Wear leads to high material and energy losses in various industries. The manufacturing of novel nano-carbide WC/Co powder feedstock materials promises a further increase in the performance of thermally sprayed wear protection coatings. A novel experimental powder and a commercial ultra-fine carbide WC/CoCr reference are thermally sprayed onto a 1.0038 substrate by High Velocity Air Fuel (HVAF) spraying. The specimens are metallographically prepared and analyzed by means of light microscopy (LM) and scanning electron microscopy (SEM). Vickers Hardness testing is conducted by microindentation and the porosities are determined by optical image analysis. X-ray diffractometry (XRD) analysis are used to investigate the phase retention. Fine nanocrystalline WC-structures are preserved in the dense coatings. A significant effect of powder type on the porosity of the coating was found. No systematic relationships could be identified between the coating structure and the parameter settings. It was possible to influence decarburization via both the powder type and the selected parameters. The resulting experimental coatings exhibit high hardness values in the range of the commercial ultrafine carbide WC reference. The novel nano-structured coating can contribute to reduced wear and therefore improve the efficient utilization of critical raw materials like tungsten.

Surface quality lifetime and wear resistance of protective coatings can be improved by decreasing carbide grain size from submicron to nanoscale. In this study, experimental WC-CoCr powders were manufactured via novel powder manufacturing approach using water-soluble raw materials. Produced powders were sprayed with the High-Velocity Air-Fuel (HVAF) spray process to control the particle temperature and to avoid in-flight decomposition of the nanocarbides. As a result, dense and wear resistant coatings with nanosized carbides were produced. Reference coatings were sprayed using commercial sub-micron WC-CoCr powder to compare the properties of the experimental coatings to the current state-of-the-art. Phase composition and microstructural characterization of the coatings were carried out with X-ray diffraction and electron microscopy, respectively. Mechanical properties were studied by using microhardness tester, as well as rubber wheel abrasion and cavitation erosion wear tests. The wear surfaces were characterized after the abrasion and cavitation erosion tests to understand the effect of nano-carbides on degradation mechanisms. Coatings with the nanosized carbides in the structure showed excellent mechanical properties in wear testing, and even outperformed reference coatings in cavitation erosion test. Based on the obtained results, these novel nano-carbide coatings are promising alternatives for demanding applications in which better surface quality lifetime is vital.

HVOF-sprayed WC–10wt%Co–4wt.%Cr coatings were obtained using experimental feedstock powders (manufactured by spray-drying + sintering), containing nanometric carbide particles. Three reference coatings were also deposited using commercially-available powders containing sub-micrometric carbide particles. The coatings obtained from nanostructured powders, although affected by decarburisation phenomena, contained very fine carbide particles (~200 nm size). Those obtained from commercially-available powders simultaneously exhibited sub-micrometric (~400 nm size) and micrometric carbide particles, and were much less decarburised. Sliding wear tests performed at room temperature against sintered Al 2 O 3 balls showed the occurrence of brittle fracture wear (detachment of near-surface material by local brittle cracking) on the nanostructured coatings, which were embrittled by decarburisation. The reference coatings, by contrast, exhibited either ductile wear behaviour (plastic deformation, pull-out of single carbide particles) or a mix of both ductile and brittle wear mechanisms. When the decarburisation of the nanostructured coatings was not too extensive, their wear loss was comparable to that of the reference ones. At 500 °C, the wear behaviour of all coatings was dominated by abrasive grooving, on account of thermal softening. The most decarburised nanostructured coatings, however, still experienced brittle cracking as well.

HVOF spraying was used to prepare coatings from mechanical blends of Cr 3 C 2 -25NiCr and NiCrBSi powders. The aim of the work was to study the influence of addition of a metallic phase on tribological properties of the coatings in sliding conditions. Tribological properties of the coatings were characterised under dry sliding. Addition of NiCrBSi decreased the coefficient of friction in high temperature, pressure and sliding speed.

