Erosion-corrosion is a severe problem observed in the coal fired thermal power plant boilers which lead to premature failure of boiler tubes. Thermal spray coatings have been applied successfully to check the erosion-corrosion of boiler tubes. In the present research work NiCrTiCRe coating powders were successfully deposited on T22 boiler steel by two different coating processes i.e. high velocity oxy-fuel (HVOF) and cold spray process. The performance of the coatings in actual power plant boiler were investigated and compared. The uncoated and coated T22 boiler steels were subjected the superheater zone of the coal fired boiler for a total of 15 consequent cycles. The thickness loss data and weight change analysis were used to establish kinetics of the erosion-corrosion. X-ray diffraction, surface field emission scanning electron microscope/energy dispersive spectroscopy (FE-SEM/EDS) techniques were used in the present work for the analysis. The results of thickness loss data indicated that the cold sprayed coating performed better in thermal power plant boiler environment.

A novel model for coating design was proposed in this research, by considering both oxidation property and interdiffusion effect, corresponding to two factors of the Cr:Al activity ratio and the potential of Al, respectively. To verify this model, oxidation tests of coated superalloys were performed at 1000 ° C for up to 5000 h. The test results indicated a strong positive correlation between GPDZ and Al potential and a clear negative correlation between oxidation kinetics parameter k p and Cr:Al activity ratio. Our research opened up new ideas for the coating design.

Light alloys are being investigated as an alternative to ferrous-based engineering components. The manufacturing of such components requires a surface modification step necessary to eliminate the top surface's poor wear and corrosion response for improved functionality. Thermally sprayed cermet coatings offer improved surface resistance to wear and/or corrosion. This work presents a customized composition of WC-CoCr feedstock cut in fine and coarse powder size distribution (PSD) to fabricate different coatings on aluminium alloy and steel substrates using two high velocity spray techniques. The WC-CoCr coatings sprayed using the high velocity air-fuel (HVAF) technique at varied parameters consist of six different coatings (four thick, ~ 200 μm and two thin ones, 60-80 μm) to investigate the relationship between processing conditions, microstructure, and performance. Using scanning electron microscopy (SEM) and electro-dispersive X-ray spectroscopy (EDX) offered a comprehensive characterization of the respective coatings. Micro indentation, dry sliding wear, dry sand abrasion, and cavitation erosion tests conducted on the samples show the performance of the coatings based on the processing techniques and spray conditions. However, despite the similarities in the microstructural makeup of the coatings and the measured micro indentation hardness of the coatings (1000-1300 HV0.1), their respective specific wear rate (SWR) varied based on spray processing techniques and the substrate on which the coatings were deposited. Three of the HVAF coatings showed ~ 60 % more wear on the aluminium alloy substrate compared to the same coating deposited on a steel substrate. However, irrespective of the substrate used the HVAF coatings showed better wear resistance than the HVOF coating. The dry sand abrasion wear results of the two thick HVAF coatings show them superior to the HVOF coating in the three-body wear experiment conducted. The cavitation erosion resistance of the coatings varied based on the processing conditions and the driving mechanisms but the best two were the AF-2 and AF-6 samples.

Despite their excellent specific mechanical properties magnesium-based alloys are not widely used in the industry due to their high affinity to oxygen. Given the need for lightweight design, there are increasing efforts to replace high density materials by magnesium. One way to cope with the high oxygen affinity of magnesium is the use of thermally sprayed anti-corrosion coatings. However, conventional thermal coating processes have various process-related limitations. A case in point is coating of complex geometries and internal coatings with small diameters that often cannot be realized by conventional processes. Due to the changed process order some of the limitations of conventional coating methods can be resolved by the transplantation of thermally sprayed coatings. This method is a composite casting process for the coating of die cast components, where the thermally sprayed coating is applied to the corresponding area of the mold prior to the casting process. The aim of this study is to compare the effectiveness of transplanted thermally sprayed coatings with corrosion protection properties to conventional coatings deposited by thermal spraying and to discuss the ramifications with respect to industrial applications.

