Mullite–molybdenum composites fabricated by pulse electric current sintering technique

Pulse electric current sintering of monolithic mullite and mullite/0–100 vol.% Mo composites was performed in vacuum of 4.5×10−5 Torr at temperatures and pressures of 1500 °C and 20 MPa, respectively. No traces of additional phases were observed by SEM and XRD for these composites. Microstructural observations reveal that Mo (molybdenum) particles dispersed uniformly at lower Mo contents and exhibited flaky and elongated structure at higher content. Simultaneous increase of fracture strength and toughness occurred with increase in Mo content. It attained a maximum of 1.1 GPa and 9.2 MPa m1/2, respectively for 90 vol.% Mo composites. The increase in flexural strength is due to smaller initial flaws in mullite/Mo composites for lower Mo contents and due to plastic deformation of Mo phase for higher Mo contents. Similarly, frontal process zone toughening and crack bridging are expected to be the responsible mechanisms for enhanced toughness in these composites. Partial debonding in the mullite–Mo interface, giving rise to plastic deformation of Mo phase also contributes in the increase of toughness values.