CNT‐induced TiC toughened Al2O3/Ti composites: Mechanical, electrical, and room‐temperature crack‐healing behaviors

• Published in: Journal of the American Ceramic Society Vol. 103; no. 8; pp. 4573 - 4585
• Main Authors: Shi, Shengfang, Cho, Sunghun, Goto, Tomoyo, Sekino, Tohru
• Format: Journal Article
• Language: English
• Published: Columbus Wiley Subscription Services, Inc 01.08.2020
• Subjects: Alumina-Titanium; Aluminum oxide; Anodizing; CNT; Composite materials; Conductors; Electrical conduction; electrical conductivity; Electrical properties; Electrical resistivity; electrochemical anodization; Fracture toughness; Healing; Reaction products; Recovery; Room temperature; room‐temperature crack‐healing ability; Sintering (powder metallurgy); TiC toughening phase; Titanium carbide; Titanium dioxide
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/jace.17152

This study addressed novel multiphase composite of Al2O3/Ti/TiC that exhibited enhanced fracture toughness and room‐temperature crack‐healing function. Al2O3/Ti/TiC composites were fabricated through hot‐press sintering of CNT, TiH2, and Al2O3 mixed powders, where the TiC was in‐situ formed by reaction of CNT and Ti. The effects of CNT (TiC) content on mechanical and electrical properties were studied. Electrochemical anodization process at room temperature was attempted to these composites to heal cracks introduced in the surface of composites. Results indicated that added CNT was invisible while metal Ti and reaction product TiC coexisted in all samples. The reaction between CNT and Ti[O] representing dissolved active oxygen into Ti was considered as the main formation route of TiC. The toughening mechanism was demonstrated as crack deflection and bridging due to the presence of TiC. In spite of the increase in electrical resistivity because of the higher resistivity of TiC than Ti, the present Al2O3/Ti/TiC composites still remain high enough electrical conductivity (8.0 × 10−3 Ωcm ~1.8 × 10−2 Ωcm for 0‐2 vol% CNT addition) which could be regarded as conductors; it allowed to heal cracks in the composites by electrochemical anodization that formed titanium dioxide phase at room temperature. It was found that crack‐healing ability in 1 vol% CNT added composite exhibited higher strength recovery ratio of 95.6% to the crack‐free sample than that of Al2O3/Ti composite (the recovery ratio of 89.6%). After crack‐healing process, mechanical strength of samples increased by 52.3% compared to cracked composites. It was concluded that the formed TiC could contribute to the appropriate electrical conduction as well as interface strengthening in the Al2O3/Ti composites. Furthermore, it was firstly speculated that the TiC could be electrochemically anodized to form an oxide like Ti metal. These characteristics enable Al2O3/Ti/TiC composites as the crack‐healing materials at room temperature.