In this investigation, aluminum-copper, aluminum-zinc, and zinc coatings were flame sprayed onto a sand-blasted mild steel substrate. The coatings were immersed in seawater and were examined on a monthly basis using EDS and XRD analysis to assess corrosion and marine fouling behaviors. The spraying and test procedures are described and the results are presented and discussed. Zinc and aluminum-zinc coatings with high zinc content proved to have good anti-corrosion and anti-fouling properties, but the aluminum-copper coatings did not.

Thermal spray coatings produced from hard materials show good potential for extending the service life of sheet metal forming tools. However, post-process methods currently used to improve coating surface quality are slow and expensive, especially on complex surfaces. A novel approach, demonstrated in this study, is the optimization of thermally sprayed coatings by roller burnishing. This process shows a high potential to not only reduce surface roughness and porosity, but also increase hardness even on free-formed surfaces. In the experiments, atmospheric plasma-sprayed CrC-NiCr coatings were produced and the burnishing process was performed on a CNC milling machine. Both the spraying and surface finishing processes are described and the results are presented and discussed.

This study investigates the tribological properties of two HVOF-sprayed tungsten carbide coatings, each with a different content of cobalt, which were subjected to electrical discharge machining (EDM). It was found that the electrospark deposition of WC8Co over the HVOF-sprayed WC12Co and WC17Co coatingsresults in the formation of a homogeneous layer of tungsten carbide with a low cobalt content. The EDM layer is well bonded with the HVOF-sprayed coating as confirmed by the gradual change in the content of the elements in the coating and layer. The friction coefficients obtained for the two coatings with the EDM layer are very similar as their composition, microstructure, hardness, and surface roughness are approximately the same.

In this study, Ni-Al powder is plasma sprayed on various substrates prepared by in-situ laser ablation and preheating. Surface topography and splat shape are examined in order to assess how laser induced heat flux affects surface modifications and variations in splat shape. The causes of laser induced surface modifications are identified for Al, Ti, and stainless steel substrates and it is shown that laser preheating improves surface absorptivity, which effectively subjects more defects to the effects of the laser.

To improve the mechanical properties of 316L stainless steel coatings prepared by plasma spraying, post-spray heat treatments were conducted at 600-800 °C for 1-2 hours. The effect on microstructure and hardness was assessed via XRD and SEM analysis and microhardness measurements. The results show that heat treatment at various temperatures improved coating hardness as well as fracture behavior.

Advances in thermal spraying are occurring in two general directions. On the one hand, spray processes are becoming colder, facilitating the production of oxide-free coatings in air atmospheres. On the other hand, new systems are being developed that enable higher powder throughput, thus making production faster and more efficient. In order to lock in these time-saving advantages, more and more applications are using CO 2 as a cooling medium to increase cooling efficiency and optimize spraying processes. This paper provides an overview of the use of CO 2 and its suitability for new applications.

This paper describes microstructure control aimed for wear-resistance improvement of Co-based (Co-Cr-W-B-Si) self-fluxing alloy coating by diffusion treatment. The diffusion treatments of thermally sprayed Co-based self-fluxing alloy coating on steel substrate were carried out at 1370K to 1450K for 600s to 6000s under an Ar gas atmosphere. Microstructural variations of the coating and the interface between the substrate and the coating were investigated in detail. A proper diffusion treatment precipitates two kinds of fine compounds in Co-based matrix. XRD and EPMA analysis revealed these precipitates to be a chromium boride dissolving cobalt and a wolfram boride containing cobalt and chromium. The size of each precipitate became larger with increasing treatment temperature and time. A coating with the proper size borides showed a superior wear-resistance.

Different post treatment methods such as heat treatment, mechanical processing, sealing, etc. are known to be capable to improve microstructure and exploitation properties of thermal spray coatings. In this work a plasma electrolytic oxidation of aluminium coatings obtained by arc spraying on aluminium and carbon steel substrates is carried out. Microstructure and properties of oxidised layers formed on sprayed coating as well as on bulk material are investigated. Oxidation is performed in electrolyte containing KOH and liquid glass under different process parameters. It is shown that thick uniform oxidised layers can be formed on arc sprayed aluminium coatings as well as on solid material. Distribution of alloying elements and phase composition of obtained layers are investigated. A significant improvement of wear resistance of treated layers in two types of abrasive wear conditions is observed.

In order to clarify the effects of two kinds of laser irradiation on plasma sprayed alumina coatings, microstructure, crystallization and mechanical properties of the spacemen were examined and heat conduction in the laser irradiation processes were analyzed by a finite element method. One is CW CO 2 laser irradiation of low power density, and the other is pulse excimer laser irradiation of high intensity but low energy density. Al 2 O 3 coatings were irradiated by CO 2 laser with low intensity, fine structure formation composed of α- Al 2 O 3 was confirmed and the surface roughness was improved although the hardness decreased a little. The modified layer was corresponding to the area that was heated above 1000 to 1100°C in the calculated maximum temperature distribution. It was also confirmed that the excimer laser pulse has a potential to improve the properties of surface layer to a depth of several micrometers.

