Properties Of Thermal Sprayed Coatings Research Articles

Development and Evaluation of Corrosion Resistance and Hydrophobic Properties of Thermal Sprayed Coatings over Carbon Steel

Various industrial parts and equipment made of steel need to withstand demanding conditions. In order to increase performance and lifetime, surface processing and functional coatings can be applied. In this study we report on the evaluation of coated carbon steel with commercial corrosion-resistant powders Diamalloy 4276 and Woka 7502 by Oerlikon Metco, using thermal spraying. Further functionalization is performed by rendering thermal sprayed surfaces syperhydrophobic via gas phase deposition of trichloro-1H,1H,2H,2H-perfluorooctyl silane, (PFOTS). Electrochemical impedance spectroscopy, contact angle and water condensation studies reveal the protective properties of coatings prepared by both materials as well as the superiority of Diamalloy 4276 based coatings. Corrosion was evaluated under a harsh 20% w/w H2SO4 environment. Rendering the coating superhydrophobic improves water condensation under the tested conditions of high (80%) relative humidity.

ВЛИЯНИЕ СТРУКТУРЫ ЖЕЛЕЗО-ТИТАНОВЫХ ГАЗОТЕРМИЧЕСКИХ ПОКРЫТИЙ НА ИХ ИЗНОСОСТОЙКОСТЬ

The paper studies the structure, phase composition and properties of thermal sprayed coatings made of Ti4Al titanium alloy and “Ti4Al + AISI420” pseudoalloy obtained by hypersonic metallization. It is shown that the deposited coatings include in the phase composition a large amount of titanium nitride TiN (up to 70 vol.%), which is formed during the metallization process. At the same time, an increase in propane pressure during metallization from 0.3 to 0.4 MPa leads to a slight decrease in the titanium nitride content in the sprayed coating. It is associated with an increase in the flight velocity of molten titanium droplets in an atmosphere of ionized gases and, accordingly, a decrease in the time of their interaction with ionized air nitrogen atoms. The porosity of the sprayed coatings made of titanium alloy Ti4Al is 30–35 vol.%, and their hardness and microhardness are 500–650 HV 1 and 1,300–1,600 HV 0.1, respectively. Coatings made of “Ti4Al + AISI420” pseudoalloy have a reduced porosity of 10–15 vol.%, and their hardness and microhardness are 500–600 HV 1 and 900–1,300 HV 0.1, respectively. It is shown that coatings made of Ti4Al alloy and “Ti4Al + AISI420” pseudoalloy are characterized by increased wear resistance under friction without lubricant. In particular, the intensity of mass wear of coatings Iq made of Ti4Al titanium alloy, obtained at propane pressures of 0.3 and 0.4 MPa, is 2.5–2.6×10–3 mg/m, and Iq for coatings made of “Ti4Al + AISI420” pseudoalloy is 1.0–1.1×10–3 mg/m. The reduced values of mass wear intensities of coatings made of “Ti4Al + AISI420” pseudoalloy are associated with the presence of TiN in them and relatively low porosity.

Enhancement of sliding wear and scratch resistance of two thermally sprayed Cr-based coatings by ultrasonic nanocrystal surface modification

This study aims to identify whether mechanical surface treatment can improve the properties of thermal spray coatings for use in fuel-lubricated sliding conditions. In this study, we investigated the effects of ultrasonic nanocrystal surface modification (UNSM) technology on thermally sprayed chromium oxide (Cr2O3) and chromium carbide-nickel chromium (Cr3C2–NiCr) coatings and the resulting changes in sliding wear in fuels and scratch resistance. The improvement in coefficient of friction (COF) and specific wear rate (SWR) of the coatings after UNSM treatment was attributed to the reduced surface roughness, increased surface hardness, and the formation of tribo-layers (oxide) having lower shear strength with good lubricating properties. The wear mechanisms of the coatings involved plastic deformation leading to abrasive and oxidation modes.

