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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.

Surface degradation (oxidation/corrosion/erosion) at elevated temperature is encountered commonly in engineering industries like gas turbines and thermal power plants. [Formula: see text]CrAl[Formula: see text] coatings which came into the picture in 1960s were used widely for surface protection in the elevated-temperature section of the gas turbine engines and in boilers to combat oxidation/corrosion/erosion. Among them, [Formula: see text]CrAlY ([Formula: see text], Co or [Formula: see text]) were developed to be used as the overlay coatings and bond coat (BC), which offer a combination of multiple features such as oxidation, corrosion and ductility. [Formula: see text]CrAlY coatings form a second layer of aluminum oxide beneath the chromium oxide layer at elevated temperatures which minimizes the oxidation/corrosion/erosive wear rates. But the desire to increase combustion efficiencies of power plants and gas turbine engines along with lower CO2 emissions poses a significant challenge for coating design. As the temperature surpasses 900∘C, NiCrAlY coating degrades quickly due to nonregeneration of chromia or alumina. The research and development (R&D) efforts are focusing continuously on improving the existing [Formula: see text]CrAl[Formula: see text] coatings or developing new sustainable [Formula: see text]CrAl[Formula: see text] coatings with improved oxidation performance. In this review, the roles of the alloying elements, microstructures, post-deposition treatment techniques and different deposition processes in the elevated-temperature oxidation/corrosion performance of [Formula: see text]CrAl[Formula: see text]-based alloys have been explored in detail.

The lifespan and performance of the industrial components used in aero engine’s and IC engines can be considerably increased by depositing thermal barrier coatings (TBCs). High-pressure gas turbines’ rotor blades and stator vanes are some of the world’s most heavily loaded engineering parts. In order to safeguard such components, more research is being conducted on TBCs, since the size of deployment and the production techniques used lead to improved life, economics, efficiency, and durability. This paper concentrates on the technological developments in the field of TBCs over the past few years in order to achieve maximum output. Current coating R&D has also placed an emphasis on the factors that contributed to the development of cutting-edge advanced coating-fabrication techniques, such as electron-beam physical vapor deposition (EB-PVD), suspension plasma spray (SPS), additive manufacturing (AM), functionally graded material (FGM) and incorporation of artificial intelligence (AI) in manufacturing of TBCs. This paper examines the current state of TBCs, including the most recent developments in terms of their performance and manufacturing, associated challenges, and suggestions for their potential usage in high temperature sector.

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.

Metallic bioimplant are widely used now-a-days to replace a part of human body in a physiologically accepted manner. However, the bio-compatibility of the metallic bioimplant was mainly achieved by the incorporation of a bio-compatible coating on its surface through suitable surface modifications techniques. In surface modifications techniques, the thermal spraying is widely used for modification of metallic bioimplant due to its versatile nature. In thermal spraying, the hydroxyapatite (HAp)-based coatings are mainly preferred because this coating responses to physiochemical environment and adapts itself accordingly. But bulk of the HAp coating give out due to less adhesion strength of the HAp coating and its poor mechanical properties. The properties of HAp-based coatings can be designed as per requirements by reinforcing this coating through hard particulates in suitable proportions. In this paper, the various thermal sprayed (TS) coatings used for performing HAp-based coatings on bioimplant were discussed. The influence of reinforcements on the mechanical and bio-compatible properties of the coatings is also discussed in detail. Lastly, the challenges in the TS HAp coatings along-with the future perspective of TS coating in fabricating of 3D biomedical implants by using cold spray (CS) has also been summarized.

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.

The implant materials used currently in field of cardiovascular and orthopedics surgery dearth in osteoconductivity. Different surface modification techniques are used, developed and investigated over the years to enhance the osteoconductivity of biomaterials like metals, polymer and ceramics. Although implants made up of metals are strong mechanically but have low bonding ability due to bio-inert nature.To overcome the limitations and to accomplish the desired purpose, composite coatings consisting of bioactive are developed on the metallic biomaterials. In general bio-inert ceramics like yttria stabilized zirconia (ysz), titania, and alumina may be incorporated into hydroxyapatite (HA) matrix to develop composite coatings with improved mechanical properties over the years. The composite coatings developed by thermal spraying have shown promising approach to have good mechanical and biological properties in comparison with single-component and/or monolayer coatings. The strategy to use composite coatings is adopted widely by the professionals/scientists in the area of biomaterials for development and production of materials in order to repair and regeneration of the human tissue. In this article, commercially used thermal spraying techniques used for deposition of composite coatings for biomedical implants are discussed.

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.

