Structural and phase states of titanium borides produced by the self-propagating high-temperature synthesis method in the field of ultrasound oscillations

Abstract

The effect of ultrasound oscillations (USO) on the velocity and temperature of combustion during self-propagating high-temperature synthesis (SHS) in the Ti-B system and structural and phase states of the produced titanium borides is studied using the earlier developed experimental setup. The effect of USO on SHS is subdivided into thermal and physical (non-thermal). The thermal influence is connected with cooling of the specimen surface because of the occurrence of forced convection of the ambient gas, and the physical effect is due to the action of USO on complex interaction processes in the SHS wave such as melt spreading, heterogeneous reactions and mass transfer in the liquid phase. Imposition of USO on the SHS process brings about changes in the phase composition of the synthesis products. For charge composition Ti–1.0В the content of orthorhombic modification of phase TiB increases from 78.2 % without USO to 82.9 % at the USO amplitude ξ = 10 mm, while the content of the cubic modification of this phase decreases from 9.2 % at ξ= 0 to 6.8 % at ξ = 10 mm. For all the examined compositions, the amount of residual titanium and Ti3B4decreases and the content of TiB2increases. It is determined that carrying out SHS in the field of USO results in a change of the specific heat capacity of the target synthesis products: with raising the USO amplitude it increases by 4–5 %. Thereby it is shown that imposition of USO on SHS is an efficient physical method for purposeful regulation of structural and phase states and therefore properties of the synthesis products and can be used as a means for controlling the synthesis process.