Mo(AlxSi1−x)2 healing particles for high temperature ceramics and encapsulation by selective oxidation of aluminium. (January 2023)

• Record Type: Journal Article
• Authors: Ding, Zhaoying; Brouwer, Johannes C.; Kwakernaak, Cees; Zhu, Jia-Ning; Popovich, Vera; Hermans, Marcel J.M.; Sloof, Willem G.
• Is Part Of: Materials & design. Volume 225(2023)
• Publication Date: 2023-01
• Subjects: Encapsulation -- Mo(Al, Si)2 -- Alumina scale growth -- Oxidation -- Self-healing thermal barrier coatings; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2022.111577
• Languages: English
• ISSNs: 0264-1275

Abstract

Graphical abstract: Highlights: Healing particles of Mo(Al x Si1- x )2 is designed for encapsulation in terms of alumina shell thickness, particle size and fraction Al dissolved. By replacing Si by Al in MoSi2, a strong crack damage healing ability is maintained (relative volume expansion ≥ 40 %). By oxidation in a low p O2 ambient, volatile Mo-oxide formation was inhibited and exclusive formation of α-Al2 O3 shell was promoted. A dense α-Al2 O3 shell with thickness of 1.3 µm envelopes the MoSi2 healing particles was achieved. The encapsulation method designed provides MoSi2 particles with 86 % less weight loss upon oxidation preserving the healing capacity. Abstract: To prevent premature triggering of the healing reaction in Mo-Si containing self-healing thermal barrier coating system, an oxygen impenetrable shell (α-Al2 O3 ) around the sacrificial healing particles (MoSi2 ) is desired. Here an encapsulation method is presented through selective oxidation of Al in Mo(Al x Si1- x )2 particles. Healing particles of Mo(Al x Si1- 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-Al2 O3, 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 p O2 of 5 × 10 -10 atm. at 1100 °C, a closed and dense shell of α-Al2 O3 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 p O2 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-Al2 O3 .