等离子喷涂羟基磷灰石涂层的相组成及其结构

研究纯钛表面羟基磷灰石(HA)涂层的相组成及其微观结构,为涂层性能与制备工艺优化提供依据.采用等离子喷涂法制备HA涂层,用X射线衍射仪和透射电子显微镜进行相细成与微观结构的表征.研究表明:涂层主要由晶相HA、非晶相和分解相组成,随喷涂功率的提高,非晶化加剧,CaO含量提高;在TEM下观察到HA晶体与非晶体共存区、HA与磷酸三钙徽晶的共存区,以及HA与Ti的反应产物CaTi03;除工艺原因外,羟基磷灰石复杂的结构和混合键的结合也是其形成非晶态的主要原因.     

等离子喷涂-激光重熔陶瓷涂层存在问题及改进措施

等离子喷涂是目前国内、外最常用的金属表面陶瓷涂层技术，但涂层的组织呈粗大的片层状、孔隙度较高、裂纹较多，且涂层与基材间为机械结合。等离子喷涂层的激光重熔为这一技术难题的解决提供了一条新的途径，使陶瓷材料的优异性能充分发挥出来。为此，综述了国内、外激光表面重熔等离子喷涂陶瓷涂层的研究现状，总结了等离子喷涂陶瓷涂层激光重熔后的组织特征与性能特点，分析了激光重熔过程中存在裂纹和剥落等问题的原因，提出了这些问题的解决途径，并展望了该项技术的应用前景。     

Adhesion behavior of plasma sprayed thermal barrier coatings on Al-6061 and cast iron substrates

In this work an investigation was carried out on adhesion strength and micro-hardness of plasma sprayed coatings on Al-6061 and cast iron substrate materials. For the adhesion test, ASTM C633, and for the micro hardness, ASTM E384 standards were used. From the results obtained it was found that the main failure locations were in the bond coat-substrate interface, which is considered as adhesion strength. The various parameters affecting adhesion strength are also discussed.     

Cyclic oxidation behaviour of plasma sprayed metallic coatings

High temperature Co- and Ni-based metallic coatings of various compositions were applied on SS-310 samples using plasma spray technique. The coated samples were exposed to air under cyclic conditions at 900°C for upto 100?h. Adhesion of coatings was measured using standard ASTM C 633-79 method. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy was used to determine the surface morphology and microchemical constitution of coatings. X-ray diffraction was used to identify different phases formed during oxidation. Experimental results indicated that high temperature oxidation of SS-310 alloy was greatly reduced by all coatings. The plasma sprayed metallic coatings on SS-310 alloy performed better than that of bare SS-310 under the selected test conditions. Moreover, when compared among the selected metallic coatings used in the study, the Co-based coatings with higher Cr concentration exhibited superior performance compared to Ni-based coating with lower Cr concentration during the reported cyclic exposure.     

Synthesis of nanophase alumina, and spheroidization of alumina particles, and phase transition studies through DC thermal plasma processing

Using a non-transferred DC plasma spray torch, nanosized alumina particles were synthesized from micron-sized aluminium particles. Irregular-shaped micron-sized alumina particles were spheroidized using the plasma spray torch. The synthesized powder particles were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis, Fourier transform infra-red (FT-IR) spectroscopy and photoluminescence (PL) spectroscopy. The synthesized alumina nanoparticles appear spherical in shape, but mostly agglomerated in the size range 30-75 nm. It was identified that the main phase is γ-alumina with a small amount of δ-alumina. In the spheroidized alumina particles, the main phase is α-alumina with a small amount of γ-alumina. The mechanism of formation of alumina and its phase change are explained in detail.     

Phase, structural and microstructural investigations of plasma sprayed hydroxyapatite coatings

The properties and performance of plasma sprayed hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, i.e. HA) coatings are closely related to their manufacturing process. The objective of the current study is to investigate the phase, structure and microstructure of the coatings and their formation mechanism due to different processing parameters. Hydroxyapatite powders were atmospherically plasma sprayed (APS) using various process parameters. The phase, structure and microstructure of the coatings were investigated and their microhardness measured. Both crystallinity and hydroxyl contents decreased with increasing spray power and stand-off distance (SOD), and increased from the coating interface to the surface. Crystallinity alone cannot reflect coating quality due to the existence of various forms of HA, i.e. unmelted, recrystallized and dehydroxylated, as well as the gradient structures consisting of these forms. Coating microstructure varied from a porous structure to a smooth glassy structure or a typical lamellar structure, and some newly formed nanocrystalline regions were revealed. These effects were associated with the temperature–time experiences of particles, their cooling rates and the heat and hydroxyl accumulation during coating buildup. The coating with highest recrystallization displayed the highest microhardness.     