The life of the components operating under various high-temperature environments decreases due to the activation of different failure mechanisms. High-temperature oxidation and erosion are the two prominent mechanisms that lead to the degradation of materials, resulting in the premature failure of the components. This paper has emphasized the failure and performance analysis of nickel-based coatings formulated by using different thermal spraying techniques. Nickel-based coatings like Ni–Cr, Ni3Al, Alloy-718, NiCrAlY, NiCrBSi and Ni-based composite coatings showed excellent resistance against the high-temperature conditions. This study helps to select specific thermal spray techniques and coating composition against high-temperature erosion and oxidation conditions.

In the current experimental study, grey cast iron (CI) substrate was coated with Inconel718-Al2O3 based composite coating with a high-velocity oxy-fuel technique. The effect of changing the Al2O3 content (10, 20 and 30 wt.%) on the microstructure, hardness, porosity and electrochemical corrosion performance of Inconel (INC718) coating was studied. Investigations on the corrosion behavior of uncoated and HVOF-coated substrates were carried out at room temperature at 3.5[Formula: see text]wt.% sodium chloride solution (NaCl) with the help of the potentiodynamic polarization approach. The surface morphologies and compositions of HVOF as-sprayed and electrochemically corroded coatings were studied through SEM and EDS techniques. The various phases existing in the INC718 and Al2O3 feedstock powders and HVOF-deposited composite coatings were determined by XRD analysis. The microhardness of INC718-based coatings was found to be increased with the increase in Al2O3 content. The highest average microhardness value of about [Formula: see text]HV[Formula: see text] was observed in INC718-30[Formula: see text]wt.% Al2O3 coating. The deposited coatings exhibited an increased porosity level with the increased amount of Al2O3 contents. However, the coating with 10[Formula: see text]wt.% Al2O3 content exhibited the maximum corrosion resistance. Its improved corrosion performance is attributed to low porosity levels, which causes the penetrating pathways of Cl− ions to be blocked completely.

Boilers in the power plant have to operate in highly strenuous conditions, where the service temperature can reach nearly the melting point of the materials. Boiler tubes inside the boilers have to face high stresses, a fluctuating environment, and high temperature. All these factors will activate various degradation mechanisms in the heat exchanger tubes, which results in their catastrophic failure. Due to this, the boiler will fail to meet its functional requirement, and consequently, in this event, the power plant will remain shut down for an extended period, resulting in a substantial economic loss to the organization. More than 75% of unexpected boiler shutdowns are due to the failure of the boiler tubes. This article discusses a failure associated with the boiler tubes inside an industry at Hoshiarpur, Punjab, India. Frequently occurring failures of boiler tubes were the cause to identify the right reasons responsible for these failures and then provide the technical solutions in the interest of the industry. During the detailed investigation, it was found that the wall thinning of boiler tubes was occurring due to high-temperature oxidation and erosion, and they could not withstand the internal pressure, leading to the bursting of tubes. Use of high-temperature oxidation- and erosion-resistant thermal spray coatings were recommended to the industry to avoid the failure of boiler tubes.

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.

Post-spray treatments have recently been popular as a means of improving the overall quality of thermally sprayed coatings, particularly those done using the HVOF technique. Thermally assisted surface treatment of deposited coatings is an effective way to improve the characteristics of coated components for specific applications. The tribomechanical properties of post-treated WC and Ni-based coatings deposited with high-velocity oxy-fuel (HVOF) technique have been addressed. The structure-property correlations concerning the as-sprayed and post-treated coatings have been considered to understand the various mechanisms responsible for improved performance in terms of wear and corrosion resistance. The recent advancement in the post-treatments such as post-processing using microwave hybrid heating, laser-assisted processing and Stationary friction processing have been incorporated in the current review. Comparative studies have been presented to understand the structure-property relationship and performance of WC and Ni-based HVOF sprayed coatings with the help of various characterization techniques in this review article.

Integration of additive manufacturing (AM) with Cold spray process is the latest solid-state supersonic deposition method that has gained significant attention of future manufacturing industry owning to its acceptability for mass production, fabrication, and restoration of typical engineering components. Cold spray additive manufacturing (CSAM) can build 3D components and this technique has the potential to change the future of the manufacturing world with remarkable sustainable benefits. This review sums up the research on state-of-the-art and identified key challenges for deploying a CSAM as a repairing, restoration and sustainable fabrication process in the future manufacturing industry. The benefits of CSAM for sustainable manufacturing have been discussed regarding the environmental concerns, and optimized product structures and designs. The outcome of the current study indicates that challenges associated with CSAM can be overcome with careful planning and manufacturing strategies. It also presents the recommended future research directions for CSAM's implementation as an established viable advanced AM process.

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.