With appropriate process control, near-net-shape coatings can be successfully applied to parts with complex geometries using HVOF spraying and fine cermet powders. This study assesses the influence of critical process parameters on the deposition rate and properties of HVOF coatings produced using fine agglomerated WC-12Co powder (2-10 µm) with nanosized WC particles. Spray angle, standoff distance, gun velocity, track pitch, and backside air cooling pressure were varied during the experiments in order to determine their effect on coating hardness, roughness, and porosity as well as deposition efficiency. Variations in spray parameters were found to have a significant effect on deposition rate and coating properties.

In this study, a path strategy for robot-based HVOF spraying is developed via deposition simulations. The simulations include the analysis of the spray plume footprint and the consideration of robot dynamics in the path planning strategy. A fine WC-Co powder was used as the feedstock material.

This study investigates the sliding wear behavior of HVOF sprayed coatings derived from conventional, fine, and nanostructured WC-Co powders. The results show that WC-Co coatings produced from fine and nanostructured feedstocks have significantly higher wear resistance and lower friction coefficients than coatings derived from conventional sized powder. This is attributed to scaling effects in the microstructure and phase evolution of the coating material as explained in the paper.

This study investigates the influence of component geometry, particularly the outer radius of curved surfaces, on the hardness and porosity of HVOF-sprayed WC-Co coatings as well as the deposition rate. A fine agglomerated and sintered WC-12Co powder of spherical shape was sprayed on steel substrates. Process parameters were held constant, while the radius of curvature was varied between 5 and 40 mm. The results show that HVOF spraying is better for depositing fine particles on curved surfaces than other spray processes, although the deposition rate decreases compared to flat substrates.

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.

Thermal sprayed WC-Co coatings are widely used for various industrial applications due to their high hardness and corresponding wear resistance. Recently, it has been reported by many researchers, that the use of agglomerated and sintered micron powders with submicron or nanosized carbides can provide the deposition of WC-Co coatings with enhanced or even superior mechanical and tribological characteristics. This can only be achieved, as long as optimized coating conditions adapted to the specific thermo-kinetic behavior of such powders are considered. However, the porosity in the coating morphology represents an inherent problem when using powders with conventional agglomerate size (10-50 µm) and high internal porosity. Consequently, a minimum coating thickness is often necessary to provide suitable wear properties, which reduces the shape or dimensional accuracy when applying such coatings to complex surfaces. In addition, a reduction in surface roughness of the coating cannot be accomplished by fine carbides, since large agglomerates are employed. In this study we used two different fine WC-12Co powders in the HVOF process to manufacture nanostructured coatings with high hardness, moderate toughness, low surface roughness and low porosity. The first powder is a fine agglomerated and sintered powder with particle size of -10+2 µm and carbides in the ultrafine range (400 nm) The second one consists in two loose mixtures of fine Co (Fisher grain size FSS = 3.5 µm) with (a) WC (FSS = 3.0 µm) and (b) WC (FSS = 0.8 µm). Statistical design of experiments (DoE) were utilized to determine main effects of spray conditions on coating properties. Mechanical properties, microstructure and the phase development has been correlated to the in-flight particle behavior. Phase analyses were performed by XRD using synchrotron radiation.