Liquid metal atomization using a De Laval nozzle has proven its efficiency in producing fine and narrow sized powder. The modeling work of gas dynamics related to nozzle geometry has led to a better understanding of the effects of the processing parameters. During the emptying of the crucible, the decrease in the static height of the melt acts on the metal mass flow rate. An experimental study on the particle size distribution in the cross-section of the spray and its evolution during the process has confirmed the unsteadiness of the process. By establishing a model to fit the gas pressure to the mass flow rate evolution, an almost steady state can be reached for the process. This has brought us to reduce the mean particle size and to improve the narrowness of the as-atomized particle size distribution.

In the thermal spraying technique, the process includes some problems such as insufficient cohesive strength between particles in the coating. It is considered that the laser treatment of thermal spray coating will be effective method to improve the coating properties. In this study, an yttrium aluminum garnet (YAG) laser treatment was carried out on the sprayed coating in order to examine the effect of laser beam on the coating properties and post laser treatment method and hybrid spraying method were carried out. Irradiation laser power conditions were 1.5kW, 2.0kW and 2.5kW, and defocus distance conditions were ±0mm, +30mm, +60mm, +90mm, changing the energy density and the traverse speed conditions were 100mm/s, 200mm/s, 300mm/s. In post treatment method the affected region in the Cr 3 C 2 -Ni-Cr coating is smaller with increasing traverse speed. Laser energy density affected the microstructure. In the case of defocus distance ±0mm and traverse speed is 100mmm/s there are three different regions, melted region, heat affected region and no affected region in the coating. The micro Vickers hardness of melted region of coatings was lower and heat affected region of coatings was higher than no laser treatment coating. It was considered that with post laser treatment method it was very difficult to treat the coating uniformly. In the blast erosion test, the wear-out rate of hybrid spray coating was lower than that of the HVOF spray coating. It is considered that the improvement of micro Vickers hardness of Cr 3 C 2 -Ni-Cr hybrid sprayed coating resulted from the precipitation of fine chrome carbide in the matrix and their strengthening affect cohesive strength between lamella in the coating. In WC-Co hybrid sprayed coating, the improvement of micro Vickers hardness resulted from the porosity decrease. The coating structure was different even in the identical processing condition by the place. The micro Vickers hardness of melted area of coatings was lower and heat affected area of coatings was higher than no laser treatment coating.

Thermal spray processes represent a cost effective and flexible method for the production of functional coatings by using metallurgical, ceramic and cermet materials. Due to the high kinetic energy of the impinging particles, the HVOF (High Velocity Oxygen Fuel) technique is able to produce extremely dense coatings with very low porosity. In this study, several yttria stabilized zirconia (YSZ) powders have been sprayed by HVOF for the fabrication of electrolyte layers for SOFCs (Solid Oxide Fuel Cells) applications. Coatings were characterized regarding their porosity, leak tightness and electrochemical properties. Results were compared to VPS sprayed coatings. The electrochemical behavior of the cells sprayed with the optimized set of parameters was determined applying U(i)-characteristics and impedance spectroscopy. With a destination thickness of about 40 µm, competitive leak tightness of the electrolyte and performance of the cells could be established.

The residual grit weight and the penetration depth of the embedded grit were investigated by dissolution of the blasted substrate with a mixed acid solution. A carbon steel substrate was blasted by white alumina grit (WA #30). The blasting angle varied from 30° to 90°. The residual grit amount and the penetration depth increased with increasing blasting angle. The residual grit amount was 2-12 g/m 2 , and the penetration depth was 26-34 µm. When the blasting angle increased from 30° to 90°, the increase ratio of the residual grit amount was 6.0, although the increase ratio of perpendicular component of impact energy by blasting was 2.0. To reduce the residual grit amount, a decrease of blasting angle is more effective than the decrease of grit mass. For the reduction of the penetration depth of the embedded grit, the blasting angle effect is small.

Yttria stabilized zirconia and lanthanum strontium manganate (YSZ/LSM) have been employed to fabricate the composite cathode functional layer for solid oxide fuel cells (SOFCs). In the present study, the YSZ/LSM composite coating was deposited by atmospheric plasma spray (APS). The electrical conductivity of the composite coating was measured by the means of Direct Current (DC) measurement in a temperature range of 500-900 °C. The electrical conductivity of YSZ- 50%LSM coating changed from 2.17 S/cm to 3.60 S/cm along the direction parallel to the coating surface at the temperature range. For the same specimen, the electrical conductivity in the perpendicular direction is less than one-tenth of that in the parallel direction. The anisotropy of the electrical conductivity is attributed to the phases of different properties in the composite coating and the APS coating structure characteristics. The activation energy of the composite coating at both directions was calculated. The results showed that the electrical conduction of the composite was strongly influenced by the YSZ content.

The flattening behavior of individual splats plays a fundamental role in the elaboration of thermal spray coatings. In the PROTAL process, an in-situ laser treatment is coupled with spraying operations. It was shown that a pulsed laser irradiation can effectively suppress the splashing phenomenon of splats. This aspect was primarily attributed to the efficient removal of surface adsorbates/condensates. But, it may also be enhanced by the modification of the surface topography that improves the surface wettability. Therefore, this study deals with the effects of the surface microroughness modifications on the surface wettability induced by the PROTAL process. Several roughness parameters characterizing the surface topography are also discussed from a static wettability point of view.

