Effect of Zr on microstructure of metallic glass coatings prepared by gas tunnel type plasma spraying

Metallic glass is one of the most attractive advanced materials, and many researchers have conducted various developmental research works. Metallic glass is expected to be used as a functional material because of its excellent physical and chemical functions such as high strength and high corrosion resistance. However, the application for small size parts has been carried out only in some industrial fields. In order to widen the industrial application fields, a composite material is preferred for the cost performance. In the coating processes of metallic glass with the conventional deposition techniques, there is a difficulty to form thick coatings due to their low deposition rate. Thermal spraying method is one of the potential candidates to produce metallic glass composites. Metallic glass coatings can be applied to the longer parts and therefore the application field can be widened. The gas tunnel plasma spraying is one of the most important technologies for high quality ceramic coating and synthesizing functional materials. As the gas tunnel type plasma jet is superior to the properties of other conventional type plasma jets, this plasma has great possibilities for various applications in thermal processing. In this study, the gas tunnel type plasma spraying was used to form the metallic glass coatings on the stainless-steel substrate. The microstructure and surface morphology of the metallic glass coatings were examined using Fe-based metallic glass powder and Zr-based metallic glass powder as coating material. For the mechanical properties the Vickers hardness was measured on the cross section of both the coatings and the difference between the powders was compared.     

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.     

Initial phase hot corrosion mechanism of gas tunnel type plasma sprayed thermal barrier coatings

The hot corrosion resistance of the top layer in TBC is one of the main constructive factors which determines the lifetime of the coatings under critical operating environments. In the present study, 8 wt% yttria stabilized zirconia (8YSZ), lanthanum zirconate (La₂Zr₂O₇) and equal weight percentage of its composite (50%8YSZ + 50% La₂Zr₂O₇) coatings were prepared by using gas tunnel type plasma spray torch at optimum spraying conditions. The hot corrosion performances of the above thermal barrier coatings were examined against 40 wt%V₂O₅–60 wt%Na₂SO₄ corrosive ash at 1173 K for 5 h in open air atmosphere. After hot-corrosion testing, the coating surface was studied using a scanning electron microscope to observe the microstructure and X-ray diffraction techniques were used to identify the phase compositions. The results showed that LaVO₄ and YVO₄ are the main hot corrosion products along with the ZrO₂ phase transformation from tetragonal to monoclinic phases in La₂Zr₂O₇ and 8YSZ coatings respectively. The microstructure and phase formation mechanism of the hot corrosion products varied with each coating and among these, composition of 50%8YSZ + 50%La₂Zr₂O₇ coating exhibited least degradation against V₂O₅–Na₂SO₄ corrosive environment compared to the other coatings.     

Wide temperature spectrum self-lubricating coatings prepared by plasma spraying

Self-lubricating, multicomponent coatings, which lubricate over a wide range of operating conditions, are described. The coatings have been successfully applied by plasma spraying mixed powders onto superalloy substrates. They have been evaluated in friction and wear experiments and in sliding contact bearing tests. These coatings are wear resistant by virtue of their self-lubricating characteristics rather than because of extreme hardness; a further benefit is low friction. Experiments with simple pin-on-disk sliding specimens and oscillating plain cylindrical bearing tests were performed to evaluate the tribological properties of the coatings. It was shown that coatings of Nichrome, glass and calcium fluoride are self-lubricating from about 500 to 900°C, but give high friction at the lower temperatures. The addition of silver to the coating composition improved the low temperature bearing properties and resulted in coatings which are self-lubricating from cryogenic temperatures to at least 870°C; they are therefore “wide temperature spectrum” self-lubricating compositions.     

Development of dense corrosion resistant coatings by an improved HVOF spraying process

