In the current work, Ni-20Cr coatings have been developed for potential use in harsh environments of power plant boilers. A pre-synthesized Ni-20Cr nanocrystalline powder was deposited on T22 boiler steel using cold-spray process. The high temperature oxidation behavior of the coating was investigated under cyclic conditions at 900° C for 50 cycles, so as to understand the kinetics of oxidation. Moreover, high temperature erosion-corrosion (E-C) behaviour of the coating was ascertained under cyclic conditions in an actual boiler at 740 ± 10°C for 1500 hours. The oxidized and eroded-corroded samples were characterized using X-ray Diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) analyses. The microhardness, oxidation and E-C data for the developed coating was compared with an earlier reported cold-spray Ni-20Cr coating, which was developed by using a commercially available micron-sized Ni-20Cr powder. The results showed that the developed coating was found to have 33% high microhardness in comparison with the microstructured Ni-20Cr coating. The oxidation and E-C rates of the steel were found to decrease significantly after the application of the developed coating by 89% and 68% respectively. Moreover the nanostructured coating outperformed the corresponding micro-structured Ni- 20Cr coating with regard to high temperature oxidation and E-C resistance to boiler steel by a significant fraction. The investigated coating was found to have oxidation protective oxides such as Cr 2 O 3 and NiO in its oxide scale and was found to be spallation-free.

In this investigation, a nanostructured NiCr coating was deposited on boiler steel by cold spraying and its oxidation behavior was evaluated under cyclic thermal conditions. Oxidation kinetics were established through weight change measurements and the oxidized samples were characterized using XRD and SEM analysis and X-ray mapping. The nanostructured coating was more than two times harder than its microstructured equivalent and in oxidation tests, reduced the weight gain of the boiler steel by 68%. The coating was found to have protective oxides in its oxide scale and was shown to be spallation-free.

This study assesses the potential of kinetic-spray coatings for dealing with the effects of soldering and erosion on aluminum casting dies. In the experiments, molybdenum-boride cermet and cobalt-based alloy powders are cold sprayed onto SKD61 substrates. Coating microstructure is assessed via SEM and XRD analysis and several mechanical properties are measured. In order to evaluate soldering resistance, the coatings are immersed in a molten aluminum bath. Although cold-sprayed CoCrNiWC exhibited high coating density and low porosity, its soldering resistance was significantly lower than that of MoB-NiCr. The boride cermet coating not only exhibited superior soldering resistance, but also higher hardness, bond strength, and wear resistance. However, its deposition efficiency needs further improvement.

In this study, Cu-based bulk metallic glass coatings were deposited by atmospheric plasma spraying with different hydrogen flow rates. The crystallization and oxidation of the coatings is assessed along with corrosion resistance. As thermal energy in the plasma jet increases, the melting fraction and oxidation of particles in the coating increases as does porosity. All of these factors have an effect on the corrosion resistance of Cu-based bulk metallic glass coatings and their relative impact is discussed.

Manufacturing of diamond abrasive wheel has been achieved through kinetic spraying in order to simplify the manufacturing process and improve the mechanical properties. However, size of the initial feedstock diamond particles is reduced by fracturing during the process. Uniform distribution of diamond particles in the coating layer is significantly important for obtaining grinding properties of diamond abrasive wheel. In this study, optimized nickel thin film which is coated around the surface of diamond particle was used to prevent the fracture of diamond particles during spraying and improve the properties. Thickness of the nickel thin film was optimized by ABAQUS 6.7-2 finite element analysis software as 3 µm for 20 µm diamond and bronze particles. Fraction and size distribution of the diamond particles present in the coating were analyzed through Scanning Electron Microscope (SEM) and Image analyzer methods.

