Consolidation and mechanical properties of MoSi2-based materials

The consolidation behaviour of MoSi2 powder, MoSi2 blended with coarse and fine niobium powder, and MoSi2 blended with SiC whiskers during hot isostatic pressing (HIP) was studied. The HIP model, developed by Ashby and coworkers, was used to guide the choice of consolidation parameters (pressure, temperature and time). Literature information, experimental measurements and, in some cases, the rule of mixtures estimates were used to determine material property data required as input to the HIP model program. Samples were subjected to HIP at 207 MPa in the temperature range 1200–1400 °C for 1 and 4 h, to produce compacts with minimal porosity and desirable microstructures. Density measurements by the Archimedes principle method were compared with model predictions. Matrix-reinforcement interfaces and secondary phases in the materials were studied. The compacts were machined to produce specimens for room temperature fracture toughness testing. Single-edge-notched specimens were loaded monotonically to failure in a three-point bending configuration. The fracture surface morphologies were analyzed by scanning electron microscopy. Fracture mechanisms were identified and correlated with consolidation parameters and microstructures.