In-Flight Temperature and Velocity of Powder Particles of Plasma-Sprayed TiO2

This paper relates to the in-flight temperature and velocity of TiO₂ particles, an integral part of the systematic research on atmospheric plasma spraying of the material. Initial powder feedstock (32-45 μm, 100% rutile phase) was introduced into the plasma jet. Six parameters were selected to represent the versatility of the plasma system and their respective influences were determined according to basic one-at-a-time and advanced Taguchi design of experiments combined with the analysis of variance analytical tool. It was found that the measured temperatures varied from 2121 to 2830 K (33% variation), while the velocities of the particles were altered from 127 to 243 m/s (91% variation). Gun net power was detected as the most influential factor with respect to the velocity of the TiO₂ particles (an increase of 8.4 m/s per 1-kW increase in net power). Spray distance was determined to have a major impact on the in-flight temperature (a decrease of 10 mm in spray distance corresponds to a drop of 36 K). A significant decrease in both characteristics was detected for an increasing amount of powder entering the plasma jet: A drop of 7.1 K and 1.4 m/s was recorded per every +1 g/min of TiO₂ powder.     

等离子喷涂ZrO2热障涂层工艺参数优化设计

为了深入研究等离子喷涂ZrO2粒子的飞行特征与涂层性能之间的关系，采用三水平四因素正交试验法对主气、辅气、电流及喷涂距离等4个主要参数进行了优化设计，并采用DPV2000热喷涂在线监测仪测定了ZrO2粒子的飞行特征参数，通过IA32定量金相分析软件对涂层的孔隙率进行了测试。结果表明，影响ZrO2粒子温度的主要因素为主气和辅气，影响ZrO2粒子飞行速度的主要因素为喷涂距离和辅气。     

等离子喷涂制备WC-Co-Cu-BaF2/CaF2自润滑耐磨涂层及其高温摩擦性能

通过大气等离子喷涂方法,使用自制的含有WC-Co、Cu和BaF2/CaF2共晶体的复合喷涂粉末,制备出WC-Co-Cu-BaF2/CaF2自润滑耐磨涂层。在200℃、400℃和600℃下进行WC-Co-Cu-BaF2/CaF2涂层和WC-Co涂层的高温摩擦试验,用扫描电镜观察涂层磨损表面微观形貌。结果表明:200℃时,由于WC-Co-Cu-BaF2/CaF2涂层摩擦产物层中含有的WC硬质颗粒引起磨粒磨损,该涂层摩擦因数和磨损率相对较高。而400℃和600℃时,WC-Co-Cu-BaF2/CaF2涂层的摩擦产物层中均无WC颗粒存在,且由于涂层中Cu和BaF2/CaF2等固体润滑剂的作用,生成的摩擦产物层光滑且致密,涂层的摩擦因数和磨损率均较低,在400～600℃下表现出比WC-Co涂层优异的耐磨性能。     

等离子喷涂制备TiO2纳米颗粒

采用液料等离子喷涂法，在不同电弧功率条件下，用钛酸丁酯的乙醇溶液作为喷涂原料，制备出了纳米TiO2颗粒。用透射电镜和X射线衍射仪分析了颗粒的显微组织和晶型结构，计算了颗粒中的锐钛矿相和金红石相的含量与晶粒尺寸。研究表明，液料等离子喷涂制备的纳米TiO2颗粒平均粒径为10～50nm，其晶型以锐钛矿为主，且随着电弧功率的增大，锐钛矿含量减少；在文中试验工艺参数下，收集速率为0．8～1．2g／min，收集效率为8％～10％。     

Thermal shock behavior of nanostructured and conventional Al2O3/13 wt%TiO2 coatings fabricated by plasma spraying

The thermal shock behavior of three kinds of Al₂O₃/13 wt%TiO₂ coatings fabricated by plasma spraying was studied in this paper. One kind of those coatings was derived from conventional fused and crushed feedstock powder available commercially; the other two kinds of coatings were derived from nanostructured agglomerated feedstock powders. These two nano coatings possess moderate pores and pre-existing microcracks, they were composed of fused structure and three-dimensional net or skeleton-like structure. For conventional coatings, the pores and pre-existing cracks were bigger, sharp-point and mostly distributed between splats. Thermal shock tests for the three coatings were performed by water quenching method. Testing result showed the two kinds of nano coatings had much higher thermal shock resistance than the conventional coatings. The improved thermal shock resistance for nano coatings could attribute to their improved microstructure and crack propagation mode. The damage evolution and failure mechanism of coatings was quite different at thermal shock temperature of 650 °C and 850 °C, which was explained by a simple model. Different crack propagating modes in nanostructured and conventional coatings during thermal shock tests were due to their different microstructures in these two kinds coatings. The stress state of coating surfaces during the thermal cycles was also discussed in this paper.     

