Degradation of TiB2 ceramics in liquid aluminum

Infiltration of liquid aluminum in three TiB2 materials with significantly different microstructures at 1000 degrees C has been studied. The results show large differences in resistance towards aluminum penetration. A TiB2 material containing transition metal sintering aid, displayed a low resistance towards penetration of liquid aluminum along grain boundaries. Grain boundary penetration was also observed in a second material containing an oxycarbide secondary phase TiC1-xOx, while Al infiltration could not be detected after 100h, in a third material with apparently no secondary phases. The flexural strength, hardness and stiffness of the exposed material showing the lowest resistance towards penetration of aluminum, decreased due to penetration along grain boundaries, and the fracture mode changed from transgranular to intergranular. The experimental observations were analyzed using a two-dimensional finite element model, reproducing the observed reduction in the stiffness due to aluminum infiltration. (c) 2008 Elsevier Ltd. All rights reserved.