Plasma-sprayed Coatings Research Articles

Tribological behaviour of bilayer alumina and mullite plasma-sprayed coatings deposited on a refractory substrate at high temperatures

Bilayer alumina/mullite and mullite/alumina coatings were sprayed on conventional silico-aluminous refractory bricks by atmospheric plasma spraying. The wear behaviour of these coatings were assessed under sliding contact conditions up to 1000 °C through a ball-on-disk test. Afterwards, a set of physical and mechanical properties were evaluated before and after the wear tests, with the aim of correlating these properties with the wear behaviour. The results of the wear tests indicate that when alumina is applied as the top coating, the wear mechanism operating on its surface at 25 and 1000 °C is ductile deformation, whereas brittle deformation occurs at 500 and 750 °C. When mullite was used as the top coating, brittle deformation was observed at all temperatures evaluated. However, both coatings possess higher wear resistances than the silico-aluminous brick used as substrate, and thus, these coatings potentially offer enhanced protection from the abrasive wearing of non-structural refractories normally used in furnaces for glass and cement production.

The Influence of Steel and Cast Iron as Substrate Materials on the Microstructure, Microhardness and Wear Resistance of Nickel-base Ti-Al Plasma Spray Coatings

This paper studies the influence of different substrate materials on the phase composition, microstructure, microhardness, and wear resistance of Ni-Cr-B-Si-C-Ti-Al plasma spray coatings. Two types of substrate metals were studied – AISI 1045 steel and Pig-P3 Si grey cast iron. It has been found that in the as-coated condition the surface layers have a phase composition of γ-Ni, Cr23C6, γ-TiAl, TiN, and α-Ti(N, O) on steel substrate, and γ-Ni, α-Ti, TiN, Ni3B, CrB, Cr23C6, α-Ti(N, O), Ni3Si on cast iron. The microhardness and wear resistance of the plasma sprayed Ni-Cr-B-Si-C-Ti-Al coatings is tested. The wear volume of the coatings has been tested for up to 60 min. The deposits on cast iron substrates demonstrate lower wear than those on the steel substrate.

Surface characteristic and corrosion resistance of different plasma-sprayed coatings (Zn, Al6061and Zn/23Al) on S960 high strength steel with subsequent micro-shot peening

The pure Zn, Al6061 alloy and Zn/23Al coatings were prepared on S960 high strength steel by plasma spraying method respectively, then these coatings were treated with subsequent micro-shot peening. The surface characteristics including surface morphology, micro-hardness, and residual stress were characterized, and the corrosion resistance of the coatings was evaluated by an electro-chemical test, salt spray test and immersion corrosion, respectively. The results showed that the coatings were densified and the surface micro-hardness was improved in the range of HV 20–30 after the micro-shot peening treatment. Taking Al6061 alloy coating as an example, after micro-shot peening, the surface residual stress changed from tensile stress (17 MPa) to compressive stress (−102 MPa). The corrosion testing results showed that the corrosion resistance of Zn coating could be improved by adding Al element and micro-shot peening in the polarization tests. According to EIS results, the impedance of Zn, and Al6061 alloy coatings were improved after micro-shot peening in 3.5 wt% NaCl solution, while the charge transfer resistance of Zn/23Al coating was decreased. In the neutral salt spray test and immersion test, the corrosion resistance of the three coatings was enhanced by micro-shot peening, and the shot-peened Zn/23Al coating illustrated the best corrosion resistance. The improved corrosion resistance of the Zn/23Al coatings can be ascribed to the densification of micro-shot peening and the addition of Al.

ТЕХНОЛОГИЧЕСКОЕ ОСНАЩЕНИЕ ДЛЯ ОПТИМИЗАЦИИ ПЛАЗМЕННОГО НАПЫЛЕНИЯ ПО ПАРАМЕТРУ СКОРОСТИ НАПЫЛЯЕМЫХ ЧАСТИЦ

The work is devoted to the issue of optimizing the processes of plasma spraying of coatings according to the criterion of the speed of sprayed particles, which is highly determining the quality of the applied coatings, and technological equipment for this using, first of all, disk devices.

