The analytic hierarchy process (AHP) has been widely used as one of decision-making method in economic, social, political and technological field, and for evaluating relative strength of preference quantitatively in decision making process. We think that AHP approach would be useful for analyzing and digitalizing expert’s skills, and for transferring to non-skilled people. In this presentation, we show the AHP approach to analyze a decision to select thermal spraying parameters for achieving high quality wear resistive Al 2 O 3 film by atmospheric plasma spraying (APS). From the result of this study, the process of expert’s subjective thinking could be clear and understood for other person.

For the promising erosion and oxidation resistance of carbide cermet coating, Cr39Ni7C cermet coatings were deposited by Diamond Jet spray process using a commercial Sulzer Metco 5241 powder in this study. The microstructure, phase composition and high temperature oxidation behavior of the deposited coatings were investigated. The speed and temperature of in-flight particles were measured by DPV-2000. The results revealed that the speed of in-flight particles decreased from 229 m/s to 150 m/s with the increasing of spraying distance from 100 mm to 300 mm, whereas the average temperature of in-flight particles increased from 1926 to 2245 K. The decarburization of Cr 3 C 2 increased with the increasing of fuel gas flow from 30 FMR to 40 FMR for higher heat enthalpy of flame. Due to the formation of Cr 2 O 3 on/in the coatings at high temperature, the sprayed coatings had good oxidation resistance at 1073 K in air atmosphere. For the lower porosity of the coating deposited under the spraying distance of 150 mm, its oxidation resistance was better than that sprayed under the spraying distance of 200 mm.

A copper electroplating method revealed that recently developed commercial Al 2 O 3 thermal spray coatings did not have the well-known lamellar structure but instead had a structure that was made up of tightly bonded particles, with many vertical microcracks in the coating. The coating in the study was prepared by the atmospheric plasma spray system. The copper electroplating method was applied to observation of the Al 2 O 3 thermal spray coating structure. Spray coating specimens were electroplated in an aqueous solution containing CuSO 4 , H 2 SO 4 , CuCl 2 , and additives so that copper was deposited in small pores and narrow cracks in the coatings. Copper in the Al 2 O 3 coatings was observed clearly by scanning electron microscopy, which also revealed the coating’s structure (boundaries of flattened particles and vertical cracks). The coating did not have a lamellar structure (horizontal apertures between flattened particles) and it was dense in spite of the many microcracks.

Hydroxyapatite (HAp Ca 10 (PO 4 ) 6 (OH) 2 ) is very known to be a biomaterial and an absorbent for chromatography. In this study, HAp was agglomerated with anatase TiO 2 to manufacture thermal spray powders to improve the absorption activity of TiO 2 and then improve its photocatalytic activity. The microstructures and compositions of plasma sprayed TiO 2 , TiO 2 -10%HAp, TiO 2 -30%HAp and HAp coatings were investigated. Due to the low thermal conductivity of HAp compound, not all HAp particles fully melted even under the arc current of 800 A. Low temperature stable β-Ca 3 (PO 4 ) 2 was detected in the sprayed HAp coatings. The addition of HAp inhibited the phase transformation of anatase TiO 2 to rutile. Under the arc current of 600 A, the anatase content in the TiO 2 , TiO 2 -10%HAp and TiO 2 -30%HAp coatings was 10.6%, 20% and 42%, respectively. Although slightly decomposition of HAp to α-Ca 3 (PO 4 ) 2 was found in the TiO 2 -30%HAp coatings, it did not decompose to CaO and P 2 O 5 according to the XRD and EDAX analysis. With the increasing of the spraying distance from 70 mm to 110 mm, the anatase content in the TiO 2 -30%HAp coatings decreased from 34% to 17% under arc current of 700 A. The addition of the secondary gas of helium has no significant influence on the melting state of the TiO 2 -HAp feedstock powders.

