Abstract
UHTC composites were prepared by self-propagating high-temperature synthesis (SHS) from the Ti–B4C reaction system with addition of Cr, Mo, and W. The starting sample composition was formulated as (3−x)Ti + B4C + xMe with x = 0.1–1.0 and Me = Cr, Mo, or W. 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, or W, solid state combustion of the 3Ti + B4C sample featuring a combustion front temperature (Tc) of 1766 °C and a combustion wave velocity (Vf) of 16.5 mm/s was highly exothermic and produced an in situ composite of 2TiB2 + TiC. When Cr, Mo, or W was adopted to replace a portion of Ti, the reaction exothermicity was lowered, and hence, a significant decrease in Tc (from 1720 to 1390 °C) and Vf (from 16.1 to 3.9 mm/s) was observed. With addition of Cr, Mo, and W, the final products were CrB-, MoB-, and WB-added TiB2–TiC composites. The absence of CrB2, MoB2, and WB2 was attributed partly to the loss of boron from thermal decomposition of B4C and partly to lack of sufficient reaction time inherent to the SHS process.
Highlights
Several borides and carbides of transition metals of the groups IVb and Vb are considered as ultra-high temperature ceramics (UHTCs) based on their melting temperatures in excess of 3000 ◦ C and other properties, such as high hardness, high flexural strength, high thermal conductivity, and excellent resistance to thermal shock and corrosion [1,2,3]
The reactant mixtures were prepared based on a modification of the 3Ti + B4 C stoichiometry
This study demonstrated the production of Cr, Mo, and WB‐added TiB2–TiC composites by an of diborides
Summary
Several borides and carbides of transition metals of the groups IVb and Vb are considered as ultra-high temperature ceramics (UHTCs) based on their melting temperatures in excess of 3000 ◦ C and other properties, such as high hardness, high flexural strength, high thermal conductivity, and excellent resistance to thermal shock and corrosion [1,2,3]. Combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) has been a promising alternative, which takes advantage of highly exothermic reactions, and has merits of low energy requirement, short processing time, simplicity, and high-purity products [10,11,12]. A number of borides and carbides of transition metals (mostly the groups IVb and Vb) have been produced by the SHS process from the elemental powder compacts of their corresponding stoichiometries [13,14,15,16,17]. Due to the low reaction enthalpy, solid state combustion between the transition metals of the group-VIb
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