Gas Tunnel Type Plasma Spraying Research Articles

Enhancement of Functional Ceramic Coating Performance by Gas Tunnel Type Plasma Spraying

A high-precision plasma system has been pursued for advanced thermal processing. The gas tunnel type plasma jet device developed by the author exhibits high energy density and also high efficiency. Among its various applications is the plasma spraying of ceramics such as Al2O3 and ZrO2. The performance of these ceramic coatings is superior to conventional ones. Properties such as the mechanical and chemical properties of the zirconia coatings were reported in previous studies. In this study, the enhancement of the performance of functional ceramic coatings by the gas tunnel type plasma spraying method was carried out using different powders. Results show that the alumina/zirconia composite system exhibited improvements of mechanical properties and corrosion resistance. The alumina/zirconia composite coating has the potential for use as a high functionally graded thermal barrier coating. Another application of the gas tunnel type plasma is for surface modification of metals. As an example, TiN films were formed in 5 s and, thick TiN coatings were easily obtained by gas tunnel type plasma reactive spraying.

Characterization of gas tunnel type plasma sprayed hydroxyapatite–nanostructure titania composite coatings

Hydroxyapatite (HA) can be coated onto metal implants as a ceramic biocompatible coating to bridge the growth between implants and human tissue. Meanwhile many efforts have been made to improve the mechanical properties of the HA coatings without affecting its bioactivity. In the present study, nanostructure titania (TiO2) was mixed with HA powder and HA–nanostructure TiO2 composite coatings were produced by gas tunnel type plasma spraying torch under optimized spraying conditions. For this purpose, composition of 10wt% TiO2+90wt% HA, 20wt% TiO2+80wt% HA and 30wt% TiO2+70wt% HA were selected as the feedstock materials. The phase, microstructure and mechanical properties of the coatings were characterized. The obtained results validated that the increase in weight percentage of nanostructure TiO2 in HA coating significantly increased the microhardness, adhesive strength and wear resistance of the coatings. Analysis of the in vitro bioactivity and cytocompatibility of the coatings were done using conventional simulated body fluid (c-SBF) solution and cultured green fluorescent protein (GFP) labeled marrow stromal cells (MSCs) respectively. The bioactivity results revealed that the composite coating has bio-active surface with good cytocompatibility.

M201 ガストンネル型プラズマ溶射によるジルコニア系セラミックス溶射被膜材の機械的性質と疲労特性に関する研究(GS3 材料力学(1),修士研究発表セッション)

M201 ガストンネル型プラズマ溶射によるジルコニア系セラミックス溶射被膜材の機械的性質と疲労特性に関する研究(GS3 材料力学(1),修士研究発表セッション)

Metallic glass coatings fabricated by gas tunnel type plasma spraying

Gas tunnel type plasma spraying is a renowned technique due to its greater advantages than other conventional plasma spraying followed by high speed and high energy density plasma jet. Furthermore, this is a simple and novel process for producing dense metallic coatings with and without secondary phases such as oxides and intermetallic phases under selective operating parameters. The present work was undertaken to study the formation mechanism and for examining the metallic glass coating properties formed through gas tunnel type plasma spraying process. For this purpose, Fe based, Zr based and Ni based metallic glass coatings were individually deposited by gas tunnel type plasma spray torch at optimum operating conditions with two different input currents (300 and 400 A). Phase and microstructure formations were examined and the results were correlated with the input current. Similarly, mechanical properties and electrochemical corrosion properties of each coating were examined and the results were correlated with the existing phase and the microstructures of the coatings. The examined results revealed that the Fe based metallic glass coatings have relatively less porosity (3–4%) and crystalline phase fraction (9–14%). These coatings also exhibit excellent sliding wear resistance (2.77 × 10−6 mm3/nm−1) and electrochemical corrosion resistance against 3.5% NaCl solution.

Hydroxyapatite and YSZ Reinforced Hydroxyapatite Coatings by Gas Tunnel Type Plasma Spraying

Chemical structure of hydroxyapatite (HA) is very close to human bone which makes it compatible with the tissue of the human body. Its good biocompatibility makes it to be used extensively in many prosthetic applications, especially as a porous material for optimal bone in growth. Currently, this material is being deposited on bio-inert metallic implants and used as recovery parts in human body. In this present study a high-power plasma jet known as gas tunnel type plasma torch (GTTP), was used to produce HA and YSZ reinforced HA coatings on stainless steel substrate. In this study, microstructure, tribological properties and bioactivity of the GTTP sprayed HA and YSZ reinforced HA coatings was investigated. The XRD spectra of the as-sprayed coatings showed that the as-sprayed pure HA coating retained its crystalline HA phase similar to the initial feed stock HA powder, even though there existed a possibility for occurrence of decomposition during its in-flight in high temperature plasma zone. In the present case the decomposition processes of in-flight HA could be well controlled by means of selective operating parameters and unique nature of GTTP jet. The presence of un-melted particles and pores inside the coating microstructure play a vital role in the bonding strength of the coating.

