Velocity and Temperature of In-Flight Particles and Its Significance in Determining the Microstructure and Mechanical Properties of TBCs

The correlation between particle in-flight parameter, defect content and mechanical property of yttria-stabilized zirconia coating was systematically studied in the present work. The melting state of in-flight particle during spraying was simulated using computational fluid dynamics. The results suggested that, with the increase of velocity and temperature of in-flight particles in the plasma jet, the particles changed from partially melted state to fully melted one. As a result, the total defect content of as-sprayed coating gradually decreased, while elastic modulus and microhardness increased correspondingly. However, the fracture toughness of as-sprayed coating reached a maximum value when the total defect content reached approximately 9.1%.     

Temperature Measurement Challenges and Limitations for In-Flight Particles in Suspension Plasma Spraying

Suspension plasma spraying (SPS) acquires a significant interest from the industry. The deposited coatings using this technique were proved to have unique microstructural features compared to those built by conventional plasma spraying techniques. In order to optimize this process, in-flight particle diagnostics is considered a very useful tool that helps to control various spraying parameters and permits better coating reproducibility. In that context, the temperature of in-flight particles is one of the most important key elements that helps to optimize and control the SPS process. However, the limitations and challenges associated with this process have a significant effect on the accuracy of two-color pyrometric techniques used to measure the in-flight particle temperature. In this work, the influence of several nonthermal radiation sources on the particle temperature measurement is studied. The plasma radiation scattered by in-flight particles was found to have no significant influence on temperature measurement. Moreover, the detection of the two-color signals at two different locations was found to induce a significant error on temperature measurement. Finally, the plasma radiation surrounding the in-flight particles was identified as the main source of error on the temperature measurement of in-flight particles.     

气相爆轰压力及环境温度对制备纳米TiO2粉末的影响

采用气相爆轰方法制备出金红石和锐钛矿相混合晶型的纳米二氧化钛粉末,并用X射线衍射(XRD)、透射电镜(TEM)等表征手法,研究了环境温度变化对其晶粒尺寸和晶相结构的影响.结果表明,随着环境温度的升高,所生成的二氧化钛颗粒的尺度变大,产物中金红石相含量增加,锐钛矿相含量减少.通过测定爆轰压力的变化,得出了反应发生爆燃转爆轰的过程中.     

Microstructure and Properties of Plasma-Sprayed Mixture of Cr2O3 and TiO2

Rutile TiO₂ and Eskolaite Cr₂O₃ powders were mechanically mixed and fed into the plasma jet simultaneously. The influence of the ratio of components on behavior of the plasma-sprayed coatings was observed using two different compositions, both at two different feeding distances. The produced coatings were analyzed by XRD, SEM, XPS, and light microscopy. Electrical resistivity was measured at voltages from 1 to 100 V. Photocatalytic decomposition of butane on the coatings was studied using visible light together with a setup typically used for UV-light tests. For the coatings with high TiO₂ content, besides rutile, low anatase content was identified. The coatings with predominant Cr₂O₃ exhibited lower porosity and higher hardness. All coatings are relatively efficient photocatalysts for butane decomposition. Moreover, they have good mechanical properties governed predominantly by Cr₂O₃ content as the harder component. It was proven that the spray process led to obtaining of robust photocatalytically active coatings.     

Effect of Porosity on Photocatalytic Activity of Plasma-Sprayed TiO2 Coating

The effect of porosity on photocatalytic activity of plasma-sprayed TiO₂ coating on steel substrate is studied by varying processing parameters viz. plasma power and powder feed rate. The relationship between porosity content and methylene blue (MB) dye decomposition rate was established to correlate coating microstructure and its photocatalytic activity. The coating with the highest porosity content exhibited best photocatalytic efficiency. The same processing parameters were used to deposit TiO₂ coating on FTO glass. The photocatalytic activity of TiO₂ coating on FTO was 2.5 times better than TiO₂ coating on the steel substrate. TiO₂ coating on FTO glass contains bimodal porosity distribution (micropores and submicron pores) which accelerated MB decomposition by accelerated diffusion of ionic species.     

