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Thermal Exposure Effects on the Strength and Microstructure of a Novel Mullite Fiber
Author(s) -
Almeida Renato S. M.,
Bergmüller Eduardo L.,
Eggert Bruno G. F.,
Tushtev Kamen,
Schumacher Thomas,
Lührs Hanna,
Clauß Bernd,
Grathwohl Georg,
Rezwan Kurosch
Publication year - 2016
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.14093
Subject(s) - mullite , materials science , microstructure , composite material , weibull distribution , fiber , ultimate tensile strength , bundle , fiber bundle , weibull modulus , acoustic emission , flexural strength , ceramic , statistics , mathematics
The mechanical behavior of the novel fiber CeraFib75 after various thermal exposures is examined. This fully crystalline mullite fiber was developed to exceed the thermal stability of commercially available oxide fibers. Therefore, heat treatments at temperatures ranging from 1000°C to 1400°C for 25 h were performed and results compared to the well‐established Nextel ™ 720 fibers. Mechanical characterization was realized with bundle tensile tests using acoustic emission sensors to determinate the fiber failure distributions. Investigations showed that the initial fiber microstructure of mullite grains with traces of alumina transforms starting at 1200°C. Changes include dissociation of the alumina‐rich mullite phase and grain growth. Thus, strength reduction is measured as a result of these microstructure transformations. Remarkably, at 1400°C, fibers become more fragile and Weibull statistics can no longer describe the failure distribution. A relation between the distribution shape and the load redistribution capability of fibers is suggested. This is more pronounced for Nextel ™ 720 fibers, which present much bigger grains and retain only 10% of their original strength. However, CeraFib75 fibers are more stable and exhibit a strength retention of 50% at the same conditions, which is attributed to the higher amount of mullite phase.