The compositions and photocatalytic activity of plasma sprayed TiO 2 , TiO 2 -30%FeTiO 3 , TiO 2 -50%FeTiO 3 and FeTiO 3 coatings were investigated. The influence of FeTiO 3 compound on the photocatalytic activity of TiO 2 coating was clarified. The TiO 2 -30%FeTiO 3 coating sprayed under the arc current of 400 A had good photocatalytic activity because the coating did not contain the unfavorable Fe 2 TiO 5 phase. The relative deposition speed of TiO 2 -30%FeTiO 3 powder under the arc current of 400 A was approximate to 4 µm/pass. Although pure FeTiO 3 compound nearly did not show photocatalytic performance, the existence of FeTiO 3 could improve the photocatalytic activity of anatase TiO 2 if FeTiO 3 contacts coherently with it, which was explained using two-steps electron transfer model.

Thermal sprayed WC-metal binder cermet coating is widely used for their resistance to abrasive wear in various harsh environments and generally sprayed by high velocity oxy-fuel (HVOF) method and atmospheric plasma spray method (APS). However, even during HVOF spraying, WC-metal binder cermet powder has to be exposed to high temperature flame jet for heating and accelerating, furthermore, oxygen is usually entrained into the flame jet, the decomposition and decarburization of tungsten carbide owing to the oxidation of WC, cannot be totally eliminated. This frequently causes defects such as pores, cracks and unmelted particles, which deteriorate coatings properties. To improve the properties of sprayed coatings, numerous studies have been examined post treatments such as laser irradiation, diffusion treatment, hot isostatic pressing (HIP) treatment, sealing treatment. Laser irradiation was speedy treatment and simplicity of process control and enables not only the post treatment but also the pre and simultaneous treatment by combining with spraying process. However, it is not easy to produce a uniformly treated coating by conventional laser treatment method as desired. To obtain a near-uniform beam intensity for practical laser irradiation, a kaleidoscope was installed in a conventional YAG laser. In this work, laser beam properties of YAG laser equipped with a kaleidoscope and its effect on surface modification of WC-25%NiCr coating was investigated. Abstract only; no full-text paper available.

The photo catalytic TiO 2 coatings on biodegradable plastic (polybutylene succinate: PBS) were prepared by using plasma splaying techniques. It is reported that there is a possibility that the performance of photo catalytic TiO 2 coating may be advanced by addition of absorption ability [1]. It is also well known that the extraordinary absorption ability of HAP (hydroxyapatite) [2]. In this study, to investigate the influence of the addition of absorption ability to the coatings, not only pure anatase TiO 2 powder but also two types of TiO 2 -HAP compound powder (TiO 2 - 10wt.%HAP, TiO 2 -30wt.%HAP) were used as thermal splay materials. The microstructure of coatings was characterized with SEM and XRD analysis, and some photo catalytic ability of coatings as a functional material was evaluated. One was the air purification performance of the coatings through the photo degradation of acetaldehyde gas, and the other was the sterilization performance to bacteria. In not only pure anatase TiO 2 powder condition, but also in TiO 2 -10wt.%HAP and in TiO 2 -30wt.%HAP powder condition, the high anatase ratio which was approximately 95% were verified. In terms of decomposition ability to acetaldehyde gas, TiO 2 -10wt.%HAP coating was predominate to the others. This result indicates the addition of absorption ability. In terms of sterilization ability to bacteria and bacteria absorption, TiO 2 -HAP compound powder coatings showed a good performance.

TiO 2 based coatings are promising photocatalyst as they are chemically stable and nontoxic. To develop more effective photocatalyst with cost effective plasma spraying technique, TiO 2 and TiO 2 -Fe 3 O 4 coatings were prepared using agglomerated anatase TiO 2 and composite TiO 2 -Fe 3 O 4 powders, respectively. The photocatalytic activity and photoelectrochemical characteristics of sprayed coatings were examined. The photo-response of the sprayed TiO 2 electrode was comparable to that of single crystal TiO 2 , but the breakdown voltage approximated to 0.5V (vs. SCE). The short-circuit current of TiO 2 was 1.05mA/cm 2 , which was 15 times comparing with that of TiO 2 -Fe 3 O 4 electrode under 30mW/cm 2 xenon light illumination. N-type TiO 2 semiconductor particle reacted with Fe 3 O 4 or Fe 2 O 3 particle and concurrently produced p-type FeTiO3 in plasma spraying processes. FeTiO3 compound obviously improved the photocatalytic activity of the TiO 2 coating for the formation of p-n junction between p-type FeTiO3 and n-type TiO 2 , which may spatially separate the photo-generated electrons and holes. As a result, plasma-sprayed TiO 2 -Fe 3 O 4 coatings are promising candidates for the applications to photocatalyst.