Characterization of plasma sprayed coatings using thermal wave infrared video imaging

A pulsed (time-domain) thermal wave infrared video imaging technique, using an IR camera, a video image processor, and a flash lamp, is described. This system is applied to the imaging of interfacial defects in plasma sprayed coatings on metallic substrates. Results are compared with the conventional point-scanned cw infrared thermal wave imaging technique.     

Nitridation of aluminum particles and formation process of aluminum nitride coatings by reactive RF plasma spraying

Nitridation of aluminum particles and formation process of aluminum nitride coatings by reactive RF plasma spraying was investigated by collecting splat and depositions and fabrication of the coating. Nitriding reaction of aluminum particles during flight in the plasma and after deposit on the substrate was confirmed by the observation of splats and the deposition morphologies, respectively. However, as nitriding reaction of aluminum particles easily forms brittle agglomerates on the substrate, the formation of sound coating was difficult. Though the coating was fabricated with the spraying condition of RF power of 5 kW, it was impossible to fabricate the coatings with RF power of 6 kW. In order to fabricate aluminum nitride coatings by reactive RF plasma spraying, it is necessary to control the plasma and the substrate temperature for the suitable conditions with changing RF power and nitrogen gas flow rate.     

A study on sliding and erosive wear behaviour of atmospheric plasma sprayed conventional and nanostructured alumina coatings

Alumina coatings on stainless steel substrate (SS304) were deposited by using atmospheric plasma spray technique with a feed stock of manually granulated and sieved nano Al₂O₃ powder. The hardness, sliding, and erosive wear of the nanostructured alumina coatings (NC) were investigated and compared with that of conventional alumina coatings (CC). Pin-on disc type sliding wear test on the alumina coatings (NC and CC) was performed with load varying from 30 N to 80 N at a sliding speed of 0.5 m/s. Pot type slurry erosion test of the coatings was conducted for different concentrations of Al₂O₃ and a mixture of Al₂O₃ and SiO₂ slurry. The microstructural features of both NC and CC of alumina were characterized by using FE-SEM/EDS and SEM analysis to substantiate the failure of coatings due to wear. Wear and erosion resistance of nano alumina coating is better than the conventional alumina coating as observed in the present work. The bimodal structure of NC contributes for the enhanced wear resistance. The high fracture toughness of NC is due to suppression of cracks by partially melted particles in the coatings.     

结晶器铜板等离子喷涂镍-石墨涂层的耐磨性

为提高连铸结晶器铜板的使用寿命和铸坯质量,采用超音速等离子喷涂技术在结晶器铜板材料Cr-Zr-Cu基体上制备镍-石墨自润滑涂层,利用扫描电镜(SEM)对喷涂粉末和涂层的组织形貌进行表征,通过球-盘式摩擦磨损实验研究载荷和温度对镍-石墨自润滑涂层、摩擦系数、磨损量的影响,并对涂层的磨损机制进行分析.结果表明:利用超音速等离子喷涂制备的镍-石墨涂层与基体结合良好,结构致密;涂层的摩擦系数和磨损量均随着载荷的增加而增加,不同载荷下涂层的磨损机制均是磨粒磨损,且随着载荷增加,磨粒磨损加剧;涂层的摩擦系数随着温度的增加而增加,且磨损机制均为氧化磨损,但是温度为225℃时,以石墨的润滑作用为主,温度为425℃时,石墨相被氧化镍覆盖,石墨的润滑作用降低,以氧化镍的润滑作用为主.镍-石墨涂层能显著降低Cr-Zr-Cu基体的摩擦系数和磨损量,提高结晶器的耐磨性能.     

