Thermally sprayed wear resistant coatings have proven their effectiveness in many applications. Their benefit is unquestionable in the case of mutual sliding contact or abrasive stress caused by hard particles. However, for the case of dynamic impact loading, either single or cyclic, the lifetime of different types of coatings is rarely described, probably due to the complex influence of many parameters. The paper deals with the evaluation of resistance to dynamic impact loading of two types of HVOF-sprayed Cr3C2-rich binary hardmetal coatings (Cr3C2-42%WC-16%Ni and Cr3C2-37%WC-18%NiCoCr) with respect to the variation of their deposition parameters and compares them to a well established Cr3C2-25%NiCr coating. For each coating, a Wohler-like curve was constructed based on a failure criterion of sudden increase in impact crater volume. Besides, coatings deposition rate, residual stress, microstructure and hardness were evaluated. Differences in the coatings dynamic impact wear resistance was found, related to their residual stress. The failure mechanism and crack propagation mode are analyzed using SEM of impact surface and cross-sections. Deformation and related stress changes in coated systems during dynamic impact loading are described using FEA analyzes.

Impact testing appears as a most promising tool for gaining information on coating behavior in load-bearing applications. During dynamic impact test an indenter impacts successively the surface of the coating with constant force and frequency. The deformation of the coated specimen during impact testing is affected by the mechanical properties of both the substrate and the coating. Varying the impact load and the number of impacts, the evolution of coating surface deformation and contact fatigue failures can be observed. In the paper, the influence of dynamic impact load and number of impacts on the resulting impact crater volume and morphology is analysed, and the interpretation of the results in form of Wohler-like dependance is suggested and demonstrated on two types of HVOF sprayed Co-based alloy coatings. The low-number impact craters evolution and subsurface cracks propagation of HVOF sprayed Co-based alloy coatings is analyzed in more detail, by means of 3D optical microscopy and SEM. The results showed, that the higher ability to deform plastically increased the coatings dynamic impact fatigue lifetime. The cracks, responsible for coatings destruction, spread predominantly along the intersplat boundaries in the pile-up area.

Deposition of hybrid plasma-sprayed coatings employing both dry powder and liquid feedstocks enables preparation of innovative coating architectures. Using this technique, miniature domains of additional (secondary) material may be introduced via the liquid feedstock route into the more conventional powder-deposited coating, providing potential benefits for the coating functionality. In this contribution, we have explored the tribological properties of hybrid coatings sprayed from alumina powder with additions of chromia (Cr 2 O 3 ), zirconia (ZrO 2 ), yttria-stabilized zirconia (YSZ), and titania (TiO 2 ) delivered from liquid feedstocks. The coatings were subjected to dry sliding wear testing and a subsequent analysis of the wear tracks to determine their wear resistance and coefficient of friction, as well as a qualitative assessment of the wear mechanisms. The hybrid coating doped with the chromia addition matched the remarkable wear resistance of highly-dense suspension-sprayed coatings. This is a significant result, especially when considering the order of magnitude better production efficiency of the hybrid coatings.

For the engines used in small turboprop aircrafts, the introduction of abradable coatings represents a feasible way to reach higher levels of overall engine efficiency, specifically by improving the fuel consumption and increasing the inter turbine temperature margin. Abradable coatings on seals also contribute to improved hot restarts capability of an engine and lead to substantial extension of service life of the rotating counter bodies. In our contribution, we concentrate on flame sprayed nickel graphite abradable coating that can be used in turboprop engines both for seals and clearance control. The focus is the impact of spraying parameters on the physical and function properties of the abradable coating.

