The effect of mechanical milling and two-step sintering technique on the microstructure, microhardness, strength, and dielectric properties of Sm2Zr2O7 ceramics

This paper investigates the effect of two-step sintering on the mechanical properties and microstructure of Sm₂Zr₂O₇ ceramics obtained from submicron powders after high-energy milling. Two key parameters of the two-step sintering process are analyzed: temperature and duration, as both can significantly influence grain growth processes in ceramics. It was found that extending the sintering duration at lower temperatures promotes ceramic densification while preserving a relatively narrow grain size distribution. In contrast, higher sintering temperatures combined with shorter durations result in broader grain size distributions and more pronounced exaggerated grain growth. Despite differences in microstructure and grain size distribution, both the sample sintered at 1350 °C for 20 hours and the one sintered at 1700 °C for 10 minutes exhibited the highest mechanical properties, with microhardness values HV1 ∼1200 and biaxial flexural strength reaching ∼125 MPa. This suggests that the enhancement of mechanical performance may be linked to a reduction in internal stresses, either due to the elevated temperature during the first sintering step or the extended holding time during the second step. Thus, in both types of sintering, whether based on prolonged holding time or elevated temperature, changes in sample morphology and grain size do not appear to have a significant impact on the mechanical properties of the resulting ceramics.