In this study, the sessile drop method was applied to examine the high-temperature interaction of liquid Mg drop on two different substrates: pure niobium and Ti-Nb alloy (26 at. % Nb). The capillary purification procedure was used to eliminate the influence of the heating history of the Mg/substrate couples and the presence of the native oxide film on the Mg samples. This procedure allows non-contact heating of Mg/substrate couples to the test temperature and mechanical cleaning of Mg drops from the native oxide film directly in the experimental chamber by squeezing the liquid metal out of a graphite capillary placed over the substrate [1-3].

Measurements were performed under isothermal conditions (700 °C) using a protective atmosphere in the form of a gaseous mixture of Ar + 5 wt.% H₂. During the high-temperature experiments, the images of Mg/substrate couples were recorded by two high-resolution, monochromatic CCD cameras at a speed of 57 fps from two perpendicular directions of observation [1]. These images were used for measurements of the contact angle values (θ) formed between the liquid metal and the investigated substrates.

The obtained Mg/Nb and Mg/Ti-Nb alloy couples were subjected to detailed structural characterization by optical microscopy and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy.

Under the conditions of the present work and according to the phase diagrams available in the literature [4] for Mg-Nb and Mg-Ti systems, liquid Mg showed non-wetting behavior (θ>90°) and no permanent bonding between liquid Mg and the tested substrates. The reason for this behavior is the unreactive and immiscible nature of the Mg-Nb and Mg-Ti systems and the negligible solubility of liquid Mg in these materials, as well as the fact that Mg does not form any compounds with both Nb and Ti.

 References 
[1] S. Terlicka, P. Darłak, N. Sobczak, J.J. Sobczak, Non-wetting and non-reactive behavior of liquid pure magnesium on pure tungsten substrates, Materials, 2022, 15(4), 9024. 
[2] S. Terlicka, N. Sobczak, P. Darłak, J. Sobczak, E. Ziółkowski, Wettability and reactivity of liquid magnesium with a pure silver substrate, Journal of Materials Engineering and Performance 2023, in press. 
[3] N. Sobczak, M. Singh, R. Asthana, High-temperature wettability measurements in ceramic-metal systems – some methodological issues, Current Opinion in Solid State & Materials Science, 2005, 9 241-253. 
[4] FactSage Version 8.2, with FTlite Database. Available online: https://www.crct.polymtl.ca/fact/documentation/FTlite/FTlite_Figs.htm (accessed on 30 January 2023). 

Acknowledgment 
This research was supported by the National Science Centre of Poland within OPUS 21 Project, no. 2021/41/B/ST5/02787.