CERAMIC MATRIX COMPOSITES IN Ti-B-Cr AND Ti-B-Nb SYSTEMS FABRICATED 'IN SITU' BY SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS

摘要

Ceramic matrix composites (CMCs) with predominant concentration of TiB_2 have recently become the focus of intensive studies due to their potential application in the nuclear industry and other high temperature devices. Thus, in this study, composites consisting of borides fabricated "in situ" (in the one stage process from elemental powders) have been investigated. Self-propagating high temperature synthesis (SHS) combined with pseudo-hot isostatic pressing (p-HIP) was used to utilize the heat of highly exothermic reaction related to the synthesis of TiB_2 with NbB_2 or CrB_2, respectively, for densification. The intended volume fraction of TiB_2 was 70% in both cases. The XRD patterns revealed that TiB_2 was a predominant phase of each composite while the second ceramic phase was NbTiB_4 or (Cr_(0.5)Ti_(0.5))B_2, solid solution respectively. No unreacted elements were detected. The composite in Ti-Cr-B system exhibited better homogeneity and higher relative density. The Vickers hardness of 20.83+/-0.26 GPa for this composite was also higher than that of 16.67+/-0.28 GPa for the composite containing Nb. Therefore, the SHS process can be seen as being applicable for the fabrication of "in situ" CMCs, thanks to the liquid phase during densification.