The effect of high-energy methods of forming on the sintering behaviour and properties of Si3N4-based materials

Abstract

In the study, Si3N4-Al2O3-Y2O3 samples were obtained in two stages. In the first stage, the materials were compacted using different methods: Isostatic Pressing, UHP (Ultra High Pressure), and SC (Shock Compaction). In the second stage, the green body samples obtained were sintered using the free sintering method.Powder mixtures, in wt%, 88 Si3N4 - 6 Al2O3 - 6Y2O3, were based on commercial nano - and micropowders. The parameters of green bodies compaction and sintering processes were optimised using the criteria of highest density, hardness, and Young's modulus. When compared to theoretical density values, the density of green body samples was 58% for the Isostatic Pressing and 82% for UHP and Shock Compaction. The Vickers hardness was measured only for Shock Compacted green body samples and was ~10.8–14 GPa depending on the applied load during the measurement. The largest changes in lattice constant parameters were measured for the Y2O3 phase for the dynamic compaction method (a = 0.02% - 2.26%).The highest relative density was measured for materials which were compacted by UHP method and subsequently free sintered (95%). Young's modulus for UHP and Isostatic green body free sintered samples was 284 GPa and 241 GPa, respectively. The hardness values of samples after free sintering were as follows: 11.7GPa for Isostatic, 14.8 GPa for UHP, and 17.6 GPa for Shock Compaction samples.