Despite their light weight, 2.3 times lighter than Al, polymers are limited to application with low thermal, wear, and abrasion demands. The enhancement of the functional surfaces of the polymers using thermal spraying techniques is a challenging task due to the thermal degradation of polymers, the low wettability, and the disparate atomic properties. The twin-wire arc spraying (TWAS) process comprises two contradictory features. Almost all spraying particles are in a molten state on the one hand, and on the other hand, the spray plume has the lowest heat output among the different thermal spraying techniques. Therefore, it is a promising spraying technique for the required surface improvement. The surface of the 3D-printed parts was metalized using two successive layers. The first layer is a TWAS coating made of low-melting ZnAl 4 to avoid thermal degradation and provide a bond coat. The topcoat is also applied using a TWAS process and was made out of Ni-WC-Co as cored wires. The top hard coating has improved the wear resistance of the polymers by 14.6 times. The erosion of the coated and uncoated specimens was determined using a low-pressure cold gas spray gun. Ni-WC-Co coating led to more than five times higher erosion resistance.

This paper reports on the performance evaluation of stainless steel (SS) thermal spray coatings aimed at shielding lightweight aluminum (Al) brake rotor disks from excessive heat and providing an adequate tribological surface in contact with brake pads. Coating wear, corrosion and heat resistance performances were evaluated using pin-on-disk, cyclic corrosion tests and thermal cycling using a custom laser rig, respectively. Arc spray optimized coatings displayed lower or equivalent wear rates when compared with the baseline gray cast iron disks, with similar frictional behavior. However, arc spray coating exhibited low adhesion which limits the maximum coating thicknesses achievable and leads to early coating spalling after about 1000 thermal cycles. Arc sprayed coatings also corroded and delaminated under corrosion tests. Optimized cold spray coatings present high corrosion resistance and could resist above 10,000 thermal cycles without spalling. However, cold spray coatings exhibit wear rates at least 4 times those of the cast iron. Taking advantage of both types of coatings, it was found that the production of a duplex coating made of a cold spray bond coat and an arc spray top coat could meet the requirements for protecting Al disks, with near 50% weight reduction.

A method measuring the thermal conductivity and the interfacial thermal resistance of thermal barrier coatings (TBCs) which consist of metallic bond-coats (BCs) and ceramics top-coats (TCs) on superalloys was newly developed. It was based on the areal heat diffusion time method analysing the heat diffusion across multilayers. The developed method was experimentally verified using the BC and the TBC specimens coated by APS. It was found that there were the interfacial thermal resistance not only between the TC and the BC but also between the BC and the substrate. Furthermore, the thermal conductivities of the BC and the TC obtained from the BC and the TBC specimens by this method considering the interfacial thermal resistance were in good agreement with those measured from the free-standing specimen of each coating. Thus, it was confirmed that the newly developed method is effective to evaluate the thermal conductivity and the interfacial thermal resistance of the TBC.

Thermal insulation performance is a measurement of the thermal protection offered by the thermal barrier coatings (TBCs) to the substrate, therefore, it is essentially important to compare different double ceramic layer (DCL) TBCs on the premise of the same thermal resistance. In this study, a series of LZO/YSZ DCL-TBCs, with the equivalent thermal insulation to 500 µm thick YSZ TBCs, were prepared, and their lifetimes were evaluated by thermal gradient cyclic test at the top coat surface temperature of 1300°C. Result show that, the lifetime of DCL-TBCs was more than doubled compared to 500 µm thick YSZ TBCs, when 100µm thick YSZ coating was substituted by LZO coating. In addition, the lifetime of DCL-TBCs decreased with the increase of LZO substitutional ratio. X-ray diffraction analysis revealed that LZO maintains the pyrochlore structure after thermal cyclic test. Microstructure examination demonstrated that, with the increase of LZO substitutional ratio, the delamination position transferred from near top/bond coating interface to near LZO/YSZ interface and finally to the inside of LZO coating. Therefore, this study would shed light to further coating structure optimization towards the next generation advanced DCL-TBCs.

Thermal cycle lifetime is essentially important to the application of thermal barrier coatings (TBCs) on the premise of the same thermal resistance. In this study, equivalent thermal insulation conception is introduced to the design of dense vertical crack (DVC) structured TBCs and the lamellar structured TBCs, to fairly compare the lifetime of TBCs with different structure. DVC-structured TBCs with the equivalent thermal insulation to lamellar YSZ TBCs were prepared, and their lifetimes were evaluated by thermal gradient cyclic test. Cross-sectional morphology and phase constitution before and after failure were examined by scanning electron microscope and X-ray diffraction, respectively. The failure mode was analysed. This study would shed light to further coating structure optimization.

