Process optimization of Ta_1.5Mo_1.5Nb_0.5Zr₂Ti refractory high-entropy alloys via multi-wire arc additive manufacturing

Refractory high-entropy alloys（RHEAs） are widely used in the aerospace field due to their excellent high-temperature performance. This study employs multi-wire arc additive manufacturing（M-WAAM） technology to fabricate Ta_1.5Mo_1.5Nb_0.5Zr₂Ti refractory high-entropy alloy. Using equipment such as optical microscopy（OM） and high-speed cameras, the influence rules of base current, peak current, and peak time ratio on forming quality are investigated. The optimal process parameters for preparing the Ta_1.5Mo_1.5Nb_0.5Zr₂Ti alloy are determined（base current 100 A, peak current 300 A, and peak time ratio 35%）. Metallographic characterization demonstrates that the fabricated components exhibit excellent forming quality, with unmelted area ratio below 10% and porosity less than 0.5%. To address the melting point differences among various wires, hot-wire technology is employed to facilitate the melting of high-melting-point Ta/Mo wires. For the first time, we propose a“single droplet pre-alloyed transfer”mechanism, elucidating the thermodynamic process of discontinuous liquid bridge transition and subsequent formation of a unified molten droplet from four simultaneously fed wires. Based on the thermodynamic mechanism of synchronous four-wire discontinuous liquid bridge transition forming a unified molten droplet, a“single droplet pre-alloyed transfer”mode is established. Parts deposited under this droplet transfer mode demonstrate good macroscopic morphology and fewer internal defects. Through force analysis of molten droplets, we establish a mechanical model incorporating key factors including gravity, electromagnetic force, and plasma flow force, demonstrating that synchronous non-continuous liquid bridge transition of four wires constitutes a sufficient condition for the formation of a unified molten droplet. Additionally, the developed bead width prediction model provides quantitative guidance for process optimization. This work establishes an important theoretical foundation for M-WAAM of RHEAs.