Kinetics of Self‐Crack‐Healing of Alumina/Silicon Carbide Composite Including Oxygen Partial Pressure Effect

Abstract

Self-crack-healing behavior under a combustion gas atmosphere with a low oxygen partial pressure, P O2 , is important for actualizing ceramic gas turbines, but to date only self-crack-healing behavior in air has been investigated. In this study, we investigated crack-healing behaviors at 1273-1773 K under several levels of P O2 . Crack-healing in atmospheres with P O2 ! 50:0 Pa gave rise to the complete strength recovery of cracked specimens, resulting from passive oxidation. Based on the obtained results, the kinetics for strength recovery by self-crack-healing was expressed as a function of healing temperature, T H (K), and P O2 (Pa). The strength recovery rate for complete crack-healing, v H (s À1 ), could be expressed as v H ¼ 6:95  10 5 expðÀ4:65  10 4 =T H ÞP O 2 0:835 Using this rate equation, one can evaluate the healing time for complete strength recovery under combustion gas in a gas turbine. B. Derby-contributing editor

Generic principles of crack-healing ceramics

“…Microcracks in crystalline SiO 2 (quartz) with a length of 100 µm and a width of 10 µm were completely healed by exposure to a water pressure of 200 MPa at 600 ℃ for 4 h [50]. Strength recovery by hightemperature oxidation induced crack healing with environmental oxygen at elevated temperatures was reported from a number of non-oxide ceramics as well as oxide ceramics loaded with SiC [26,30,34,[39][40][41]51,[69][70][71][72][73][74]. For example, annealing of SiC reinforced Al 2 O 3 nanocomposites in inert Ar atmosphere resulted in a strength increase of 50% relative to the unannealed specimen whereas annealing in air yielded a three-fold improvement in the indendation strength [69].…”

“…Crack healing reactions involving (a) Oxidation and vapour diffusion (b) Oxidation and grain boundary diffusion external (environment gas atmosphere) or internal (repair fillers) reactants may be represented by simple polynomial fitting to experimental f (a) data or by a logical model in accordance with the suggested reaction mechanism [85]. Experimentally an expression was derived for crack healing governed by oxidation reaction of SiC containing ceramics [39] …”

“…Filling very large surface cracks (>2 mm) prepared on alumina with a borosilicate glass at 1500 ℃ was demonstrated to yield even stronger material than the mother material which was attributed to thermal expansion mismatch induced compressive surface stress [44]. Critical thresholds for oxygen partial pressure [39] as well as constant and cyclic stress loading were reported to control the recovery of strength [45,46].…”

“…Lower temperatures of 1000-1300 ℃ were reported for oxidation induced crack healing of surface flaws in a variety of Si-containing ceramics where viscous SiO 2 and silicate based reaction products are able to fill the space between crack walls [36][37][38]. Ceramics containing more than 10 vol.% of SiC particles or whiskers were reported to exhibit efficient crack healing ability triggered by SiC oxidation reaction [39] resulting in a pronounced improvement of strength and reliability as well as reduction of the manufacturing costs [40,41]. Oxidation in air as well as viscous flow were successfully demonstrated to trigger healing reaction in ceramic matrix [42] and in glass matrix [43] fiber composites even at relatively low temperatures of 500-600 ℃.…”

Finite Element Analysis of Self-Healing and Damage Processes in Alumina/SiC Composite Ceramics

“…The self-healing approach is a new material design concept that aims for self-healing of the damaged material under the operating conditions during service, similar to the healing of bones in a living body. Based on this concept, many self-healing ceramics have been studied so far [3][4][5][6][7].…”