The Effect of Spraying Parameters of the Inner-Diameter High-Velocity Air-Fuel (ID-HVAF) Torch on Characteristics of Ti-6Al-4V In-Flight Particles and Coatings Formed at Short Spraying Distances

High-velocity air-fuel (HVAF) is a combustion process that allows solid-state deposition of metallic particles with minimum oxidation and decomposition. Although HVAF and cold spray are similar in terms of solid-state particle deposition, a slightly higher temperature of HVAF may allow further particle softening and because of it, more particle deformation upon impact. The present study aims to produce dense Ti-6Al-4V coatings by utilizing an inner-diameter (ID) HVAF gun. The ID gun is considered a scaled-down version of the standard HVAF with a narrower jet, beneficial for near-net-shape manufacturing. To explore the potential of the ID gun in the solid-state deposition of Ti-6Al4V, an investigation was made into the effect of spraying parameters (i.e., spraying distance, fuel pressure, feeding rate, traverse speed, and nozzle length) on the characteristics of in-flight particles and the attributes of the as-fabricated coatings such as porosity, phases, and hardness. For studying in-flight particles characteristics, using online diagnostics is challenging due to the exothermic oxidation reaction of fine particles, while larger particles are too cold to be detected from their thermal emission. However, DPV diagnostic system was successfully employed to differentiate the non-emitting solid particles from the burning ones. It was found that increasing air and fuel pressure of the ID-HVAF jet as well as increasing the nozzle length led to an increase in the velocity of the in-flight particles and resulted in improved density and hardness of the as-sprayed samples. However, increasing the spraying distance had a negative effect on the density and hardness of the manufactured coatings.

Automated summary

High-velocity air-fuel combustion process can deposit metallic particles with minimum oxidation and decomposition. The study focused on using an inner-diameter HVAF gun to produce dense Ti-6Al-4V coatings. Increasing air and fuel pressure and nozzle length improved particle velocity and resulted in improved density and hardness of the coatings, while increasing spraying distance had a negative effect.