Thermally sprayed hard metal coatings are the industrial standard solution for numerous demanding applications. Often the performance of thermally sprayed coatings is improved by using finer particle sizes due to improved surface finish and decreased defect sizes. In the aim of utilizing finer particle and primary carbide sizes in thermal spraying of hard metal coatings, several approaches have been studied to control the spray temperature. The most viable solution is to use the modern high velocity air-fuel (HVAF) spray process, which has already proven to produce high quality coatings with dense structures. In HVAF spray process, the particle heating and acceleration can be efficiently controlled by changing the nozzle geometry. In this study, fine WC-10Co4Cr powder (-25+5 µm) was sprayed with three nozzle geometries to investigate their effect on the particle temperature, velocity and coating microstructure. The study demonstrates that the particle melting and resulting W2C formation can be efficiently controlled by changing the nozzle geometry from cylindrical to convergent-divergent. Moreover, the average particle velocity was increased from 780 to over 900 m/s. This increase in particle velocity significantly improved the coating structure and density while deposition efficiency decreased slightly. Further evaluation was carried out to resolve the effect of particle in-flight parameters on coating structure and cavitation erosion resistance, which was significantly improved with the increasing average particle velocity.

The 3 commercially available CrC-based powders with different kind of matrix (Cr 3 C 2 -25%NiCr; Cr 3 C 2 - 25%CoNiCrAlY and Cr 3 C 2 -50%NiCrMoNb) were deposited by HVOF JP-5000 spraying gun, evaluated and compared. The sliding wear resistance, measured at room and elevated (T=600°C) temperature according to ASTM G-133, the influence of heat treatment on the microstructure and properties, as well as the oxidation resistance in hot steam environment (p=24 MPa; T=610°C) were evaluated with respect to their potential application in steam power industry. The surface oxidation and microstructure changes were evaluated by SEM and XRD. The NiCr matrix proved to provide high oxidation and sliding wear resistance of the coating regardless volume content. On the contrary, the Cr 3 C 2 -25%CoNiCrAlY coating was subjected to massive oxidation of carbide particles. The low cohesive strength and high porosity of Cr 3 C 2 -25%CoNiCrAlY was identified responsible for its poor oxidation resistance in hot steam environment. The sliding wear resistance was found comparable at room temperature, regardless the matrix composition and content, while at elevated temperatures, the higher volume content of matrix led to higher wear of coating material.

Cr 3 C 2 -25%NiCr, Stellite 6, NiCrBSi and Hastelloy C-276 coatings were deposited on substrate material P91 by HP/HVOF (High Pressure / High Velocity Oxygen Fuel) thermal spraying technology. The resistance against high temperature corrosion was evaluated exposition of coatings to corrosive-aggressive environment in the form of molten salts mixture with composition of 60% V 2 O 5 and 40% Na 2 SO 4 at temperature of 750 °C. Further, coatings were exposed to cyclic conditions. After the corrosion tests, all coatings were analyzed using scanning electron microscope (SEM), and analysis of elemental composition (EDX). Alloys-based coatings showed very similar corrosion mechanism in the selected aggressive environment and the same can be stated about cermet coatings. The obtained results prove that HVOF deposited coatings can replace current surface protection of components in power equipment such as nitriding.

In this study, the influence of main laser cladding parameters on the final microstructure of cladded WC-NiCrBSi coating is discussed. As the used powder is the blend of 60% tungsten carbide spherical particles and 40 % NiCrBSi matrix, the carbides’ morphology and distribution in the final coating are dependent on laser cladding parameters. The variability of coating’s microstructure strongly influenced their wear resistance. In the paper, the influence of laser processing parameters on final coating microstructure is studied. The functional properties of cladded coatings are evaluated by dry sand rubber wheel test ASTM G-65. The wear resistance of the coating is dependent on the amount of undissolved carbides particle in the coating.

This paper summarizes the results of high-temperature corrosion and erosion tests conducted on a wide range of coating materials, including Cr 3 C 2 -NiCr, Cr 3 C 2 -CoNiCrAlY, TiMoCN-Ni, Stellite 6, NiCrBSi, and Hastelloy C-276. All coatings were deposited on stainless steel substrates by HVOF spraying, and after high-temperature testing, were evaluated by means of SEM and EDX analysis. Of the coating materials evaluated, Hastelloy C-276 provided the best protection against high-temperature corrosion. It also exhibited the highest erosion resistance at a particle impact angle of 90°, but at the sharpest impact angle of 15°, Cr 3 C 2 -NiCr coatings were found to be the most erosion resistant, likely due to the strong bonding of carbide particles in matrix. NiCrBSi coatings, on the other hand, exhibited the highest values of volume loss.