Three Fe-based powder alloys, Höganäs Fe SP529, Fe SP586 and 6AB, have been deposited by HVOF and HVAF spraying onto mild steel plates. The sprayed samples were first ground and then shot peened using glass shot in order to seal the surface interconnected pores and other surface imperfections. The samples as ground and ground/glass shot peened were tested by salt spray (fog) exposition for 238 h according to ASTM B117/ISO 9227. FeSP586, HVOF and HVAF sprayed and glass shot peening samples achieved surface sealing enough to pass the test with appearance rating RA = 9 according to ISO 10289. All other samples achieved moderate to excessive pitting and/or moderate to excessive staining types of corrosion defects.

Cavitation and corrosion on hydrodynamic components and systems reduces the operational efficiency. The use of wear resistant coatings have been studied as a solution to the problem of corrosion and cavitation in the industrial environment. Thermal spray processes are recognized as excellent technique to deposit coatings. The high velocity oxy-fuel process (HVOF) can produce high density and bond strength coatings. High velocity air-fuel process (HVAF) is an alternative process, shown to be superior regarding corrosion protection and production costs. HVAF can deposit coating with shorter dwell time and lower temperature, producing coating with lower oxide content. This paper presents the use of HVOF and HVAF process to deposit FeCrMnSiNi and FeCrMnSiB coatings, studying the resistance against corrosion and cavitation in comparison to 316L HVOF coating. Microstructure was analyzed by XRD, microscopic means and mechanical testing. Cavitation and corrosion behavior of the coatings were also studied comparatively. HVAF coatings presented lower porosity and oxide levels, as well as higher hardness values, compared with the coatings deposited by HVOF process. The HVAF process presented better cavitation resistance than HVOF coatings. The FeCrMnSiNi HVAF coating had the best corrosion protection performance between the developed alloys.

In the present work, commercially available NiCr and NiCr-TiC powder blends were deposited on boiler steel substrates by HVOF spraying. To evaluate coating performance, bare and coated steel samples were placed in the superheater zone of a coal fired boiler for 15 cycles. Weight change and thickness loss were measured and the results were used to establish erosion-corrosion kinetics. XRD and SEM/EDS techniques were used to analyze the microstructure and phase composition of as-sprayed and eroded-corroded specimens. The improvement in erosion-corrosion resistance provided by the coating may be attributed to the formation of nickel and chromium oxides and spinels.

This work assesses the behavior of thermally sprayed corrosion-resistant alloy (CRA) coatings in an aqueous solution containing supercritical CO 2 . 316L stainless, Ti, alloy 625, and alloy C-276 powders were sprayed on carbon steel using a HVOF torch and 8 mm holidays were drilled in the coatings to expose the substrate. The samples were divided into two sets and placed in autoclaves for 30 days, where they were exposed to a salt solution, bubbled with 10 MPa CO 2 , at temperatures of 40 and 80 °C. Sample cross-sections showed that wherever the coating was intact, it protected the substrate from CO 2 corrosion, but in holiday regions, where bare steel was exposed, a siderite scale had formed and severe undercutting occurred, possibly due to galvanic interactions with the CRA coating.

TiAl 3 -Al composite coatings are believed to hold promise for extending the service temperature range of titanium alloys used as structural materials. In this study, 0.6 x 40 mm Ti-6Al-4V specimens are coated with a 30 μm thick layer of TiAl 3 -Al by low-temperature HVOF spraying. Cross-sectional imaging shows that the as-sprayed coatings have a dense laminar microstructure and are well bonded to the substrate. Following the initial examination, the coating samples were placed in a muffle furnace, where they were held at 700 °C for up to 1000 h. Mass gain was detected starting at 200 h and remained nearly constant for the remainder of the test. This is an indication of excellent corrosion resistance, which is verified by SEM cross-sectioning and elemental EDS analysis. A brief explanation of the protective mechanism of the coating is provided.

This work evaluates the potential of using a plasma spray process to introduce SiC into zirconia diboride ceramic coatings. Controlling the spraying of the ultra-refractory compound ZrB 2 is the first challenge as it represents the matrix in which SiC particles will reside. To that end, the experiments focus on spraying parameters that influence the plasma jet and the nature of the precursor feedstock. The results show that ZrB 2 coatings containing controlled amounts of SiC can be obtained through high-energy suspension plasma spraying. The ZrB 2 -SiC coatings will be evaluated in a high-temperature oxidative environment in future work.

