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Internal rotating plasma spraying has been widely used in industrial applications to enhance performance properties and prolong the service life of internal components, such as gas turbines, engine blocks, and oil pipelines. As it is difficult to dissipate the excess heat in the limited and semi-enclosed space, the temperature characteristics of the internal parts have a significant influence on the spraying process. In this study, a three-dimensional (3D) numerical model was developed to describe the temperature evolution and distribution of a cylinder under different heating modes that considers one (plasma jet only) and two contributions (plasma jet and sprayed particles), respectively. Moreover, air and water cooling modes were also implemented to alleviate the heat accumulation of the cylinder. The results indicated that heat accumulation was mainly caused by plasma jets, whereas the sprayed drops contributed slightly. The temperature increased abruptly from initial 283 to 550 K after two back and forth movements within the cylinder without the application of coolants. However, the temperature could be controlled at 420 K under the condition of air cooling and at 390 K under the condition of water cooling. Using an infrared camera and temperature sensor, experiments were conducted to validate the numerical model corresponding to the working conditions implemented in the numerical simulation. A decrease in the porosity and increase in micro-hardness of the coating could be achieved under the cooling effect of water, rather than the compressed air. The percentage improvements in the porosity and micro-hardness of the coating were approximately 14.2 and 6.1%, respectively, by the application of water cooling. [ABSTRACT FROM AUTHOR]

The aim of present study is to monitor the delamination failure of plasma sprayed Al 2 O 3 –40 wt% TiO 2 composite ceramic coating (AT40 coating) in rolling contact condition by acoustic emission (AE) technology. The AE signals of the delamination failure process were divided into three types (type I: normal contact; type II: fatigue crack initiation; type III: delamination failure) based on the feature of AE count. The waveforms and frequency spectrums of different types of AE signals during delamination failure process of the coatings were obtained by Empirical mode decomposition (EMD) method. The relationship between the waveform/frequency of the AE signals and the delamination failure mechanism of the AT40 coatings were discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract: The influence of contact stress on rolling contact fatigue performance of plasma sprayed Al2O3–40wt% TiO2 composite ceramic coating was investigated using a double-roll test machine under pure rolling contact condition. The shear stresses within the coating were analyzed with the three-dimensional finite element method. Three modes of failures, i.e., surface abrasion, spalling, and delamination, were observed during this investigation. The failure mechanisms of surface abrasion, spalling, and delamination were discussed in detail. The initiation and propagation of fatigue cracks were mainly caused by the shear stress, which were highly influenced by the contact stress. [Copyright &y& Elsevier]

Fe-Cr coating was prepared by plasma-spraying process. As-sprayed coatings were machined by grinding, lapping, or polishing processes as appropriate to get different surface roughnesses. Rolling contact fatigue (RCF) experiments were conducted using a ball-on-disk setup. RCF lifetime of the coating was calculated. The worn morphologies of the coating were observed. Results show that surface roughness obviously influences RCF behavior of the coating. The smooth coatings showed longer RCF lifetimes, and always failed by delamination. The rough coatings always failed by abrasion or spalling. The failure of smooth coatings was driven by the orthogonal shear stress and radial stress, whereas the failure of rough coatings was driven by the asperity contact. [ABSTRACT FROM AUTHOR]

Abstract: Acoustic emission (AE) technique was used to monitor rolling contact fatigue (RCF) experiments of plasma sprayed coatings. AE signal response was investigated. Worn morphologies of the coating were observed. Results show that typical AE signal mode owns three stages, i.e. running-in, stable and jump stage. Observations of worn coating release there are three kinds of AE signal sources, i.e. the crack initiated from surface, cracks embedded within the coating and cracks on the coating/substrate interface. The combined effect of orthogonal shear stress (OSS) and radial stress (RS) is main reason of the initiation and propagation of cracks within the coatings. [Copyright &y& Elsevier]

Abstract: In this paper, the residual stress in the plasma-sprayed FeCrBSi coating was determined by nanoindentation and X-ray diffraction (XRD). The XRD results showed that tensile residual stress was generated in the FeCrBSi coating, and the through-thickness values range between 40MPa and 112MPa. The residual stress measured by nanoindentation is 753MPa. The difference between the XRD and nanoindentation results was discussed. It is found that the factors limiting the nanoindentation measurement of residual stress include the ‘sink-in’ deformation around the indenter, the roughness of the FeCrBSi coating, and the use of reference sample without residual stress. The above three factors lead to the over-prediction of residual stress by nanoindentation. [Copyright &y& Elsevier]

