Thermal spray of polymers has had limited investigation due to the narrow processing windows that are inherent to polymer powders, especially their low temperatures of thermal degradation. The polymer poly aryl ether ether ketone (PEEK) has a high thermal degradation temperature and high resistance to alkaline and acidic attack. These properties led to PEEK being selected for investigation. To minimise thermal degradation of the particles, the high velocity air fuel (HVAF) technique was used. To investigate the effect of substrate pre-treatment on single splat properties, single splats were collected on aluminium 5052 substrates with six different pretreatments. The single splats collected were imaged by scanning electron microscopy (SEM) and image analysis was performed with ImageJ, an open source scientific graphics package. On substrates held at 323°C it was found that substrate pretreatment had a significant effect on the circularity and area of single splats, and also on the number of splats deposited on the substrates. Increases in splat circularity, area, and the number of splats deposited on the surface were linked to the decrease in chemisorbed water on the substrate surface and the decrease of surface roughness. This proved that surface chemistry and roughness are crucial to forming single splats with good properties, which will lead to coatings of good properties.

PEEK was sprayed with a Browning Aerospray HVAF thermal spray gun to enable the study of the wetting and interaction of single splats with an aluminium 5005 substrate. Single splats were obtained by exposing the substrate to the spray flame for 0.02 s by dropping a steel shutter with a 25 mm aperture milled in the centre. The single splats were then analysed through SEM (scanning electron microscopy) and FIB microscopy (focussed ion beam). Splat shape was found to be dependant on nozzle length, with a 100 mm nozzle resulting in more splashing, and a 450 mm spray distance providing more disc splats. PEEK splats do not wet the aluminium oxide surface well. Porosity occurs independently of nozzle length, in the form of cracks and pores in the splats, some cracks completely segmenting a splat.