High Temperature Oxidation of Nickel-Based Cermet Coatings Composed of Al2O3 and TiO2 Nanosized Particles

The use of co-electrodeposited nickel-based cermet coatings has been recently considered as a low cost method for protecting the surface of mechanical equipment and machinery against corrosion and high temperature oxidation that are being used in a new oil extraction techniques known as the in situ combustion (ISC) process. In the ISC process, the presence of high temperature atmospheric air can degrade the surface of commercially alloyed components rapidly. This paper investigates the high-temperature oxidation behaviour of novel nanostructured cermet coatings composed of two types of dispersed nanosized ceramic particles (Al₂O₃ and TiO₂) in a nickel matrix and produced by co-electrodeposition technique. For this purpose, high temperature oxidation tests were conducted in dry air for 96 h at 500, 600 and 700 °C to obtain the mass changed per unit of area at specific time intervals. Statistical techniques as described in ASTM G16 were used to formulate the oxidation mass change as a function of time. The cross-section and surface of the oxidized coatings were examined for both visual and chemical analyses using wavelength dispersive X-ray spectroscopy element mapping, X-ray diffraction and energy-dispersive X-ray spectroscopy. The results showed sub-parabolic oxidation behavior up to 600 °C and quasi-liner at temperatures between 600 and 700 °C for the coatings. The spectroscopy results showed formation of two Ni–Ti–O compounds (Ni₃TiO₅ and NiTiO₃) between the dispersed TiO₂ and nickel that can ultimately reduce the oxidation rate for the coatings.     

超音速等离子喷涂参数对粒子速度温度的影响

采用高效能超音速等离子喷涂系统,选用纯Al2O3粉末,研究了电功率、电流、电压、气体流量、送粉量对飞行粒子速度和温度的影响.研究结果表明:Al2O3粒子的温度、速度随功率的增大分别呈持续上升与先增大后下降的趋势;在相同功率时,电流对粒子速度、温度的影响大于电压的影响;加大主气流量,粒子速度和温度均先增大后减小;增大送粉量,粒子速度先增大后减小,而粒子温度则一直减小.最后结合涂层的形貌、孔隙率、显微硬度,优化出最佳的喷涂参数.     

Study of In-Flight and Impact Dynamics of Nonspherical Particles from HVOF Guns

High velocity oxygen fuel thermal spray has been widely used to deposit hard composite materials such as WC-Co powders for wear-resistant applications. Unlike gas atomized spherical powders, WC-CO powders form a more complex geometry. The knowledge gained from the existing spherical powders on process control and optimization may not be directly applicable to WC-Co coatings. This paper is the first to directly examine nonspherical particle in-flight dynamics and the impingement process on substrate using computational methods. Two sets of computational models are developed. First, the in-flight particles are simulated in the CFD-based combusting gas flow. The particle information prior to impact is extracted from the CFD results and implemented in a FEA model to dynamically track the impingement of particles on substrate. The morphology of particles is examined extensively including both spherical and nonspherical powders to establish the critical particle impact parameters needed for adequate bonding.     

放电等离子烧结过程中粉末颗粒内部温度场的模拟及颈部演变

摘要建立了用于模拟导电材料在放电等离子烧结（SPS）过程中粉末颗粒热传导行为的计算模型,以球形铜粉为研究对象,对颗粒内部温度分布和颈部尺寸变化进行了模拟计算和分析,模拟结果表明;SPS过程中颗粒内部的温度分布极不均匀,烧结颈部的长大速率在烧结过程中并不一致．不同烧结阶段颈部尺寸变化的模拟结果和实验测定结果基本吻合,揭示了SPS过程中烧结颈部形成和长大的根本原因是颗粒接触部位的局部高温。     

Yb2O3／TiO2纳米颗粒的制备及表征

采用溶胶-凝胶法制备了微量 Yb2O3掺杂纳米 TiO2颗粒,采用 XRD, TG-DTA, TEM等手段对试样经不同温度热处理后的结构相变、表面形貌、颗粒大小等特性进行了表征.实验表明温度不高于 400℃时,试样的颗粒粒径较小,粒径在 15 nm以下,比表面积大于 107.22 m2@ g-1, TiO2呈锐钛型;在 400℃以上, TiO2粒径迅速增大,微粒出现锐钛相与金红石相混晶结构;800℃时 TiO2微粒完全转化成金红石相.     

RuO2包覆的TiO2纳米复合粒子的表面与界面分析

将溶胶-凝胶法与水热合成技术相结合制备了RuO2包覆量为1.5%的TiO2纳米复合粒子,并采用X射线衍射(XRD)、原子力显微镜(AFM)、傅立叶变换红外光谱(FT-IR)及X射线光电子能谱(XPS)详细研究了纳米复合粒子的表面与界面性质.结果表明,RuO2以非晶态高度分散在TiO2纳米粒子表面形成包覆层,TiO2的晶型为锐钛矿型;纳米复合粒子呈球形,平均粒径约为47.5nm,RuO2包覆层的平均厚度约为0.75nm;RuO2包覆层与核材料TiO2纳米粒子表面存在化学键的作用,这种化学包覆有利于提高纳米复合粒子结构和性能的稳定性.     