Evaluation of metallic structures and material properties of thermal sprayed coatings using stainless-steel wires

ABSTRACT To evaluate the fundamental differences between the standard wire flame-sprayed coatings of stainless-steel wires, the differences in their characteristics are discussed from a metallurgical point of view. Austenitic (SUS304 and SUS316) and martensitic (SUS420J2) stainless steels were used in this study. The SUS420J2 and SUS304 sprayed coatings were composed of austenite and martensite, whereas the SUS316 sprayed coating was composed of only austenite. The dense thermally sprayed coating of SUS316 was due to oxygen distribution, which corresponds to marble-pattern oxidised structures. Additionally, an increase in the carbon content was observed after thermal spraying. However it is difficult to determine the distribution of carbon; therefore, it is considered that carbon distribution is supersaturated at a certain amount and carbon exists as a solid solute in the austenite phase. Finally, the increase in the carbon content is related to the progress of corrosion.

Evaluation of High Temperature Dry Sliding Wear Behaviour of Thermal Sprayed and Microwave Fused WC12Co and CeO2 Modified WC12Co Composite Coatings

Thermal spray methods are used to increase the wear resistance of working surfaces. Microwave post-treatment is the advanced approach for enhancing the properties of thermal spray coatings. The current investigation focuses on the wear behavior of HVOF-sprayed and microwave-treated coatings. The WC12Co and CeO2 modified WC12Co composite coatings were successfully deposited on AISI4140 steel using the HVOF thermal spray technique. The coatings were tested in both as-sprayed and microwave post-treatment conditions. The dry sliding wear tests were carried out at temperatures of RT, 200, 400, and 600 ℃ with various loads. Vickers hardness tester, Scanning Electron Microscopy (SEM), and X-ray diffraction (XRD) equipments were used to investigate the microhardness, microstructure, and phases of coatings, respectively. In both compositions, the microwave-fused coating had a fine homogeneous structure and higher hardness than the as-sprayed depositions. For typical loads of 20 N and 40 N for both compositions, the friction coefficient decreased with increasing temperature in the as-sprayed and fused coatings. At all conditions, the microwave fused coating outperforms the as-sprayed coating in terms of wear resistance. During sliding action, the fused coatings exhibit tribo-oxide layers, which provide the best wear resistance of the microwave fused composite coatings. The wear resistance of the WC12Co coatings is improved as compared to CeO2 modified WC12Co coatings.

Формування газотермічних покриттів

Розглянуто перспективи використання методу неруйнівних випробувань безперервним вдавленням індентора для визначення механічних властивостей газотермічних покриттів. Проведено випробування з оцінки мікротвердості й модуля пружності композиційних покриттів на основі карбідів вольфраму і хрому, отриманих методом детонаційно-газового напилення. Розглянуто діаграми проникнення для покриттів з порошків ВК8, ВК15, ВК18С, КХН15С. Показано, що при оптимальних режимах напилювання мікротвердість одержуваних покриттів близька до мікротвердості спечених твердих сплавів того ж складу. Визначено значення коефіцієнтів варіації значень мікротвердості зі збільшенням глибини відбитка для зразків зі спеченого твердого сплаву і напилених покриттів. При оптимальних режимах напилювання досягаються не тільки максимальні значення мікротвердості та модуля пружності покриттів, але і більш однорідні структура і механічні властивості покриттів. Більш чутливими до змін технологічних параметрів є значення модуля пружності напилених покриттів, що більш зручно при відпрацюванні технологічних процесів.

The Comparison Study on Abrasive and Erosive Resistance Properties of Thermal Spray Coatings

Thermal spraying is a technology which improves and restores the surface of a solid material. The process can be used to apply coatings to a wide range of materials and components, in order to provide resistance to wear, erosion, cavitation, corrosion, abrasion or heat. In this paper, the study of abrasive and erosive properties of Cr3C2/20%NiCr and FeCrB + Al thermal sprayed coating samples were focused. It was revealed that both received thermal spray coating samples show outstanding abrasive and erosive resistance properties.

Дослідження механічних властивостей детонаційно-газових покриттів методом мікроіндентування

Розглянуто перспективи використання методу неруйнівних випробувань безперервним вдавленням індентора для визначення механічних властивостей газотермічних покриттів. Проведено випробування з оцінки мікротвердості й модуля пружності композиційних покриттів на основі карбідів вольфраму і хрому, отриманих методом детонаційно-газового напилення. Розглянуто діаграми проникнення для покриттів з порошків ВК8, ВК15, ВК18С, КХН15С. Показано, що при оптимальних режимах напилювання мікротвердість одержуваних покриттів близька до мікротвердості спечених твердих сплавів того ж складу. Визначено значення коефіцієнтів варіації значень мікротвердості зі збільшенням глибини відбитка для зразків зі спеченого твердого сплаву і напилених покриттів. При оптимальних режимах напилювання досягаються не тільки максимальні значення мікротвердості та модуля пружності покриттів, але і більш однорідні структура і механічні властивості покриттів. Більш чутливими до змін технологічних параметрів є значення модуля пружності напилених покриттів, що більш зручно при відпрацюванні технологічних процесів.