Study on Damage Behavior of NiCoCrAlY/MSZ Plasma-Sprayed Coating in Neutral Salt Spray Environment

In order to explore the corrosion damage behavior of plasma-sprayed NiCoCrAlY/magnesia-stabilized zirconia (18~22 wt.% MgO-ZrO2, MSZ) thermal barrier and anti-ablation coatings in a salt spray environment, a series of neutral salt spray (NSS) tests for 96 h (N-2), 192 h (N-4) and 288 h (N-6) were carried out on the coatings. The microstructures, composition distributions, potentiodynamic polarization curves, bonding strengths and anti-ablation properties of the coatings before and after the NSS tests were characterized. The results show that, with the increase in salt spray time, the expansion and overflow of corrosion products (FexOy) led to more defects forming inside the coating; the porosity of the top coat (TC) of N-6 increased to 15.2% in comparison to that of the blank control sample (N-0), which was 8.5%. According to the potentiodynamic polarization curves, accelerated corrosion occurred in the coating samples after the salt spray time reached 192 h, and the corrosion current density rapidly surged from 2.2 × 10−8 A·cm−2 (N-4) to 2.2 × 10−5 A·cm−2 (N-6). Similar degradation tends could be found in the bonding strengths and mass ablation rates of the coatings due to the accumulation of loose corrosion products on the substrate, which affected the bonding states of the coatings and promoted their spalling under an oxyacetylene flame (OAF). As a result, the maximum service life of the NiCoCrAlY/MSZ coatings in the neutral salt spray environment was about 192 h. This work is instructive for studying the environmental adaptability of metal/ceramic double-layer coatings.

Effect of Varying Plasma Powers on High-Temperature Applications of Plasma-Sprayed Al0.5CoCrFeNi2Ti0.5 Coatings.

In this work, the microstructure and mechanical properties of atmospheric plasma-sprayed coatings of Al0.5CoCrFeNi2Ti0.5, prepared using gas-atomized powders at varying spray powers, are studied in as-sprayed and heat-treated conditions. Gas-atomized powders had spherical shapes and uniform element distributions, with major FCC phases and metastable BCC phases. The metastable BCC phase transformed to ordered and disordered BCC phases when sufficient energy was applied during the plasma-spraying process. During the heat treatment process for 2 hrs, disordered BCCs transformed into ordered BCCs, while the intensity of the FCC peaks increased. Spraying power plays a significant role in the microstructure and mechanical properties of plasma sprayed because at a high power, coatings exhibit better mechanical properties due to their dense microstructures resulting in less defects. As the plasma current was increased from 500 A to 700 A, the coatings’ hardness increased by approximately 21%, which is directly proportional to the decreased wear rate of the coatings at high spraying powers. As the coatings experienced heat treatments, the coatings sprayed with a higher spraying power showed higher hardness and wear resistances. Precipitation strengthening played a significant role in the hardness and wear resistances of the coatings due to the addition of the titanium element.

The Influence of Substrate Materials on the Microstructure, Microhardness and Wear Resistance of Nickel-base Plasma Spray Coatings

This paper studies the influence of the substrate material on the phase composition, microstructure, microhardness, and wear resistance of Ni-Cr-BSi-WC (Ni95Al5) coatings. Three types of substrates were studied, AISI 5060 Steel, SAE J431 automotive gray cast iron, and Ti-6Al-4V. It has been found that in the as-coated condition the surface layers have a phase composition of crystalline ɣ-Ni solid solution, amorphous, Ni3B, CrB, and Cr23C6. There are different changes of the surface after 80 min abrasive wheel.

Fabrication of graphene oxide reinforced plasma sprayed Al2O3 coatings

Graphene oxide (GO) reinforced Al2O3 ceramic coatings were prepared on the surface of medium carbon steel by plasma spraying. The microstructure of the raw materials and coatings were characterized and analyzed by XPS, XRD, Raman and SEM. The bonding strength of the coatings was studied using a scratch method. The wear resistance of the coatings was assessed by the sliding test. The results showed that, after adding GO, the porosity of the coating reduced by about 31%, the hardness increased by approximately 10%, the bonding strength improved by 250%, and the wear rate reduced by 81% (Load: 30 N) and 84% (Load: 60 N), respectively.