The most commonly used structural materials for blades and other high temperature components of gas turbines are nickel superalloys such as Inconel 738, MAR M247M or Hastelloy. Thermal barrier coatings (TBCs) are widely used on these substrates as protection against high temperatures and oxidation. A TBC system consists of a top coat of yttria partially stabilized zirconia deposited by air plasma spray and an underlying bond coat (usually MCrAlY, where M is Ni, Co or a combination of both). MCrAlYs are normally deposited by thermal spray processes such as air plasma spray, vacuum plasma spray (VPS/LPPS) or high velocity oxygen fuel (HVOF). In general, the adhesion of the whole thermal barrier system is strongly dependent on the surface preparation of the substrate and it is generally believed that a certain degree of roughness promotes better adhesion. OEM’s (Original equipment manufacturer) procedure for preparation of substrates and analysis have been reviewed and considered as basis of this work. The scope of this work is to set up a new cleaning methodology in order to obtain a completely pollution free surface to be coated afterwards with HVOF or VPS/LPPS. The properties of this new methodology have been compared with standard surface preparation techniques such as blasting with corundum and silicon carbides. The obtained samples have been analysed by means of metallography and chemical composition of the interface in order to measure the interfacial pollution between substrate and coating. Finally adhesion of MCAlY coating have been tested and compared with specification of the main OEMs.

Being the 7th most abundant element on the earth, magnesium and its alloys have become very promising in numerous industrial applications because of some of their distinguished properties, including high thermal conductivity, high strength/weight ratio, good machinability etc. However, some inferior properties especially the poor wear and corrosion resistance have obstructed a widespread use. As one of the most effective solutions, thermal spraying can deposit an adequate protective coating on the substrate, but the necessary grit-blasting operation before spraying leads to high grit-residues on the magnesium surface therefore degrading the deposit performance. The PROTAL® process, combining a laser surface preparation with the deposition stage, can avoid this kind of disadvantage. This paper presents the possibility of employing PROTAL® to prepare a resistant Ni-Cr coating on a magnesium substrate. The coating adhesion and interface microstructure were especially investigated.

The tribological behaviour of HVOF-sprayed Co-28%Mo- 17%Cr-3%Si coatings, both as-sprayed and after heat treatments at 200°C, 400°C, 600°C for 1h, has been studied. Microstructural and micromechanical properties were characterized by SEM, XRD, depth-sensing indentation (microhardness, elastic modulus, indentation fracture toughness); pin-on-disk dry sliding wear tests were performed against 100Cr6 and sintered alumina spherical pins. The as-sprayed coating contains splat boundary oxide stringers and is mostly amorphous (splat quenching). It has low hardness (≈6.7GPa) and toughness (≈1MPa*m 1/2 ); thus, much adhesive wear occurs against 100Cr6 steel. The friction coefficient increases up to ≈0.9, raising the contact point temperature up to a critical coating oxidation value; then, it decreases, increases again and finally settles. Much of the adhesive wear occurs in the first stage of the test. Abrasive wear prevails with the alumina pin: the coating wear rate is lower because the metallic alloy possesses intrinsically good plasticity. Adhesive phenomena still occur, leading to the same thermal effects. After the 200°C and 400°C heat treatments, no major changes occur. The 600°C treatment causes the formation of some submicrometric crystals. The hardness increases (≈8.8GPa), adhesion to steel pin is prevented, and the friction coefficient soon settles at ≈0.8 with no peaks. The coating undergoes no wear loss and the pin wear rate largely decreases. With the alumina pin, coating and pin wear rates remain quite low. However, adhesion is reduced, so that the friction coefficient has no peaks and its final value is lowered (from 0.84 to 0.75).

Although it is widely used prior to the spraying stage to eliminate the surface contaminants and to improve the splat contact with substrate, a preheating operation should be precisely controlled to keep the metallic substrate away from an excessive oxidation. In most cases, the oxide scale can deteriorate the interface adhesion. A nanosecond pulsed laser treatment is a powerful tool to remove the surface oxide layers. It is also the fundamental principle of the PROTAL process that combines a laser surface preparation and the thermal spraying process. In this paper, a nanosecond pulsed laser was used to remove the thermally induced oxide while keeping the advantage of preheating. It is shown that the particle splashing was suppressed and the deposit adhesion was significantly improved resulting from the laser cleaning effects. The mechanism of oxide removal is also investigated.

A carbon steel was blasted by white alumina, and removability of residual grit was investigated. Blasting parameters such as grit particle size were varied. Residual grit was removed from substrate surface by dissolving the substrate in mixed acid solution, and the amount of residual grit was measured. Removal of residual grit was carried out by ultrasonic cleaning. The amount of residual grit was 7-17 g/m 2 , and penetration depth of embedded grit of most residual grit was 25-40 µm. The amount of residual grit increased with decreasing the grit size. However, the minimum amount of the substrate dissolution required for the grit removal increased with increasing the grit size.