Hybrid plasma spraying can be utilized to deposit novel coating microstructures by combining the simultaneous injection of a dry coarse powder and a liquid feedstock into the plasma jet. Using this approach, the coating microstructure contains both coarse powder-made splats and a dispersion of fine liquid-made splats. Furthermore, the so-called external feeding hybrid method allows the incorporation of fine particles of materials susceptible to decomposition at high temperatures thanks to the by-passing of the hot plasma jet and deposition of the temperature-sensitive material directly onto the coated surface from a suspension. In this study, microstructures of ceramic coatings with embedded self-fluxing sulfides were studied and the wear resistance of the system was evaluated using the dry sliding pin-on-disc method.

Composite coatings using mixed alloy matrices reinforced with carbon-based solid lubricants as feedstock materials were prepared by atmospheric plasma spraying. The aim of the present study was to investigate the tribological characteristics of such coatings exploring potential benefits of CNTs as nano-additive to reduce friction and wear, improving lubrication conditions during operation in tribosystems, such as piston ring – cylinder liner systems. The chemical composition of feedstock materials and the thermal spray parameters during coatings deposition are correlated to friction coefficient and wear rate using pin-on-disk measurements. The developed coatings hybrid behaviour is studied. Co-based cermet as well as metal alloy anti-wear performance along with the promoted lubrication conditions during operation is revealed. The dependence of the developed coatings quality and performance on the characteristics of the feedstock powder is thoroughly 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.

High-temperature tribology plays an important role in many engineering applications such as metal forming operations and aerospace industry. Several problems in hot-metal forming of high strength steels occur such as oxidation of tool and workpiece surfaces, increased wear of tools and scaling of workpiece. Moreover, operations at elevated temperatures can significantly influence frictional behavior of tool steels. Present research attempts to analyze experimentally and understand tribological behavior of AISI H11 and AISI H13 under dry conditions at room temperatures. High velocity oxy-fuel (HVOF) thermal spray NiCrBSi coating was developed on tool steels. The room-temperature wear performance of uncoated and coated tool steels was evaluated on pin-on-disc tribometer in the laboratory. In-depth analysis of exposed as-sprayed samples was examined with X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS).

A special pin-on-disc test setup designed for vacuum environments was used to conduct wear tests in a large chamber scanning electron microscope. Arc-sprayed NiCrBSi and HVOF-sprayed WC-12Co coatings were tested using a pin with an Al 2 O 3 ceramic ball as the wear counterpart. During testing, different wear mechanisms were identified and the processes were recorded in short video streams.

High velocity oxygen fuel has been used as fabrication technique for manufacturing aluminium coatings reinforced with different weight percents of silicon carbide particles on Mg-Zn alloys used as substrates. The aim of the investigation is to improve the tribological performance of the ZE41A magnesium alloy. The parameters of the thermal projection system have been optimized in order to maximize the SiC particles incorporation in the aluminium matrix of the coating. Pin-on-disc tests were developed to characterize the tribological behavior of the different specimens. Minor degradation of the magnesium alloy was achieved after . Composite coatings with thicknesses of about 120 µm, reinforced with about 10 wt.% and with high adhesion to the substrate were achieved. After the coating parameters were optimized, the wear rate of the magnesium with the composite coatings decreased by two orders of magnitude in comparison to that of the uncoated magnesium alloy.

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.

This paper describes an inner diameter HVOF spraying technique and associated tests methods. In the experiments, WC-CoCr was applied to an internal diameter of 150 mm and evaluated using a dedicated pin-on-disk wear test and standard axial fatigue tests. The results are presented and discussed along with the potential for further development of the inner diameter HVOF spraying technique.

Thermal spray processes are widely used in industries to compensate for worn surfaces of different power transmission steel shafts. These include plain carbon, alloyed and stainless steels. This comes as a means of saving the worn parts by reusing them after they have been thermally sprayed by suitable wear-resistant coatings. As there are several factors to be controlled in this process, this makes it necessary to get the best combination of process parameters to provide the required level of wear resistance and, hence part life. In this study the oxy-fuel process is applied to 4140 alloy steel. Process parameters have been varied using a 2k experimental design. The Pin-on-Disc test was used to estimate the wear resistance of the different material-coating-parameters combinations. The data were analyzed and a statistical model, explaining the effect(s) of different parameters as well as their interaction, was obtained.

A bulk amorphous NiTiZrSiSn produced using an inert gas atomization was sprayed onto the Cu substrate. As the oxygen to hydrogen gas fraction was increased, oxide phase fraction was increased at the expenditure of amorphous phase fraction. The phase evolution was mainly due to the in-flight particle oxidation according to flame gas composition. Tribological behaviors were investigated in view of friction coefficient and weight loss by a pin-on-disc dry sliding test. Both friction coefficient and weight loss were largely dependent on the phase composition of the coating. As the amorphous phase fraction was increased, the friction coefficient was decreased with the increase of the transfer film formation. On the other hands, major weight loss mechanism was changed from transfer film formation to pull-out of coat material as the amorphous phase fraction was decreased.