We have already shown at ITSC2004 that the questionnaire results obtained from job shop small and medium companies in Japan. In this presentation, we would show the results obtained by analyzing questionnaire from the wiewpoint of cost. We show one example here. As for the companies think that their thermal spraying work is profitable rathen than other company's work, expert’s skill is more important for in-process monitoring during thermal spraying. However, as for the companies think that sales obtained from coating is less than that of other companies, they needed expert's skill when doing pretreatment. In this way, the result obtained from our questionnaire would be helpful for establishing company's technological strategy. Abstract only; no full-text paper available.

Although thermal spraying technique is used in many industries, it suffers from several problems. For example, the hardness of the coatings is lower than that of sintered material for the incompleted cohesiveness. An yttrium aluminum garnet (YAG) laser was used during HVOF spraying to improve the properties of the applied coating. Several carbide powders were used as thermal spray materials, and stainless steel (SUS304) was used as substrate. Coatings were sprayed by hybrid spraying method, which was combined HVOF spraying with YAG laser. The hardness of coatings sprayed by hybrid spraying was higher, and the weight loss in a blast-erosion test was smaller than that of coatings applied by HVOF spraying only. The particles deposited in the coatings obtained by hybrid spraying were very fine. Laser irradiation to the HVOF flame improve the adhesion strength between particles and the deposition of fine carbide particles in the coating. It was considered that mechanism of coating strengthening in hybrid spraying was resulted from strengthening of cohesiveness by heating effect and decreasing of porosity by flattening effect according to observation results of Ni splats sprayed by hybrid spraying method.

The photocatalytic TiO 2 coatings on bio-degradable plastic(polybutylene succinate:PBS) were prepared by HVOF and plasma spraying techniques using three kinds of agglomerated powders (P200: 200nm, P30: 30nm, P7: 7nm). The microstructures of coatings were characterized with SEM and XRD analysis, and the photocatalytic efficiency of coatings was evaluated through the photo degradation of gaseous acetaldehyde. Furthermore, for the estimation of the mechanical characteristics, wear resistance of coatings was estimated by weight loss obtained from the abrasion wear test. The results indicated that with respect to both the HVOF sprayed P200 and P30 coatings, the high anatase ratio of 100% can be achieved regardless of fuel gas pressure. On the other hand, the HVOF sprayed P7 coating exhibited largely decreased anatase ratio (from 100% to 49.1%) with increasing the fuel gas pressure, which may be attributed to the much higher susceptibility to heat of 7nm agglomerated powder. In terms of photocatalytic efficiency, HVOF sprayed P200 and P30 coatings seem to predominate as compared to that of plasma sprayed P200 coatings owing to the higher anatase ratio. However, the HVOF sprayed P7 coatings didn’t show the photo catalytic activity, which may result from the extremely small reaction surface area to the photo-catalytic activity and low anatase ratio. In addition, it was found that the thermal sprayed TiO 2 coatings improve the wear resistance of PBS. Therefore, in the present study, possibility of production of further functional PBS plastic with photocatalytic performance and wear resistance by spraying of ceramics such as TiO 2 , was found.

Fracture strength of a WC-12Co thermal sprayed coating is investigated experimentally and analytically. In the experiments, a pair of coated butt cylindrical specimens is subjected to combined tension with torsion stresses. Stress distributions in the coating at critical loading conditions are analyzed by using FEM analysis and the fracture criterion of the coating is investigated. It is found that normal stress distributions are common to all cases of testing stress conditions and so fracture condition of the brittle coating is represented as K ≧ Kcr in the normal stress distribution even under mixed deformation mode I and III. By using the experimental method presented in this paper and the corresponding FEM analysis, an approximation for the critical bonding strength of a coating under shearing load can be estimated.

