The innovation engine for new materials

Angus Braithwaite

Angus Braithwaite and David Poerschke


University of Oxford


Materials Science


David Poerschke

Faculty Sponsor(s): 

Carlos Levi

Faculty Sponsor's Department: 


Project Title: 

Investigating amorphous-crystalline transformation in polymer-derived ceramics for applications in jet turbine engines

Project Description: 

Silicon carbide (SiC) based ceramic matrix composites (CMC’s) are being developed to replace metals in turbine engines where their higher-temperature capabilities will improve the thermal efficiency of the engines. However, processing challenges have limited the implementation of CMC’s. One promising route involves infiltrating a fiber preform with a ceramic forming polymer, heating the polymer to form an amorphous ceramic matrix (pyrolysis), and finally crystallizing the amorphous ceramic to form SiC. Our current investigation focuses on the amorphous-crystalline transformation with the aim of understanding the underlying kinetics and microstructural changes. Bulk amorphous specimens were heat treated in the range of 1300 °C to 1500 °C for between 1 h and 100 h. Based on Powder X-Ray Diffraction (PXRD) analysis, incomplete crystallization (65-70 wt%) occurred at 1300 °C and 1400 °C even at longer times, whereas more significant crystallization (80-85 wt%) only took place at the higher temperature of 1500 °C at times of 24 hr and longer. A quantitative PXRD method, validated as part of the study, was used to determine the crystalline content of each specimen separately. The same samples were analysed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to observe microstructural changes. The microstructure became increasingly porous upon crystallization, accounting for changes in composition, mass loss, and the large shrinkage observed in the samples. The improved understanding of the amorphous to crystalline transformation will be used to design heat treatments for CMC coupons with the aim of further optimising the processing of SiC CMC’s.