Aluminum-based metal matrix composites (MMCs) are very attractive due to their excellent strength-to-weight and stiffness-to-weight ratios with improved wear and corrosion resistance [1]. In the Al/Al3Ti metal matrix composite case, the reinforced particles are formed by adding the compressed Ti-based flux to the molten Al [2]. On the other hand, it is well known that the surface of the Ti powders is oxidized, which significantly affects their wettability or infiltration by the liquid metal. Consequently, it contributes to the formation of structural discontinuities that reduce the mechanical properties of MMCs [3-5].

This research is focused on understanding the high-temperature interaction between pure liquid Al and two different types of pure Ti substrates. One Ti substrate was made of compressed Ti powder (Tip), while the other was cut from a wrought Ti rod (Tib). The high-temperature behavior between the liquid metal and the solid substrate was studied using a sessile drop method combined with a capillary purification (CP) procedure. This procedure allows for non-contact heating of Al/substrate couples to the desired temperature, as well as mechanical cleaning of Al drops from the native oxide film directly in the test chamber by squeezing liquid metal from an alumina capillary placed above the substrate [6-7]. The experiments were conducted under isothermal conditions at 800°C in a high vacuum atmosphere (10-6 mbar). During the measurements, images of the Al/Tip and Al/Tib couples were recorded using high-resolution CCD cameras at a speed of 57 frames per second. From these images, the contact angles between liquid Al and the substrates were calculated.

The structure and chemistry of the solidified sessile drop couples were characterized comprehensively using optical, and scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS).

It was observed that, under the applied conditions, in both cases, there was an immediate reaction between the liquid aluminum shortly after its contact with the Ti substrate. In the case of the Al/Tib couple, the substrate was completely covered and completely wetted (the contact angle Θ<5°) by the liquid Al drop about 2 min after the contact with liquid Al. In contrast, for the Al/Tip couple, the liquid metal did not spread over the entire surface of the substrate. SEM+EDS observations revealed that the surface of the solidified Al drop was matte and dark gray due to secondary oxidation of the drop taking place upon the sessile drop test. The mechanism of this phenomenon and its effect on the wetting behaviour of the Al drop on pressed powder Tip substrate vs. bulk Tib one will be discussed in detail.

References

[1] S.J.S. Chelladurai, et al., Materials Today: Proceedings, 2020, 37, 908-916.

[2] X. Wang, et al., Materials Science and Engineering: A, 2004, 364, 339-345.

[3] M. Fattahi, Ceramics International, 2020, 46, 12400-12408.

[4] I. Brynjulfsen, et al., Journal of Crystal Growth, 2010, 312, 2404-2410.

[5] S. Lanka, et al., Journal of Tribology, 141, 2019, 101301.

[6] S. Terlicka, et al., Materials, 2022, 15(4), 9024.

[7] S. Terlicka et al., Journal of Materials Engineering and Performance, 2023, DOI: 10.1007/s11665-023-07950-1.

Acknowledgments

This research was supported by the National Science Centre of Poland within OPUS 22 project no. 2021/43/B/ST8/03271