Search results

The purpose of this study is to investigate the effect of plasma pretreatment on the corrosion and adhesion behavior of Al coating deposited on iron steel by ion vapor deposition (IVD).

Ar plasma sputtering was carried out for 0, 5, 10 and 15 min, and then IVD Al coating was performed. Surface free energy measurements were conducted on the plasma-sputtered surfaces. Cross-sectional observations were carried out on the coating/substrate interface by using scanning electron microscopy. Corrosion resistance of the deposited films was characterized using potentiodynamic polarization curve test and electrochemical impedance spectroscopy (EIS).

Results demonstrated that surface free energy values were increased by increasing the sputtering time before coating process. The corrosion current density of the IVD Al coating deposited after 15 min Ar plasma pretreatment is three orders of magnitude lower than that of steel ST37 substrate. The EIS tests confirm the excellent anticorrosive properties of the Al-coated specimens.

With the increase in the plasma pretreatment time, coating adhesion would ameliorate because of the presence of plasma, which makes substrates a better place for Al ions to set and prevent any gap between coatings and substrates. This fact can be attributed to an increase in the surface free energy and reduction of contact angle of substrate exposed to plasma pre-treatment.

The purpose of this study is to prepare WC-10Co-4Cr coatings using two processes of plasma spraying and high-velocity oxygen fuel (HVOF) spraying. The decarburization behaviors of the different processes are analyzed individually. The microstructural characteristics of the as-sprayed coatings are presented and the wear mechanisms of the different WC–10Co–4Cr coatings are discussed in detail.

The WC–10Co–4Cr coatings were formed on the surface of Q235 steel by plasma and HVOF spraying.

Plasma spraying causes more decarburizing decomposition of the WC phase than HVOF spraying. In the plasma spraying process, η(Cr25Co25W8C2) phase appears and the C content decreases from the top surface of the coating to the substrate.

In this study, two WC–10Co–4Cr coatings on Q235 steel prepared by plasma and HVOF spraying were compared with respect to the sliding wear behavior.

The wear mechanisms of the plasma- and HVOF-sprayed coatings were abrasive and oxidation, respectively.

The aim of this study is to present an experimental research on a Al₂O₃ · TiO₂ plasma coating on AISI 316 stainless steel substrate with and without SiC particulate reinforcement to show how SiC particulate effect on the hardness, wear resistance and microstructure of the coating.

The main objective of the paper is to investigate the effect of SiC particulate on the coating properties such as hardness, wear resistance and microstructure. Achieving of this purpose, harness and sliding test, surface roughness measurements were carried out. In addition to that parallel work on microstructural examination by optical microscope were also conducted. Owing to SiC particulate is harder than Al₂O₃ · TiO₂ plasma coating, it influence hardness and tribological behavior and result in increasing in hardness values and wear resistance of the coating reinforced with SiC particulate compare with unreinforced Al₂O₃ · TiO₂ plasma coating.

This study provides experimental results about the Al₂O₃ · TiO₂ plasma coating with and without SiC_p reinforcement. The obtained experimental results indicate that SiC_p in the coating is influence hardness, wear resistance and microstructure of the coating and make them much harder and having wear resistance. This result is consisted with the values obtained previous studies that is available in literature.

SEM or TEM studies may be needed for better understanding of wear mechanism. Various percentage of SiC particulate in the coating can be used in the further researches and provide more detailed information about effecting on SiC_p reinforcement of the coating.

The results show that SiC_p reinforcement contribute increasing in hardness and wear resistance of the coating. Those compositions of the coating can easily used in related industrial applications.

This paper fulfils some useful information about SiC_p Al₂O₃ · TiO₂ plasma coating and offers practical help to students, related academicians and researchers in the industry.

Plasma spray coating technologies are capable of depositing a wide range of compositions without significantly heating the substrate. The objective is to characterise plasma sprayed metallic coatings on a Fe‐based superalloy.

