The growing need for new materials and material combinations with superior properties for severe service applications has led to the development of near net-shape forming techniques for certain materials, such as superalloys, refractory metals (Ta, W, and Mo) and highly reactive metals (Ti and its alloys). Vacuum plasma spray (VPS) was used to produce dense Ti-6Al-4V deposits for mechanical properties evaluation. Spherical Ti-6Al-4V powder, produced by Plasma Atomization (PA), a novel patented powder fabrication technique, was used as the starting powder. Plasma atomized Ti-6Al-4V powder characteristics include: high purity, tight particle size range, highly spherical with no attached satellites, and excellent flowability. The resulting as-sprayed Ti-6Al-4V deposits were dense and low in oxygen content. Thermal treatment was conducted after spraying in order to improve the structure and the properties of the spray formed material. The mechanical properties of the material, including tensile strength, elongation and hardness, in both the as-sprayed and the heat treated conditions were compared. The mechanical properties of these preliminary VPS Ti-6Al-4V specimens indicate that the combination of high purity starting powder and controlled environment deposition can be used to produce dense spray formed Ti-6Al-4V structures with properties comparable to those of cast or sintered powder metallurgy parts.

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.