Dynamic Strength of a Fine-Grained Alumina Ceramic Obtained by Spark Plasma Sintering

Dynamic compressive tests of alumina samples with different grain sizes obtained by spark plasma sintering (SPS) of submicron- and micron-sized α-Al 2 O 3 powders have been performed. The effect of heating rate ( V h ), sintering temperature ( T s ), holding time ( t s ), and cooling rate ( V c ) on the hardness, crack resistance, and dynamic ultimate strength (σ Y ) of Al 2 O 3 has been studied. An amorphous layer of a nanometer thickness was on the surface of submicron powders in the initial state. The transformation of an amorphous structure with an excess free volume into a crystalline phase occurs upon the SPS process with the formation of dislocation-type defects at the grain boundaries, which induce long-range internal stress fields. It has been shown that nanopores less than 50–100 nm in size are observed at the grain boundaries of ceramics. It has been shown that the nonmonotonic pattern of the dependence of σ Y on the temperature and time of the SPS is due to the simultaneous change in the density, the nonequilibrium state of grain boundaries, and the grain size of the ceramic. It has been shown that a decrease in the degree of nonequilibrium of the grain boundaries of alumina due to an increase in the SPS temperature or an increase in the holding time makes it possible to increase the dynamic strength of alumina. It has been established that an increase in the cooling rate leads to the formation of compressive residual stresses and a slight increase in σ Y of the ceramic. The maximum dynamic strength (σ Y = 1755 MPa) was reached for the alumina ceramic with an average grain size of 1.6–2 μm obtained by SPS at V h = 50°С/min, T s = 1520°С, and t s = 50 min.