This paper describes the properties and behaviors of alumina and titania coatings that have recently been produced using suspension spraying techniques. It examines coating microstructures and phase compositions are shows how they are influenced by different operating parameters and interactions. A selection of new experimental results obtained by the authors is also presented. In the case of Al 2 O 3 , the goal was to retain a high ratio of the thermodynamically stable α-phase. In the case of TiO 2 , the spraying process was optimized to preserve the anatase phase in order to obtain photocatalytically active layers.

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.

Functional characteristics of materials including the mechanical, electrical, environmental and tribological performance can be significantly improved using nanostructured feedstock. Over the last few years much research has been dedicated to the development of thermal spraying techniques with liquid precursors to prepare fine nanostructured coatings. In this work nanostructured ceramic coatings were prepared using the technique of suspension spraying. Titania and alumina powders with sizes in the nanometre to submicrometre range were used to prepare aqueous and alcoholic suspensions. Atmospheric plasma and high-velocity flame were employed as enthalpy sources. The morphologies and crystalline structures of the sprayed ceramics were mainly characterised by SEM and XRD. The aim of this work was to carry out a comparative study and to discuss the nanostructured ceramic coating microstructures as a function of the physicochemical properties of the feedstock suspensions and spraying parameters.

High power diode lasers (HPDL) at the level of ? 6 kW are efficient cladding tools in heavy engineering applications where thick (up to 5 mm) wear and corrosion resistant coating layers are required. Large beam geometry makes possible the overlap of thick 20 mm wide cladding tracks side by side without coating defects. Compact size and closed cooling water circulation enable HPDL cladding process to take place also at a site of new or worn high-value machine parts, which have worn in operation or been damaged already during overseas transportation. Instead of moving parts of several tons’ weight, it would be perhaps more cost efficient to transport HPDL cladding unit.

Laser cladding is a surface treatment technology in which thick, dense and metallurgically adhered metallic layers are deposited on various structural steels with relatively low heat input, high accuracy and reproducibility. Laser cladding processes used in industrial cladding are largely based on the use of CO 2 or Nd:YAG lasers. High power diode lasers (HPDL) with rectangular beam spots are regarded as ideal laser sources for laser cladding processes, due to their compact size, high electrical to optical efficiency, easy operation, and low investment and running costs. In laser cladding of large surface areas, the affectivity of the laser cladding process becomes more important, i.e. high laser powers, wide laser beam spots, and high coating material feedrates are regarded as beneficial. In order to optimise the cladding process for such applications, special attention has to be put on devices used to deliver the coating power to the process. In the present work, various parameters in effective HPDL cladding are described and new approaches to optimised HPDL cladding process are described. The performance of a new HPDL cladding powder delivery nozzle will be presented and discussed. Abstract only; no full-text paper available.

The repair and quick geometrical changes of components and tools are currently the most important applications of laser build-up welding. Advanced laser technology permits the integration of the main process steps into one machining center for a very efficient and flexible manufacturing process. The solution presented in this paper consists of a 3axes CNC milling machine, in which a 3 kW Nd: YAG laser, a coaxial powder nozzle, and a digitizing system are integrated. All functions (data processing, laser process, powder feeding, and milling) are controlled by one CNC controller using specially developed software. In the first step the workpiece needs to be adjusted to the machine table. Then the contour of the damaged surface is determined by either an optical or mechanical digitizing system. Using the resulting data, a software system generates automatically the laser build-up strategy and the CNC programs for the laser and the milling processes. After laser free-forming, a raw piece with an oversize of 0.3 to 0.6 mm is made. From this geometry the end contour is milled with an accuracy of some 10 microns. This way the machine produces a completely finished tool.

Titanium oxide is established as an oxide material for thermally sprayed coating solutions and has received increasing interest over the last few years. Scientific and technological research focuses on electrical conductivity, solid lubrication and photocatalytic properties of titanium oxide (TiOx) coatings of differing stoichiometry. The aim of this study was to investigate the effect of oxygen loss by reduction with hydrogen occurring in the conditions of vacuum plasma spraying (VPS) from commercial titanium oxide feedstock on coating microstructure, hardness, phase composition, abrasion wear resistance and electrical resistivity. The X-ray diffraction pattern showed the presence of rutile, with peaks decreasing in intensity with increasing hydrogen content in the plasma-forming gas. The intensities of the peaks showed significant deviations from those of the standard. An increase in hydrogen flow rate did not influence the coating microstructure, hardness or abrasion wear resistance, but it caused the electrical resistivity to decrease. VPS coatings prepared from commercial fused and crushed powder show a resistivity in the range of 0.01-0.1 Ohm*cm, which corresponds exactly to the range published in the literature. Comparison with results for APS- and HVOFsprayed coatings reveals that VPS coatings yield the best combination of abrasion wear resistance and electrical resistivity when commercial titanium oxide spray powder is used.