Ball-milling treatment of gas-atomized Ti 48Al 2Cr 2Nb powder and its effect on preventing smoking during electron beam powder bed fusion building process

Abstract

Smoking is the explosive powder-scattering by Coulomb interaction, and it is a difficult issue to avoid in electron beam powder bed fusion (EB-PBF) process. In this study, we investigated the effectiveness of mechanical ball milling to prevent powder-bed smoking in EB-PBF using gas-atomized Ti 48Al 2Cr 2Nb powder. The surface of the gas-atomized powder was confirmed to be composed of outer porous TiO 2 + Al 2 O 3 and inner dense Al 2 O 3 rich bilayer oxide film that gives rise to a high electrical resistance. The electrical resistivity after ball milling with 300 rpm (BM300) was significantly decreased due to the formation of the degenerated TiO 2 and Ti n O 2n–1 -type suboxide. The electrical equivalent circuit of the powder bed of BM300 was essentially a single resistor-capacitor (RC) circuit, owing to the mechanically deformed outer oxide film. Besides, through ball milling at 300 rpm for 30 min, the relaxation time of the gas-atomized powder was significantly decreased 1/16 times, and its electrostatic force decreased approximately 1/57 times. Finally, the suppressing effect of smoking on the EB-PBF building process was experimentally examined using ball-milled powders. It was clearly demonstrated that mechanical ball milling is an effective method to restrict smoking during the EB-PBF building process without any chemical treatment and composition change.