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.