According to our modeling of oxygen input into particles at arc spraying (AS) a cored wire of Fe-25Cr-5Al type was developed. The oxidation behavior of AS coatings from this wire was studied in air under atmospheric pressure at 700°C. Influence of Si, Ti was studied by means of mass-change measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is determined that addition of Si and Ti lead to preventing formation of complex carbides like (Fe, Cr) 7 C 3 , spinels like (Fe, Cr) 2 O 3 and nitrides like AlN. Absence of these carbides, spinels and nitrides leads to significantly improving a protective property of surface oxide layer of Al 2 O 3 . Heat resistance of developed coatings was compared with austenitic steels like Tempaloy A-1 and TP 310 ASME SA312 and with ferritic steels like T11 and T122 ASME A213 which are widely used as boiler materials.

Fracture toughness and phase stability are crucial properties of thermal barrier coatings (TBC) during highly loaded thermomechanical operations in gas turbines. While several alternative TBC materials have exhibited excellent thermal resistance, their potential applicability has been limited due to poor endurance to cyclic stresses. The addition of TiO 2 to the non-transformable tetragonal t´-YSZ has been found to effectively enhance the fracture toughness and phase stability of YSZ at high temperature exposures. Thermal cycling tests in a burner rig were conducted on TBCs prepared from atmospheric plasma sprayed titania-doped YSZ to verify this phenomena. Exposure temperature was 1400°C at the surface and thermal gradient across the sample was provided by simultaneous back-cooling treatment. Cycling tests reveal that the slight increase in the tetragonality of the deposited coatings with increasing amount of dopant did not cause a significant effect to the lifetime of the TBCs. Moreover, increasing amount of Ti-substitution did not influence the fracture toughness of the bulk YSZ.

The PAS method was used to produce W-ZrC and W-HfC composite powder, and the LVPS process technologies were used to create W composite coating layers. In addition, the mechanical properties, high-temperature resistance, and ablation characteristics of the W composite coatings were compared and analyzed for different types of carbides. For comparison and analysis, Vickers hardness, porosity, and adhesive strength were measured, and plasma torch tests were conducted. The use of the LVPS technologies led to successful production of W composite coatings (W-HfC; W-ZrC), approximately 1,000 μm or above in thickness. ZrC particles were observed in the layers of W-ZrC coating. The porosity was 3.59 % in W-HfC and 7.74 % in W-ZrC, indicating the W-HfC coating had a better pore quality than W-ZrC. Vickers hardness was approximately 120Hv higher in W-ZrC than in W-HfC due to the presence of ZrC particles in the W-ZrC coating. Adhesive strength was found to be nearly identical in both coatings. Results of the evaluation of high thermal resistance characteristics of the W composite coating materials showed that W-ZrC coating performed better in resisting high thermal conditions than W-HfC coating, due to the strengthening effects of ZrC particles in the layers and the generation of ZrO 2 phase with high levels of stability in high temperatures.

Casting molds in the aluminium industry show a short lifespan due to the high corrosiveness of aluminium melts and alternating thermal and mechanical loads. By using new materials, in example pseudoalloys containing tungsten, the lifetime of casting molds can be elongated up to hundredfold. Today, casting molds made of steel are state of the art. In spite of the advantages of pseudoalloys, high manufacturing cost and the increasing commodity price of tungsten prohibit the use of molds consisting of these progressive materials. By coating the standard steel molds with a FeNiW-layer, the excellent thermal and corrosive resistance of the pseudoalloy surface can be combined with minimal manufacturing costs. For present work steel substrates had been coated with FeNiW-pseudoalloys. Therefore, arc spraying and different deposit-welding methods (Laser, Plasma, TIG) had been compared. By modifying the machine parameter set, a smooth transition between substrate and coating was realized. Thermal and chemical resistance of the samples will be tested. In this paper first results are presented.

