Surface Tension Measurement of Ti‐6Al‐4V by Falling Droplet Method in Oxygen‐Free Atmosphere

Surface tension plays a key role in determining melt behavior, wetting, and defect formation in high‐temperature processes such as laser powder bed fusion and wire‐based deposition welding. Accurate surface tension data are therefore essential for optimizing process quality, especially for titanium alloys, like Ti‐6Al‐4V, which are widely used in aerospace and biomedical applications due to their high specific strength and biocompatibility. In this article, the surface tension of Ti‐6Al‐4V is derived from the oscillation of falling droplets using Rayleigh's formula. Conventional levitating droplet techniques for reactive materials require complex evaluation algorithms and specialized hardware to maintain microgravity conditions. In contrast, the presented approach employs only a single high‐speed camera for simultaneous temperature and droplet oscillation measurements, enabling flexible and cost‐effective integration into various technical systems. The method is applied to investigate the influence of residual oxygen on the surface tension by performing experiments in argon and in a monosilane‐doped oxygen‐free atmosphere (<10 −15 ppm O 2 ). The surface tension follows the linear relation γ ( T ) = 1.512 N m −1 − 1.468 × 10 −4 N m −1 K −1 × ( T − 1933 K). No measurable influence of residual oxygen was observed, as the droplet lifetime was four orders of magnitude shorter than the time required for substantial oxygen diffusion.