Wetting behavior of Mo, Ta, and stainless steel substrates in contact with molten Mg

Abstract

The sessile drop method combined with a capillary purification procedure was used, for the first time, to analyze the high-temperature behavior of molten Mg on three dissimilar substrates: 1) molybdenum, 2) tantalum and 3) AISI 316L stainless steel. All tests were performed under isothermal conditions at 720 °C in a protective atmosphere (Ar + 5 wt.% H₂). Images of Mg/substrate couples recorded during the experiments were used to calculate the contact angles (θ) formed between the liquid Mg drop and the selected substrates.

After the sessile drop tests, the Mg/Mo, Mg/Ta, and Mg/AISI 316L couples were subjected to in-depth microstructural characterization using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).

Under the employed experimental conditions, oxide-free Mg drops on all tested couples presented non-wetting behavior (θ > 90°). The average values of the calculated contact angles after 40 s of liquid Mg deposition were θ_Mg/Mo = 124°, θ_Mg/Ta= 125°, and θ_{Mg/AISI 316L}= 126°, respectively. The SEM/EDS analysis showed no mass transfer and no bonding between solidified drops and the substrates. This non-reactive and non-wetting behavior of investigated couples can be associated with the immiscible nature of the Mg-Mo, Mg-Ta, and Mg-Fe systems, where the solubility of liquid Mg with all tested materials is negligible, and Mg does not form any compounds with them.