Plasma-sprayed, molten molybdenum particles (~55 µm diameter) were photographed during impact on grit-blasted glass surfaces that were maintained at either room temperature or at 350°C. Droplets approaching the surface were sensed using a photodetector and after a known delay, a fast charge-coupled device (CCD) camera was triggered to capture time-integrated images of the spreading splat from behind the glass. A rapid two-color pyrometer was used to collect the thermal radiation from the spreading droplets to follow the evolution of their temperature and calculate the splat cooling rates. It was found that as the surface roughness increased, the maximum spread diameters of the molten molybdenum droplets decreased, while the splat cooling rates increased. Impact on non-heated and heated roughened glass with similar roughness values produced splats with approximately the same maximum spread diameters, skewed morphologies, and cooling rates. On smooth glass, the splat morphologies were circular, with larger maximum spread diameters and smaller cooling rates on non-heated smooth glass. An established model was used to estimate the splat-substrate thermal contact resistances. On highly roughened glass, the thermal contact resistance decreased as the glass roughness increased, suggesting that splat-substrate contact was improved as the molten metal penetrated the spaces between the large asperities.

Plasma-sprayed, molten nickel particles (60 µm diameter) were photographed during impact on oxidized 304L stainless steel surfaces that were maintained at room temperature or at 350oC. The steel samples were oxidized at different temperatures. Droplets approaching the surface were sensed using a photo detector and after a known delay, a fast charge-coupled device (CCD) camera was triggered to capture time-integrated images of the spreading splat from the substrate front surface. A two-color pyrometer was used to collect the thermal radiation from the particles to follow the evolution of their temperature after impact. Molten nickel particles impacting on oxidized steel at room temperature fragmented significantly, while heating the surfaces produced splats with disk-like morphologies. Impact on steel that was highly oxidized induced the formation of finger-like splash projections at the splat periphery. The splat cooling rate and thermal contact resistance between the splat and non-heated oxidized steel varied significantly as the degree of oxidation increased; heating the oxidized steel greatly reduced the variations. It was suggested that the large variations in splat cooling rates and thermal contact resistances on the non-heated oxidized steel was due primarily to the presence of adsorbates on the steel surface.

“Testing Method for Heat Resistance under Temperature Gradient” is a Japanese Industrial Standard (JIS) newly established by the Minister of Economy, Trade and Industry, after deliberations by the Japanese Industrial Standards Committee, in accordance with the Industrial Standardization Law. This standard specified the testing method for heat resistance under temperature gradient of materials and coated members of equipment exposed to high temperature, such as aircraft engines, gas turbines, reciprocating engines, accelerators, power switchgears etc. Three kinds of testing method, such as burner heating test, arc heating test and various beam heating tests are involved.

Nickel based self-fluxing alloy coating extends the service life of furnace wall tubes at waste incineration plants due to its excellent corrosion resistance and heat resistance. With our system, fusing of such coatings is performed by induction heating, which offers improved efficiency and reliability of products. Compared with conventional plasma, flame, and HVOF thermal-sprayed coatings, induction-fused coatings provide a far stronger metallurgical bond at the interface, while minimizing the inclusion of pores. In addition, the tubes are less costly than those with welded coatings, and the process reduces the distortion of the products, facilitating easier final assembly. A successful experimental application of 11 units (four, six-meter pipes per unit) revealed virtually no corrosion on the exposed surfaces, and showed an improved water heating efficiency over that of the original mortar-coated tubes. Over 200 such units are now being employed in four incinerators in Taiwan, and further installations are in progress.

Many properties (thermal, electrical, mechanical) of thermal sprayed coatings are strongly linked to the real contacts between the “piled-up” splats. The quality of this contact depends on droplet parameters at impact (size, temperature, velocity) and substrate parameters (temperature, topography). Two different techniques have been developed in order to study the plasma sprayed particle behaviour at impact. The first one allows direct observation under direct current (dc) plasma spray conditions, while the latter one, based on the millimetre sized free falling drop, enables the visualization of flattening phenomena, but at larger scale. These two techniques bring complementary approaches and results. The latter show that flattening time and cooling rate of the lamellae (metallic and ceramic) are improved with the stainless steel substrate surface modification at the nanoscale when corresponding to a positive skewness parameter obtained by preheating it over the transition temperature. Experiments of wettability show that the presence of nanopeaks increases the contact angle of the liquid on the substrates and reduces thermal contact resistance at interface. It has also been shown that, when adsorbates and condensates are not eliminated from the surface, even with a positive skewness, the thermal contact resistance is increased.