NiCrAlY, Ni‐20Cr, Ni3Al and Stellite‐6 metallic coatings were deposited on a Fe‐based superalloy (32Ni‐21Cr‐0.3Al‐0.3Ti‐1.5Mn‐1.0Si‐0.1C‐Bal Fe) by the shrouded plasma spray process. The coatings were characterised in relation to coating thickness, porosity, microhardness and microstructure. The high temperature oxidation behaviour of the coatings was investigated in brief. The techniques used in the present investigation include metallography, XRD and SEM/EDAX.

All the coatings exhibited a lamellar structure with distinctive boundaries along with the presence of some porosity and oxide inclusions. The microhardness of the coatings was observed to vary with the distance from the coating‐substrate interface. The St‐6 coating had the maximum microhardness, whereas the lowest hardness was exhibited by the Ni3Al coating. The phases revealed by XRD of the coatings confirmed the formation of solid solutions, whereas EDAX analysis of the as‐sprayed coatings confirmed the presence of basic elements of the coating powders. So far as high temperature oxidation behaviour is concerned, all of the coatings followed the parabolic rate law and resulted in the formation of protective oxide scales on the substrate superalloy.

The plasma spray process provides the possibility of developing coatings of Ni3Al as well as commercial available NiCrAlY, Ni‐20Cr and St‐6 powders on Fe‐based superalloy Superfer 800H

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.

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.

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.

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 this work, Cr₃C₂-25NiCr coatings were deposited on 410 stainless steel substrate by using the atmospheric plasma spray technique, at varying spaying parameters. The porosity and microhardness, adhesion strength and corrosion behaviour of coatings were examined in relation to these spraying parameters.

The microstructure of prepared coatings was examined by using scanning electron microscopy. The coating compositional analysis was performed by using X-ray diffraction (XRD) technique. The corrosion resistance of coated steel was investigated by potentiodynamic polarization. Results indicate that optimal factors for minimalizing the porosity were as follows: 10 g/min feed rate, 600 A plasma current and 100 mm spraying distance. The spraying factors influencing corrosion resistance of coating were also evaluated.

Under this optimal condition, the porosity of coating reached its minimal value of 3.1 per cent. The microhardness and adhesion of coatings also reached their maximum values of 64.8 Rockwell Hardness scale C and 60 MPa, respectively. XRD results indicated the transformation of Cr₃C₂ originating from Cr₃C₂-25NiCr source powder into Cr₇C₃ and Cr₂₃C₆ crystalline phases, due to the high temperature during spraying process. The undetectable Cr₃C₂ peaks indicating that this phase was remained in coating at very low concentrations. The potentiodynamic polarization and salt spray tests confirmed the highest corrosion resistance for the coating prepared by optimal spraying parameters.

The application of Cr₃C₂-NiCr cermet carbit coating for protection of steel from corrosion-erosion is very promising.

The purpose of this study is to investigate the application of Ni₃Al coating for boilers and other power plant equipment, which suffer severe erosion-corrosion problems resulting in substantial losses. Currently, superalloys are being used to increase the service life of the boilers. Although the superalloys have adequate mechanical strength at elevated temperature, they often lack resistance to erosion-corrosion environments.

In this paper, the erosion-corrosion performance of plasma-sprayed nickel aluminide (Ni₃Al) coating on nickel- and iron-based superalloys have been evaluated by exposing them to the low temperature primary superheater zone of the coal-fired thermal power plant at the temperature zone of 540^°C for ten cycles of 100 h duration. The exposed products were analysed along the surface and cross-section using scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron micro probe analysis (EPMA).

The XRD, SEM and EPMA analyses have shown the formation of mainly NiO, NiAl₂O₄ and indicated the presence of Ni₃Al, Ni and Al₂O₃. In the boiler environment, Ni₃Al coating partially oxidizes and acts as a perfect barrier against erosion-corrosion of superalloys. The partially oxidised Ni₃Al coating remains intact even after 1,000 h cycle exposure.