For 6 years, we have developed corrosion resistant coatings to protect steel structures in the marine environment by using a thermal spray technique. This paper summarizes the major developments and results obtained. Such a coating requires primarily impermeability and secondarily homogenous and clean microstructure. In order to make denser and highly corrosion resistant coatings, we selected spray materials and improved fabrication processes. HastelloyC was a suitable material for High Velocity Oxy-Fuel (HVOF) spraying to form corrosion resistant coatings because of its high resistance against thermal oxidation as well as seawater corrosion, especially crevice and pitting corrosion. An inert gas shroud system was attached with a commercial HVOF apparatus and this attachment increased the in-flight velocity of spray particles over 750 m s^?1 and simultaneously suppressed oxidation significantly. In addition, some new methods were designed to evaluate the sprayed particle’s state and the coating properties with high accuracy and sensitivity. Thermal energy of in-flight spray particles was revealed by molten fraction of spray particles, determined by quantitative analysis of melted and unmelted particles captured in an agar gel. Through-porosity of the coatings with open porosity below 0.1% was determined by using Inductively Coupled Plasma analysis of dissolved substance from substrate through the penetrating path of the coatings. The coating of HastelloyC nickel base alloy by the HVOF spraying with the gas shroud attachment had zero through-porosity and 0.2 mass% of oxygen content. The laboratory corrosion tests showed that the on-shroud HastelloyC coating was comparable to the bulk material of HastelloyC in terms of corrosion resistance. This coating, formed on steel, demonstrated an excellent protective performance over 10 months in the marine exposure test.     

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.     

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

Yttria-stabilized ZrO₂ powders with initial sizes of 5–22 μm 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 μm/min, which is promising for the fabrication of next-generation novel thermal barrier coatings.     

In situ synthesis of TiC/Ti coatings by reactive plasma spraying

ABSTRACT

Sucrose, as a precursor of carbon, and titanium powders were used to prepare TiC powders by a spray-drying/precursor-pyrolysis method. Using the powders, TiC/Ti composite coatings were deposited by reactive plasma spraying. The results show that submicron-sized TiC is formed. The TiC phases have three kinds of crystal morphology: spherical TiC with a diameter of about 600?nm, dendrite TiC with a primary dendrite spacing of about 450?nm and a secondary arm spacing of about 150?nm, and cellular-dendrite TiC with a width of about 120?nm and a length of about 600?nm. The TiC/Ti coatings exhibit high microhardness and excellent wear resistance, which is about 2–3 times and about 200 times higher than that of TC4 alloys, respectively.     

Gas tunnel type plasma spraying deposition and microstructure characterization of silicon carbide films for thermoelectric applications

Gas tunnel type plasma spraying deposition has been applied successfully to the deposition of the SiC films on stainless-steel substrates. The microstructure and the surface morphology of the SiC films were characterized by means of X-ray diffraction (XRD) and scanning electron microscope (SEM). The control of the processing parameters such as powder feeding rate, composition of plasma working gases, spraying distance, and carrier gas flow rate allowed the deposition of dense, uniform, continuous, and high purity crystalline SiC films. The thickness of the SiC films varied from 3 to 10 μm. EDS analysis confirmed the presence of SiO₂ in the deposited SiC films.     

Aluminide formation on Alloy 800 by plasma spraying and heat treatment

Specimens of Fe–Ni–Cr based Alloy 800 were subjected to atmospheric plasma spraying using aluminum powder. Quantitative microscopic analysis of as-sprayed specimen revealed formation of aluminum-rich oxygen-containing layer (～100?µm) on the uppermost surface, while adjoining layer (～25?µm) comprising oxygen-rich Fe–Ni–Cr–Al-containing phase. Microscopy with quantitative analysis of as-sprayed?+?heat-treated (at 1273?K) substrate revealed formation of FeAl type layer (～80?µm) on the uppermost surface with an Al-rich intermediate layer (～25?µm) adjacent to substrate. Knoop hardness number was obtained as 764 (±20), 477 (±10), and 210 (±10) for FeAl layer, Al-rich intermediate layer, and substrate, respectively. During scratch tests at 2, 4, and 6?N loads, friction coefficient for the aluminides was recorded in the range of ～0.05–0.15, while that was ～0.18 for the substrate. Scratched surfaces at 2 and 4?N load tests revealed neither cracking nor peeling off at aluminides or interfaces indicating good adherence, whereas cracking occurred at aluminides during 6?N load test. Penetration depths for the aluminides were recorded as lower than that of the substrate during the scratch tests. X-ray photoelectron spectroscopy on thermally oxidized FeAl layer revealed formation of Al₂O₃ type oxide on the surface.     

Investigation of composite hydroxyapatite powder for plasma spraying bioceramic coatings

Powder synthesis on the basis of a matrix from nanocrystalline titanium dioxide with incorporated HA particles was developed. Using scanning and transmission electron microscopy (SEM and TEM), the shape, size, and relief of TiO₂-HA powder particles are investigated. When calculating for the powder particles using the SEM photos and TEM negative films on a picture analyzer, the granulometrical composition and the average maximum particle diameter (0.7 μm) are determined.     

