Powder stream characteristics of replaceable alumina and brass nozzle tips for directed energy deposition

Abstract

This study explores the performance of a replaceable alumina nozzle tip for directed energy deposition (DED), highlighting its advantages over traditional copper and brass nozzles, which are prone to high-temperature wear. Key innovations include a modular design for easy replacement of worn sections and the use of alumina, which provides superior resistance to mechanical, thermal, and chemical degradation, along with low laser absorption, making it ideal for prolonged high-temperature deposition. CFD simulations combined with a discrete phase model predict that alumina’s higher restitution coefficient (e) increases powder stream divergence and shifts the powder focus plane upward. High-speed camera observations confirmed that the alumina nozzle tip results in a wider powder spot size (∼26.1 %) and an elevated powder focus plane (∼19.3 %) compared to brass. Deposition experiments showed that the optimal substrate position for maximizing deposition height is well below the powder focus plane. To explain this, the study introduces powder incorporating efficiency (η_i), which, alongside powder focusing efficiency (η_f), significantly affects powder deposition efficiency (η_d), expressed as η_d = η_f × η_i. The alumina nozzle tip demonstrated a ∼5 % higher deposition height and ∼16 % lower nozzle tip temperatures compared to brass, making it suitable for high-powder-flow processes, such as high-deposition-rate DED and high-speed laser material deposition.