Evaluation of metastable degree in amorphous Al2O3-ZrO2-Y2O3 and its effect on plastic deformation

Novel plastic deformation was exhibited in amorphous oxides, attributed to the metastable state of amorphous phase with free volume and disordering structure; however, metastable degrees can be quite different in amorphous phases, and the effect of metastability on plastic deformation was never reported in amorphous oxides. In this work, the metastable degree of amorphous phase was controlled by adjusting the temperature in powder calcination, and evaluated through free volume and disordering degree, using the true density of amorphous powder, DSC and 27Al MAS-NMR. Under compression at 500 °C, the sample with lowest metastability exhibited brittle fracture; however, the other two with higher metastable degrees displayed plastic strain of 3.5% and 5.2%. The enhanced plastic deformation benefited from higher metastability was mainly attributed to easier formation of shear bands. For amorphous phase with higher metastability, the atomic mobility and local free volume were larger, which could improve the formation of shear bands and promote the plasticity according to free volume theory. This work could inspire new methods to improve the plastic deformation in amorphous materials.