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.

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.

Coatings deposited by thermal spraying are widely used for applications where enhanced resistance to wear is a crucial factor. In this work we focused on HVOF and plasma sprayed WC-Co, NiCrSiB, Cr 3 C 2 -NiCr, AISI 316L and Cr 2 O 3 coatings. The materials were examined by wet slurry abrasion tests, microhardness and roughness measurements. Systematic fractographic analysis in SEM was devoted to determine the main failure mechanisms of selected coatings. The WC-Co coating exhibited the lowest wear rate while 316L coating exhibited the highest wear rate. The plasma sprayed Cr 2 O 3 coating exhibited wear rate higher than HVOF sprayed cermet coatings but lower than metal coating. In most cases it was found that the higher microhardness, the higher is the wear resistance of the coating. The most favorable microstructure was found to be a mixture of hard particles dispersed in tough metal matrix. Matrix-like structure and internal splat microstructure were the main factors controlling the wear resistance of the investigated HVOF and WSP coatings.

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.