A new process has been developed to incorporate graphite particles in a stainless steel coating during its formation. Four means have been tested to inject the graphite particles outside the plasma jet and its plume : graphite suspension, a graphite rod rubbed on the rotating sample, powder injection close to the substrate with an injector or an especially designed guide. The latter process has been shown to be the most versatile and the best controllable one. It allows to incorporate uniformly between 2 and 12 vol % of graphite particles (2-15 µm) within the plasma sprayed stainless steel coatings. A 2 vol % seems to give the best results : a low decrease (6%) of the coating hardness and the best results in dry friction studied with a pin on disk set up. In this case, depending on the sliding velocity (0.1 to 0.5 m/s) and loads (3.7 to 28 N) the dry friction coefficient against a 100C6 pin is reduced by a factor between 1.5 and 4 compared to that obtained with plasma sprayed stainless steel.

The aim of this study is to find a coating that can improve the wear resistance of bushings and sleeves used in continuous hot-dip galvanizing facilities. In the experiments, a number of wear-resistant alloys and their carbide composites are applied to stainless steel substrates by plasma transferred arc (PTA) surfacing and the resulting deposits are characterized based on XRD and SEM analysis, microhardness measurements, and pin-on-disk sliding wear tests conducted in a molten Zn-Al bath at 470 °C. Changes in microstructure during solidification are discussed and correlations are made with phase composition, hardness, wear behavior, and suspected wear mechanisms. Paper includes a German-language abstract.

Quasicrystalline (QC) alloys constitute a family of materials with low coefficient of friction, high hardness, and high yield strength under compressive stress. This paper examines the characteristics of QC composite coatings deposited by LPPS and HVOF spraying. It compares the coatings based on phase distribution and microstructure. Both compositions studied are extremely wear resistant, but their friction properties require further development. Paper includes a German-language abstract.

Borides are promising materials with good wear and corrosion resistance properties. Boride coatings are expected to perform better where wear and corrosion resistances are simultaneously required. Zirconium diboride is an important emerging material for such applications, due to its high hardness, high melting point, good wear resistance and corrosion as well as high temperature oxidation resistance. Special properties of laser beam like beam directionality, high intensity and spatial resolution makes laser alloying a fast and efficient technique for producing improved wear resistance coatings. In the present work, mild steel was laser alloyed with ZrB2, using "two-stage" technique of laser alloying. These coatings after characterization by optical microscopy, SEM, EDAX and XRD techniques were tested on a "Pin-on-Disk" machine for determining their wear resistance.

During the last decades, improved understanding of tribological behavior of different material combinations led also to an intensified development of thermal spray applications. In the field of e.g. hard chromium replacement by thermal spraying, significant amount of work has been done and published world wide, however, the authors manly focused on only one tribological aspect like friction, abrasion, erosion, cavitation or corrosion, respectively. In real applications, often more than one of those factors influence the successful use of these coatings. Besides the bulk properties of the materials, the coating micro structure, which is strongly spray system dependent, needs to be considered and investigated. Higher functionality and reliability than conventional competitive coatings still has to be proved at laboratory scale and under field conditions for thermally sprayed coatings. This paper describes the state of the art of thermally sprayed coatings as alternatives for other coatings. Published literature data and a wide range of own tribological investigations and field tests, reveals the potential for other applications.

Co-based alloys are used extensively in applications requiring good wear resistance, corrosion and heat resistance. This paper presents the wear data of Co-based plasma sprayed coatings for aeronautical applications at temperatures up to 750 deg C, evaluated in a pin-on-disk unit. Investigation of the coating structure and the wear mechanisms revealed the processing-structure-functionality relationships. The analysis of the tribological results was supported by structure, microhardness and X-ray diffraction studies of the coatings. An SEM examination of the wear marks revealed the predominantly active wear mechanisms in each case. Paper includes a German-language abstract.

The tribological behaviour of WC-Co-Cr coatings deposited by HVOF and HVAF and WC-Co coating deposited by HVAF was investigated in pin-on-disc tests. Wear rates were determined and wear tracks on the coatings and counterbodies were investigated in SEM. The HVAF sprayed coatings showed greater wear resistance compared to the HVOF coatings. The main wear mechanism in the WC-Co coatings was adhesive wear. The cobalt matrix is lubricious, resulting in very low wear rates and low debris generation. The main wear mechanisms in the WC-Co-Cr coatings were adhesive and abrasive wear. Adhesive wear results in pull-outs that are trapped in the contact zone and act as a third-body abrasive. Particle pull-out of the coating significantly increases the wear rate of the coated specimen. The HVAF WC-Co-Cr coatings proved to have a better resistance to particle pull-out which reflected in a considerably lower wear rate than the HVOF WC-Co-Cr coatings.