Evaluation of tribological properties of thermally sprayed tungsten carbide coating on AISI1045

The plasma based thermal coatings have been used for over five decades. The provision of plasma spray coatings on the low strength materials such as low carbon steels find prominent position in cost savings and replacement cycles of sliding components. Particularly the AISI 1045 based components find important role in automotives and marine structures. A clear understanding of the impact of thermal conditions on enhancement of surface characteristics for low carbon alloys during plasma spray coating is needed for deciding the lifecycle of products involving high temperature sliding conditions. Plasma Spray Coating was employed on AISI1045 plates and the improvement of strength, hardness and wear resistance along with the material composition was studied. Plasma Spray Coating is improved the wear resistance of AISI1045 sheets by 30 percent. The problems faced by the practicing professional such as frequent replacement of siding components and shorter life expectancy are reduced much by employing the thermal spray coating.

Advancing knowledge of plasma spraying coatings for Li||Sb-Sn liquid metal batteries by X-ray micro-CT

The performance of Li||Sb-Sn liquid metal batteries (LMBs) is hindered by the corrosion of the Sb-Sn cathode on its current collector. Herein, a uniform, dense, and low-oxidized W coating was prepared by plasma spraying, which can effectively resist the corrosion of the cathode and improve the cycle stability of the Li||Sb-Sn LMBs. For the first time, micro-CT nondestructive inspection is applied in the field of LMBs. The corrosion micromorphology and composition evolution of the SS304 matrix and Sb-Sn cathode with or without the plasma-sprayed W coating is obtained without disassembling the battery, which proves that the W coating can effectively protect the SS304 matrix. Our autonomous new LMB device for nondestructive inspection is universal and can be applied to different LMBs systems for advancing knowledge of corrosion mechanism and protection. This work guarantees the ability to directly visualize the inner critical positions in three dimensions and fills the knowledge gap in the field of LMB detection technology. The corrosion micromorphology and composition evolution of the SS304 matrix and Sb-Sn cathode with or without the plasma-sprayed W coating can be observed without disassembling the battery, which indicates that the W coating has excellent service characteristics as a cathode current collector for Li||Sb-Sn LMBs.

Effect of Dy2O3 doping on phase compositions, microstructures, thermophysical properties and fracture toughness of YSZ coatings

Yttria-stabilized zirconia (YSZ) coatings with different Dy2O3 doping contents were prepared via plasma spraying. The effects of phase compositions, microstructures and lattice defects on the thermal conductivity, fracture toughness and thermal shock resistance were analyzed. The result indicates that the Dy2O3 doping significantly affects thermophysical properties of YSZ coatings. The Dy2O3 doping can improve the insulation performance of the YSZ coating and the minimum thermal conductivity of the coating has reached 0.89 W/K·m. A decrease in thermal conductivity with increasing Dy2O3 doping content can be attributed to the lattice distortion, ions substitution, oxygen vacancies and reducing grain size. Meanwhile, the Dy2O3 doping causes the fracture toughness of YSZ coatings to decrease. Consequently, the Dy2O3-doped YSZ coatings exhibit weaker thermal shock resistance because the Dy2O3 doping promotes the formation of the cubic YSZ phase. The tetragonal phase in plasma-sprayed coatings is beneficial for service lifetime owing to its phase transformation and ferroelasticity-induced toughening under stress. Although the Dy2O3-doped YSZ coatings undergo more severe sintering owing to a decrease in the activation energy of grain growth caused by lattice distortion, they exhibit better phase stability than the YSZ coating under high temperatures because the Dy2O3 doping inhibits the diffusion of Y. Finally, a Dy2O3-doped ZrO2 coating composed mainly of the tetragonal ZrO2 phase was designed, which exhibited a better thermal shock resistance.