Comparative study of structure and properties of thermal spray coatings using conventional and nanostructured hydroxyapatite powder, for applications in medical implants

The objective of this paper is to study and compare the structure and properties of thermal spray coatings prepared with conventional and nanostructured hydroxyapatite powder, in order to assess their suitability for future use in medical implants. Four coatings were prepared via Atmospheric Plasma Spray process (APS). Two kinds of feedstock material were employed for the spray process, namely, commercial XPT-D-703 hydroxyapatite powder for half the samples and novel nanostructured PYRO 4 hydroxyapatite powder, which had previously been mechanically treated, for the remaining samples. The substrate of all the samples was stainless steel 304. Finally, the plasma spray parameters were altered for two out of the four coatings, each produced with a different type of powder, in order for a sufficient amount of porosity to be achieved for future incorporation of biomolecules. The coatings were also examined in terms of bioactivity in vitro. It was concluded that the coating produced with the nanostructured powder, under lower plasma energy and at greater spraying distance presented the best results regarding its roughness, bioactive response, crystallinity, adherence and porosity content.

Investigation into the Effects of High Temperature on Mechanical Properties of Thermal Spray Coatings Applied by Plasma Spraying

C. C. Berndt advanced investigations of mechanical properties of thermal spray coatings under 4-point bending. He found that this investigation method is sensitive to the mechanical properties of thermal spray coatings.This paper contains the detailed investigation results for thermal spray coatings of zirconium dioxide under 4-point bending, i.e. tests of the specimens subjected to spraying at varying conditions and pre-test soaking with the various duration at 1100 °С.It was established how the mechanical properties of thermal spray coatings changed depending on the spraying mode and high temperature soaking. The test results show that the double heat treatment of coatings is more preferable than one-time heat treatment as it make the properties change linearly. It is more easily controllable during operation of the components with thermal spray coating.

Application of FEM to Estimate Thermo-Mechanical Properties of Plasma Sprayed Composite Coatings

The presence of defects such as voids, inter-lamellar porosities or cracks causes a decrease in the effective thermal conductivity of plasma-sprayed coatings as well as a decrease in corresponding mechanical properties, such as the Young’s modulus. In general, the effective properties of thermal spray coatings are thus very different from that of bulk materials and thus have to be quantified to validate in service performances. A complementary approach allowing us to understand the relationships between the microstructure of a coating and its macro-properties is that of Finite Element Modeling (FEM). The case of composite coatings is more complicated still, due to the presence of different materials. In the present study, thermo-mechanical properties of a plasma-sprayed composite coating were estimated by numerical modeling based on FEM. The method applied uses directly cross-sectional micrographs without simplification, using a one-cell per pixel approach. Characteristics such as the thermal conductivity, the Young’s modulus, the Poisson’s ratio and the dilatation coefficient were considered. The example selected was an AlSi/polyester coating used as an abradable seal in the aerospace industry.

Optimization of the Arc Spraying Process Parameters of the Fe–Base Mn-Si-Cr-Mo-Ni Coatings for the Best Wear Performance

In this paper, the use of Fe–base Mn-Si-Cr-Mo-Ni and Fe–base Mn-Si-Cr wires for thermal arc spraying is presented. For this purpose the mechanical and physical properties of coatings were evaluated. The quality of the coating’s was dependent on the selected equipment, spray materials, technological parameters of the spray and spray technology. The aim was to qualify and optimize the parameters for spray coating to get the best coatings properties with good tribological properties. All coatings were deposited on mild steel S235JR substrates. Two experimental cored wires of unique chemical composition – STEIN-MESYFIL 932 V and STEIN-MESYFIL 954 V – were used for thermal arc spraying. The wires of 1.6 mm diameter were used for the surfacing material. Hardness, porosity and oxide measurements were used to verify the spray parameters and analyze the coatings. Rubber wheel test, which is based on the standard ASTM G65, was used. Dry-sand, rubber-wheel procedure according ASTM G65 was used to investigate low stress abrasion, whereas for high stress abrasion investigations a rubber wheel was used. This experiment was carried out by changing the speed of disc friction, travel distance and measuring the mass loss of surface friction. Miller Test according to ASTM G75-95 Standard was carried out in experiment with friction. The samples were immersed in water with corundum and polished with 22 N load, for 8 hours. Furthermore a correlation was performed between the spraying current and voltage parameter. The coatings’ cross sections were examined using scanning electron microscope (SEM) and optical microscopy. The influence of the composite components of the coatings’ microstructure, such as porosity, microhardness, oxide inclusions, on the tribological properties of thermal sprayed coatings is discussed in this paper. DOI: http://dx.doi.org/10.5755/j01.ms.22.1.7339

