Abstract
In the twin wire arc spraying (TWAS) process, it is common to use compressed air as atomizing gas. Nitrogen or argon also are used to reduce oxidation and improve coating performance. The heat required to melt the feedstock material depends on the electrical conductivity of the wires used and the ionization energy of both the feedstock material and atomization gas. In the case of ZnAl4, no phase changes were recorded in the obtained coatings by using either compressed air or argon as atomization gas. This fact has led to the assumption that the melting behavior of ZnAl4 with its low melting and evaporating temperature is different from materials with a higher melting point, such as Fe and Ni, which also explains the unexpected compressive residual stresses in the as-sprayed conditions. The heavier atomization gas, argon, led to slightly higher compressive stresses and oxide content. Compressed air as atomization gas led to lower porosity, decreased surface roughness, and better corrosion resistance. In the case of argon, Al precipitated in the form of small particles. The post-treatment machine hammer peening (MHP) has induced horizontal cracks in compressed air sprayed coatings. These cracks were mainly initiated in the oxidized Al phase.
Highlights
In the twin wire arc spraying (TWAS) process, the spray particles are atomized off the molten part of the intersecting wires by a steady and continuous fast-moving atomization gas stream [1,2,3,4,5]
The arc ignition in the TWAS process determines the primary stage of the particle initiation, where the arc melts the feedstock material, and the atomization gas detaches droplets, in subsequent process stages known as spray particles, out of the molten parts of the feedstock [1,3]
The spray particles ization gas and metal vapor determine the conductivity of the gap between the approaching tion and temperature loss during their inflight phase are due to the velocity di wires and the induced arc heat in the TWAS process [13]
Summary
In the twin wire arc spraying (TWAS) process, the spray particles are atomized off the molten part of the intersecting wires by a steady and continuous fast-moving atomization gas stream [1,2,3,4,5]. The arc ignition in the TWAS process determines the primary stage of the particle initiation, where the arc melts the feedstock material, and the atomization gas detaches droplets, in subsequent process stages known as spray particles, out of the molten parts of the feedstock [1,3]. The formation of these droplets depends directly on the wires used, the adjusted arc energy, type and pressure of the atomization gas, and the nozzle configuration. High atomization gas velocity with low turbulence led to smaller and faster spray particles, which, in turn, produced coating with low porosity and oxide content, as well as increased adhesion [5,7,8]
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