Microstructure and Sliding Wear Performance of Plasma-Sprayed TiB2-Ni Coating Deposited from Agglomerated and Sintered Powder

This work is aimed at developing a route for the deposition of TiB₂-Ni cermet coating. The feedstock was firstly prepared by agglomeration and sintering, which was subsequently subjected to plasma spraying. The microstructures and the phase composition of the powder, as well as the sprayed coating were analyzed by scanning electron microscopy and x-ray diffraction. The microhardness (Hv) and the fracture toughness (K _IC) of the coating were evaluated. A sliding wear test was also performed on the sprayed coating by SRV^® tribo-tester using GCr15 steel as a counterpart. The results showed that the phase of sprayed TiB₂-Ni coatings consisted of TiB₂, Ni, and Ni₂₀Ti₃B₆, whose amount varied depending on the powder calcination temperature and the TiB₂ content in the powder. Both the hardness and the fracture toughness of the coating were also changed with different powders. The Ni₂₀Ti₃B₆ brittle phase was the main factor affecting the fracture toughness of coating, which also had detrimental effect on the sliding wear performance. The 60TiB₂-40Ni coating deposited from the powder calcined at 1250 °C had better sliding wear performance as it presented more dense structure, higher TiB₂ content and less retained Ni₂₀Ti₃B₆ phase in the coating.     

Hybrid Plasma-Sprayed Thermal Barrier Coatings Using Powder and Solution Precursor Feedstock

A novel approach of hybridizing the conventional atmospheric plasma spraying (APS) technique with the solution precursor plasma spray (SPPS) route to achieve thermal barrier coatings (TBCs) with tailored configurations is presented. Such a hybrid process can be conveniently adopted for forming composite, multi-layered and graded coatings employing simultaneous and/or sequential feeding of solution precursor as well as powder feedstock, yielding distinct TBC microstructures that bear promise to further extend coating durability. TBC specimens generated using conventional APS technique, the SPPS method and through APS-SPPS hybrid processing have been comprehensively characterized for microstructure, phase constitution, hardness and thermal cycling life, and the results were compared to demonstrate the advantages that can ensue from hybrid processing.     

等离子喷涂Al2O3与Al2O3/TiO2涂层中的相变及涂层的耐腐蚀行为

研究了采用等离子喷涂法制备Al2O3涂层与Al2O3／TiO2复合涂层，以及喷涂前后涂层中相变及涂层的腐蚀行为。结果表明，在喷涂过程中有9％的α-Al2O3及45％的β-Al2O3转变成为γ-Al2O3；机械混合的Al2O3与TiO2之间没有新相Al2TiO5形成，但有39％的TiO2由金红石晶型转变为锐钛矿晶型。在5％沸腾的HCl内γ-Al2O3及β-Al2O3较α-Al2O3被优先腐蚀，TiO2相也同时被腐蚀。     

Influence of Deposition Temperature on the Microstructures and Properties of Plasma-Sprayed Al2O3 Coatings

Al₂O₃ coatings were deposited on 1Cr13 substrates by atmospheric plasma spraying at different deposition temperatures of 140, 275, 375, 480, 530, and 660 °C to investigate the effect of coating surface temperature on the lamellar bonding formation. The fractured cross section morphology was characterized by scanning electron microscopy to reveal the lamellar interface bonding. X-ray diffraction was used to characterize the phase contents in the coating. Micro-hardness, Young??s modulus, and thermal conductivity of the deposits were measured for examining the dependency of coating properties on its microstructure. The results show that the interface area bonded through columnar grain growth across splat-splat interfaces was increased with increasing deposition temperature. Moreover, micro-hardness, Young??s modulus and thermal conductivity were increased with the increase of deposition temperature. However, the phase structure of the coating changed little with deposition temperature. The results evidently indicate that the apparent bonding ratio and properties of deposits can be significantly changed in a wider range through controlling the deposition temperature.     