To protect structural and functional materials against influence of the severe environments, various coating technologies can be used. This study considers the use of high velocity oxy-fuel process the coatings available for applications based on deposition using the continuous detonation spray process. The properties of the continuous detonation sprayed WC-NiCr and Cr 3 C 2 -NiCr cermet coating are investigated through the mechanical, corrosion and wear resistance test. The test results are also compared with the properties of the duplex phase stainless steel substrate and the atmospheric plasma sprayed coatings with the same powders. The corrosion resistance was examined by electochemical method, corrosion potential monitering. Furthermore, the erosion wear resistance was examined by the abrasive and cavitation erosion wear test. The experimental results exhibited that the anti-corrosive and anti-erosive properties of the continuous detonation sprayed coatings are superior to that of their plasma sprayed coatings. It was found that the WC-NiCr cermet coating appears to be more effective than the Cr 3 C 2 -NiCr cermet coating in abrasive erosion environment, whereas the Cr 3 C 2 -NiCr cermet coating is more effective in cavitation erosion environment.

TiO 2 and TiO 2 -Al composites coatings were prepared by plasma spraying using a reconstituted nanosized feedstock via a spray drying method. Effects of various spray conditions on the microstructure, porosity, microhardness and wear resistance related to the mechanical performance of coatings were evaluated. The coatings sprayed at relatively low plasma power were composed of two distinct microstructures of well defined lamellar structure, similar to microstructure of conventional plasma sprayed coatings typically observed from fully melted particles, and embedded nano or sub-micron particles originated from partial/non-molten particles of feedstock materials. The fraction of partial/non-molten particles in coating layers was increased by Al additive. Such a characteristic of blended microstructure of coatings was clearly confirmed from a bimodal distribution of microhardness described by Weibull plots. The optimized addition of Al into TiO 2 improved mechanical properties such as microhardness and wear resistance.

The photoelectrochemical characteristics of plasma sprayed porous TiO 2 , TiO 2 -5%ZnO and TiO 2 -10%ZnO electrodes in 0.1N NaOH solution were studied through a three-electrode cell system. The microstructure, morphology and composition of the electrodes were analyzed using electron probe surface roughness analyzer (ERA-8800FE), scanning electron microscope (SEM) and X-ray diffraction. The results showed that the sprayed electrodes had a porous microstructure, which was affected by the plasma spraying parameters and composition of the powders. TiO 2 -ZnO electrodes consisted of anatase TiO 2 , rutile TiO 2 and Zn 2 Ti 3 O 8 phase. The photoresponse characteristics of the plasma sprayed electrodes were comparable to that of single crystal TiO 2 , but the breakdown voltage was approximate to 0.5V (vs. SCE). The short-circuit photocurrent density increased with a decrease of donor concentration, which was calculated according to Garner-Bulter model. For the lowest donor concentration of a TiO 2 -5%ZnO electrode prepared under the arc current of 600A, the short-circuit photocurrent density was approximately 0.4mA/cm 2 higher than that of the TiO 2 electrodes under 30mW/cm 2 xenon light irradiation. The photocurrent density increased linearly with light intensity.

Titanium dioxide (TiO 2 ) is one of the most important photocatalyst that allows the environmental purification of water and air by the decomposition of toxic organic compounds and removal of harmful gases. In the photocatalytic applications, TiO 2 can be used in form of powder or coating. In this paper, two techniques of deposition were used to elaborate thin deposits starting from an agglomerated TiO 2 anatase nanopowder: conventional plasma spraying in atmospheric conditions and suspension plasma spraying. The photocatalytic efficiency of the coatings was performed with respect to nitrogen oxides (NOx) and compared with the photocatalytic activity of the TiO 2 Degussa P25 powder. Differences in the photocatalytic efficiencies of the nanocoatings obtained by the two techniques of plasma spraying were obtained. The coatings elaborated by suspension plasma spraying have poor mechanical properties but better photocatalytic efficiencies. This method is a promising technique to elaborate photocatalytic coatings for the removal of different air pollutants.

