Influence of MgO on microstructure and properties of mullite-Mo compositesfabricated by pulse electric current sintering

Mullite-Mo (10 vol.%) composites and monolithic mullite were fabricated usi ng a pulse electric current sintering technique. Both monolith and composit es of mullite were sintered up to theoretical density at 1500 degreesC with in few minutes. MgO of 0.25 wt.% was added as a sintering aid to both the m ullite and composites. Addition of MgO significantly increased the bending strength of the monolithic mullite and mullite/10 vol.% Mo composites to 44 1 and 634 MPa respectively. The apparent increase in the bending strength o f the composites was attributed to the combinational effect of Mo and MgO p resent in the composites. The fracture toughness of the composites also inc reased from 2 to 3.9 MPa.m(0.5) for the mullite/10 vol.% Mo composites, whi ch was nearly twice that of the mullite. Crack-bridging and frontal process -zone elongation were expected to be the toughening mechanisms operated in these composites. The addition of Mo having high thermal diffusivity slight ly increased the thermal diffusivity of the composites, because the 10 vol. % Mo particles were well dispersed and discontinuous in the matrix. Elongat ed mullite grains were observed for the composites without MgO, whereas the composites with MgO have a controlled microstructure. (C) 2001 Elsevier Sc ience Ltd and Techna S.r.l. All rights reserved.