The ongoing development of new HVOF spray guns for internal diameters is driving demand for finer spray powders. Fine spray powders (< 20 µm) are necessary to achieve short spray distances, but they also create new challenges. The first steps in the thermal spray process chain are powder preparation and feeding. If these steps are not stable, no sufficient coating quality can be obtained. This present work compares volumetric and fluidization powder feeding methods and investigates the feeding behavior of agglomerated and sintered WC-Co(Cr) powders with particle fractions of -5+15 µm, -20+5 µm, and -10+2 µm. Particle size fraction was measured ex situ by laser diffraction and particle outflow from the injectors was recorded in-situ by means of particle image velocimetry.

This research looks at the work of Polycontrols in the field of additive manufacturing. Several technological breakthroughs are presented. We mainly draw upon tests performed with the ultrafine powder feeder at the National Research Council of Canada, and data gathered from different systems operating worldwide in aerospace facilities. This paper outlines the very unique capabilities of the feeder in the field of cold spray and finely-dispersed-particle air plasma spray (FAPS).

This study investigates the influence of powder feed rate on the deposition efficiency of HVOF sprayed materials, including NiCr, FeNiCrMoCSi, 316L stainless, Cr 3 C 2 /NiCr, WC-Co/Cr, and WC-Cr 3 C 2 /Ni. A liquid-fuel HVOF spray gun is used in combination with a modified injector block that increases the number of powder injection ports from two to four. In the experiments, powder feed rates were incremented from a baseline of 100 g/min to 400 g/min for the metal powders and up to 500 g/min for the cermets, while measuring deposition efficiency for each run. Coating samples were also produced for metallographic analysis, hardness testing, and the evaluation of porosity and roughness. All results are presented and discussed along with potential implications on coating costs.

This paper reviews the capabilities of portable low pressure cold spraying systems and presents examples of the repairs that have been made and the different materials involved. It discusses the recent development of ceramic nozzle inserts that extend continuous operating time to more than 10 h and non-pressurized rotating-vibratory powder feeders that provide higher, more stable powder feed rates for production environments.

Studies on atmospheric plasma spraying have generally focused on the influence primary parameters such as gas flows and plasma current. However, the APS process is also influenced by a large number of disturbance variables including electrode wear, cooling system irregularities, and disruptions in powder injection. This study investigates both the cause and effect of each of these factors in the context of aluminum oxide spraying. Numerous measurements are made showing how electrode wear, cooling fluctuations, flow measurement inaccuracy, and variations in powder feed rates affect in-flight particle characteristics, deposition efficiency, and layer thickness. Paper includes a German-language abstract.

Aluminum oxide ceramic coatings are widely used to extend the life of machine components. These protective layers are usually applied via atmospheric plasma spraying. In this study, alumina coatings are produced using a low-power plasma spraying method and assessed based on hardness, porosity, and microstructure. Test results show that alumina coatings applied using low-power plasma spraying with internal injection are harder than those produced using traditional APS techniques. The effect of process parameters, including current, voltage, powder feed rate, and plasma energy, is also investigated. Paper includes a German-language abstract.

Arc instability in conventional plasmas causes variations in particle properties that can lead to poor coating quality and low deposit efficiencies. In this paper, the authors explain how the use of molecular gases with higher enthalpy mitigates the effects of arc instability, resulting in higher spray rates, better coating quality, and lower cost per kilogram of material deposited. They also describe the design and operation of a commercial high-enthalpy plasma spraying system and present and analyze coatings of different materials thereby produced. Paper includes a German-language abstract.

The demand for highly continuous thermal spray deposition processing to gain manufacturing efficiency and enhanced control of deposition microstructure has driven the search for powder feedstocks that exhibit uniform flow behavior in pneumatic feeding devices even at low carrier gas flow ratios. This paper compares the continuous powder feeding characteristics of one type of feeding device for two different powder alloys fabricated by a representative set of powder processing methods, including spray dried, fused (cast) and crushed, and inert gas atomized. Powders were fabricated by both commercial vendors and Ames Laboratory processing equipment. The powder mass flow rate was found to depend directly on the apparent density of a specific powder type instead of the dry powder flowability, as initially expected.