This paper investigates the mechanical properties of plasma-sprayed Al 2 O 3 -TiO 2 coatings. Micro and nano powders were deposited on hot and cold substrates under different conditions using atmospheric and vacuum plasma spraying. The coatings were then characterized based on microstructure, hardness, phase composition, abrasive wear rate, and adhesion strength. It is observed that Al 2 O 3 -TiO 2 layers are very dependent on the coating system, powder form, and spray parameters used. The layers sprayed with nanopowder in a vacuum were found to have the best combination of properties. Paper includes a German-language abstract.

A systematic study of sample preparation methods tailored to different types of thermal spray coatings was recently conducted. This paper presents the results of investigations on polishing methods and materials and their effect on the quality of cuts. The results show that the type of polishing cloth used has a major influence on layer breakouts, while the direction of rotation and embedding medium have relatively little effect. Paper includes a German-language abstract.

In order to properly characterize the entire deposition process, evaluation of the coating, including a reliable metallographic preparation technique which reveals the true microstructure, must be performed. Often, recommended metallographic sample preparation methods for thermally sprayed coatings are generic and are not tailored to specific materials. They are time-consuming and, in some cases, may provide inaccurate details (pull-outs, smearing, etc). This could lead to a wrong interpretation of the coating quality. The aim of the investigation was to develop new metallographic sample preparation procedures tailored to different types of coatings (metallic, ceramic, multilayer and composites), in order to reveal a more representative microstructure. A comparative study of different preparation procedures for the examination of various as-sprayed coatings is presented using an optical microscope. The coatings were deposited by atmospheric and vacuum plasma spray (APS and VPS) and high velocity oxygen fuel (HVOF) processes. A separate approach is recommended for choosing the right metallographic preparation procedure for ceramic, metallic, or composite coatings. Applied load and positioning of the mounted sample during preparation are identified as key factors in developing proper procedures. The microhardness of the coating must be considered when determining the applied load. Interesting practical trends in preparation procedures that may lead to superior coating representation and, in some instances, cost and time savings are presented.

Pressure acid leaching (PAL) of lateritic nickel ores requires the use of extremely severe processing conditions (250 °C, > 4000 kPa, 98 % H2SO4). In addition to the severe corrosive nature of the acid solution, up to 30% of abrasive solids are present in the slurry. PyroGenesis Inc. has applied its expertise in materials science and thermal spray technologies into developing and commercially applying coatings for the protection of ball valve components used in PAL autoclaves. Vacuum plasma spray (VPS) and atmospheric plasma spray (APS) processes are used to apply coatings of metals and ceramics for corrosion and wear resistance, respectively. A comparative study on the microstructure and mechanical properties of different coatings, applied with the two processes, will be presented. Although APS coatings provide enhanced abrasive resistance, VPS coatings have shown the potential for superior properties. The extreme temperatures and pressures associated with the actual PAL conditions are too severe to simulate in laboratory conditions, hence, corrosion testing was not possible. Microstructural analysis, microhardness, adhesion, and abrasion testing were determined for each coating/processing combination.

Zirconia-based thermal barrier coatings (TBCs), produced using Vacuum Plasma Spray (VPS) technology, were recently subjected to burner rig testing. The VPS TBC performance was compared to TBCs deposited using conventional Atmospheric Plasma Sprayed (APS) and Electron Beam Physical Vapor Deposition (EB-PVD) techniques. All of the coatings consisted of an MCrAlY bond coat and a partially stabilized ZrO 2 -8%Y 2 O 3 (PSZ) top coat. The TBC coated pins (6.35 mm in diameter) were tested using gas temperatures ranging from 110CC to 1500°C. The pins were tested to failure under severe conditions (1500°C gas temperature, with no internal cooling). The initial testing indicated that under typical operating gas temperatures (1400°C), the VPS TBC performance was comparable, if not superior, to conventional TBCs. Following the encouraging results, thick composite TBCs, produced in a single-step operation, were investigated. Preliminary work on ZrO 2 -8% Y 2 O 3 /Ca 2 SiO 4 composite TBCs with interlayer grading included thermal shock testing and temperature drop measurements across the TBC. The composite TBC thicknesses ranged from 850µm to 1.8 mm. Initial results indicate that thick adherent composite TBCs, with high resistance to severe thermal shock, can be produced in a single step using the VPS process.