Formation of High Heat Resistant Coatings by Using Gas Tunnel Type Plasma Spraying

Zirconia sprayed coatings are widely used as thermal barrier coatings (TBC) for high temperature protection of metallic structures. However, their use in diesel engine combustion chamber components has the long run durability problems, such as the spallation at the interface between the coating and substrate due to the interface oxidation. Although zirconia coatings have been used in many applications, the interface spallation problem is still waiting to be solved under the critical conditions such as high temperature and high corrosion environment. The gas tunnel type plasma spraying developed by the author can make high quality ceramic coatings such as Al2O3 and ZrO2 coating compared to other plasma spraying method. A high hardness ceramic coating such as Al2O3 coating by the gas tunnel type plasma spraying, were investigated in the previous study. The Vickers hardness of the zirconia (ZrO2) coating increased with decreasing spraying distance, and a higher Vickers hardness of about Hv = 1200 could be obtained at a shorter spraying distance of L = 30 mm. ZrO2 coating formed has a high hardness layer at the surface side, which shows the graded functionality of hardness. In this study, ZrO2 composite coatings (TBCs) with Al2O3 were deposited on SS304 substrates by gas tunnel type plasma spraying. The performance such as the mechanical properties, thermal behavior and high temperature oxidation resistance of the functionally graded TBCs was investigated and discussed. The resultant coating samples with different spraying powders and thickness are compared in their corrosion resistance with coating thickness as variables. Corrosion potential was measured and analyzed corresponding to the microstructure of the coatings. High Heat Resistant Coatings, Gas Tunnel Type Plasma Spraying, Hardness,

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.

Wear behavior of gas tunnel type plasma sprayed Zr-based metallic glass composite coatings

Gas tunnel type plasma spraying is a prospective method to produce metallic glass composite coatings with high quality due to its noteworthy feature of process controllability. In this study, Zr55Cu30Al10Ni5 metallic glass composite coatings were produced by gas tunnel type plasma spraying torch under optimum spraying conditions with selected plasma currents. The formation mechanism, sliding, and erosive wear behaviors of the coatings with respect to plasma current was examined. The phase and thermal analyses as well as microstructure of the plasma sprayed coatings produced at different plasma currents were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) techniques. The sliding and erosive wear behaviors of the coatings were studied using a pin-on-disc and a specially designed erosive wear tester, respectively. The results showed that an increase in plasma current increased the crystalline content in the metallic glass composite coatings, which enhanced the hardness and wear resistance of the coatings.

Sliding wear behavior of gas tunnel type plasma sprayed Ni-based metallic glass composite coatings

Ni60Nb20Zr20 glass composite coatings were successfully produced in a single step using gas tunnel type plasma spraying torch. The resultant phases and structures obtained were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, respectively. The sliding wear behavior of the developed metallic glass composite coatings was evaluated under unlubricated condition using Ball-on-Disk (BOD) tribometer. The results showed that minimum amount of metal oxides and intermetallic phases can be obtained in the coatings at intermediate plasma current only. It is evident that the sliding wear rate of the metallic glass composite coating varied with the loading conditions and its amorphous-crystalline composition. The coating produced at a plasma current of 300 A gives the minimum wear rate and friction coefficient during sliding.

Mechanical properties, electrochemical corrosion and in-vitro bioactivity of yttria stabilized zirconia reinforced hydroxyapatite coatings prepared by gas tunnel type plasma spraying

Yttria stabilized zirconia reinforced hydroxyapatite coatings were deposited by a gas tunnel type plasma spray torch under optimum spraying conditions. For this purpose, 10, 20 and 30 wt% of yttria stabilized zirconia (YSZ) powders were premixed individually with hydroxyapatite (HA) powder and were used as the feedstocks for the coatings. The effect of YSZ reinforcement on the phase formation and mechanical properties of the coatings such as hardness, adhesive strength and sliding wear rates was examined. The results showed that the reinforcement of YSZ in HA could significantly enhance the hardness and adhesive strength of the coatings. The potentiodynamic polarization and impedance measurements showed that the reinforced coatings exhibited superior corrosion resistance compared to the HA coating in SBF solution. Further the results of the bioactivity test conducted by immersion of coatings in SBF showed that after 10 days of immersion of the obtained coatings with all the above compositions commonly exhibited the onset of bioactive apatite formation except for HA+10%YSZ coating. The cytocompatibility was investigated by culturing the green fluorescent protein (GFP)-labeled marrow stromal cells (MSCs) on the coating surface. The cell culture results revealed that the reinforced coatings have superior cell growth than the pure HA coatings.

