Plastic Creep Features of Sapphire at Near-Melting Point Temperatures

Abstract

The anomalous plastic creep of sapphire crystals in the temperature range of 1890–2050°С, which includes their melting point, has been studied. A method is developed for maintaining crystal in the state of crystal–melt phase transition for a long time, sufficient for carrying out and finishing mechanical tests. Crystal deformation was performed in the creep mode under uniaxial compression along the [10\(\bar {1}\)2] direction. A sharp (stepwise) increase in the creep rate is found when reaching the melting point: it becomes more than an order of magnitude higher as compared with that at near-melting point temperatures. A hypothesis is proposed to explain the found phenomenon by the existence of a transition state between the solid and liquid phases of aluminum oxide, which is characterized by lattice conservation at a sharp increase in the self-diffusion rate.