During the last 20 years, numerous scientists have studied the formation of thermally sprayed WC-Co coatings. Most of them focused on the direct connection between parameter variations and coating properties, such as the microstructure, wear or hardness. As the formation of single splats is the foundation for any thermal spray coating, this work focuses on the investigation of single splat morphologies. The aim of single splat interpretation is to determine the influence of different spray parameters on the morphological distribution of particles inside the flame. This distribution is indispensable to understand the formation of each coating layer during the process. Unfortunately, most of the methods presently used for generating single splats do not allow an assignment of each splat to its radial position in the flame. A method to create a footprint of a spray jet with an extremely short exposure time was used in this paper. The resulting field of splats enables the assignment of the splats on the specimen to their radial position in the cross-section of the spray jet. The footprints were analyzed by correlating the quantities and morphology of the splats to measurements of the spray jet properties and the splat’s radial position inside the jet.

Numerous factors, such as the spray parameters and non-predictable conditions, during the spraying process influence the properties of thermally sprayed coatings. However, the condition of the particles at the moment of impact on the substrate is the most crucial factor for the morphology and the mechanical properties of a coating. Thus, nowadays particle analyzing systems are employed in order to explain the relation between the process parameters and the properties of a layer. Yet, modeling of thermal spray processes is conducted disregarding particle parameters and only correlating process parameters with layer properties. This article presents a new approach on process modeling, for relating spray parameters to particle-inflight conditions. The modeling of the particle properties in relation to the process parameters shall allow conducting targeted adjustments during the running process, to optimize particle properties. This method will enable to influence coating properties during the spraying process, eliminating the influence of unpredictable environmental or process-related disturbances. In a series of experiments, spray beam properties were measured in an HVOF thermal spray process with agglomerated and sintered WC-Co powder. Spray parameters were correlated to the particle-in-flight conditions, which were measured by utilizing two particle analyzing systems.

Hydroxyapatite Composite (HAC) Coatings made by Low Pressure Gas Dynamic Spray (LPGDS) on the grit blasted Ti alloy substrate were studied. The powder feedstock for the HAC coating by LPGDS was prepared by mixing HA powder with Phosphate Glass particles in polyvinyl alcohol, drying and stirring. As-sprayed HAC films on the substrate were heat-treated by two steps (400-500°C and 600-900°C) and their physical characteristics were investigated by scanning electronic microscopy (SEM), X-ray diffractometer (XRD). During sintering-heat treatment, HA particles were consolidated and melted to form a dense and homogeneous coating layer which exhibits the grain structure. Application of HA-glass feedstock is found to be effective for Cold Spray HA based coatings.

Thermal spraying processes are well known in industry for providing relatively dense components. The Gas Dynamic Spray (GDS) technologies are a growing alternative, especially after the great success of certain applications such as plasma and thermal spray formed components. One of the advantages of GDS is the possibility to obtain complex thin-walled shapes of various powder materials and composites. The optional post-spraying processes such as sintering, sizing and little machining may be applied. Using the low pressure radial injection GDS method, some new thin wall components have been formed. The process involves the automatic mechanical removal of sprayed ring components from a mould. Both the structure and properties of powdered material along with the GDS technology itself were studied. The main spraying and mould parameters were found to achieve high durability of moulds, which allowed the realization of a large scale GDS forming technology.