This paper presents the results of mechanical and tribological property measurements obtained from NiCrBSi alloy coatings and evaluates the effect of different heat treatments. Coating specimens were deposited by means of flame spraying and heat treated using an acetylene torch. HVOF samples were also prepared as a reference for comparison. The microstructure of as-sprayed and heat-treated coating samples were compared, hardness and surface roughness were measured, and erosion resistance tests were performed. The processes and procedures used are described and the results obtained presented and discussed.

Lowering the thermal energy and increasing the kinetic energy of sprayed particles by newly developed HVAF systems can significantly reduce material decarburization, and increases sliding wear and corrosion resistance of hard metal coatings, making HVAF coatings attractive both economically and environmentally over its HVOFs predecessors. Two agglomerated and sintered feedstock powder chemistries, respectively WC-Co (88/12) and WC-CoCr (86/10/4), with increasing primary carbides grain size from 0.2 to 4.0 microns, have been deposited by the latest HVAF-M3 process onto carbon steel substrates. Respective dry sliding wear behaviours and friction coefficients were evaluated at room temperature via Ball-on-disk (ASTM G99-90) wear tests against Al 2 O 3 counterparts, and via Pin-on-disk (ASTM G77-05) wear tests against modified martensitic steel counterparts in both dry and lubricated conditions. Sliding wear mechanisms, with formation of wavy surface morphology and brittle cracking, are discussed regarding the distribution and size of primary carbides. Corrosion behaviours were evaluated via standard Neutral Salt Spray (NSS), Acetic Acid Salt Spray (AASS), accelerated corrosion test and electrochemical polarization test at room temperature. Optimization of coating tribological properties are discussed regarding the suitable selection of primary carbide size for different working load applications.

This study evaluates the base mechanical properties of Hastelloy C-276, WC-Co, and Cr 3 C 2 -NiCr coatings produced by HVOF spraying at angles ranging from 60° to 90°. Examinations and tests were conducted to characterize changes in microstructure, density, hardness, wear resistance, surface roughness, and deposition efficiency based on spraying angle. Only minor spray-angle dependencies were found for base mechanical properties, although thickness, roughness, and deposition efficiency varied greatly.

This paper evaluates and compares five wear-resistant coatings produced by HVOF spraying for high-temperature use. CrC-NiCr, CrC-CoNiCrAlY, Stellite 6, NiCrBSi, and TiMoCN-Ni coatings were sprayed on grit-blasted carbon steel substrates. Abrasive, sliding, and fretting wear resistance were measured and changes in microstructure and hardness due to high-temperature exposure were recorded. CrC-NiCr coatings exhibited the best wear properties, but the oxidation of carbides at high temperatures proved to be a problem. Based on test results, alternative coatings would include CrC-CoNiCrAlY for abrasive wear, Stellite 6 for erosive wear, and NiCrBSi for sliding wear.

This paper presents the results of a study on the tribological properties of TiC-based coatings deposited by HVOF spraying. Four powder feedstocks consisting of (Ti,Mo)(C,N) hardmetal with Ni and Co binders were prepared by agglomeration and sintering. The feedstocks differ in composition and particle size distribution, the latter being optimized for fuel type and equipment requirements. Coating specimens are evaluated based on microstructure, hardness, bonding strength, and friction and wear behavior. The results are presented and correlated with spray parameters, equipment differences, and feedstock characteristics.

