INVESTIGATION OF THE EFFECT OF GRAIN SIZE ON THE DYNAMIC STRENGTH OF FINEGRAINED ALUMINUM OXIDE OBTAINED BY SPARK PLASMA SINTERING

Abstract

The results of testing the dynamic strength of ceramic samples of aluminum oxide with different grain sizes are presented. Ceramics are obtained by electropulse plasma sintering (EPS) of industrial submicron and micron ?Al2O3 powders. Heating was carried out at a rate of 10 °C/min; The ceramic grain size was varied by changing the EPS temperature. The ceramics had a high relative density (more than 98%), a uniform finegrained microstructure, and the average grain size varied from 0.8 to 13.4 µm. The ceramic grain size was varied by changing the sintering temperature and heating rate, as well as by changing the initial particle size of the ?Al2O3 powder. Dynamic compression tests were carried out according to the modified Kolsky method, using a split Hopkinson rod. The tests were carried out using a gas gun with a caliber of 20 mm (PG20), at room temperature, with a deformation rate of ~ 103 s–1. It has been established for the first time that the dependence of the dynamic tensile strength of aluminum oxide on the grain size has a nonmonotonic character, with a maximum. The maximum value of the dynamic compressive strength (?Y = 1060 MPa) is provided with an average grain size of ~ 2.9–3 µm. It is shown that the decrease in ?Y of aluminum oxide in the region of submicron grain sizes is due to a decrease in the relative density of ceramics sintered at lower temperatures of SPS. It has been suggested that the decrease in ?Y of ceramics in the region of micron grain sizes is due to the formation of internal microstresses near the grain boundaries. It has been established that with an increase in the grain size, the hardness HV of aluminum oxide decreases, and the minimum Palmquist crack resistance coefficient KIC increases. The results obtained demonstrate that there is no need to ensure the formation of a nanostructure in ceramics to ensure high characteristics of their dynamic strength.