Combustion synthesis of UHTC composites from Ti-B 4 C solid state reaction with addition of VIb transition metals

Abstract

UHTC composites were prepared by self-propagating high-temperature synthesis (SHS) from the Ti-B 4 C reaction system with addition of Cr, Mo, andW. The starting sample composition was formulated as (3-x)Ti + B 4 C + xMe with x = 0.1-1.0 and Me = Cr, Mo, orW. For all samples conducted in this study, self-sustaining combustion was well established and propagated with a distinct reaction front. With no addition of Cr, Mo, orW, solid state combustion of the 3Ti + B 4 C sample featuring a combustion front temperature (T c ) of 1766 °C and a combustion wave velocity (V f ) of 16.5 mm/s was highly exothermic and produced an in situ composite of 2TiB 2 + TiC. When Cr, Mo, orWwas adopted to replace a portion of Ti, the reaction exothermicity was lowered, and hence, a significant decrease in T c (from 1720 to 1390 °C) and V f (from 16.1 to 3.9 mm/s) was observed. With addition of Cr, Mo, andW, the final products were CrB-, MoB-, and WB-added TiB 2 -TiC composites. The absence of CrB 2 , MoB 2 , and WB 2 was attributed partly to the loss of boron from thermal decomposition of B 4 C and partly to lack of sufficient reaction time inherent to the SHS process.