Microstructure and Thermal Behaviour of Plasma Sprayed Zirconia/Alumina Composite Coating

In thermal barrier coatings (TBC), failure occurs near or at the interface between the metallic bondcoat and topcoat. On high temperature conditions, an oxide scale which is named thermally grown oxide (TGO) occurs along the bond/topcoat interface. For diminishing the creation of TGO, a dense coating with low residual stress and thermal stress buffer layer was preferable. High hardness ceramic coatings could be obtained by gas tunnel type plasma spraying, and the deposited coating had superior property in comparison with those deposited by conventional type plasma spray method. In this study, the gas tunnel type plasma spraying system was utilized to produce a zirconia/alumina functionally graded thermal barrier coating and discussed its physical and mechanical properties, thermal behavior and high temperature oxidation resistance of the coating are discussed. Consequently, the proposed system exhibited superior mechanical properties and oxidation resistance at the expenses of a slightly lower thermal insulating effect. This interlayer is preferred in order to minimize the detrimental effect of the phase transformation of gamma-Al2O3 to alpha-Al2O3.

Effect of spraying condition on property of Zr-based metallic glass coating by gas tunnel type plasma spraying

Metallic glass has excellent functions such as high strength and high corrosion resistance. However, as metallic glass is expensive, a composite material is preferred for better cost performance. Thermal spraying is one of the potential candidates to produce such metallic glass composites. Gas tunnel type plasma spraying is useful in obtaining high quality ceramic coatings because it can easily control the condition of spraying powder. In this study, Zr-based metallic glass (Zr55–Cu30–Al10–Ni5) coatings were produced by gas tunnel type plasma spraying, and the effect of spraying conditions on the properties of Zr-based metallic glass coating was investigated. Dense Zr-based metallic glass coatings of more than 200 μm in thickness were prepared with a Vickers hardness of about Hv = 550 at a plasma current of 250 A, and the amorphous phase of this metallic glass coating appeared to remain in good condition.

Smart coating technology by gas tunnel type plasma spraying

Nano-science & technology is one of the most important scientific fields, and the material processing using the nano-technology is now advanced towards more precise and controllable smart stage. Regarding thermal processing, plasma system with high precise, has been expected for smart thermal processing. The gas tunnel type plasma system developed by the author exhibits high energy density and also high efficiency. Among the applications to the various thermal processing, one practical application is plasma spraying of ceramics such as A12O3 and ZrO2. The characteristics of these ceramic coatings were superior to the conventional ones. The ZrO2 composite coating has the possibility of the development of high functionally graded TBC (thermal barrier coating). In this study, the performance such as the mechanical properties, thermal behavior and high temperature oxidation resistance of the alumina/zirconia functionally graded TBCs produced by gas tunnel type plasma spraying was investigated and discussed. The results showed that the alumina/zirconia composite system exhibited the improvement of mechanical properties and oxidation resistance. Now, one of the advanced plasma application, a smart coating technology, is expected to obtain the desired characteristics of ceramics with improved corrosion resistance, thermal resistance, and wear resistance.

Bonding strength of DLC film on zirconia coating prepared by gas tunnel type plasma spraying

Bonding strength of diamond-like carbon (DLC) films on zirconia coatings prepared using a novel gas tunnel plasma spraying method has been studied and discussed. The emphasis is on the getting better characteristics of such doubly structured coatings (DSC) as comparing compared with properties of both components involved in the coatings. For the study of various failure mechanisms zirconia coatings of different thicknesses on aluminum substrates were prepared. The as-sprayed coatings were firstly polished and then subjected to deposition of DLC films. Adhesion of the DSC has been evaluated using a scratch test method. It has been found that the thicker coatings have higher hardness and lower porosity. The adhesion failures of DLC films on zirconia coatings (DSC) are caused by two different main mechanisms: (i) DLC films separation from the zirconia coatings, and (ii) DLC films breaking under stress load due to the brittleness of the material. In addition the adhesion failures are due to flaking of DLC films on the thinner zirconia coatings caused by a distortion of the aluminum alloy substrate coatings; and, chipping of DLC films themselves on the thicker zirconia coatings.

