Abstract
Wetting characteristics of the Al/ZrB2 system were experimentally determined by the sessile drop method with application of separate heating of the ZrB2 and Al samples and combined with in situ cleaning of Al drop from native oxide film directly in vacuum chamber. The tests were performed in ultrahigh vacuum of 10−6 mbar at temperatures 710, 800, and 900 °C as well as in flowing inert gas (Ar) atmosphere at 1400 °C. The results evidenced that liquid Al does not wet ZrB2 substrate at 710 and 800 °C, forming high contact angles (θ) of 128° and 120°, respectively. At 900 °C, wetting phenomenon (θ < 90°) occurs in 29th minute and the contact angle decreases monotonically to the final value of 80°. At 1400 °C, wetting takes place immediately after drop deposition with a fast decrease in the contact angle to 76°. The solidified Al/ZrB2 couples were studied by scanning and transmission electron microscopy coupled with x-ray energy diffraction spectroscopy. Structural characterization revealed that only in the Al/ZrB2 couple produced at the highest temperature of 1400 °C new phases (Al3Zr, AlB2 and α-Al2O3) were formed.
Highlights
Zirconium diboride ZrB2 belongs to a family of transition metals borides known as Ultra-High-Temperature Ceramics (UHTCs) (Ref 1)
The contact angle values of obtained in the present wettability tests for Al/ZrB2 couples are presented in Fig. 1, whereas the real-time experiments are demonstrated by the movies placed in Supplement 1
For the Al/ZrB2 and the Al/TiB2 systems at 900 and 1400 °C, we suggest that wetting has reactive character, despite two important facts, i.e., [1] no interfacial reactive products were noted in the Al/ZrB2 and Al/TiB2 couples and their interfaces were smooth after testing at 900 °C, [2] for the 1400 °C test, new interfacial phases (Al3Zr or Al3Ti, AlB2 and a-Al2O3) did not form continuous layers in the triple line area and their effect on wetting behavior is negligible
Summary
Zirconium diboride ZrB2 belongs to a family of transition metals borides known as Ultra-High-Temperature Ceramics (UHTCs) (Ref 1). It has extremely high melting temperature, high thermal and electrical conductivity, excellent thermal shock resistance, high hardness and chemical inertness. Such unique combination of thermophysical, mechanical, and utility properties makes ZrB2-based ceramics suitable for the extreme thermal and chemically aggressive environments (Ref 2). This class of materials has received much attention to explore for wide. A comprehensive knowledge concerning wetting behavior and reactivity in the Al/ZrB2 system is of great practical importance
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