Improving operational properties of thermal sprayed coatings by electropulse treatment on a biphasic high-temperature flow and subsequent heat treatment

The article considers the possibility of increase of the operational properties of the electric arc sprayed coatings Sv-08G2S of wire and plasma coatings PG-19M-01 of powder by the electropulse treatment on the biphasic high-temperature flow with the subsequent heat treatment. It is determined that the wear resistance of the electric arc sprayed coatings increases to 1.7 times under the electropulse treatment, the strength of adhesion to the substrate – by 30%. The wear resistance of the plasma coating increases to 1.5 times, the strength of adhesion to the substrate increases by 18 % compared to the conventional technology of their application. The optimum heat treatment modes of prerecrystallization thermal treatment of coatings under the electropulse treatment which help to increase the hardness of the electric arc sprayed coatings by 50 %, plasma coatings – by 42 %.

Thermal Spray Maps: Material Genomics of Processing Technologies

There is currently no method whereby material properties of thermal spray coatings may be predicted from fundamental processing inputs such as temperature-velocity correlations. The first step in such an important understanding would involve establishing a foundation that consolidates the thermal spray literature so that known relationships could be documented and any trends identified. This paper presents a method to classify and reorder thermal spray data so that relationships and correlations between competing processes and materials can be identified. Extensive data mining of published experimental work was performed to create thermal spray property-performance maps, known as “TS maps” in this work. Six TS maps will be presented. The maps are based on coating characteristics of major importance; i.e., porosity, microhardness, adhesion strength, and the elastic modulus of thermal spray coatings.

Determination of the Effective Properties of Thermal Spray Coatings Using 2D and 3D Models

Models, which are developed to determine the effective properties of thermal spray coatings, require the material properties of each constituent of the coating as well as the information about the spatial positions and the geometries of these constituents as input parameters. The complex microstructure of thermally sprayed Yttria-stabilized zirconia (YSZ) coatings consists of irregular voids which are distributed non-uniformly in the coating. It is a common practice in the literature to employ two-dimensional (2D) cross-sectional images of the coatings to derive the geometrical model of the microstructure and conduct the simulations in 2D. In the context of this study, contrary to the 2D approach, a new three-dimensional (3D) reconstruction approach has been developed to model the microstructure of thermally sprayed coatings in 3D. The effective properties of an YSZ coating have been calculated by means of asymptotic homogenization and virtual testing methods. The results of the models, which have been conducted in 2D and 3D, are compared with each other. Finally, the capabilities of these methods with respect to the modeling approach (in 3D and in 2D) are analyzed on the basis of reference measurements.

Metal-Matrix Hardmetal/Cermet Reinforced Composite Powders for Thermal Spray

Recycling of materials is becoming increasingly important as industry response to public demands, that resources must be preserved and environment protected. To produce materials competitive in cost with primary product, secondary producers have to pursue new technologies and other innovations. For these purposes different recycling technologies for composite materials (oxidation, milling, remelting etc) are widely used. The current paper studies hardmetal/cermet powders produced by mechanical milling technology. The following composite materials were studied: Cr3C2-Ni cermets and WC-Co hardmetal. Different disintegrator milling systems for production of powders with determined size and shape were used. Chemical composition of produced powders was analysed. To estimate the properties of recycled hardmetal/cermet powders, sieving analysis, laser granulometry and angularity study were conducted. To describe the angularity of milled powders, spike parameter–quadric fit (SPQ) was used and experiments for determination of SPQ sensitivity and precision to characterize particles angularity were performed. Images used for calculating SPQ were taken by SEM processed with Omnimet Image Analyser 22. The graphs of grindability and angularity were composed. Composite powders based on Fe- and Ni-self-fluxing alloys for thermal spray (plasma and HVOF) were produced. Technological properties of powders and properties of thermal sprayed coatings from studied powders were investigated. The properties of spray powders reinforced with recycled hardmetal and cermet particles as alternatives for cost-sensitive applications were demonstrated.DOI: http://dx.doi.org/10.5755/j01.ms.18.1.1348

