X-RAY-DIFFRACTION STUDY OF THE T-TO-M PHASE-TRANSFORMATION IN 12-MOL-PERCENT-CERIA-DOPED ZIRCONIA AT LOW-TEMPERATURES

The t-to-m phase transformation in a 12-mol%-ceria-doped zirconia at s ubzero temperatures was studied in situ by XRD with a cryogenic sample stage. It mas found that the t-to-m transformation continuously proce eded to 30 vol% as the temperature decreased to 125 K, when a burstlik e transformation suddenly occurred with a transformation to 75 vol%. A preferred orientation of the (<(1)over bar 11>)(m) plane parallel to the surface during the preburst transformation and XRD line broadening of both m and t phases after the burst were observed. The preburst tr ansformation, which has not been revealed by previous dilatometry stud ies, is explained as surface martensitic transformation. This surface transformation occurs at higher temperatures than the burstlike transf ormation due to less matrix constraint and the higher probability of n ucleation.