Corrosion resistance of the Al 2O 3+ZrO 2 thermal barrier coatings on stainless steel substrates

Al 2O 3 + ZrO 2 composite thermal barrier coatings (TBCs) were deposited on SUS304 substrates using the gas tunnel type plasma spraying method. Groups of coating samples with different mixing ratios of Al 2O 3 and different thicknesses were respectively obtained. The graded microstructure of the coatings was examined using optical microscopy (OM) and a scanning electron microscope (SEM). It is well known that the thermal oxidation of interfaces is the main reason for the spallation of TBC coatings, because sprayed TBCs contain micropores and microcracks. The anodic polarization characterization of sprayed TBCs provides a way, to some extent, to investigate the mechanism of the interface oxidation. In this research, anodic polarization was performed to investigate the effect of coatings on the corrosion resistance. The results showed that a higher alumina mixing ratio and thicker coatings lead to higher corrosion resistance. The corrosion potential and deactivated corrosion current of the samples were correlated and analyzed according to the coating porosity, because the through pores in the coatings provided the way for the oxidants of the ambient solution to access the interface. The analysis indicated that lowering the porosity and increasing the gradient of coating porosity help lowering the oxidation.

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.

ガストンネル型プラズマ溶射による複合機能膜の作製

ガストンネル型プラズマ溶射による複合機能膜の作製

Development of ZrO 2/SiO 2 bioinert ceramic coatings for biomedical application

Gas tunnel-type plasma spraying (GTPS) was employed to deposit ZrO 2/SiO 2 bioinert ceramic composite coatings with an appropriate thickness on SUS 304 substrate. Zirconia and fused silica powders, with equal wt%, have been mixed together in ceramic pot for 30 min and internally fed in the plasma jet. The composite coatings were sprayed at two different gas flow rates (120 and 150 l/min) and constant vortex arc current of 450 A and gun current of 50 A. The microstructure of as-sprayed coatings was examined by scanning electron microscope. Elemental analysis was achieved for the composite coatings using EDS analysis unit which is attached to SEM. Phase structure was investigated by X-ray diffraction. The hardness and abrasive wear test of the coatings were investigated. The biological property of the coatings was examined by immersing the as-sprayed coatings in simulated body fluid (SBF) solution for 20 days at 36.5 ∘C. The growth of apatite (HA) on the coatings surfaces was observed by SEM and EDX analysis.

Fe-based metallic glass coatings produced by smart plasma spraying process

Metallic glass has excellent functions such as high toughness and corrosion resistance. Therefore it is one of the most attractive materials, and many researchers have conducted various developmental research works. However, the metallic glass material is expensive and a composite material is preferred for the industrial application. Thermal spraying method is a potential candidate to produce metallic glass composites. The gas tunnel type plasma system is useful for smart plasma processing to obtain high quality ceramic coatings such as alumina (Al 2O 3) and zirconia (ZrO 2) coatings. Also, the gas tunnel type plasma spraying can produce metallic glass coatings. In this study, the Fe-based metallic glass coatings were produced by gas tunnel type plasma spraying, and the microstructure and some properties were investigated. The amorphous phase of this metallic glass coating was confirmed by the XRD method. The Fe-based metallic glass coatings of about 200 μm in thickness were dense with a Vickers hardness of about Hv = 1100 at plasma current of 300 A.

Mechanical property of Fe-base metallic glass coating formed by gas tunnel type plasma spraying

Metallic glass has excellent functions such as high toughness and corrosion resistance. Therefore it is one of the most attractive materials, and many researchers have conducted various developmental research works. However, the metallic glass material is expensive and a composite material is preferred for the industrial application. Thermal spraying method is one of potential candidates to produce metallic glass composites. The gas tunnel type plasma system, which has high energy density and efficiency, is useful for smart plasma processing to obtain high quality ceramic coatings such as alumina (Al 2O 3) and zirconia (ZrO 2) coatings. Also, the gas tunnel type plasma spraying can produce metallic glass coatings. In this study, the Fe-base metallic glass coatings were formed on the stainless-steel substrate by the gas tunnel type plasma spraying, and the microstructure and mechanical property were investigated. The Fe-base metallic glass coatings of about 200 μm in thickness were dense with a Vickers hardness of about Hv = 1100 at plasma current of 300 A. The abrasive wear resistance of Fe-base metallic glass coating was higher than the SUS substrate.