Abstract: The rolling contact fatigue (RCF) failure prediction of the coating Fe–Cr alloy coatings was investigated. The acoustic emission (AE) technique was used to monitor RCF tests of the coatings. The failure mechanism was investigated. Results showed AE signals sensitively detected the initiations and propagations of the fatigue cracks within the coatings before the obvious surface material losses. AE signals also reflected the cumulate damage procedure. So the coming RCF failures can be predicted by AE signal responses. Moreover, the micro-defects within the coatings were considered to be the fatigue crack origins. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we develop a method for determining the hardness of FeCrBSi coating on a 1045 steel substrate. The nano-indents of the FeCrBSi coating exhibit obvious pile-up. The proposed method models the projected contact area as an equilateral triangle bounded by arcs to correct for the effect of pile-up on the contact area. The new method is described in detail and leads to improvement in obtaining coating hardness compared with the widely adopted Oliver–Pharr method. [Copyright &y& Elsevier]

Abstract: The plasma spraying technique was used to get the solid lubrication iron sulfide coating on the 1045 steel. The iron sulfide powder, which was employed to spray, was ball-milled with granularity of 40 μm. AFM and SEM were made use of observing and analyzing the morphologies of surface and worn scar of the coatings. A scratch testing machine was utilized to measure the bond strength between substrate and coating. The coating was formed by the accumulation of irregular FeS grains. The bond strength between the coating and substrate was about 32 N belonging to the mechanical bonding. The friction test of the FeS coatings, tested on a ring-on-block tester, showed that the plasma spraying FeS coatings possessed the remarkable friction-reduction performance. The worn failure mechanism of the coatings was flaking off. [Copyright &y& Elsevier]

Abstract: Plasma sprayed technology has been utilized to prepare solid lubrication FeS coatings with thicknesses of 0.3 mm, 0.8 mm and 1.5 mm. Their tribological properties were comparatively investigated under oil lubrication. An SEM equipped with EDS, and XRD were employed to analyze the surface and worn scar morphologies of the coatings, as well as the surface phase structures. A scratch testing machine was utilized to measure the bond strength between substrate and coating. The results showed that the tribological properties of the sprayed FeS coatings were superior to the original 1045 steel. The 0.8 mm thick coating possessed the best tribological properties. The differences in tribological properties of the three coatings were determined by the differences of their thickness and structure. [Copyright &y& Elsevier]

Intrinsic structural limitations of plasma-spray TiO 2 coating deteriorate its wear resistance. Herein, CNTs are incorporated in the coating to assess their effects on the microstructure and tribological properties. Structurally, degradation degree of CNTs in TiO 2 matrix during plasma spraying was revealed by Raman spectroscopy. And high resolution transmission electron microscopy manifested that TiO 2 /CNT interface was well bonded along with presence of notable interfacial carbothermic product Ti n O 2n-1 at atomic scale. The phenomenon indicates a beneficial effect for transferring stress from matrix to CNTs effectively. Then, the influence of CNTs on coating’s friction behavior was investigated by zirconia ball-on-disk tribometer under dry-sliding condition. As compared to TiO 2 coating, the nanocomposite coating exhibited a moderate decrease in friction coefficient and an enormous reduction (∼93.6%) in wear volume. The remarkable advance in tribological properties of the reinforced coating can be attributed to four kinds of frictional effects of CNTs: tribo-reorientation, tribo-protruding, tribo-film and tribo-degradation. [ABSTRACT FROM AUTHOR]

ASTM1045 steel was used as substrate that was laser processed with surface texturing. Ni-based coatings were deposited on the substrates using the atmosphere plasma spray technology. Surfaces with different dimples diameter and depths were acquired by adjusting the processing parameters and their effect on the bonding behavior between coatings and substrates were investigated. Scanning electron microscopy was used to characterize the cross section morphology of sprayed coatings, investigating the filling quality of coatings in the dimples. The image analysis method was also applied to calculate the contact area ratio resulting from texturing, evaluating the energy release rate at the surface/interface. XRD diffraction and nanoindentation tests were used to measure the residual stress of substrates after laser treatment and coatings near interface, respectively. The calculation analysis was carried out to research the relationship between the coating filling quality and the texturing parameters. The adhesion strength of coatings was evaluated through tensile tests. The results showed that the bond strength values present an initial increase followed by a decrease when the state of the coatings goes from full filling state to air entrance in the coatings and partial filling state following the texturing depth rising. The analysis indicates that the air volume in the dimples is determined by their diameter and depth, which are key parameters defining the filling quality as well as the adhesion strength. As the depth increases, the adhesion strength depends on the competition between residual stress caused by the presence of air and stress release due to the improvement of contact area ratio. [ABSTRACT FROM AUTHOR]