This study shows that thermal spraying is a viable technique for the deposition of barium hexaferrite layers suitable for microwave absorption applications. More specifically, the study shows that impact quenching of molten BaCoTiFe 10 O 19 hinders the crystallization of the hexaferrite phase. Consequently, when spraying conditions induce near-full melting of the feedstock, the coating mostly consists of spinel and a glassy phase, a state with poor magnetic properties. These phases can be converted to hexaferrite by annealing, but in order to obtain enough crystalline hexaferrite in as-deposited layers, a controlled amount of unmelted material must be preserved. Atmospheric plasma spraying proved to be well suited for this purpose, producing layers with excellent magnetic properties, close to those of pure crystalline BaCoTiFe 10 O 19 . In these coatings, dense regions entrain many unmelted agglomerates of micron-sized particles, effectively preserving the hexaferrite phase.

Superior wear performance combined with excellent friction properties against metals makes chromium oxide (Cr 2 O 3 ) an interesting coating material for many industrial applications. However, Cr 2 O 3 is a challenging material for HVOF spraying due to its high melting temperature. Fracture toughness and lamella cohesion of a coating is limited and may be improved by using ceramic-ceramic –nanocomposite powders, which forms phases with improved properties. In this study Cr 2 O 3 -TiO 2 systems were selected aiming to improve the toughness and lamella cohesion of coating without reducing the excellent wear properties.

Perovskites are considered as potential materials in solid oxide fuel cells (SOFC) for different reasons at different parts of the fuel cells. Perovskites such as La 0.8 Sr 0.2 MnO 3 (LSM) and other compositions are electrically conductive which is necessary for SOFC applications. One possible application is protection coating for interconnect plates (bipolar plate) to avoid chromium oxide evaporation from the surface of ferritic stainless steel. Different commercial and experimental perovskite powders were sprayed by plasma and HVOF spraying under different spray conditions. Spraying of pervoskites was found to be challenging and required careful parameter optimization in both spray methods. Microstructure and phase structure of the coatings were investigated. A very fine crack structure, possibly caused by low mechanical strength and low ductility of the compounds, was easily formed in coatings prepared by plasma and HVOF spraying. Spraying method, parameters and spraying atmospheres were found to affect the stability of the perovskite compounds due to low chemical stability at high spray temperatures. Oxygen deficiency or oxygen surplus was concluded to cause distortion of the compounds crystal structure, causing thus shifting of XRD-peaks due to change of lattice parameters. Electric conductivity was affected by the crystal structure.

The potential of the high velocity oxy-fuel (HVOF) thermal spray process to produce coatings with reduced porosity is well known. The ability to produce high density ceramic coatings offers potential in high performance applications in the fields of wear, corrosion resistance and dielectric coatings. It has been, however, demonstrated that benefits from HVOF ceramic coatings can be obtained only if particles are melted enough and good lamella adhesion is produced. Therefore, due to the operational limits of the HVOF process, the process-structure- relationship must be well optimized. One strategy to improve melting of ceramic particles in the relatively low flame temperatures of the HVOF process is to modify particle crystal structure and composition. In this paper, the effects of the powder structure and the composition on coating microstructure and deposition efficiency of the HVOF spray process are studied. The effect of fuel gas, hydrogen vs. propane, was also demonstrated. The studied materials were agglomerated alumina- and titania-based pure and composite powders. Coating properties such as microstructure, hardness, and abrasive wear resistance, were compared to the coating manufactured by using conventional fused and crushed powders.

HVOF sprayed WC-CoCr coatings are used to in wear and corrosion applications. Commercially available hard metal powders for HVOF spraying are normally manufactured from virgin raw materials. In the present work, the possibility to manufacture WC-CoCr spray powder with excellent properties and quality from recycled cemented carbide tools and tool bits was studied. The powders were manufactured from hard metal scrap by a series of processing steps. The powders were sprayed by using the HVOF process. The properties of the powders and coatings were studied and compared to those of commercially available state-of-the-art WC-CoCr powders and coatings with the same nominal composition. Experimental powders worked well during spraying and the quality of the coatings was equal or even better than that of the reference coatings. Equal or even better corrosion properties compared to reference coatings were obtained with the new spray powder manufactured from recycled hard metal.