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.

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.

The composition WC-(W, Cr) 2 C-Ni is one of the standard hardmetal compositions used for the preparation of thermally sprayed coatings by high velocity oxy-fuel (HVOF) spraying. Surprisingly, this composition has been poorly investigated in the past. Frequent use of the commercial designations WC-“CrC”-Ni, WC-Cr 3 C 2 -Ni, and WC-NiCr indicate the insufficient knowledge about the phase compositions of the powders and coatings. In this paper, the processability of five commercial feedstock powders was studied. These feedstock powders were of different origin and were sprayed with two different liquid-fueled HVOF systems (K2 and JP-5000). The microstructures and phase compositions of the powders and the coatings were studied. Focus was on the appearance, composition, and distribution of the (W, Cr) 2 C phase, which is either formed or changes its Cr/W ratio during the spray process. The composition of the (W, Cr) 2 C phase was estimated from the lattice parameters. Hardness, density, and Young’s modulus were determined for the coatings. Additionally, the abrasion wear resistance of the coatings was studied. Unlike WC-Co and Cr 3 C 2 -NiCr, WC-(W, Cr) 2 C-Ni is not a simple binary hard phase-binder metal composite. The excellent properties of this composition, for instance, its oxidation and corrosion resistance, will surely attract more attention to this composition than it has in the past.

Tungsten carbide – cobalt powders (WC-17wt.%Co) were plasma sprayed by a water-stabilized system WSP. A matrix of experiments with variable feeding distances and spray distances was carried out. Thinner coatings were carried out on carbon steel substrates and thicker coatings on stainless steel substrates to compare fast cooling conditions – the former with slower cooling conditions. Basic characterization of coatings was done by XRD, SEM and light microscopy plus image analysis. Microhardness was measured on polished cross sections. The main focus of investigation was on resistances against wear in dry as well as wet conditions. The appropriate tests were performed with set-ups based on ASTM G65 and G75, respectively. The influence of spray parameters onto coating wear performance was observed. The results of mechanical tests are discussed in connection with changes of phase composition and with the character of the coating’s microstructure. The results show that for obtaining of the best possible WC-17Co coating with WSP process, from the viewpoint of wear resistance, the desired parameters combination is long feeding distance combined with short spray distance.

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.