及摩擦磨损性能。结果表明：在氧燃充枪比为60%的喷涂参数下,制备WC-Co/CoMoCrSi复合涂层平均结合强度高达66 MPa,涂层截面组织致密、均匀,孔隙率小于0.6%,平均显微硬度为667 HV0.1,复合涂层摩擦因数0.53~0.56,具有优异的耐磨性能。     

The role of torch instabilities in the suspension plasma spraying process

In spite of the fact that plasma spraying is a commonly used technique for coating elaboration, it remains important to follow in time the characteristics of the arc jet delivered by the plasma torch. Arc voltage and heat loss measurement could be used, together with the control parameters such as arc current and plasma gas flow rate, to investigate the global behavior of the torch in association with a simple analytical model. It is shown that the specific enthalpy and the isentropic coefficient of the plasma gas have a strong influence on the jet velocity, this latter being also significantly modified by the drift of the torch performance. This work is completed by the analysis of the plasma jet instabilities that are responsible for the discrepancy in particle thermal histories. The rear part of the torch is involved in self sustained oscillations, so that the torch shows the characteristics of a Helmholtz resonator, giving rise to periodic variations of the torch voltage, higher in amplitude than the commonly admitted restrike mode. It is also evoked, that the generated acoustic waves are interacting with the solvent vaporization.     

电弧喷涂FeBC涂层的微观结构与磨粒磨损性能

采用电弧喷涂技术制备了不同硼、碳元素含量的FeBC系涂层。采用光学显微镜、X射线衍射(XRD)、扫描电镜(SEM)等方法分析了涂层的微观组织及相结构,并对涂层的显微硬度和磨粒磨损性能进行了测试。结果表明,制备的FeBC涂层中氧含量较低,含有微小裂纹和未熔颗粒,随着B,C含量的增加,涂层中未熔颗粒增多,所形成的Fe2B,Fe23(C,B)6硬质相可显著提高涂层硬度和耐磨性,试验中添加质量分数为8%的B和0.4%的C时涂层耐磨性能最好,随着B,C含量的继续增加,耐磨性降低。     

等离子喷涂AT13/MoS2复合涂层的组织和耐腐蚀性

采用等离子喷涂技术在45钢基体表面上制备了4种不同MoS2含量的AT13/MoS2复合涂层,研究MoS2含量对涂层组织和耐蚀性能的影响。结果表明,AT13/MoS2复合涂层的孔隙率随MoS2含量的增加而升高。由于较高孔隙率的原因,AT13/MoS2复合涂层在80℃的10%H2SO4腐蚀介质中耐蚀性能下降。     

氧化镧的加入对PREP制备钨粉末性能的影响

采用等离子旋转电极雾化技术(plasma rotating electrode processing,PREP)制备出纯W和W-La合金球形粉末,对比分析了2种类型粉末的化学成分、形貌、物理性能、缺陷和粒度分布。结果表明:PREP法制备的球形纯W粉末表面光滑、球形度高,小于106μm粉末的收得率为70%。在棒料中加入La₂O₃后,大部分La₂O₃在PREP过程中挥发,残余的La₂O₃优先附着于液滴表面,降低了的液态金属钨的表面张力,将小于106μm粉末的收得率提升至90%;但是,表面张力的降低同时也导致W-La合金粉末表面出现少量缺陷。La₂O₃提高粉末收得率的现象为研究提高PREP技术粉末收得率提供了新思路。     

铝基表面等离子喷涂Al2O3-TiO2-Ta涂层的制备及防腐性能

采用等离子喷涂技术在铝基表面构建Al₂O₃-TiO₂涂层和Al₂O₃-TiO₂-Ta涂层。由于钽元素的引入,Al₂O₃-TiO₂-Ta涂层表面形貌更均匀、致密。同时钽金属具有极强的耐酸碱特性,因此,Al₂O₃-TiO₂-Ta涂层相对于Al₂O₃-TiO₂涂层具有更强的耐腐蚀性。Tafel曲线结果显示,Al₂O₃-TiO₂涂层使得基体的腐蚀电位仅正移了99.6 mV,Al₂O₃-TiO₂-Ta涂层使得铝基体腐蚀电位正移了208.9 mV。因此,由于耐蚀性极强的Ta金属的掺入,Al₂O₃-TiO₂涂层的防腐性得到了极大的增强,Al₂O₃-TiO₂-Ta涂层有效地防止铝合金腐蚀。