Search results

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.

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.

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 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.

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.

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.

The purpose of this paper is to report the resistance of plasma‐sprayed titanium dioxide (TiO₂) nanostructured coatings in a corrosive environment.

Weight loss studies are performed according to ASTM G31 specifications in 3.5 wt% NaCl. Electrochemical polarization resistance measurements are made according to ASTM G59‐91 specifications. Corrosion resistance in a humid and corrosive environment is determined by exposing the samples in a salt spray chamber for 100 h. Microstructural studies are carried out using an atomic force microscope and scanning electron microscope.

The nanostructured TiO₂ coatings offer good resistance to corrosion, as shown by the results of immersion, electrochemical and salt spray studies. The corrosion resistance of the coating is dictated primarily by the geometry of splat lamellae, density of unmelted nanoparticles, magnitude of porosity and surface homogeneity.

The TiO₂ nanostructured coatings show promising potential for use as abrasion, wear‐resistant and thermal barrier coatings for service in harsh environments.

The paper relates the corrosion resistance of nanostructured TiO₂ coatings to their structure and surface morphology.

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.

The purpose of this paper is to study the effect of slurry erosion at different parameters on plasma sprayed Cr₃C₂ coated 13Cr4Ni turbine steel and compare the results of coated steel with bare steel.

Cr₃C₂ + 25NiCr coating was successfully developed on 13Cr4Ni turbine steel using plasma spraying method. The slurry erosion test was performed using a simulated erosion testing rig. The commercially available silica sand was used as abrasive media and the effect of concentration (ppm), average particle sizes and rotational speed on the slurry erosion behavior were studied at 300 and 900 impact angles. Developed coatings were characterized by scanning electron microscope, XRD, EDS and micro hardness tests and study of erosion wear.

Results revealed that three times higher hardness of coatings was obtained because of the hard phases of chromium carbide and nickel carbide, which restricted the abrasive wear in comparison to uncoated steel. Lower abrasive wear was observed at 900 impact angle coupled with lower levels of slurry concentration and rotational speed. Further, it was observed that initially cumulative mass loss rate was high which gets stabilized after the surface become smooth and on exposing for higher periods. Overall results indicated that erosive wear was reduced significantly by the application of developed coating.

The developed plasma sprayed coating is very useful to enhance the service life of turbine steel by lowering the effect of slurry erosion.

This study systematically investigated the effect of the binary rare earth oxide of La₂O₃ and Sm₂O₃ on the properties of the Al₂O₃/TiO₂ (AT) coating, including phase transform, wear behavior, etc.

AT coatings mixed with different components of binary rare earth oxides of La₂O₃ and Sm₂O₃ are prepared by atmospheric plasma spraying. The adhesion strength, micro-hardness, phase transition and tribological behavior of coatings are systematically investigated.

The X-ray diffraction (XRD) analysis shows that phase transformation is obvious after spraying, and a-Al₂O₃ is almost translated into γ-Al₂O₃ when La₂O₃ and Sm₂O₃ are doped together. Meanwhile, solid solution generated between rare earth oxide and Al₂O₃/TiO₂ coatings results in disappearance of TiO2 and rare earth oxide phase. The photos under the scanning electron microscope (SEM) indicate that binary rare earth oxide could increase the melting degree of powder and decrease porosity of coatings.The increasing of Sm₂O₃ rarely affect micro-hardness and adhesion strength, and the coating with 4 per cent Sm₂O₃ and 1 per cent La₂O₃ exhibits the best wear resistance and lowest friction coefficient among all the samples.

AT coatings mixed with different components of binary rare earth oxide of La₂O₃ and Sm₂O₃ are prepared by atmospheric plasma spraying. Binary rare earth oxide could increase the melting degree of powder and decrease porosity of AT coatings.