TiC-based coatings have proven to be very suitable candidates in various areas of thermal spraying when high corrosion and wear resistance is required. The most important advantages of these coatings are their high corrosion resistance compared to conventional coatings such as WC+Co and WC+Co+Cr, but also their low density. However, the main problem with HVOF spraying these materials is their high reactivity with the oxygen necessary for the flame. In this paper, Self-Propagating High-Temperature Synthesis-TiC+Ni-Ti base powder are processed with two different spray guns (Diamond Jet Hybrid (DJH) and CDS 100). This allows to compare the properties of the resultant coatings (wear and corrosion mainly) as a consequence of the main advantages of each variable (gun and gas) particularly in relation to the oxidation processes. It is observed that DJH coatings showed the best corrosion resistance whilst CDS coatings showed a corrosion potential closer to the steel value. Paper includes a German-language abstract.

This paper aims to characterise and to study several Ni-based alloys bond coatings and to determine the very best spraying conditions to achieve FGMs by means of a single gun with independent powder feed. First, adhesive layers made of NiCr, NiAl, and NiCrAlY were sprayed onto a steel substrate. All samples were tested by isothermal oxidation at 1000 deg C. The oxides formed and the conversions of the original oxides were studied on the samples and characterized using scanning electron microscope and EDS. It is observed that the study of three different bond coating sprayed with the same conditions reveals the best performance for the NiCr coating. Paper includes a German-language abstract.

In this paper, the processes associated with the formation of the tungsten carbide phase are studied and determined. A plasma-compressed WC+12%Co powder is sprayed with a CDS-100 gun. WC+Co coatings are obtained by (High Velocity Oxygen Fuel technology. The coatings are characterized using scanning electron microscopy, energy dispersive system, and transmission electron microscopy in order to record and identify the tungsten carbide phase. The mechanisms for the formation of the tungsten carbide phase are discussed. Paper includes a German-language abstract.

The feasibility of using the HVOF process for the thermal spray-forming of free-standing components has been investigated. HVOF spray forming offers a number of potential advantages compared to the established procedure of plasma forming, including increases in component density, and reduction in material decomposition during spraying. Using blends of carbide and superalloy powders in various proportions, HVOF spraying has been successfully used to form free-standing cylinders and cones of various lengths and thicknesses. Microstructural examination of the spray-formed material, using optical microscopy and scanning electron microscopy (SEM), has shown a homogeneous distribution of carbides in the superalloy matrix, with very low levels of porosity. Vickers microhardness has been measured on several sprayed forms. In order to complete the study of the different systems, abrasion (Rubber Wheel Test), friction (Ball on Disk Test) and erosion wear results have been obtained. These wear results have been used in order to evaluate the behaviour of the sprayed samples with a different powder percentage in the blends. Corrosion tests have been done to evaluate the corrosion resistance of the sprayed samples (ASTM D-1411).

The development of new spraying processes has increased the demand for high quality protecive coatings. Many thermal spraying processes have been developed to obtain coatings for a wide spectrum of materials and substrates. The High Velocity Oxygen Fuel (HVOF) process involves lower temperatures and higher velocities than those required by other techniques to obtain high density coatings. It is desirable to know which are the main factors that affect the corrosion behaviour of coated materials. The corrosion behaviour in chloride solution of a 34CrMo4 steel coated with different kinds of powder have been studied. The electrochemical corrosion of the coating-substrate system was characterised by corrosion potential measurements and potentiodynamic polarisations. Microscopic studies have also been performed by means of SEM. The corrosion tests were performed in synthetic marine water (ASTM D-1l41) in the presence of dissolved air. Polarisation resistances have been obtained from potentiodynamic studies. Measurements were carried out on two different (Ti,W)C+Ni coatings, as well as on the coatings obtained from a TiC+Ni-Ti powder which had been previously Ni coated using an electro less method. The best corrosion results were obtained from these last coatings.

The ball-on-disk wear test is widely used in order to determine the sliding wear resistance behaviour of the samples. Although a great number of authors consider the ball-on-disk test to be far from the real situation, the results obtained permit to develop a preliminary idea about the wear behaviour of the tested samples. During the development of the ball-on-disk test a wear track is formed on the test specimen. Scanning white light interferometry can be used to determine the surface damage in the wear track by obtaining images which relate to the surface profile and general morphology. From measurements on interferometric profiles it is possible to determine accurately the track depth and width and hence the volume of the coating removed by wear. It is also possible to determine by optical microscopy the volume of metal lost from the ball. The results obtained have improved the general understanding of the energy absorption during wear and of the observed changes in the coefficient of friction. The results obtained have shown that with the coatings of WC-Co deposited by the HVOF process no volumetric changes occur when using a WC-6%Co sintered ball. Tests on coatings containing TiC or Cr3CZ as the carbide phase or stainless steel coatings show significant losses of material.

The feasibility of using the HVOF process for the thermal spray-forming of free-standing components has been investigated. HVOF spray forming offers a number of potential advantages compared to the established procedure of plasma forming, including increases in component density, and reduction in material decomposition during spraying. Using blends of carbide and superalloy powders in various proportions, HVOF spraying has been successfully used to form free-standing cylinders and cones of various lengths and thicknesses. Microstructural examination of the spray-formed material has shown a homogeneous distribution of carbides in the superalloy matrix, with very low levels of porosity. Refinement of the procedure has allowed reduction of the matrix content, and the forming of fragile materials.

The technology of thermal spraying is approaching maturity, and in the quest to reduce production costs whilst maintaining coating quality, attention is turning increasingly to more cost-effective routes for the manufacture of the starting powders. One such route is self-propagating high-temperature synthesis (SHS), which reduces the required energy input for powder production. In this work, TiC-Ti+Ni and (Ti, W)C-Ni powders produced by the SHS process have been studied in the as-received and as-sprayed states, to evaluate the suitability of SHS powders for the production of wear-resistant coatings. The starting powders and the coatings produced by atmospheric-plasma and HVOF spraying have been characterised using analytical (XRD, EDS) and microscopical techniques (optical, SEM). The technological properties of the as-sprayed coatings have also been characterised, including hardness, wear resistance (using a Rubber-Wheel test (ASTM G-65)) and corrosion resistance (in marine water environment).