Preparation and spray drying of Al2O3-TiO2 nanoparticle suspensions to obtain nanostructured coatings by APS

Al₂O₃-TiO₂ coatings were deposited on austenitic stainless steel coupons from nanostructured powders by atmospheric plasma spraying (APS). Commercial suspensions of nanosized Al₂O₃ and TiO₂ particles were used as starting materials. Mixtures of these suspensions and of more concentrated suspensions of Al₂O₃ and TiO₂ were then agglomerated into plasma sprayable feedstock. Agglomeration was performed by spray drying, followed by consolidation thermal treatment.These powders were successfully deposited, yielding coatings that were well bonded to the substrates. The coating microstructure thus consisted of semi-molten feedstock agglomerates surrounded by fully molten particles that acted as binders. Agglomerates from suspensions with higher solids contents yielded coatings with lower porosity and fewer semi-molten areas.     

Al_2O_3含量对等离子喷涂TiO_2-Al_2O_3陶瓷涂层组织性能的影响

采用大气等离子喷涂方法制备TiO2–Al2O3陶瓷涂层,利用SEM和XRD分析了涂层的显微组织和相结构,并研究了涂层的电阻率随温度变化的规律。研究结果表明:TiO2–Al2O3陶瓷涂层主要由金红石型TiO2、锐钛矿型TiO2、Magneli相、α–Al2O3及γ–Al2O3组成。涂层的显微硬度和电阻率随Al2O3含量的增加而增加,在通电升温条件下涂层的电阻率随温度升高而降低。     

Influence of Plasma Spray Parameters on the Microstructure and Property of ZrO2-7 wt%Y2O3 Coating

The plasma sprayed ZrO2-7 wt%Y2O3(7YSZ)coating has been widely applied in aircraft engine as a thermal barrier coating.In this study,the duplex TBC system(MCrAlY+7YSZ)were deposited onto 304 stainless steel substrate by APS.Four principal spraying parameters during the deposition of 7YSZ coating were optimized by using orthogonal experimental design,including the stand-off distance,plasma power,preheating temperature and powder feeding rate.Their influences on the coating’s microstructure,adhesion and its mechanical properties were studied and the optimized parameters were finally obtained.The results showed that the dependence of the spraying parameters on the properties of 7YSZ coating is highly correlated to the melting condition of the in-flight particles.     

超音速等离子喷涂工艺参数对 Cr2O3涂层硬度的影响

目的研究影响超音速等离子喷涂Cr2O3涂层硬度的主要因素,制备出高硬度涂层。方法首先采用单变量法研究超音速等离子生成气体压力(空气压力)和喷涂距离对涂层显微结构的影响,然后采用正交试验研究喷涂电流、空气压力、喷涂距离对Cr2O3涂层硬度的影响。结果工艺参数对Cr2O3涂层硬度影响的主次顺序为:空气压力>喷涂电流>喷涂距离。结论获得高硬度涂层的最佳工艺参数组合为:空气压力0.4 MPa,喷涂电流270 A,喷涂距离200 mm。在该工艺条件下获得的涂层致密、均匀,孔隙率小。     

基于响应曲面的Ar气氛超音速等离子喷涂钛涂层

采用超音速等离子喷涂可低成本、高效率制备钛涂层。采用响应曲面法（RSM）中的Box-Behnken（BBD）设计分析了Ar流量、功率、喷涂距离3个因素与超音速等离子射流中钛粒子飞行速度和温度的交互性,利用SEM和显微硬度计研究了钛涂层的微观结构和显微硬度。结果表明：建立的线性模型可靠,喷涂距离对粒子飞行速度和温度影响最大,且随喷涂距离增加粒子飞行速度减小温度增加,而Ar流量和功率对粒子飞行速度和温度的影响与喷涂距离相反。超音速等离子喷涂制备出的钛涂层硬度较低,且呈多孔结构,随粒子飞行速度增加孔隙率降低。     