It is very important to clarify the characteristic deformation behaviors of thermal barrier coatings. Monotonic and cyclic deformation behaviors of thermal barrier coatings under uniaxial compressive loading were examined. Specimens of plasma-sprayed ZrO 2 -8%Y 2 O 3 and CoNiCrAlY were fabricated to test the coating materials independent of the substrates. The specimen was fabricated by dissolving out the substrate only at the region of gauge length. Thicknesses of the coatings were 300 μm. The stress-strain response was measured using the laser speckle strain / displacement gauge (SSDG). ZrO 2 -8%Y 2 O 3 coating showed the nonlinear stress-strain response with a considerably lower elastic modulus which value was about 10% of sintering ceramics. The coating was found to leave permanent strain by compressive loading: the compliance of the coating decreased by compressive loading. The compliance was also found to decrease furthermore by undergoing cyclic compressive load. On the contrary, CoNiCrAlY coating deposited by low pressure plasma spraying was found to show the stress-strain response with insignificant nonlinearity. The compliance of the stress-strain curve didn’t also decrease with increasing the number of compressive stress cycles. It was found that coating with many defects and pores showed stress-strain response with large nonlinearity.

In order to improve the efficiency of gas turbines, thermal barrier coatings (TBCs) have been applied to components in the hot sections of advanced gas turbines. During service, thermally grown oxide (TGO), which consists of an Al 2 O 3 layer and a mixed oxide layer, forms at the interface between the top coating and bond coating. It is supposed that the reason for failures of TBCs, such as cracking, delamination or spalling, is due to decreased bond strength caused by TGO growth or due to the formation of stress concentration sites caused by porosities in the mixed oxide. In this study, to inhibit the growth of TGO, plasma sprayed CoNiCrAlY bond coating was remelted with a YAG laser prior to spraying the top coating. A thin Al 2 O 3 layer formed at the top coating/bond coating interface, and the formation of porous mixed oxide during thermal aging tests was inhibited. Four-point bending tests showed that the bond strength of TBC with remelted CoNiCrAlY was superior to standard TBC.

Thermally sprayed ceramic coating consists generally of porosity up to over ten percent. The existence of voids in the coating will degrade mechanical performance and corrosion resistance. The infiltration technique has been used to enhance the coating performance. In the present work, the adhesives of high strength are used as infiltrator for plasma sprayed alumina coatings to investigate the effect of the infiltration on the adhesive strength and erosion resistance. The adhesive strength of coating after infiltration is tested following ASTM-C-633 standard with the same adhesive. The commercial adhesives used are liquid types of adhesives. Alumina coatings are deposited by plasma spraying to a thickness about 500ìm. The adhesive strength of as-sprayed coating was tested using another epoxy resin adhesive. The test pieces are prepared without infiltration of adhesive into the coating. The results revealed that the infiltration of adhesive to alumina coating can improve significantly the adhesive strength and erosion resistance. The adhesive strength from 40 to 55 MPa can be obtained in spite of deposition conditions. The erosion resistance of the coating at 90 degrees can be improved by a factor about 3.

To clarify the formation micromechanism of plasma spray deposits, internal microstructures have been examined by transmission electron microscopy on the thin films prepared from different depths of the plasma sprayed Al 2 O 3 deposits. Microstructures in the top layer have consisted of both the coarse grains of 1 µm and the fine ones of 0.2 µm in average diameter. Point defects were contained mostly in γ phase grains. In the mid-layer, columnar structures often developed in parallel or in radial directions which adjoined with γ phase grains. From the SAD analyses, columnar grains were identified as α phase and lay in a twin crystal orientation relationship to each other between the joined grains. The bottom layer was composed of a mixture of the coarse grains of 0.2 µm and the fine ones of 0.02 µmin average grain diameter. It was found that the spray deposit was composed of different microstructures in crystallization, depending on depth to the thickness direction of the spray deposit.