Recently, a new class of materials with applications for biodegradable implants that imitates human bone with variable and directed porosity has been intensively investigated [1]. Magnesium and its alloys are one of such materials. Compared to traditional implant materials, i.e. stainless steel or pure Ti and its alloys, magnesium and Mg-based alloys are degraded and absorbed by the human body, effectively avoiding repeated implant removal surgeries [1].

In this work, the sessile drop method was used to study the behavior of liquid Mg drop on two types of pure titanium substrates. One Ti substrate was cut from a wrought rod, and the other was formed from compressed Ti powder. The high-temperature tests were performed under isothermal conditions (700 °C) under a flowing gas mixture of Ar + 5 wt. % H₂. To avoid the negative effect of native oxide film on the Mg sample on reliability of contact angle (θ) measurements, the non-contact heating of examined couples of materials to the investigated temperature was combined with in situ cleaning of the Mg drop directly in a high-temperature chamber using a capillary purification procedure [1-3]. For this, an Mg sample was placed in a graphite capillary above Ti substrates and after reaching the test temperature, the Mg drop was mechanically squeezed from the capillary and deposited on the substrate [1-3]. During high-temperature tests, the images of the Mg/Ti couples were recorded by two high-speed monochromatic CCD cameras (57 fps) from two directions of observation. These images were used for measurements of the contact angle values formed between the liquid metal and the titanium substrates.

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

The obtained results are discussed in terms of the role of primary oxide films on both Mg and Ti samples on the wetting and spreading behavior of liquid Mg on selected substrates. This is related to high-temperature capillarity and methodological issues preferring the capillary purification method vs. the classical sessile drop method accompanied with contact heating, resulting in a significant improvement in wetting and rapid spreading when non-oxidized Mg is contacted with a non-oxidized/oxidized Ti substrates.

 References 
[1] S. Terlicka, N. Sobczak, P. Darłak, J.J. Sobczak, E. Ziółkowski, Wettability and reactivity of liquid magnesium with a pure silver substrate, Journal of Materials Engineering and Performance 2023, in press. 
[2] 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. 
[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. 

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