In this study, interconnect layer of solid oxide fuel cell (SOFC) was built up from spray-dried La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) and blended LSCF-Ag through atmospheric plasma spraying (APS). Microstructure and phase of each coating was analyzed through scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. Furthermore, bond strength, micro-hardness, thermal cycle test and oxidation test were performed and compared. The coatings prepared from spray-dried LSCF have higher porosity and cracks at inter-particle boundaries. However, the coatings with silver addition presented reduced cracks and porosity due to relatively high ductility of silver, resulting in higher mechanical properties.

In this work, effect of substrate roughness on the deposition behavior of the particles through kinetic spray technology is studied. Finite element analysis program, ABAQUS 6.7-2 was used to estimate the results. Particle impact on the planar and roughened substrates were analyzed and compared. Interface temperature, contact area and contact time were found to be higher for the particle impact on roughened surfaces than that of the planar one for constant spray condition. These factors are significant for bonding mechanism. Experiments were performed on the polished and grit blasted surfaces in order to compare the results. The deposition efficiency and the bond strength values were used to evaluate the effect of surface roughness.

In this study, individual particle impact behaviors of soft particle on hard substrate were observed. The ratio of bonds was compared to the difference between adhesion and rebound energies. To improve the existing model, the equation for effective yield strength was modified and finite element analysis was applied to estimate the temperature and strain gradients. The energy difference was derived from the strain and temperature of the elements and compared to the experimental ratio of bonds.

In this study, three kinds of engineering metals, which are aluminum (1100-H12), commercially pure titanium and mild steel were combined as particle/substrate and classified into four cases, i.e., soft/soft, hard/hard, hard/soft and soft/hard, according to their physical and mechanical properties respectively. Based on finite element modeling, impacting interface elements of four cases were analyzed and impact behaviors were numerically characterized. For soft/soft and hard/hard cases, the maximum temperature at the substrate side, which approached melting point, is higher than that of particle side when the shear instabilities occur. In particular, the different size of thermal boost-up zone was numerically estimated and theoretically discussed for these two cases. Meanwhile, for soft/hard and hard/soft cases, the specific aspect of shear instability, which has very high heat-up rate, was always observed at the relatively soft impact counterpart, and a thin molten layer was expected as well. Thus, the successful bonding of the above mentioned four cases can be predicted as a result of the synergistic effect of localized shear instability with interfacial melting.

A group of blended and spray dried solid lubricants with the same nominal composition were deposited by atmospheric plasma spraying (APS). The wear resistance of two coatings formed at room temperature and 350°C was evaluated using a rig test to simulate actual application conditions. The results showed that the blended powder coating showed inferior mechanical and tribological properties due to its non-uniform microstructure, which were induced by the differences in the physical and thermophysical properties of each constituent phase. However, the nanostructured spray-dried feedstock coating showed a better wear resistance due to its lower porosity, higher hardness and higher bond strength. In addition, the friction coefficient decreased with an increase of the Ag fraction and the uniformity of the Ag solid lubricant in the coating.

Thermal spray coatings of surfaces with metal, alloy and ceramic materials for protection against corrosion, erosion and wear is an intense field of research. The technique involves injection of the powder into a plasma flame, melting, acceleration of the powder particles, impact and bonding with the substrate. Feedstock powders of thermal spray applications have to meet several requirements. Particle shape, size and its distribution, powder flow characteristics and density are the important factors to be considered in order to ensure high spray efficiency and better coating properties. For smooth and uniform feeding of powders into the plasma jet, the powder particles have to be spherical in shape. In the present investigation powder particles are fed into the thermal plasma and spheroidized. The plasma was generated in a dc atmospheric plasma spray torch operating in non-transferred mode. Plasma processed powders were allowed to cool in atmospheric air inside a plasma reactor. The particle while free fall and cooling got spheroidized by surface tension forces. The feedstock powders were in the size range from 40 to 100 microns. The processed powders were analyzed through XRD, SEM/ Optical microscopy and irregularity parameter (IP) and roundness factor were determined. The same parameters were determined through theoretical methods and compared with experimental results.