Factors determining the flowability and spreading quality of gas-atomized Ti-48Al-2Cr-2Nb powders in powder bed fusion additive manufacturing

A high-quality powder bed is necessary for obtaining high-quality products using powder bed fusion-based ad-ditive manufacturing. In this study, mechanical ball milling was suggested to improve the flowability and spreadability of gas-atomized (GA) Ti-48Al-2Cr-2Nb powder in the powder bed fusion additive manufacturing process. The deformation mechanism of the GA powder significantly differed depending on the ball milling media. Surface grinding mainly occurred during Al2O3 ball milling, while the pulverization was dominant in WC ball milling because of the higher impact force. The flowability of the GA powder under dynamic conditions was improved after Al2O3 and WC ball milling owing to the decreased cohesive force. The high cohesive force in the GA powder under dynamic conditions was attributed to the electrostatic force caused by charge accumulation on the oxide film. The packing density of GA powder was increased after WC ball milling despite the formation of numerous irregular particles owing to the synergetic effect of rapid energy dissipation, minimized wall effect, and void filling effect. Furthermore, the spreadability of the GA powder was improved by ball milling because of the decrease in the cohesive force. Therefore, it was demonstrated that the flowability and spreadability of the GA powder can be improved via ball milling because of changes in particle size, shape, and surface properties.