MAX-phase coatings produced by thermal spraying

This paper presents a comparative study on the Ti₂AlC coatings produced by different thermal spray methods, as Ti₂AlC is one of the most studied materials from the MAX-phase family. Microstructural analysis of coatings produced by High Velocity Air Fuel (HVAF), Cold Spray and High Velocity Oxygen Fuel (HVOF) has been carried out by means of the scanning electron microscopy equipped with an energy dispersive spectrometer (EDS). The volume fraction of porosity was determined using the ASTM standard E562. The phase characterization of the as-received powder and as-sprayed coatings was conducted using the X-ray diffraction with CrKα radiation. Impact of the spray parameters on the porosity and the mechanical properties of the coatings are discussed. The results show that the spraying temperature and velocity play a crucial role in coatings characteristics.     

Nanostructured coatings by liquid flame spraying

Modifying surface properties has become a market of great potential. Self-cleaning, which customarily relies partly on hydrophilicity or hydrophobicity of the surface, has instigated investigation into many different means of modifying surfaces. This study investigates the feasibility of manufacturing a hydrophilic surface on glazed ceramic tile by means of liquid flame spraying. The tiles used were commercial domestic tiles. The hydrophilic surface was produced by synthesising nano-sized titanium dioxide (TiO₂) particles from liquid precursors and depositing them on the surface of heated tiles. The treated tiles were subjected to ultra-violet radiation and their hydrophilic properties were evaluated by contact angle measurements. The surfaces of the tiles were investigated by scanning electron microscopy. The TiO₂ particles were analysed by energy-dispersive spectrometry. The contact angle of water decreased significantly as a result of the treatment. The reason for this could be the nanostructured nature of the TiO₂ particles on the surface of the tiles.     

Formation of coatings resistant to contact impact loading by various borochromizing methods

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 1, pp. 101–104, January–February, 1989.     

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.     

Study of the structure and adhesive properties of ceramic coatings prepared by plasma spraying

We study the influence of technological parameters on the formation and structure of ceramic coatings based on Al₂O₃ and deposited by plasma spraying. We present the results of investigations of the adhesive properties of plasma-sprayed coatings based on Al₂O₃ and ZrSiO₄ that form tribological couples with 19,436 and 12,050 steels and polyamide. It is shown that the parameters of an A-160 plasma torch with aqueous plasma stabilization are suitable for the high-quality melting of ceramic materials based on Al₂O₃ if we use powders with particles 40–100 μm in size and perform spraying from a distance of 200–600 mm. Ceramic layers are formed by three types of particles of different shapes with different arrangements. Defects in the structure of the layers (pores, hollows, branched cracks, and large particles) deteriorate the properties of the coatings. The coatings based on Al₂O₃ and ZrSiO₄ exhibit the best properties under the conditions of abrasive wear, and this material, in combination with 19,436 steel, is suitable for application in friction couples. The degree of wear corresponds to the the value of the friction coefficient for the investigated tribocouples determined by the hardness of the material surfaces in the couple. The ceramics-polyamide couple seems to be quite promising due to the low friction coefficient and minimum wear. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 2, pp. 62–70, March–April, 2008.     

炭/炭复合材料表面等离子体喷涂羟基磷灰石涂层的生物学性能

采用等离子体喷涂法在炭/炭复合材料基体上制备了羟基磷灰石涂层,并对所制材料开展体外模拟和试验.结果表明:在体外模拟生理环境的Ringer溶液中,涂层组成相随浸泡时间发生变化.涂层表面有新生羟基磷灰石结晶析出并聚集长大.骨内种植试验期间,动物末出现排异和炎症反应,涂层与基体结合良好.组织学观察发现,涂层与骨界面处有明显的组织改建和新骨形成形态.炭/炭复合材料表面等离子体喷涂羟基磷灰石涂层作为一种潜在的骨组织修复材料具有良好的应用前景.     

The fatigue resistance of heat resistant alloys with coatings

The effect of various thermal coatings on the fatigue resistance of heat-resistant alloys at room and high temperatures is examined. The Locati method is seen to be ineffective for determining the endurance level of materials with brittle coatings. Data are presented which point out the effect of condensation coatings on the endurance limit of a series of heat-resistant alloys at room temperature.Translated from Problemy Prochnosti, No. 5, pp. 51–56, May, 1990.