The probable mechanism of attack for the plasma-sprayed Ni₃Al coating in the given boiler environment is presented.

This paper aims to verify weather atmospheric plasma spray (APS) in situ remelting posttreatment is effective for densifying the porous FeCoCrMoCBY amorphous alloy (FAA) coating and improving the antiabrasion and anticorrosion performances or not.

APS was used to deposit and in situ densify FAA coating on the 40Cr substrate. Scanning electron microscope, X-ray diffractometer, energy dispersive spectroscopy, neutral salt spray, hardness and wear behavior test were used to evaluate the densifying effects.

APS remelting technology can effectively improve the hardness of the coating by reducing the porosity. After remelting at 30 kW power, the hardness of the coating increased by about 260 HV0.2 and the porosity decreased to 2.78%. The amorphous content of the coating is 93.9%, which is about 3.5% lower than original powders. The electrochemical impedance spectrum and neutral salt spray test results show that APS remelting can reduce the corrosion rate by about 62.7%.

APS remelting method is firstly proposed in this work to replace laser remelting or laser cladding methods. APS remelting method can effectively improve the corrosion and abrasion resistance of the FAA coating by increasing the densification with much low recrystallization, which is big progress for application of FAA coatings.

To characterise the high temperature oxide scales for some plasma sprayed NiCrAlY coated Ni‐ and Fe‐based superalloys.

Ni‐22Cr‐10Al‐1Y metallic coatings were deposited on two Ni‐based superalloys; Superni 601 and Superni 718 and one Fe‐based superalloy; Superfer 800H by the shrouded plasma spray process. Oxidation studies were conducted on uncoated as well as plasma spray coated superalloys in air at 900°C under cyclic conditions for 50 cycles. Each cycle consisted of 1 h heating followed by 20 min of cooling in air. The thermogravimetric technique was used to approximate the kinetics of oxidation. X‐ray diffraction, SEM/EDAX and EPMA techniques were used to analyse the oxide scales.

All of the coated, as well as the uncoated, superalloys followed an alnost‐parabolic rate of oxidation. The NiCrAlY coating was found to be successful in maintaining its continuous contact with the superalloy substrates in all the cases. The oxide scales formed on the exposed NiCrAlY coated superalloys were found to be intact and spallation‐free. The main phases analysed for the coated superalloys were oxides of nickel, chromium and aluminium and spinel of nickel and chromium, which are expected to be useful for developing oxidation resistance at high temperatures.

The coated superalloys showed remarkable cyclic oxidation resistance under simulated laboratory conditions. However, it is suggested that these coated superalloys also should be tested in actual industrial environments of boilers and gas turbines, etc. so as to obtain more practical and reliable oxidation data.

The knowledge of the reaction kinetics and the nature of the surface oxide scales formed during oxidation is important for evaluating the alloys for their use and degradation characteristics in high temperature applications such as steam boilers, furnace equipment, heat exchangers and piping in chemical industry, reformer, baffle plates/tubes in fertilizer plants, jet engines, pump bodies and parts.

The aim of the research is to increase piston and engine performance by using ceramic coated pistons instead of pistons which are manufactured from aluminum alloys and having a coated flame chamber.

Thermal torch and thermal shock tests were performed on the pistons and some specimens of 1.5 mm thick were prepared according to ASTM standards; both have the same material characteristics. In the present work, plasma spray technique was used for ceramic coating.

It was found that the ceramic coating, which, when performed properly, has compatible expansion coefficient with the aluminum alloy pistons, increases performance of pistons and engines.

Coatings were limited with one type of bonding and two ceramics, and coated parts were subjected to thermal torch and thermal shock tests.

For future work, instead of using other coating materials, stable yttria is used as the best coating material with optimum thermal resistance. By this process, working life of the machine parts can be extended and a number of economical advantages may also be obtained.

This paper fulfils the identified information and offers practical help to the industrial firms working with ceramic coatings and also to the academicians working on wear of materials.