Mo(Al&lt;sub&gt;x&lt;/sub&gt;Si&lt;sub&gt;1−&lt;/sub&gt;&lt;sub&gt;x&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt; healing particles for high temperature ceramics and encapsulation by selective oxidation of aluminium

Ding, Z.; Brouwer, J.C.; Kwakernaak, C.; Zhu, Jia-Ning; Popovich, V.; Hermans, M.J.M.; Sloof, W.G.

doi:10.1016/j.matdes.2022.111577

Mo(Al_xSi₁₋_x)₂ healing particles for high temperature ceramics and encapsulation by selective oxidation of aluminium

Title

Mo(Al_xSi₁₋_x)₂ healing particles for high temperature ceramics and encapsulation by selective oxidation of aluminium

Author

Ding, Z. (TU Delft Team Marcel Hermans)
Brouwer, J.C. (TU Delft Team Marcel Hermans)
Kwakernaak, C. (TU Delft Team Maria Santofimia Navarro)
Zhu, Jia-Ning (TU Delft Team Vera Popovich)
Popovich, V. (TU Delft Team Vera Popovich)
Hermans, M.J.M. (TU Delft Team Marcel Hermans)
Sloof, W.G. (TU Delft Team Joris Dik)

Date

2023

Abstract

To prevent premature triggering of the healing reaction in Mo-Si containing self-healing thermal barrier coating system, an oxygen impenetrable shell (α-Al₂O₃) around the sacrificial healing particles (MoSi₂) is desired. Here an encapsulation method is presented through selective oxidation of Al in Mo(Al_xSi_1-_x)₂ particles. Healing particles of Mo(Al_xSi_1-_x)₂ is designed in terms of alumina shell thickness, particle size and fraction Al dissolved. By replacing Si by Al in MoSi₂ up to the maximum solubility (x = 0.65) a strong crack healing ability is maintained (relative volume expansion ≥ 40 %). The formed exclusive α-Al₂O₃, featuring a two-layered structure, results from a counter-diffusion process along the grain boundaries, and its oxidation kinetics fits well with the 3D diffusion-Jander model. After 16 h exposure in gaseous ambient with a pO₂ of 5 × 10^-10 atm. at 1100 °C, a closed and dense shell of α-Al₂O₃ is formed with a thickness of about 1.3 µm. The oxide shell produced under this condition provided healing particles with significantly improved stability upon exposure to high pO₂ of 0.2 atm. at 1100 °C for 50 h. The particles after exposure feature an inner core of MoSi₂ with Al completely consumed and an oxide shell of α-Al₂O₃.