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The weakest part of the FGM structure occurred at the interface between transition phase and the CMC , which was also the interface between the ductile and brittle phases .
 FGM, interface, transition phase, CMC, interface, ductile, brittle
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 FGM, interface, transition phase, CMC, interface, ductile, brittle