The HVOF sprayed wear resistant hardmetal coatings with favourable sliding properties are suitable for increasing the lifetime of sliding applications, such as pistons of combustion engines, pumps and other hydraulic devices. In practice, the coatings face the problem of their interaction with other media, in the case of sliding wear usually lubricants. In the paper, the friction properties of five different HVOF sprayed coatings are evaluated by pin-on-disk test according to ASTM G-99 under dry and lubricated conditions and lubricated block-of-ring test according to ASTM G77. Several types of lubricants designed for combustion engines were used to compare their influence on coatings sliding wear behavior. Based on the results, the suitability of coatings for the application on the engines parts is discussed and the effect of counterpart material and different types of lubricants on the coefficient of friction and coatings wear rate is analyzed. It was confirmed, that the CrC-based coating are more suitable for the application under the condition corresponding to combustion engines, e.g. elevated temperature and steel counterpart, than the WC-based coatings. From the group of CrC-based coatings, the superior behavior was observed at the CrC-CoNiCrAlY coating, the matrix material of which offers further enhancement of the sliding wear behavior.

The work deals with the evaluation of strength characteristics of thermally sprayed coatings. The main aim was concentrated on the tensile and shear loading of HVOF (Stellite Alloy 6, Tribaloy 400) and arc sprayed (13%Cr, CuAl8) coatings. The investigation of the coatings behaviour on the coating-substrate interface is important for the evaluation of one of significant coating mechanical properties that influence properties of the whole coating-substrate system. The magnitude of the coating bond strength during tensile and shear stresses predicates the coating stability, reliability, impact resistance, resistance against failure and mostly operating lifetime. The determination adhesive-cohesive strength was performed according to EN 582 and EN 15340 Standards.

This paper compares the results of two approaches of instrumented indentation for characterization of mechanical properties of HVOF coatings. Three types of industrially used HVOF sprayed coatings (Cr 3 C 2 -NiCr, WC-Co, (Ti, Mo)(C,N)-NiCo) were selected. The indentation methods applied were: isolated nanoindentation in metallic matrix and carbides with 2 mN peak load and grid indentation with 2 mN peak loads, comprising 400 indentations. The results of the isolated indentation revealed hardness and elastic modulus of the individual phases with surprisingly low standard deviation and in good agreement with the corresponding bulk equivalent. The grid indentation method, based on statistical evaluation of a large number of indentations, was influenced by the carbide-matrix interface, which gave rise to a strong third peak apart from the two peaks corresponding to the hard carbides and softer metallic matrix. This makes the statistical analysis much more complex than using simple bimodal Gaussian fit for separation of matrix and carbide properties. Nevertheless, the results of both grid indentation and isolated nanoindentation compared with microindentation values obtained at higher loads gave important information about the cohesion of the coatings.

Hardmetal coatings prepared by high-velocity oxy-fuel (HVOF) spraying represent an advanced solution for surface protection against wear. The work presented in this paper focussed on the comparison of the tribological behaviour of WC-Co, Cr 3 C 2 -NiCr and (Ti,Mo)(C,N)-NiCo hardmetal coatings under dry sliding wear conditions at room and elevated temperatures (at 500°C and 700°C). The friction properties of these HVOF-sprayed coatings were studied in detail. The progression of the coefficient of friction (CoF) was measured during the pin-on-disc tests at the different temperatures. The mechanisms of wear and the heat-related changes in surface roughness and microhardness of the coatings were studied.

Indentation tests were provided with various applied loads and indentors’ profiles to determine the mechanical properties of selected HVOF coatings. The four well-known wear resistant coatings, WC-17%Co, Cr 3 C 2 -25%NiCr, NiCrSiB and AISI 316L, sprayed by TAFA JP-5000, were tested. Besides the common indentation tests (e.g. coatings surface hardness and microhardness), the indentation fracture toughness (IFT) and Young modulus of elasticity (E) were measured using Vickers and Knoops indentors profiles, resp. From the Vickers indentation results, the IFT was evaluated in terms of 18 models for KIc determination. The big differences between results of used models were found. For evaluation of E, the Knoop indentation in three different orientations was used. The measurement results show the anisotropic behavior of sprayed coatings. Based on the measured data, the relation between coatings properties with respect to the coating unique microstructure was proved.