This study assesses the fireside erosion-corrosion behavior of nanostructured NiCr coatings in a power plant boiler operating at 750 °C. In the experiments, Ni-20Cr nanocrystalline powder was synthesized by ball milling and deposited on T91 boiler steel substrates by HVOF spraying. Coated and uncoated steel specimens were thermally cycled in the superheater zone of a coal fired boiler. After 15 heating and cooling cycles, the specimens were examined and erosion-corrosion kinetics were established via weight-change and thickness-loss measurements. The results show that the nanostructured coatings reduced the erosion-corrosion rate of T91 steel by 85%.

In this study, detonation spraying was used to deposit commercially available Ni-20Cr and WC-Co powders on SA213-T22 boiler steel. Coated and uncoated specimens were subjected to 50 thermal cycles in a molten salt boiler environment 900 °C in order to evaluate their hot corrosion behavior. Mass change measurements were made at the end of each cycle to assess corrosion kinetics and XRD and SEM/EDS were used to characterize corrosion products. An analysis of the reaction kinetics and the formation of oxide scales is provided in the paper.

In this study, WC-CoWC coatings were produced by HVOF spraying using bimodal-structured WC-Co powder with both micro- and nano-sized WC particles. Due to the melting characteristics of the powder during spraying, the microsized particles are retained in the deposit, but the nanosized particles dissolve into the Co matrix, forming a Co-W-C ternary phase. Compared to coatings sprayed from conventional WC-CoWC powder, the bimodal coatings are more resistant to corrosion and wear and are comparable in microhardness.

The high strength nickel alloys, and in particular Inconel type alloys, are extensively used in several applications, such as aeronautics and petroleum industry, thanks to the combination of their high mechanical properties and their thermal and chemical resistance. In particular Inconel 625 is already used in oil pipelines and pipelines of large thermal plants, and the possibility to replace high cost bulk Inconel parts with Inconel coated steel parts is of great interest. On this context the first topic to allow the use of coated parts instead of bulk Inconel is the capability to provide high corrosion and thermal resistance. The aim of this study is to investigate the capability of Coldspray in the deposition of high strength materials, such as hard nickel alloys, for corrosion protection, and to compare the corrosion behaviour of Coldspray coatings with commercial HVOF deposited coatings. Inconel 625 coatings were deposited by using CGT Kinetic3000 deposition system with nitrogen as carrier gas on AISI316L flat substrates. The coating thickness ranges between 0.3 and 1.0 mm. Different feedstock materials were used and the effect of powder size distribution on the growth capability, as well on coating microstructure and porosity, were evaluated. The corrosion behaviour of Coldspray coatings were studied by electrochemical potentiondynamic analysis and compared with the behaviour of commercially available coatings deposited by HVOF that could be considered as a high-quality benchmark. In particular, the effects of the different coating microstructures due to the different deposition processes were related with the corrosion resistance. Further development and key features are finally outlined in order to candidate the Coldspray as promising technology for the deposition of high-strength nickel alloys.

Nickel-chromium alloys have been used as coatings to deal with oxidation environments at high temperature. The present work is a comparative study of HVOF and cold sprayed Ni-20Cr coating on a boiler steel (SAE 213-T22) in a molten salt environment of Na 2 SO 4 -60%V 2 O 5 at 900°C under cyclic conditions. The weight change technique was used to establish the kinetics of corrosion. X-ray diffraction, surface and cross-sectional FE-SEM/EDS techniques were used to analyse the corrosion products. The hot corrosion resistance of both the coatings was better than the uncoated steel. This may be attributed to the formation of oxides and spinels of nickel and chromium in the coated steels. These oxides might have blocked the pores and splat boundaries, and acted as diffusion barriers to the inward diffusion of corroding species. Based upon the overall results and subsequent analysis of hot-corrosion data the cold spray process may be recommended as a better choice for the deposition of the Ni-20Cr coating on Mo-containing T22 steel in comparison with the HVOF spray process for hot corrosion protection.