Microstructural characterization of plasma sprayed Al2O3-40 wt.% TiO2 coatings on high density graphite with different post-treatments

Graphite is one of the candidate materials proposed for application in pyrochemical reprocessing plants involving aggressive molten chloride environment. Post treatments are promising techniques for the improvement of properties of thermal spray coatings for different industrial applications. In the present work, the effect of post treatments like vacuum annealing (VA) and laser melting (LM) on the microstructure and chemical modification of plasma sprayed Al2O3-40wt.% TiO2 coatings over high density (HD) graphite substrates has been investigated. When compared with sprayed coatings (SC), VA coatings showed cluster morphology and LM coatings exhibited homogenous microstructure. On laser melted surfaces networks of cracks were observed. XRD studies showed that the metastable γ-Al2O3 phase present in the SC is transformed to stable α-Al2O3 after post treatments. In LM coatings Al2TiO5 phase was more predominant in contrast to SC and VA coatings. The microhardness enhancement was observed in case of LM coating compared to the VA and SC. Due to elimination of coating defects in LM samples, there is a considerable reduction in the surface roughness.

Application of Structure-Based Models of Mechanical and Thermal Properties on Plasma Sprayed Coatings

Mechanical and thermal properties of thermal sprayed coatings, especially ceramics, are strongly influenced by cracks and pores that are present in the coating microstructure. In the recent past, there have been efforts to find an analytical model describing the coating properties based on the microstructural characteristics. Various analytical models were developed and published in the literature. In this study, several major models were applied to ceramic and metal coatings to describe their elastic modulus and thermal conductivity. The sensitivity of the models to the variations in the microstructure and relevancy of their use in specific cases were examined. The results were compared with those obtained by FEM modeling and experimentally measured values.

Research on Zn-Al15 thermal spray metal coating and its organic painting composite system protection performance

In the aluminium content on corrosion resistance of zinc - aluminum alloy coating effects research foundation, through our country typical natural atmosphere and seawater, freshwater environment exposure test and laboratory conditions of neutral salt spray corrosion test and electrochemical methods,study on thermal spraying Zn, Al and Zn-Al15 metallic coatings in different natural environment protection performance of steel. Study found that compared with thermal spraying Zn, Al coating, Zn-Al15 alloy coating on the steel has the same excellent electrochemical cathode protection features of thermal spraying Zn coating, but also has high corrosion resistance characteristics of thermal sprayed Al coating. To further improve the protective properties of thermal spray coatings, on the basis of above, composite protective technology research which is about thermal spray metal coating was carried out. Exposure corrosion tests in Qingdao seawater and Wuhan Yangtze freshwater environment for two years showed that the composite system of thermal spray metal coating which is formed after its closed / coating treatment, is superior to single metal thermal spraying in protection performance. At present, thermal spray Zn-15Al alloy coating and sealing / coating composite protective system has been used in the national water, bridges and other key infrastructure projects.

IFTHSE Global 21: heat treatment and surface engineering in the twenty-first century Part 10 – Thermal spray coatings: a technology review

Thermal spray coatings (TSCs) are used widely in all major industrial sectors and are a cost effective technique for surface engineering solutions. These coatings are used, for example, as wear resistant layers, thermal barrier coatings and within aqueous corrosion environments. Metals, polymers, ceramics and combinations of these materials can be deposited within an industrial shop setting or in the field at the point of use. The thermal spray technique has been well documented from the perspective of the operational science and engineering applications. The economic perspective is not as well known since currency changes and local market conditions are fluid. There is, though, a wealth of information concerning success stories of TSCs within the various sectors of industry. This paper focuses on applications of TSCs within mainstream industrial sectors. The intent is to relate the microstructure and so formed physical properties of TSCs to their benefits and attributes as solutions for adverse engineering environments.