The laser method was used to process dimples with different diameters and distances on ASTM 1045 steel substrates. Ni60 alloy powders were deposited on the textured substrates using atmosphere plasma spray technology. Single sprayed particles were collected to study the spreading behavior. Scanning electron microscopy was applied to characterize the cross-section morphology of splats and coatings, investigating the deposition behavior of droplets. Image analysis was used to calculate the open angle of first particle, thus also providing information on the subsequent particles. Transmission electron microscopy was used to investigate the crystal structure of coatings near the interface. The bonding strength of coatings was evaluated by pull-off tests. The impact of various texture parameters on the adhesion strength of coatings was investigated. The results showed that bonding strength improved with increasing texture diameter and decreasing texture distance. Wetting behavior between two particles as well as bond style between particles and substrates have great influence on bond strength of coatings with the variant texture diameter and distance. The diameter-to-distance ratio was found to be the factor directly determining the adhesion strength between substrates and coatings. [ABSTRACT FROM AUTHOR]

The rolling contact fatigue (RCF) failure procedure of Fe-based alloy coating, fabricated by high efficient plasma spray (PS) technology, was investigated by a double-roller test machine with oil lubrication under pure rolling contact condition. The fractal dimension (FD) was utilized to quantitatively characterize the profile of the worn surface at different experiment stage and the failure mechanism of the coating was discussed. The results indicated that the nonlinear morphologies of the worn surface of Fe–Cr alloy coating possessed excellent fractal properties. The failure procedure could be divided into four stages according to the value and change rule of FD, i.e. (1) running-in stage, (2) stable abrade stage, (3) accelerated damage stage, (4) unstable removal stage. [ABSTRACT FROM AUTHOR]

Highlights: [•] The statistical method used to estimate the mechanical property data is novel. [•] The mechanical property data can be characterized by unique bimodal distribution. [•] The mechanical properties of the composite coating we studied are excellent. [ABSTRACT FROM AUTHOR]

Internal rotating plasma spraying (IRPS) plays an important role in improving the properties and prolonging the service life of internal parts and components of mechanical systems. IRPS is conducted in the confined and semi-enclosed spaces at a spraying distance of 30–70 mm to coat the engine cylinders of automobiles or heavy equipment. Occasionally, particles cannot be appropriately treated in the plasma flow, and owing to several factors, the particles remain suspended in the air rather than being deposited onto the substrate. Consequently, the suspended particles are difficult to remove efficiently within the confined space, and can thus have severe effects on the properties of coatings, including porosities and inclusions. It is therefore essential to develop appropriate methods to avoid defects in the coating by removing suspended particles inside the cylinder. In this study, numerical simulations were conducted to investigate the flow-velocity field and particle-mass-concentration distribution within the cylinder. The flow-velocity and particle mass concentration in the cylinder space were analyzed under different working conditions that can induce different suction pressures driven by a three-phase asynchronous motor connected to the bottom of the cylinder by a suction tube. The results showed that the flow-velocity field is symmetrical along the axis of the cylinder and the mass concentration of particle is concentrated on the region from middle to bottom of the cylinder, under the effect of the suction pressure. In addition, the low-velocity and high-particle-mass-concentration regions are mainly located in the vicinity of the internal wall. Furthermore, the flow velocity was measured using a hot-wire-anemometer and the coating microstructure was observed using scanning electron microscope (SEM). We compared numerical simulation results and experimental measurements, which validated the flow-velocity field directly and the distribution of particle mass concentration indirectly. Based on the numerical results that consider the removal degree of suspending particles and the stability of the plasma jet, it can be determined that the optimal suction pressure is −100 Pa for decreasing dust pollution during the spraying process. • Numerical simulations and experiments are both used in the research. • The flow-velocity field is symmetrical along the axis centerline of cylinder. • The mass concentration of particle is concentrated on the region from middle to bottom of the cylinder. • The optimal suction pressure is −100 Pa for decreasing dust pollution problem. [ABSTRACT FROM AUTHOR]