In-situ TiB2-Al2O3 formed composite coatings by atmospheric plasma spraying: Influence of process parameters and in-flight particle characteristics

In the present study, mechanically alloyed Al-12Si, B₂O₃ and TiO₂ powder was deposited onto an aluminum substrate using atmospheric plasma spraying (APS). The effects of mechanical alloying (MA) time and plasma parameters (arc current and primary/secondary/carrier gas flow rate) on in-situ reaction intensity and in-flight particle characteristics (temperature and velocity) have been investigated. It has been observed that MA time has a remarkable effect on powder morphology and relative amount of in-situ formed TiB₂ and γ-Al₂O₃. In-flight particle diagnostic measurements demonstrate that among the plasma parameters arc current has the strongest effect on in-flight particle velocity and temperature. Also, results indicate that in-flight particle velocity is more dominant than temperature on the relative amount of in-situ formed phases.     

Parameters affecting reaction rate and conversion of TiO2 chlorination in a fluidized bed reactor: Experimental and modeling approach

Pilot scale chlorination of TiO₂ was carried out with CO as reducing agent. The experimental analysis and modeling of chlorination process of TiO₂ in the presence of CO and Cl₂ in a semi-continuous fluidized bed reactor were aimed. Chlorination process was continuously monitored by measuring the amount of produced TiCl₄ with time. The effects of different operating parameters including chlorination temperature, feedstock particle size and size distribution, amount of feedstock and Cl₂ and CO flow rates on the conversion were systematically investigated. A gradual increase in chlorination temperature led to monotonous increase of conversion rate. Conversion decreased with increased particle size of feedstock. An increase in loaded feedstock led to a decrease in reaction conversion. A model was proposed to predict conversion, particle size distribution and mole fraction of components in gas phase as reaction proceeds. A good agreement between conversions predicted by the model and experimental data under various operating conditions was observed.     

高能球磨制备Ni60-TiB2纳米金属基陶瓷结构喂料及其结构特性

以Ni60和TiB2粉为原料,在氩气保护下采用高能球磨技术制备Ni60-TiB2纳米金属基陶瓷结构喂料,并研究了其结构特性。用XRD、SEM、EDS和激光粒度分布仪等对粉末进行表征和分析,结果表明:Ni60-TiB2粉体在室温条件下,经20h球磨后其晶粒尺寸和微观应变分别为38nm和0.237%,显微组织为纳米级硬质相TiB2均匀弥散分布于粘结相NiCr上,粉末近似球状,流动性良好,稍加过筛后可直接用于HVOF喷涂。     

CO2气氛和喷涂距离对电弧喷涂铁基非晶涂层组织及耐蚀性能的影响

为提高电弧喷涂铁基非晶涂层的非晶含量及耐蚀性,以CO₂为载流气体代替空气进行电弧喷涂试验,并研究喷涂距离对涂层组织与耐蚀性的影响。结果表明,喷涂层的厚度约为200 μm,涂层均主要由结晶相与非晶相构成。相比于空气介质,CO₂抑制了晶化,从而提高了涂层中的非晶含量。同时,喷涂距离对涂层的组织及耐蚀性能有较大影响。随着喷涂距离的增加,涂层中的非晶含量减少。当喷涂距离为100 mm时,涂层具有最高的开路电位-0.498 V(vs SCE)及最小的自腐蚀电流密度4.281 μA/cm²,耐蚀性能最好;当喷涂距离为150 mm时,涂层的耐蚀性最差。提高非晶含量和组织的均匀性可增强该涂层的耐蚀性能。     

反应等离子喷涂 Al2O3-TiB2-Al 复相涂层的反应机理

目的在铝合金表面制备Al2O3-TiB2-Al复合涂层,研究Al,TiO2,B2O3在等离子喷涂中的反应机理。方法采用反应等离子喷涂技术在铝合金表面制备复合涂层,应用扫描电镜与X射线衍射技术测试复合涂层的物相组成和显微组织,并通过燃烧波淬熄试验分析等离子喷涂产物。结果机械球磨可以有效降低粉末发生反应的活化能,等离子喷涂最佳飞行距离范围为150~200 mm。结论喷涂粉末在飞行过程中发生反应,经历了预热、熔化、分解、团聚等过程,验证了最终引燃发生燃烧化学反应的机理。     

