Assessment of the microstructure, adhesion and elevated temperature erosion resistance of plasma-sprayed NiCrAlY/cr3C2/h-bn composite coating

This study uses an air jet erosion tester to investigate the erosion behavior of NiCrAlY/Cr3C2/h-BN composite coatings that are plasma-sprayed at three different temperatures and 40 m/s on T22 boiler steel alloy. 30 and 90° are the impingement angles. To identify the erosion mechanism, SEM and X-ray diffraction techniques are used to analyze the surface morphology and phase generated on the eroded surface. Findings of erosion test indicate that the erosion resistance was notably enhanced by addition of Cr3C2 and h-BN because of its lubricating characteristics and capacity to reduce frictional forces during erosion. The combined influence of Cr3C2 and h-BN enhanced the coating hardness and erosion wear resistance, thereby improving its overall resistance to erosion. The weight loss method was employed to calculate the erosion rate, and the NiCrAlY/Cr3C2/h-BN coating showed up to 30.55% and 34.48% lower erosion rate as compared to uncoated T22 substrate at 600 °C for 30° and 90° impact angles, respectively. This characteristic is affected by the hard reinforcement Cr3C2's high-temperature stability, the h-BN's self-lubricating ability, the formation of a protective oxide layer that forms at 600 °C, and the eroded coating's ductile behavior of material removal. The study also reveals that the NiCrAlY/Cr3C2/h-BN coating system on T22 boiler steel alloy has excellent erosion resistance, making it suitable for use in high-temperature and erosive environments in boiler systems and similar industries

Elevated temperature erosive wear behavior of superalloy coatings deposited using cold spray technology

The boiler tube components in thermal power plants and steam generating systems suffer from erosion and corrosion problems and are even today posturing a grave threat to industries, resulting in forced outages. Unrelenting efforts to decrease the components’ maintenance costs have been made by protecting with coatings. Among the various coating methodologies are thermal spray, chemical vapour deposition (CVD), physical vapour deposition (PVD), etc., in vogue. However, recently, the additive manufacturing-based cold spray technique is gaining interest among material scientists, incorporating high-velocity impacts associated with the low-temperature regime. Nickel-based superalloy Inconel 625 has been chosen and cold sprayed on The American Society of Mechanical Engineers (ASME) T11 and T22 boiler steels. The coated surface is characterized by scanning electron microscopy and energy dispersive X-ray analysis (EDAX), X-ray diffraction, micro-hardness, and elemental X-ray mapping techniques. The solid particle erosion studies have been carried out both at room and an elevated temperature of 700 °C as per American Society for Testing and Materials (ASTM) standard for 30°C and 90 °C impact angles. An optical profilometer has been used to evaluate the erosion volume loss. The results showed that the coated samples exhibit superior erosion resistance than the uncoated samples at both room and elevated temperatures. The erosion data obtained have been substantiated using scanning electron microscopy by analyzing the damage features and correlating with the erosion data. </jats:p

EFFECT OF LASER POST-TREATMENT ON MICROSTRUCTURAL AND SLIDING WEAR BEHAVIOR OF HVOF-SPRAYED NiCrC AND NiCrSi COATINGS

In this study, NiCrC and NiCrSi coatings are deposited on the MDN 310 steel using High-Velocity Oxy-Fuel (HVOF) process. Laser Surface Melting (LSM) post-heat treatment is carried out on as-sprayed coatings using Laser Engineered Net Shaping (LENSTM) with a power of 300[Formula: see text]W. The characteristics of both coatings in terms of mechanical and metallurgical properties have been investigated. The thicknesses of the as-sprayed NiCrC and NiCrSi coatings are in the range of 170–200[Formula: see text][Formula: see text]m. Laser-treated NiCrC and NiCrSi coatings exhibit a thickness range of 162–185[Formula: see text][Formula: see text]m, respectively. The microstructure of laser-treated NiCrC-300W coating clearly shows a dendrite-like structure, whereas the laser-treated NiCrSi coating exhibits hard layer and columnar homogeneity. Microhardness of as-sprayed NiCrC coating is [Formula: see text] [Formula: see text] and that of NiCrSi coating is [Formula: see text] HV[Formula: see text]. Microhardness of laser-treated NiCrC coating is [Formula: see text] HV[Formula: see text] and that of NiCrSi coating is [Formula: see text] HV[Formula: see text]. Dry sliding wear tests are conducted at room temperature (RT) and 400∘C with 10-N and 20-N loads. The wear rates at 400∘C temperature of laser-treated NiCrC and NiCrSi coatings produced are slightly below [Formula: see text][Formula: see text]mm3/m and [Formula: see text][Formula: see text]mm3/m, respectively. Laser-treated coatings produced better dry sliding wear behavior compared with as-sprayed coatings owing to dense microstructure. Formation of SiC phase in NiCrSi coating imparts high wear and frictional resistance compared to the NiCrC coating. </jats:p

HIGH-TEMPERATURE DRY SLIDING WEAR BEHAVIOR OF COLD-SPRAYED INCONEL 738 COATING

This paper deals with the dry sliding wear behavior of cold-sprayed Inconel 738 (IN 738) coating up to 600∘ C. The coating was deposited by a high-pressure cold spray system using helium as the propellant on T11 low-carbon steel substrate. The dry sliding wear behavior of uncoated specimens is compared with IN 738 coating using pin-on-disk tribometer (ASTM G99). SEM, EDX, and XRD analyses provide better insights on the worn surface morphology, changes in oxide scales, and phase transformation. At 400∘C, the tribo-layer developed at the interface contains NiO, which is a lubricious oxide, which reduces the wear rate of the coating. With further increase in temperature up to 600∘C, there is a formation of a protective layer, which results in the enhancement of high-temperature dry sliding wear resistance of the coating. At 600∘C, sliding wear resistance offered by the coating is approximately four times higher than T11 low-carbon steel. Therefore, the developed cold-sprayed IN 738 has high potential for usage at elevated-temperature dry sliding applications. </jats:p

Comparative study on high temperature oxidation behaviour of CoCrAlY coatings by various reinforcement composition profile analysis

In this article, high temperature oxidation behaviour of plasma sprayed carbides and oxides reinforced composite CoCrAlY coatings were investigated at 700°C. CoCrAlY was reinforced with Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;+YSZ, CeO&lt;sub&gt;2&lt;/sub&gt;, WC-Co, Cr&lt;sub&gt;3&lt;/sub&gt;C&lt;sub&gt;2&lt;/sub&gt;-NiCr individually to produce four different coatings. SEM, EDS and XRD are used to analyze the oxide scales formed during oxidation process on the coatings surface. From the results it is found that, all these coatings exhibited parabolic weight gain nature, indicating presence of protective oxide scale on coating surface, whereas changes in total weight gain is observed. CoCrAlY+Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;+YSZ coatings exhibited higher oxidation resistance than other coatings. The distribution of thermodynamically stable á- Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; in the coating is shown slow-scale growth kinetics during the oxidation.</jats:p