Crystallographic study on the isothermal and athermal martensite of zirconia

点击翻译按钮获取中文摘要

The tetragonal phase of zirconia doped with a small amount of yttria (1.5-1.9 mol%) can be retained metastably at room temperature by rapid cooling. The metastable tetragonal phase undergoes both isothermal transformation by heating at around 200℃ and athermal transformation by subzero cooling. Both transformation products are believed to be martensite, but the crystallographic features can be different because of the large transformation temperatures and kinetics. In the present work, the crystallographic features of these martensites were studied by means of the scanning and transmission microscopy, atomic force microscopy, electron back scattering kikuchi pattern technique, etc. and the results were compared with the phenomenological theory of martensite crystallography.The main results are summarized below.1.The isothermal martensite exhibits a typical thin plate form, while the athermal martensite exhibits either lens-shaped or pyramid-shaped form.2.The lens shaped martensite contains no mid-rib but TEM observation revealed the striations of which direction were consistent with the (101)m twin trace. The thin plate martensite also contains striations but less dens than in lens shaped martensite.3.The habit planes of both isothermal thin plates and athermal lens were close to (310)c, which was in agreement with the prediction from the phenomenological theory where (101)m twins were assumed as the lattice invariant shear.4.The tilt angle of the surface relief of plate martensite was also consistent with the prediction from the phenomenological theory5.The pyramid-shaped martensite was found by TEM observation to be consisted of four variants. The details of the variant combination needs further study.