基于遗传神经网络的等离子喷涂纳米ZrO2-7%Y2O3涂层工艺参数优化

将BP神经网络和遗传算法相结合用于等离子喷涂纳米ZrO2-7％ Y2O3涂层的工艺参数优化,根据正交试验结果对模型结构进行训练,建立了喷涂距离、喷涂电流、主气压力、辅气压力与涂层结合强度和显微硬度之间的BP神经网络模型,并基于遗传算法对涂层结合强度和显微硬度进行了单目标和多目标参数优化.结果表明,模型预测值与试验值十分接近,说明该网络模型是正确和可靠的.遗传算法优化的涂层最大结合强度和显微硬度(HV)分别为44.0 MPa和12.663 GPa;当涂层结合强度和显微硬度两个性能参数权重相同时,在喷涂距离90.66 mm、喷涂电流934.63 A、主气压力0.304MPa和辅气压力0.898 MPa时涂层综合性能最优.     

Electrical Properties of Atmospheric Plasma-Sprayed La10(SiO4)6O3 Electrolyte Coatings

In this present work, La₁₀(SiO₄)₆O₃ as a promising electrolyte candidate for intermediate temperature solid oxide fuel cells (IT-SOFCs) has been synthesized and its electrical property was investigated as a function of temperature. In order to improve the density and oxide ion conductivity of La₁₀(SiO₄)₆O₃, the feedstock powder was prepared by sintering the oxide mixture powders at proper sintering temperatures and times. The hexagonal apatite-type ceramic coatings with a typical composition of La₁₀(SiO₄)₆O₃ were deposited by atmospheric plasma spraying (APS) with different hydrogen flow rates. With increasing hydrogen flow rate oxide ion conductivity successively decreases. The highest ionic conductivity of the dense composite electrolyte coatings reaches a value of 2.4 mS/cm at 900 °C in air, which is comparable to other apatite-type lanthanum silicate (ATLS) conductors.     

超音速等离子喷涂NiCr-Cr3C2工艺的参数优化

采用四因素三水平正交试验,通过在线监测喷涂粒子的温度和速度,对电流、电压、喷涂距离和主气流量四个超音速等离子喷涂的主要参数进行优化设计.结果表明:四个因素对喷涂粒子温度的影响均较大,电压和主气流量对喷涂粒子速度的影响较大;优化的工艺参数为电压150 V、电流400A、喷涂距离85 cm、氩气流量4.2m3/h,采用该优...     

Microstructure and composition analysis in plasma sprayed coatings of Al2O3/ZrSiO4 mixtures

Plasma spraying of Al₂O₃/ZrSiO₄ was performed using spray dried and plasma spheroidised powder feedstock. The mixtures were sprayed using different spray stand-off distances and plasma power levels. X-Ray diffraction (XRD) was used to characterise the phase composition and scanning electron microscopy (SEM) examined the morphology of the sprayed surface and polished cross-sections. The results showed that the plasma spray process parameters played an important role in the final outcome of microstructures of the coatings. The coatings produced with spheroidised powders displayed a much denser structure than those produced with the spray-dried powders. The phase composition analysis showed the presence of amorphous phases in addition to crystalline alumina, zircon and tetragonal (t) zirconia (ZrO₂). Transmission electron microscopy (TEM) showed that amorphous phases and t-ZrO₂ crystals with particle size 100–200 nm could coexist within a single splat due to the relatively low local cooling rate.     

基于孔隙率的Cr2O3涂层工艺优化及回归分析

孔隙率是评价Cr2O3涂层质量的重要指标之一。根据Box-Behnken二阶响应曲面法设计了3因素3水平的回归分析试验,采用大气等离子喷涂技术在TC4钛合金表面制备了Cr2O3涂层,以不同工艺条件下的涂层孔隙率作为响应值,建立了喷涂电流、等离子气体和喷距影响因子与响应输出之间的数学模型,讨论了3种影响因子的显著性及交互作用影响,得到涂层孔隙率的连续变量响应曲面和等高曲线。模型可以用于大气等离子喷涂Cr2O3涂层的工艺优化和性能预测,最小孔隙率的预测参数是电流I=500A,氩气流量QAr=40L/min和喷距d=80mm,能获得的最小孔隙率为1.5%。