The impact and solidification of 4 mm molten aluminum alloy 380 droplets on a tool steel substrate was studied both analytically and experimentally. Temperature histories at different radial location on the substrate surface under impacting droplets were recorded using an array of thin film thermocouples with response times less than 1 µs. Photographs were taken of droplet impact onto the substrate. Initial substrate temperature was varied from room temperature to 300°C and average surface roughness from 0.5 to 5.0 µm. Estimates of thermal contact resistance were made by matching measured substrate temperatures with an analytical solution for surface temperature variation. A model of the true area of contact between molten metal and a rough surface was developed in order to predict how contact resistance changes with surface roughness and contact pressure. Impact of molten aluminum alloy droplets was simulated using a three-dimensional numerical. Using values of thermal contact resistance predicted by the model gave good agreement between computed and observed droplet shapes during impact.

Plasma-sprayed, molten molybdenum particles (~50 µm diameter) were photographed during impact (with velocity ~135 m/s) on a glass surface that was maintained at either room temperature or 400°C. A droplet approaching the surface was sensed using a photodetector and after a known delay, a laser was triggered to illuminate the spreading splat and photograph it with a CCD camera. A rapid two-color pyrometer was used to collect the thermal radiation from the impacting particles to follow the evolution of their temperature and size after impact. Molten molybdenum particles impacting on a surface at room temperature splashed and broke up after impact leaving only a small portion adhering to the substrate. On a surface held at 400°C, there was no splashing and a circular splat remained on the surface. Splats on a glass surface held at room temperature had a large maximum spread diameter, approximately 2.7 times that on a hot surface. The cooling rate on a cold surface was an order-of-magnitude lower than that on a hot surface, suggesting that thermal contact resistance was much greater.

A numerical study has been conducted on yttria stabilized zirconia and molybdenum splat cooling taking into account the effects of various parameters. In particular, the effect of the splat thickness, the splat/substrate interface thermal resistance, the latent heat of solidification and the substrate initial temperature on the solidification occurrence and kinetics have been studied. A two-dimension model of heat transfer taking into account the phase change during rapid solidification with an enthalpy formulation has been used for these calculations.

Advances in the functional properties of thermal barrier coating (TBC) deposits are important for increasing the efficiency of, and reducing emissions from both stationary and aircraft turbine engines. Computer modeling is the preferred method for developing new materials with minimum cost and development time. However, modeling of TBCs is complex and must take into account interactions among the layers and with the substrate, in-service phase changes, oxidation, and stress development. Understanding the microstructure of the ceramic layer is important for building these models, as it strongly influences the properties responsible for the basic TBC function – thermal resistance. As is well known the ceramic microstructure changes in service, potentially leading to coating and engine failure. A major challenge is ensuring that the model reliably describes the actual material. Thus, it is important to develop representative models, which can be related to real practical coating systems. We present such a model. It has been developed to interpret small-angle X-ray scattering data that characterize TBC ceramic deposit microstructures. This model is also suitable for incorporation into computer algorithms such as are used in finite-element analysis. Quantitative parameters that describe the microstructure changes occurring under service conditions are readily obtainable for current systems, and these can then be re-measured for future materials of interest.

This work investigates the processes involved in the formation of fragmented layers produced on the surface of ceramic coatings by means of laser melting. For the experiments, plasma sprayed zirconia was applied to steel substrates and treated with CO 2 and Nd:YAG lasers. The modified layers were found to consist of macro-fragments 500-2000 µm in size, which in turn consist of micro-fragments 20-70 µm in size. Crack gaps were observed at both levels with widths of 10-15 µm and 1-5 µm, respectively. Heat resistance, hardness, density, and roughness were determined before and after laser melting, and the changes measured are shown to depend on emitted laser power. Paper includes a German-language abstract.

In the present paper mathematical model of the deformation behavior of a liquid spherical particle upon its impingement onto a solid surface, including flattening and simultaneous solidification is developed. Particle-substrate interactions are investigated for typical thermal spray process. Numerical simulation for the complete Navier-Stokes equations is based on the finite-difference method on rectangular mesh in cylindrical coordinates. The energy equation is solved for both particle and substrate regions using the adjoint conditions for the temperature. In this paper main attention is paid to investigation of the temperature in contact of the particle with substrate. In connection with the oxide films effect on the surface substrate taking onto account thermal resistance of oxide is simulated. Heat transfer process in particle and substrate has been modeled by 2-D problem of heat conduction with influencing hydrodynamic processes into molten particle. Particle solidification and the movement of the solidification front have been described by means of one-dimensional Stefan problem. Numerical results for the heat transfer process and the effect of some important processing parameters such as particle diameter, viscosity, oxide films and temperature of plasma on the flattening and solidification of a single liquid particle have been discussed. Numerical algorithms were realized in the form of applied programs complex.