High-pressure sintering of bulk MoSi2: Microstructural, physical properties and mechanical behavior

In this study, using MoSi2 powder as starting material, the bulk MoSi2 samples were sintered at 1000-1600 °C under 5.5 GPa in a DS6 × 14MN cubic press. Furthermore, their sintering behavior and mechanical properties were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM) and indentation tests. XRD results elucidate that MoSi2 can still maintain its body-centered-tetragonal structure after the high pressure and high temperature (HPHT) sintering. SEM images imply the combination between grain growths and re-crystallization. Strong covalent bonding between the grains is crucial for improving the mechanical properties of samples. But re-crystallization results in a large number of pores between grains in the sintered body, so that the density and hardness was reduced. Indentation tests indicate that sintered MoSi2 have hardness values of 13.6-15.0 GPa, which increase with increasing temperature and is harder than polycrystalline and single crystal MoSi2. The results demonstrate that the sintered MoSi2 at 5.5 GPa/1300 °C possesses outstanding mechanical properties, including a high relative density (6.23g/cm3), Vickers hardness (15.0 GPa) and fracture toughness (10.7 MPa m1/2) at applied load of 29.4 N. In addition, the oxidation resistance of the prepared samples is measured using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis. The results show that the oxidation resistance has been significantly improved from this work compared with polycrystalline MoSi2.