Abstract
The application of fine powders in the thermal spray technology represents an innovative approach to apply dense and smooth near-net shape coatings on tools with complex geometry. However, this aim can only be achieved, as long as the influence of the handling parameters of the spray process such as the spray angle are sufficiently understood. In this study the influence of the spray angle on the deposition rate as well as on the coating properties (microhardness, roughness and porosity) of HVOF-sprayed, fine-structured coatings is investigated. A fine agglomerated and sintered WC-l2Co powder (agglomerate size: 2-10 pm, WC-particle size: FSS = 400 nm) was used as feedstock material. It has been shown that HVOF spraying of fine powders is less susceptible to an alteration of the spray angle than most other thermal spray processes such as plasma- or arc-spraying. The reduction of the spray angle results in a decrease of the deposition rate, while no significant degradation of the coating properties was found up to 30°. However, at spray angles below 30° the coating strength is negatively affected by the formation of pores and cracks.