This work compares the oxidation behaviour of CoNiCrAlY coatings manufactured by the HVOF, APS and CGDS processes when submitted to temperatures of 1000°C and 1100°C. The as-sprayed coating microstructural features were characterised using SEM and XRD analysis before being subjected to isothermal heat treatments in an air furnace. Oxide scale composition was determined using XRD, SEM and EDS analysis while the oxide growth rates were obtained using mass gain measurements. The as-sprayed HVOF and CGDS coatings exhibit similar microstructures while the APS samples have a significantly higher porosity and oxide content levels. Results from the oxidation experiments indicated that the oxide growth rate of HVOF and CGDS were lower than that of the APS samples. The results also indicated that samples oxidised at 1100°C have a lower oxide growth rate than those oxidised at 1000°C. Analysis of the oxidation process up to 100 hours indicates that the formation of dense α-Al 2 O 3 is more favourable at 1100°C while a transition alumina, θ-Al 2 O 3 is more favourable at 1000°C. Furthermore, the surface profile of the samples oxidised at 1100°C were more uniform and free of protrusions.

The study of corrosion protection of magnesium and aluminum becomes increasingly important as the use of these alloys increases rapidly in the automotive and aerospace industries due to their advantages of light-weight, adequate mechanical properties and moderate cost. Corrosion, however, limits the application of magnesium and aluminum alloys. Fasteners, spot welds of dissimilar materials and their galvanic corrosion is of major concern in automotive applications. The paper presents first results of Low Pressure Cold Spray (LPCS) of Al based coatings for corrosion protection. The corrosion protection provided by these coatings was evaluated by electrochemical measurements in 1M NaCl electrolyte. The microstructures and electrochemical behavior of the coated joints were investigated. The electrochemical corrosion mechanisms of the coatings and microstructure were discussed.

The dense refractory is applied for the high-temperature glass melting equipment. Furthermore, platinum or its alloy-clad refractory bricks are utilized to melt high quality glass in fields of optical and display glasses. From the viewpoint of the resource saving of rare metal, the decreasing of Pt-consumption is very serious problem for glass manufacturing. The platinum thermal spray coating is effective alternative technology to solve this problem for platinum cladding. A Pt-spray coated ceramics is difficult to get reliability due to the large difference of thermal expansion between the ceramic and the metal. In this study, we have investigated the bond strength of the platinum coat on the dense refractories which was textured by the mechanical process. As a result, the bond strength between the ceramic and the metal is 3-5 MPa. It is almost the same as the thermal spray ceramics coating on the metal. Furthermore, in case of the ceramics substrate that contains the glass phase, the bond strength between the ceramic and the metal increased to 14-17 MPa after 1773 K heat treatment.

Coatings containing up to 65 volume % of silicon carbide were deposited by plasma spray. Potential applications can be found in the protection of CMC (Ceramic Matrix Composite) against wear and high temperature oxidation. It is well known that SiC can not be deposited by thermal spray because it decomposes before melting. To face this problem, a mixture of SiC and ZrB 2 was deposited, since those two compounds form an eutectic phase, at a temperature lower to the one of SiC decomposition. Coatings microstructure was characterised by XRD, SEM, and EDS, confirming the presence of SiC in the deposited layer and the formation of the eutectic phase during spraying. Samples of the coatings were exposed in air at high temperature, in the range between 1373 and 1873 K. The oxide scale was investigated by means of SEM and EDS. It was constituted by a SiO 2 layer, which includes islands of ZrO 2 . Test results showed the good potentiality of the material investigated to be used as a protection against the high temperature oxidation.

The trend in thermal spraying is increasingly towards a globally uniform level of high-grade spray coatings. It is therefore extremely important that auxiliaries such as spray materials or industrial gases undergo precise examination in order to exactly define their influence. This is not only made possible by selecting the right system, but also by choosing the right gas and gas mixture. In order to broaden the range of thermal spray applications, we have endeavoured to investigate the issue of the right gas mix for arc spraying. In doing so, it was concluded that, by using wire as the spray material, this cost-effective process can often be used as an equally viable alternative to other methods. The optimization of costs, extended lifetime of systems and tailoring of coating properties to suit specific applications are just some of these influencing variables