Process optimization of Ta1.5Mo1.5Nb0.5Zr2Ti 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 Ta1.5Mo1.5Nb0.5Zr2Ti 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 Ta1.5Mo1.5Nb0.5Zr2Ti 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.