Particle In-Flight Velocity and Dispersion Measurements at Increasing Particle Feed Rates in Cold Spray

Cold spray (CS) is attracting interest of research and industry due to its rapid, solid-state particle deposition process and respective advantages over conventional deposition technologies. The acceleration of the particles is critical to the efficiency of CS, and previous investigations rarely consider the particle feed rate. However, because higher particle loadings are typically used in the process, the effect of this cannot be assumed negligible. This study therefore investigates the particle velocities in the supersonic jet of an advanced CS system at low- and high pressure levels and varying particle feed rates using particle image velocimetry. The particle dispersion and velocity evolution along the jet axis were investigated for several feedstock materials. It was found that the average particle velocity noticeably decreases with increasing particulate loading in all cases. The velocity distribution and particle dispersion were also observed to be influenced by the feed rate. Effects are driven by both mass loading and volume fraction, depending on the feedstock’s particle velocity parameter. Increased particle feed rates hence affect the magnitude and distribution of impact velocity and consequently the efficiency of CS. In particular, numerical models neglecting this interconnection are required to be further improved, based on these experimental studies.     

Ce改性TiO2纳米粒子的制备及光催化活性

采用浸渍法制备了Ce/纳米TiO2复合粉体,用XRD对复合粉体的晶体结构进行了表征.以紫外光照下降解甲基橙为目标,研究了Ce掺杂量和焙烧温度对Ce/纳米TiO2复合粉体的光催化能力的影响规律,并分析其机理.结果表明:Ce掺杂能有效地提高纳米TiO2光催化降解甲基橙的能力,在400℃～700℃的焙烧温度下,纳米TiO2为锐钛型晶型结构,0.4%Ce(质量分数,下同)掺杂的复合粉体具有最好的光催化降解甲基橙的能力,其原因在于Ce4+掺杂有利于在TiO2纳米粒子中心和表面之间产生电势差,实现光生电子-空穴对的有效分离,因此存在一个最佳掺杂浓度使得光催化活性最高;焙烧温度对Ce/TiO2纳米复合粉体的影响依赖于Ce的掺杂量,低掺杂量时,较高的焙烧温度降解效果较好;高掺杂量时,较低的焙烧温度降解效果较好.     

Ce改性TiO2纳米粒子的制备及光催化活性

采用浸渍法制备了Ce/纳米TiO2复合粉体,用XRD对复合粉体的晶体结构进行了表征.以紫外光照下降解甲基橙为目标,研究了Ce掺杂量和焙烧温度对Ce/纳米TiO2复合粉体的光催化能力的影响规律,并分析其机理.结果表明Ce掺杂能有效地提高纳米TiO2光催化降解甲基橙的能力,在400℃～700℃的焙烧温度下,纳米TiO2为锐钛型晶型结构,0.4%Ce(质量分数,下同)掺杂的复合粉体具有最好的光催化降解甲基橙的能力,其原因在于Ce4+掺杂有利于在TiO2纳米粒子中心和表面之间产生电势差,实现光生电子-空穴对的有效分离,因此存在一个最佳掺杂浓度使得光催化活性最高;焙烧温度对Ce/TiO2纳米复合粉体的影响依赖于Ce的掺杂量,低掺杂量时,较高的焙烧温度降解效果较好;高掺杂量时,较低的焙烧温度降解效果较好.     

Effect of Powder Injection on the Interfacial Fracture Toughness of Plasma-Sprayed Zirconia

Adhesive strength of the plasma-sprayed thermal barrier coating is one of the most important parameters which influence their durability and reliability during service. While many methods exist to measure the adhesive strength, in general, they require cumbersome and time-consuming specimen preparation. Furthermore, considerations of the adhesion strength from the point-of-view of fracture toughness or for that matter, their systematic correlation to both processing variances are limited. Consequently, there is an opportunity to both simplify the measurement procedure and establish correlations among methods and linkages between processing parameters and interfacial fracture toughness. In this paper, we report results on adhesion strength of plasma-sprayed yttria-stabilized zirconia (YSZ) coating on aluminum substrates based on both interfacial indentation test (to measure interfacial fracture toughness) and the modified tensile adhesive test. Carrier gas flow for powder injection into the plasma torch was systematically varied to introduce variances in particle melting with concomitant impact on the measured adhesive strength. The results indicate the correlation between the particle melting index and the measured interfacial fracture toughness.     

硼热/碳热还原TiO_2合成高纯TiB_2粉末

用B4C在H2气氛中硼热/碳热直接还原TiO2合成TiB2工艺进行初步探讨鸦研究了原料的配比及工艺条件对合成的粉末纯度、粒度及其分布、相结构和形貌的影响。结果表明,原料配比和合成温度是影响粉末质量的关键因素。通过选择适当的原料配比和合成温度,可制得结晶完整,粒度细,纯度高的TiB2粉末,而且其生产效率高,工艺稳定可靠。