Mechanical properties of thermally sprayed Fe based coatings

Abstract

An additional coating against wear or corrosion on component parts is required for many applications. These coatings protect the substrate material against external influences, thus increasing the economic lifetime of the component. Coating processes such as build-up welding and thermal spraying are well established and commonly used. The thermal spray process, in particular, permits deposition of metals, ceramics, or cermets materials to produce near net shape coatings on complex surface geometries. However, commonly used coating materials suffer from high raw material costs, thus decreasing the cost effectiveness of the coating process. Fe based materials are low priced and possess noteworthy mechanical properties; they thus provide the possibility of substituting the expensive Ni and Co based materials commonly used for thermal spray processes. In this work, 2 mm thick high velocity oxyfuel sprayed Fe based coatings in the as sprayed and thermally sprayed and hot isostatic pressed condition were investigated with respect to their mechanical and wear properties. Additionally, the fracture surface was investigated by scanning electron microscopy to characterise the fracture behaviour. It could be demonstrated that the substrate and the heat treatment have the greatest impact on the shear strength of thermally sprayed cold work tool steel. It is shown that the substrate materials as well as the heat treatment are promoting diffusion processes across the interface between the coating and the substrate. Hence, a material integrated bond is formed. The microstructures of the thermally sprayed coatings become more important regarding the mechanisms of failure of the four point bending tests. The material strength is influenced by quenching and tempering and the specimen deflection is influenced by diffusion reactions induced by hot isostatic pressing treatment. The thermally sprayed coatings in the as sprayed condition feature the highest wear resistance due to their hardness.     

The contribution of ion plasma sprayed coatings to performance of diamond dressing tools

The paper addresses the effect of ion plasma sprayed coatings on performance of diamond dressing tools under diamond abrasive machining conditions. The use of thick wear-resistant titanium nitride and carbide coatings with a compensating interlayer of a plastic metal (cobalt) is demonstrated to be a promising method for improving efficiency of dressing tools manufactured by electroplating and electroforming.     

Ti-Al球磨粉反应等离子喷涂涂层的组织与性能

为制备Ti-Al金属间化合物复合涂层并研究其性能,以机械球磨的Ti-Al混合粉在Q235钢表面进行反应等离子喷涂实验,分别采用X射线衍射、扫描电子显微镜对涂层的成分、显微组织进行了分析,并测试了涂层的结合强度、显微硬度和耐腐蚀性能.结果表明:涂层由Al3Ti、TiN、Al2O3、少量TiAl与Ti3Al、以及残留的Al和Ti组成;球磨可促进喷涂时的反应,但喷涂时Al和Ti仍未完全反应,且在空气环境中喷涂容易氧化和氮化;涂层与基体之间是镶嵌式的机械结合,结合强度平均为30.24 MPa;涂层表面的显微硬度平均为206.1 HV,涂层的耐腐蚀性优于基体.总体上看,当球磨时间较长、电流较大、喷涂距离较大、气流量较小时,喷涂时的反应较充分,且涂层比较均匀、致密,其强度、硬度以及耐腐蚀性能较高.     

Properties of titania/hydroxyapatite nanostructured coating produced by gas tunnel type plasma spraying

Anatase phase titanium dioxide has a photo-catalytic performance for environmental protection. In this study, titanium dioxide/hydroxyapatite photo-catalytic coating was deposited by gas tunnel type plasma spraying using powders with nano-sized grains. The porous structure coating with high photo-catalytic activity could be prepared to vary the injecting position of powder. The phase compositions and microstructures of the coating were characterized using X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM), etc. The results showed that the porous structure coatings with relatively high anatase content could be obtained by controlling the injecting position of the powder. The bimodal microstructure of the coatings was also controllable.     

Novel structured yttria-stabilized zirconia coatings fabricated by hybrid thermal plasma spraying

Yttria-stabilized ZrO₂ powders with initial sizes of 5–22 mm were chsosen as feedstock for hybrid thermal plasma deposition. At 100 kW RF input power, the microstructures of the deposited coatings varied from mostly sprayed splats to physical-vapor-deposited nanostructures when the powder feeding rate was reduced from 4 to 1 g/min. At a powder feeding rate of 2 g/min, a peculiar layered coating consisting of both structures was deposited at a rate over 50 mm/min, which is promising for the fabrication of next-generation novel thermal barrier coatings.     

