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Current research work focuses on the investigation of surface topology of plasma sprayed (PS) Inconel625-Al2O3 (IN625-Al) composite coating. This paper reveals the microstructural features and microhardness of composite coatings developed with plasma spraying. SEM/EDAX analysis was used to reveal the average feedstock particle size, elemental composition and surface morphological aspects of as-sprayed IN625-Al composite coating. EDS mapping of IN625-Al composite coating reveals the uniform distribution of major elements like Al, Ni, Cr, Mo, and Nb in composite matrix. The microstructure of IN625-Al coating during plasma spraying (PS) exhibits splats (fully melted), un-melted particles, pores and voids indicating typical features of PS. The micro-hardness, and porosity of the as-sprayed coating were also determined. The average hardness and porosity value of IN625-Al coating was found to be 880Hv0.2 and 1–2.5%. The paper is helpful in selecting the presented composition for erosion and oxidation resistance.

Purpose In the present study, Al2O3 coatings were deposited on stainless steel AISI-304 material by using atmospheric plasma spraying technique to combat high temperature solid particle erosion. The present aims at the performance analysis of Al2O3 coatings at high temperature conditions. Design/methodology/approach The erosion studies were carried out at a temperature of 400°C by using a hot air-jet erosion tester for 30° and 90° impingement angles. The possible erosion mechanisms were analyzed from scanning electron microscope (SEM) micrographs. Surface characterization of the powder and coatings were conducted by using an X-ray diffractometer, SEM, equipped with an energy dispersive X-ray analyzer. The porosity, surface roughness and micro-hardness of the as-sprayed coating were measured. This paper discusses outcomes of the commonly used thermal spray technology, namely, the plasma spray method to provide protection against erosion. Findings The plasma spraying method was used to successfully deposit Al2O3 coating onto the AISI 304 substrate material. Detailed microstructural and mechanical investigations were carried out to understand the structure-property correlations. Major findings were summarized as under: the erosive wear test results indicate that the plasma sprayed coating could protect the substrate at both 30° and 90° impact angles. The coating shows better resistance at an impact angle of 30° compared with 90°, which is related to the pinning and shielding effect of the alumina particle. The major erosion wear mechanisms of Al2O3 coating were micro-cutting, micro-ploughing, splat removal and detachment of Al2O3 hard particles. Originality/value In the current study, the authors have followed the standard testing method of hot air jet erosion test as per American society for testing of materials G76-02 standard and reported the erosion behavior of the eroded samples. The coating was not removed at all even after the erosion test duration i.e. 10 min. The erosion test was continued till 3 h to understand the evolution of coatings and the same has been explained in the erosion mechanism. The outcome of the present study may be used to minimize the high temperature erosion of AISI-304 substrate.

In the present work, Inconel-718 (IN718) coating was developed on a gray cast iron (C.I) substrate by utilizing a high-velocity oxy-fuel spray technique. The microstructural analysis was performed to know the topological characteristics of the deposited IN718 coating. Corrosion testing of bare and coated samples was carried out at an ambient temperature in a NaCl solution (3.5 wt.%) using potentiodynamic polarization technique. The kinetics of corrosion and surface characteristics of the as-sprayed and corroded coatings were studied by scanning electron microscopy/energy-dispersive spectroscopy techniques. The different phases in the feedstock powder and as-sprayed coating were determined through X-ray diffraction analysis. The reported average microhardness value of the developed IN718 coating was 563 ± 15 HV0.2. The increased hardness of the IN718 coating is credited to the existence of Mo and Ti elements in the IN718 coatings. Corrosion testing showed that the IN718 coating exhibited the maximum corrosion resistance compared to a C.I. substrate due to a stable passive layer in the IN718 specimen.

In future industries like gas turbine engines, steam turbines and coal gasification will reach new heights in terms of operating temperatures and efficiencies. These advancements in technologies bring challenges for engineers to develop corrosion resistant materials for these systems to minimize corrosive wear, which are the main factors responsible behind downtimes at elevated temperatures. Therefore development of protective systems for the components operating in these harsh conditions is a significant topic both from an engineering and economic view point. The main focus of this article is to review the corrosion behavior of super alloys at elevated temperatures.

Distinct methods of depositing the coatings are available according to the intended area of application with a sole objective to protect the surface of structural component like boiler, boiler tubes, and heat exchangers from any mechanical or chemical damage. The main benefit is to minimize the manufacturing cost of a new component and also its fabrication. Thermal spraying is the commonly used technique to tailor the surface properties with a cost-effective approach. The different techniques of thermal spraying such as plasma, HVOF, cold spraying, etc. were investigated and introduced. Although each of these processes has advantages, there are also certain disadvantages associated with them, which limit their application. In the chapter, different methods of depositing coating by thermal spray are discussed and compared. By developing advanced techniques and new coating materials, the life and efficiency of power plants can be enhanced in the future.

The socio-economic development of any country is completely dependent on the energy and the demand for energy is not completely fulfilled from a single source. As a result, renewable sources of energy like solar, wind, and hydro come into the picture. Countries like India and Nepal are naturally gifted with the potential of hydrodynamic energy, where a large number of small and medium hydro-power plants have been installed on the rivers coming from the Himalayas. Most of the hydrodynamic plants are situated in the Himalayan belt and have to deal with the problem of silt erosion in the hydrodynamic machinery. The hydraulic turbine is the heart of any hydropower plant and once it gets damaged due to silt erosion, not only the efficiency of the plant gets affected but it also increases the associated maintenance cost. Over the last two decades, researchers have been continuously working on this problem and focusing extensively to minimize the erosion rates with different materials processed by using surface modification techniques. To prevent the degradation of materials, protective coatings are used, which act as a barrier between the material and the working environment. The current manuscript reviews the performance of modified surfaces, which have been developed by using various surface engineering techniques to combat the slurry erosion failure in hydrodynamic turbines. The deposition of the coating by using different techniques and the evaluation of enhancement in the coating characteristics (mechanical and micro-structural) as well as coating efficiency under different slurry erosion conditions are reported. The effects of different operating parameters such as the angle of impingement, erodent size and shape, and slurry concentration on the performance of coating materials have been studied and discussed in detail.