Investigation of Tribological Behavior of Plasma Sprayed NiTi Coating for Aerospace Application

Investigation of Tribological Behavior of Plasma Sprayed NiTi Coating for Aerospace Application

Improvement of Corrosion Resistance and Structural Integrity of Plasma Sprayed Ni-clad Al Coatings via Pre-oxidation

Improvement of Corrosion Resistance and Structural Integrity of Plasma Sprayed Ni-clad Al Coatings via Pre-oxidation

Microstructural, mechanical and tribological properties of carbon nanotubes reinforced plasma sprayed molybdenum disulphide composite coatings

The development of 1-Dimensional (1D) and 2-Dimensional (2D) materials have gained considerable attention towards achieving solid-state lubricity. Herein, we present the effect of carbon nanotubes (1D) reinforcement into the molybdenum disulphide (2D) coatings. Plasma sprayed MoS2 coatings reinforced with 2-4 wt% CNTs were fabricated using shroud plasma spraying over steel substrates. The shroud attachment envelops the plasma plume and cut down its exposure to surroundings, which minimizes the oxidation of MoS2 powder during spraying. The microstructural analysis revealed the presence of MoS2 and CNTs in the composite coating. The mechanical hardness and elastic modulus of MoS2 coating improved by 2–3 folds in the composite coating. In tribological performance, the coefficient of friction (COF) decreased from 0.13 to 0.07 in M2C coating. The wear weight loss was estimated as 0.89 ± 0.07 mg, 0.18 ± 0.02 mg and 0.39 ± 0.03 mg for M, M2C and M4C coatings respectively. It can be attributed that tubular CNTs acted as bearing on MoS2 layers. This work opens an impressive stepping for the synergistic mixture of 1D (CNTs) and 2D (MoS2) material to obtain high-quality wear-resistant coatings.

Microstructure and high-temperature sintering properties of APS coatings prepared from spherical thin-walled hollow-shell powders

High-performance thermal barrier coatings (TBCs) made of 4 mol.% Y2O3–stabilized ZrO2 (4YSZ) powder with a spherical thin-walled hollow-shell (STHS) structure exhibited a special microstructure different from the conventional lamellar structure of air plasma-sprayed (APS) coatings. The as-sprayed STHS APS coatings had a completely tetragonal prime (t′) structure and non-lamellated closed-cell structure with high porosity, which resulted in relatively low thermal conductivity (∼1.0 W m−1 K−1) and high Vicker's hardness (∼6 GPa). The influences of high-temperature aging on the microstructure stability, phase stability, and sintering capability were investigated after long-time heat treatment at different temperatures. The characterization results indicated that the pore content was basically constant, and it was less than 0.5% for sintered linear shrinkage of the STHS coatings after heat treatment at 1500 °C for 100 h. Furthermore, no spalling appeared in the STHS APS coating with the t′ phase structure after 101 thermal cycles of the water-quenching method at 1050 °C, and no monoclinic ZrO2 (m-ZrO2) phase was present in all of the STHS coatings after aging at 1200 °C for 1–1100 h. The excellent anti-sintering properties and phase stability of the STHS coatings are attributed to the closed-pore microstructure and the highly pure t′ phase composition with uniform distribution of ions, respectively. The results suggested that the non-lamellated closed-cell microstructure is beneficial for improving the coating properties, and the results also provide guidelines for microstructure design of TBCs using a feedstock powder.

Microstructure, Phase Composition, Mechanical Properties and Tribological Properties of Plasma Sprayed Al-25Si Wear-Resistant Coatings

Owing to the light weight and high energy, the “All-aluminum engine” can reduce fuel consumption and pollutant emissions, showing a great significance in saving resources and protecting the environment, and becoming a research hotspot. However, the aluminum alloy cylinder liners have difficulty withstanding extremely harsh working conditions, such as strong friction and wear, making the engine extremely easy to damage. In this work, Al-25Si wear-resistant coating was deposited by inner hole supersonic plasma spraying technique to improve the wear resistance of the aluminum alloy cylinder liner. The microstructure, phase composition, mechanical properties and tribological properties were tested by SEM, XRD, tribological machine, etc. The results indicated that the coating exhibited an excellent bonding strength of 44.1 MPa, and the average hardness and average friction coefficient of the coating are 267.09 ± 14.85 HV0.2, and 0.20, respectively. The total wear amount, the wear scar width and the wear scar depth of the coating are 2.77 × 10−3 mm3, 654.3 μm and 8.95 μm, respectively, which showed that the coating can significantly improve the tribological properties of the “All-aluminum engine”. The wear mechanism of the coating was mainly interpreted by furrow cutting, extrusion and spalling in two-body abrasive wear, three-body abrasive wear and a small amount of oxidative wear.