Accelerating the decarbonization of carbonaceous gold ore by suspension oxidation roasting towards the improvement of gold leaching efficiency

Eliminating the gold preg-robbing effect of carbonaceous matter in carbonaceous gold ores is crucial for gold leaching. In this study, suspension oxidation roasting was proposed to accelerate the decarbonization of carbonaceous gold ore. The characteristics of oxidation reaction process and gas release were analyzed by TG-DTA-FTIR. The phase transformation and microstructure evolution of samples during roasting were analyzed by XRD, SEM and BET. The results show that the gold preg-robbing effect was eliminated after the gasification of carbonaceous matter, and the CaO generated by decomposition of carbonates can effectively capture the SO₂. After roasting for 75 min at 650 °C in a 20% O₂ atmosphere, the total carbon removal rate reached 99.42%, the distribution of exposed gold increased from 28.85% to 77.10% and the gold leaching efficiency increased from 4.55% to 84.83%. In addition, about 70% sulfur was mainly fixed in the roasted products in the form of sulfate. Therefore, the suspension oxidation roasting process is an efficient and clean pretreatment method for carbonaceous gold ores.     

超音速电弧喷涂Ti-Al涂层抗滑动磨损性能研究

采用二次正交回归试验设计原理和钛铝双丝超音速电弧喷涂Ti-Al合金复合涂层方法，对LY12铝合金进行了表面强化研究，并采用金相、XRD、SEM、硬度和磨损试验方法，对涂层的组织结构及力学性能进行了表征，考察了喷涂工艺参数对涂层孔隙率、显微硬度和耐滑动磨损性能的影响，研究结果表明：在本文的实验条件下，涂层的体积磨损量、孔隙率、显微硬度与喷涂电压和喷涂距离之间的变化规律，可用回归模型进行描述；随喷涂电压的增大，涂层磨损量逐渐下降；喷涂距离小于220mm时，随喷涂距离的增大涂层磨损量逐渐增大；喷涂距离为220mm时，磨损量达到最大，继续增加喷涂距离，涂层的磨损量逐渐下降；在干摩擦条件下，Ti-Al合金涂层的磨损机制主要以化合物相剥落引起的磨粒磨损和氧化磨损为主。     

In vivo biological responses of plasma sprayed hydroxyapatite coatings with an electric polarized treatment in alkaline solution

The plasma sprayed hydroxyapatite coatings were post-treated by an electric polarized treatment in alkaline solution (PAS). The compositions, stabilities, surface charges, bone-like apatite formation abilities of the PAS coatings were investigated. The bioactivity of the PAS coatings was characterized in vivo. The results showed that the stabilities of the PAS coatings were improved because of the increased crystallinity and the decreased impurity phase. The bone-like apatite formation abilities were also improved after the PAS treatment because of the negative charges formed on the coating surfaces. Animal experiments showed that the PAS coatings could accelerate the initial fixation of the implant. The results indicated that the PAS is a promising post-treatment method to improve the biological properties of the plasma sprayed hydroxyapatite coatings.     

Solution precursor plasma sprayed tungsten oxide particles and coatings

Solution precursor plasma spray process was used to deposit single particles and coatings of tungsten oxide (WO₃), and the microstructures of single particles and coatings were characterized by field emission scanning electron microscopy. The effects of substrate temperature and spraying distance on the microstructure of single particles and coatings were studied. In the case of WO₃ particles, the particle spheroidization degree became better as the increase in substrate temperature. When the substrate temperature increased up to 200°C, bubble-like morphologies appeared. For the deposited WO₃ coatings, a highly porous structure was obtained when a 100?mm spraying distance was used. Besides, the grain size of coatings decreased through increasing the spraying distance from 60 to 100?mm.     

Anti-bacterial and cytotoxic properties of plasma sprayed silver-containing HA coatings

Silver-containing hydroxyapatite (HA) coatings have been prepared on titanium substrate by vacuum plasma spraying (VPS) method and anti-bacterial properties of the coatings were examined. Three types of bacteria stains, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, were employed in this test. The results showed that the silver-containing HA coatings exhibited significant anti-bacterial effects against the three bacteria with anti-bacterial ratios higher than 95%. The release of silver ions in the physiological environment ensured excellent anti-bacterial properties of the silver-containing HA coatings. International standard ISO 10993-12 was adopted for cytotoxicity evaluation using fibroblast cell line L929, and it was found that the cytotoxicity for the coatings ranked 0 that showed no cytotoxicity for the coatings. Hemolysis test was processed according to ASTM F 756 standard with anti-coagulated rabbit blood, and the hemolysis ratios of the coatings were below 0.4%, indicating of non-hemolysis for the coatings.