Parameter-dependent tribological properties of sinusoidal-textured plasma-sprayed coatings

Texture parameter was an important factor affecting tribological property. In this work, the friction experiments and orthogonal analysis method were combined to investigate the effects of texture parameters on the tribological properties of sinusoidal-textured Ni-based MoS2 coatings under dry conditions. Results showed that only the texture area ratio, width–depth ratio, and angular velocity have significant effects on the tribological properties, and the influence order was as follows: area ratio > angular velocity > width–depth ratio. Good tribological properties could be obtained when the texture area ratio was 9–10%, the angular velocity was 6 rad/s, the width–depth ratio was 0.67–1.36, the amplitude was 0.1 mm, and the relative motion angle was 90°.

Microstructural Characterization, Residual Stress, and Mechanical Properties of Plasma Sprayed 8YSZ Thermal Barrier Coatings

Microstructural Characterization, Residual Stress, and Mechanical Properties of Plasma Sprayed 8YSZ Thermal Barrier Coatings

Phase formation and microstructure evolution of plasma sprayed Cr2AlC MAX phase coatings under post annealing

In this study, thick Cr2AlC coatings were first synthesized via plasma spraying of Cr3C2–Al–Cr agglomerated powders and post annealing. The microstructure evolution and mechanical properties of the Cr2AlC coatings annealed at 500–1000 °C were investigated. The as-sprayed coatings exhibited a lamellar structure, primarily consisting of Cr2AlC, Cr7C3, Cr23C6, and (Cr, Al)Cx solid solutions. The short residence time during spraying led to incomplete reactions in the Cr3C2@Al–Cr agglomerates, resulting in the formation of (Cr, Al)Cx. Post annealing provided sufficient energy for the transition of (Cr, Al)Cx → Cr2AlC. With an increase in the annealing temperature (<900 °C), gradual transition of the (Cr, Al)Cx phase led to a slight increase in the Cr2AlC content, and thus, the as-annealed coatings maintained high hardness (>1000 HV0.2) with improved fracture toughness. Higher annealing temperatures (>900 °C) promoted clear enhancement of the Cr2AlC content, thus reducing the coating hardness. The transition phase (Cr, Al)Cx and high temperature annealing were the primary factors to promoting the formation of the Cr2AlC phase in sprayed coatings. This study indicates that the Cr3C2@Al–Cr agglomerates can be effective alternatives to expensive MAX phase powders as feedstock for plasma spraying of Cr2AlC coatings.

Effects of Laser-Remelting on the Microstructure, Hardness and Oscillating Wear Resistance of Atmospheric Plasma Sprayed Alumina-Rich Coatings

Thermally sprayed ceramic coatings such as alumina have a specific microstructure characterized by porosity and microcracks. In addition, a process-related phase transformation from α-Al2O3 to γ-Al2O3 typically occurs, which affects the properties of the coatings compared to sintered alumina. In a previous study, simultaneous additions of Cr2O3 and TiO2 have already extended and improved the property profile of pure alumina coating (i.e., sliding wear resistance and corrosion resistance against 1N H2SO4). Depending on the powder material used, the phase composition of the coatings differs considerably, influencing the property profile. Chemical integration through reactive bonding promises a previously untapped potential for improvement. In this study, these alumina-rich ternary oxide coatings are remelted by laser, and the effect of different parameters such as speed, laser power or distance on the macro- and microstructure of the coatings is investigated. For this purpose, both light microscopic and SEM examinations are used as well as the determination of the phase composition by XRD and element distribution by EDS. The created coating microstructures are studied with respect to hardness and oscillation wear resistance.